# Trouble with cut off operations



## Luiz Fernando Pinto (Dec 23, 2019)

I am in trouble with cut off operations. I tried with a 3mm tool, then with 2mm tool (see photo). I don´t know if it the rigidity of my lathe. I´m lost. Could you help me? Even when i try to cut alluminun or brass.
troubles that i found in the operations:
- lougth noise
- it don´t cut
- i am afraid, kkk

Could you give me some tips?

Thanks a lot.


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## Luiz Fernando Pinto (Dec 23, 2019)

I'm searching here on the same site, already found something. Only after the post that I remembered this research, sorry. But if you want to contribute new information I appreciate it. Thanks.


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## Arnak (Dec 23, 2019)

Hi Luuiz,

Have you made certain that the tool is at center height?

With steel make sure you use plenty of coolant.

I would recommend running the lathe at it's slowest speed, (Backgear).

Make sure the overhang from the tool post is as short as possible.

Martin


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## ShopShoe (Dec 23, 2019)

Adding to wnat Arnak said above:

Also cut near the chuck.

Feed the tool at a steady definite rate, You can work-harden some materials if you are not feeding steadily and cutting..

If you are using a HSS cutting tool and you can sharpen it, sharpen it often. If the cutting edge is not cutting you can also be work-hardening your part. 

You mention rigidity is unknown. Try to check that out. There are things we can say about how to improve that situation. 

What lathe are you using and what size stock are you trying to work with?

--ShopShoe


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## Luiz Fernando Pinto (Dec 23, 2019)

Arnak said:


> Hi Luuiz,
> Have you made certain that the tool is at center height?
> With steel make sure you use plenty of coolant.
> I would recommend running the lathe at it's slowest speed, (Backgear).
> ...



Have you made certain that the tool is at center height?
- Yes,  I aligned with the live center.

With steel make sure you use plenty of coolant.
- Ok, noted.

I would recommend running the lathe at it's slowest speed, (Backgear).
- Even with the slowest possible speed i´m in trouble.

Make sure the overhang from the tool post is as short as possible.
- Yes it is, in the first photo you can see it.


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## Luiz Fernando Pinto (Dec 23, 2019)

ShopShoe said:


> Adding to wnat Arnak said above:
> Also cut near the chuck.
> Feed the tool at a steady definite rate, You can work-harden some materials if you are not feeding steadily and cutting..
> If you are using a HSS cutting tool and you can sharpen it, sharpen it often. If the cutting edge is not cutting you can also be work-hardening your part.
> ...



Also cut near the chuck.
- Its a 150mm long.

Feed the tool at a steady definite rate, You can work-harden some materials if you are not feeding steadily and cutting..
- Ok, noted.

If you are using a HSS cutting tool and you can sharpen it, sharpen it often. If the cutting edge is not cutting you can also be work-hardening your part.
- It is not HSS, i don´t know the name but it is for steel. I can use it for alluminun, right?

 You mention rigidity is unknown. Try to check that out. There are things we can say about how to improve that situation.
- Ok

What lathe are you using and what size stock are you trying to work with?
- The lathe is a Optimun 7x12, size stock of 100mm


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## Luiz Fernando Pinto (Dec 23, 2019)

I am thinking that is a too long piece, 150mm is too far away to the chuck, right? I'm doing the cut off near the live center.
it is aluminum 2" x 150mm.


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## XD351 (Dec 23, 2019)

If you need to part off from a long bar that doesn’t fit inside the spindle bore set up a fixed steady close to the end where you are going to part off , I don’t like parting off when the part is between centres as it can cause a jam up .
Try some WD40 on Aluminium as this will help to stop the Aluminium from welding to the parting  tool insert and don’t skimp on it !
Tighten the gibs on or lock the compound slide if possible and make sure the tool is parallel to the chuck face which will give you 90degrees from the workpiece being parted off and lock the saddle of the lathe .

Are the parting tool inserts of a reasonable quality or known good brand ? I have a few cheap ones that no matter what i do they just won’t work .


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## Luiz Fernando Pinto (Dec 23, 2019)

XD351 said:


> If you need to part off from a long bar that doesn’t fit inside the spindle bore set up a fixed steady close to the end where you are going to part off , I don’t like parting off when the part is between centres as it can cause a jam up .
> Try some WD40 on Aluminium as this will help to stop the Aluminium from welding to the parting  tool insert and don’t skimp on it !
> Tighten the gibs on or lock the compound slide if possible and make sure the tool is parallel to the chuck face which will give you 90degrees from the workpiece being parted off and lock the saddle of the lathe .
> 
> Are the parting tool inserts of a reasonable quality or known good brand ? I have a few cheap ones that no matter what i do they just won’t work .



Thanks for the considerations, XD351. I did not know much of it and other colleagues' information. I will improve my fixation, position and lubrication and then I send news. Thank you again.

Ah, I don't know the quality of the machining inserts. So if after all this doesn't work out, I buy new inserts.


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## XD351 (Dec 23, 2019)

I forgot to ask , 
When you set the height of the tool dis you set the outside edge of the insert or the bottom of the groove in the top to centre height ?


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## goldstar31 (Dec 23, 2019)

I've had my fingers wrapped about recommending books but really when you have had the same cut off tool for  more years than some of the members here have lived, I think that people should share the knowledge or damn me with proven criticism.

My rear tool post with an inverted pair of tools was published in Volume 142 of Model Engineer and susequently went into George Thomas's Model Engineers Handbook with the kit( if you don't want to make one from your scrap bin is available from HemingwayKits in the UK. Apparently it has been such a success that Hemingways scaled the original design up for larger lathes.

Mine has served on a number of lathes, not only all 4 Myfords but has gone on to be used with a subplate on a 918 and presently on a SiegC4.

It is rather nice to see swarf coming off and falling in neat little curls. 

Cheers

Norm


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## Charles Lamont (Dec 23, 2019)

I agree there Norm. George Thomas's rear parting toolpost works a treat. Still needs a *sharp* blade though.


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## xpylonracer (Dec 24, 2019)

Hi Luiz
Looks like you are using an insert type parting tool, you need to be more agressive with this type of tooling so faster spindle speed and constant force on the tool. 
But to do this you need to have the material well supported as has already been stated by other comments, using a fixed steady is essential when parting long pieces.
You may be able to buy some ground edge uncoated inserts for use on aluminium.

Marcus


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## kvom (Dec 24, 2019)

When the depth to cut is a big multiple of the tool width, I find it useful to make a cut wider than the tool. I.e., cut in a bit, but when it gets noisy, back out, move the carriage over half the tool width, and cut.  Alternate sides until done.


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## goldstar31 (Dec 24, 2019)

The George Thomas tool will cut a maximum of 2" diameter and properly set up will part off steel at one setting of the blade and tool. 
OK,  I use the traditional parting off fluid which is nothing more than refined lard oil. It is nice on the hands because that is what ladies hand-cream was made from. It gets hot and smells better than  a McDonal's 
Again, I use it for normal turning tasks and mixed with candle tallow, it is a pretty good thing for tapping.
 I've had a 5 litre container of the stuff in an unheated shed exposed to winter and summer temperatures and what remains is as good as the day that I bought it.

Frankly there is a lot of drivel talked about the problems of parting off.  If you have this, then you have the wrong tooling. Remember that a proper HSS blade can be re-sharpened with only a lick of the grinder on the front of the tool whereas an insert or cemented carbide one probably needs a diamond wheel on a tool and cutter grinder which from the correspondence elsewhere here is only a pipe dream for most.

Well that is my experience


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## tornitore45 (Dec 24, 2019)

Contrary to the common wisdom I found that the toll should be a trifle under the center line. If it is above is just a ram trying to push the part.
Also, parting is not for the timid. Is a fine line between scraping and playing the part like a violin and jamming. The chip should look like a watch spring and flow out smoothly.
I think everybody had terrible experience parting until they got the hang of it. It is a matter of feeling and sensitivity hard to learn from a book or a web site.
Eventually you will master the skill.


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## ShopShoe (Dec 24, 2019)

Some additional comments:

I tried to find more information on your 7x12 lathe, and was not very successful. It may not accomodate the rear-mojnted, inverted parting tool that is recommended (and I agree that is an option if your lathe can do it. If you can do it, you may want to try it.)

To be absolutely clear, if you are parting, you should not support your workpiece from both ends, I.E.: with a tailstock center or with any other workholder on the end that you will be cutting off. I tried it when I was learning and what I learned was "Don't do that!" As you cut material away, the piece you are cutting off will want to fall off and the whole thing will break at the cutoff point and crash your machine, possibly taking lots of things with it and creating a chance for you to be injured.

If you are cutting a short piece off a long bar, you can support the bar in the chuck, and use a steady rest close to the cutoff point, but position it to the chuck side of the cutoff point. this will also have the advantage of allowing you to keep the end of the bar where you are cutting from wobbling. You may have an additional learning curve in adjusting the steady rest. If your bar is not round or is rough, You may have to turn the bar so it is round in an earlier operation, at least in the area where you will locate the steady rest. Many of the YouTube machinists cutting large round bars on large lathes often demonstrate how they go through this process.

I would recommend that you may want to try different cutoff tools, not just different inserts in your indexable tooling. It is true that you have to push carbide harder than HSS to keep a cut going and that may be hard with a small machine. If you have to use carbide, you may want to try different ones, as you have suggested you will do, but you may need some additional help in determining what to try, either by researching or by asking a good source. I have HSS, brazed carbide, and some indexable tooling for both lathe and mill, and I have found there is no perfect tool for all uses. I consider the cost of tooling to be sometimes an educational expense worth pursuing.

I do think HSS and a grinder are part of the learning curve, as you can really determine what works best in your situation with mostly only a time investment. (If THAT didn't work, Regrind the tool to  a new profile and try again.)

With a small lathe and small projects, I found that I learned parting better if I could closely watch the cut: I have one of the circular lamps with a magnifier in the middle that I can position to watch the cut, and I also have a "Magnivisor" headworn binocular loupe. That way I can watch the chips being formed right at the edge of the cutting tool down inside the parting cut.

If you can't cut your piece off completely and cleanly, there is nothing wrong with using the parting tool to cut most of the way down, then stop and disconnect the lathe and cut the rest of the way with a hacksaw: Then all you have to do is face the cut to clean it up, which you might have had to do anyway.

I use lubricants more intensely with cutting off. I have settled on WD-40 for Aluminum and either WD-40 or "Tap Magic" for ferrous metal. Brass may call for experimentation because it is more "grabby" than other metals. This is on my small lathe. This is also with a traditional "T" HSS parting tool held in a holder for that type of tool.

--ShopShoe


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## petertha (Dec 24, 2019)

I have some offshore inserts similar to what you are showing. They are great value unless you got unlucky & it does happen occasionally. Some thin, uncoated ones I use for aluminum & grabby materials & some thicker coated ones for steels. I cant tell the difference in coating but the nose geometry is a bit different. Aside from the usual rigidity & geometry prerequisites (square approach, minimized tool stick out, lock the carriage travel)... they work great & last forever. One thing to watch though is vertical centering. I don't prefer the eyeball to tailstock center method. A couple thou up or down is the difference between a nice shaving & lesser results. The geometry of some cutters is a bit more complex than plain faceted angles so your eyes could trick you. Also your tail stock may well be a couple thou high but we are hair splitting now.

Its best if you can set up your parting tool permanently for that cutter/toolholder by gaining access to the end of the scrap stock to assess tool height. A remaining nib indicates cutter is below center, plowing over the top of nib indicates its high of center. A few passes to shave it off exactly through the middle of the nib & you are set to go, no more second guessing. If you have to set tool height on the fly with a non dedicated tool holder, I find trapping a thin steel rule along the side of the work is better. The length of the vertical rule exaggerates the setup, its easy to see the vertical 'hang' line of the ruler to your tool post or square to the bed, whatever is a convenient reference. As tornitore45 says, you may find your lathe/situation prefers is a smidge low (some people say high to account for bend). But I would start out with center just as a point of reference. Careful you don't damage the fragile carbide against a hardened rule. Get the thickest section tool shank your tool holder can accommodate or at least match it to the job.

Sometimes people have parting problems & its rooted in lathe issues. For example the carriage cant be locked or the crossfeed leadscrew has excessive backlash or dovetails are sloppy or compound assembly is drifting or deflecting. Or its just a small lathe attempting a big job. These may not parting but can make for ugly cut, harmonics or deflection issues. But if things are reasonably rigid these tools go through material like butter. I don't push my luck with deep parting, I prefer the saw. The inserts & toolholders are so cheap its probably giving HSS a run these days. HSS blades still have much utility - you can custom grind for purpose situations. But for plain lopping off I cant be bothered. Cutting fluids is a matter of experimentation. There is no magic solution & it wont make up for more fundamental setup issues

Example pic. Bronze used to give me grief. By the time I fiddle farted HSS to cut properly I could have made 20 parts. Now its easy.


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## accelo (Dec 24, 2019)

Learning to part on such a small lathe can be an exercise in frustration.
It will require everything being perfect to work.
If you can cut on the back side upside down it will give you the best chance at success. 
Once you get it figured out on the 7x12 lathe, every other lathe will seem like a walk in the park.


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## tornitore45 (Dec 24, 2019)

Supporting the right end with the tail-stock is obviously a problem when the blade cut through the off piece, the loose piece cocks, jams and the tool breaks.  That said, sometime one got to do what needs to be done. One can support the end with the tail-stock until the tool is almost through, leaving the last 1/4" or 3/8" to the hack saw.
If you use the hack saw, absolutely make sure to place a protection piece on the ways. Despite your best effort the saw will hit the ways and nick them.


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## Charles Lamont (Dec 24, 2019)

ShopShoe said:


> If you are cutting a short piece off a long bar, you can support the bar in the chuck, and use a steady rest close to the cutoff point, but position it to the chuck side of the cutoff point. this will also have the advantage of allowing you to keep the end of the bar where you are cutting from wobbling.


I would do this to part off a longish piece, more than about 4 or 5 inches on my Myford. To cut a shorter piece off a long bar you have to work the other way round because there is no room for the steady between chuck and tool. In that case I put the steady half way along what will be the long remnant bar, so that when it separates it sits balanced in the steady.
Of course if the bar is small enough to go through the spindle then all of this is academic.


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## XD351 (Dec 24, 2019)

I can’t say i like the type of toolholder the OP is using as you can’t shorten the tool right up to the lathe toolholder and thus eliminating as much overhang as possible .
I was using the blade and insert style holder but got sick of paying for inserts and blades - decent quality items are expensive !
I switched over to the T shaped HSS crobalt blade from Eccentric engineering and run the blade in the front but inverted and the machine in reverse ( doesn’t have a screw on chuck! ). I find the QCTP holder will pop up if i set the clamping force  just right if i get a jam up .


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## MikeG (Dec 24, 2019)

Hi all and Merry Christmas.
I have found by using the" lathe center finder level" made by "Echo Technolgies" and adjusting my cutoff tool either HSS or carbide insert at level with the center line of the lathe axis and using copious amounts of lube I have no problems.  Maybe I"m just lucky.  I usually (depending on the circumstances) use power feed (slowest infeed) or sometimes manual infeed again depending in the circumstances.

Mike


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## goldstar31 (Dec 24, 2019)

Re the 7x14 lathe I cannot say except that I transferred the GHT tool onto a short Myford 7 boring table rear- with overhang and I used the same tool on a Sieg C4 which is slightly larger than 7x14 using a sub table which was merely a thickish bit of mild steel plate.  Nothing fancy or such and I tend to pepper such things with tapped holes. 

Traditionally, older folks always used an block of metal and peppered and tapped it at nauseam until it became only fit for scrap.  All the Best people had them-- and there was me too.

Why do anything else?


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## tornitore45 (Dec 24, 2019)

When I cut off a short piece from a long bar that does not fit inside the spindle I part near the chuck and hold the bar with my hand mainly to dampen vibrations and toward the end of the cut push it and the last 1/4" breaks by metal fatigue. No falling because the bar is in my hand.
If the bar is rough, like crusty HRS or CI, I have a piece of leather that is always at hand to grip the key-less tail stock chuck notoriously hard to tighten with arthritic hands an various uses to protect from pliers jaws.


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## goldstar31 (Dec 25, 2019)

Perhaps others may correct me but I see this as an extremely dangerous practice.

I would be using either a catspaw or a bell chuck in these circumstances.


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## ignator (Dec 25, 2019)

Luiz Fernando Pinto said:


> - The lathe is a Optimun 7x12, size stock of 100mm


I see this as an Optimum D180x300. This is a bench lathe. 
I didn't see anyone post about how the lathe MUST be mounted to a rigid bench. Preferably steel, and then bolted to the floor. And leveled to ensure no twist in the bed.
I experienced problems with a 10x24 lathe for years doing any cutoff operation. I had my lathe on a sheet metal stand, it weighs ~180Kg. So I always thought gravity was enough. Cutting 1/2" steel close to the 3 jaw chuck, would send the whole lathe into harmonic oscillations, and it would 'dance' on the floor. I purchased a piece of 2" steel plate large enough for the base of the lathe 5 years ago, drilled it for my lathe bolt down pattern, and mounted this back on the sheetmetal stand. I now can do cutoff operations, as well form tool cutting, as this is similar with a wide cutting area (i.e. not a point tool operation), that requires a rigid machine.
If anyone commented about this, I'm sorry I didn't see it.


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## Richard Carlstedt (Dec 25, 2019)

Tornitore45  has it right  !
You can use a tailstock  or steady rest for help in parting-- but not through !
How much so--- is dependent on the rigidity of the Lathe ---and the Live Center  !!
If you push on the workpiece and you can move it......beware !
The more "flexible" the workpiece , the more you have to do it  with "stepovers" as you go deeper


Luiz ,   review the setups in post 22 in the follow link- your photo shows right side overhang 

https://www.homemodelenginemachinist.com/threads/parting-made-easy.31690/page-2#post-330434

For delicate work, use a HSS parting tool- Carbide is never as sharp as HSS can be .

Rich


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## Luiz Fernando Pinto (Dec 26, 2019)

XD351 said:


> I forgot to ask ,
> When you set the height of the tool dis you set the outside edge of the insert or the bottom of the groove in the top to centre height ?





XD351 said:


> I forgot to ask ,
> When you set the height of the tool dis you set the outside edge of the insert or the bottom of the groove in the top to centre height ?



I align this way


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## Luiz Fernando Pinto (Dec 26, 2019)

Thank you all I learned a lot from all the posts.

Thanks also for the "dont do that", obviously i am still learning and your help was essential.


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## TSutrina (Dec 26, 2019)

You tuber Wink's Metal Working Tips has been working on cut off tooling.
Chuck overhang issue effecting cut off: 
Cutt off tool design: 
modifying cut off tool part 1 and 2:


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## kwoodhands (Dec 26, 2019)

Luiz Fernando Pinto said:


> I am in trouble with cut off operations. I tried with a 3mm tool, then with 2mm tool (see photo). I don´t know if it the rigidity of my lathe. I´m lost. Could you help me? Even when i try to cut alluminun or brass.
> troubles that i found in the operations:
> - lougth noise
> - it don´t cut
> ...



Luiz, I would only score the work with the lathe. I imagine the cutter digs in when parting. You can cut as deep as it is safe before digging in ,then cut the work with a hacksaw. The live center is okay to cut part way thru but will jam the work if you were able to part most of the way thru. Advice you are given is spot on.
IF you could part your work you should use HSS , widen the cut to prevent binding, use a T type HSS cut off blade with a small projection. Use a proper lubricant for the metal your parting. 
It may be futile to try and part large rounds, better off hack sawing 1/8" wider than needed and then face to dimension.  If you hack saw the work while it is in the lathe, make sure you put a board under the round and on the ways. If the work falls off  and hits the ways then damage will be likely. 
Also , the carriage must be locked when parting off. If you do not have a carriage lock then make one. Do a search for carriage lock and you will find several that will work for you. 
Usually the cutter is set at dead center, larger rounds may benefit from slightly lower than center. 
The cutter is set at slightly more than the radius of the work. Example, 1-1/4" round stock, radius is 5/8", cutter extends 9/16".  To quickly find dead center try this, Take a 6" scale and place it on the round with the scale centered by eye. Run the cutter up to the scale and hold the scale in place with the cutter. Now observe the scale, if it is plumb the cutter is centered. If the top of the scale tips away from you then the cutter is too high. If it tips towards you the cutter is too low. Adjust the tool height so it is plumb and you're done. 
Remember that small lathes can do very nice work but do have limitations. I have found that the "Armstrong method" of hack sawing works better for me than holding a hack saw frame over the cut while the chuck turns. Your stock is best put in a vice and sawed off, hence "Armstrong method". Then face to dimension with the carriage locked down.

mike


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## Gerald Pierce (Dec 26, 2019)

Luiz, I use a parting tool to make small boiler fittings and live steam locomotives parts. My parting operations is usually under 5/8 inch diameter.
My Cowells lathe has a rear tool post which is helpful since it it is easy to placed in operation. I use a front tool on my Maximat.

I don't work with aluminum, but I have seen several large diameter aluminum parting operations on line. Can't understand what is being made, perhaps fender washers which are available at any hardware.


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## XD351 (Dec 26, 2019)

Luiz Fernando Pinto said:


> I align this way
> View attachment 113042



I had an issue with my lathe when setting up a parting tool using the tailstock .
I set the height and locked the toolholder down then tried a cut and had a dig in so i scratched my head a little and thought I would go over the set up again just to make sure I didn’t stuff something up .
I spun the tool post around and wound the  carriage along to bring the tool up to the point of my centre and it showed that the tool was too high so i reset it and tried again- even worse dig in than before ! Now i was really confused ! while i was standing there completely confused by this i rested my hand on the centre and it moved ! I either didn’t set it in correctly or i may have wound the tailstock barrel in to far releasing the centre , the vibration of the machine was enough to make it move a little causing the tip of the centre to drop as it worked its way out of the morse taper !
Now i do my centre height adjustments for my parting tool the same as i do for all the others - rough set using the tailstock centre then set up some scrap in the chuck and take a light facing cut and fine adjust until it leave no pip or nub in the centre .


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## Ozwes007 (Dec 26, 2019)

Parting off is relatively simple. Set tool height at centre, keep your spindle speed at around 2/3 of your turning speed(don’t slow it down to much, that will make it worse) and power feed or hand wind in the same feed rate you face with. Parting through with a hole , use a small loose fit drill up the centre, no hole: leave a little , then saw it of.
In 40 years of machining, I can count on one hand the number of times I have had a failure, and always it was because I was going to slow! Or the tool wasn’t setup properly. ALWAYS USE A LUBRICANT, except for brasses and cast irons. If this doesn’t work your machine needs to be made rigid, or mounted rigid. Vibration is caused by job rigidity, turning to slow, or machine rigidity. I have seen countless blades or tips destroyed by people that have the speed to slow. back mount is purely to eliminate rigidity problems in the machine, also don’t  use a 4mm or even 3mm on a Taig or similar really small Lathe, try a 2mm. It’s pure mechanics with these lathes, how often do you take a 3 or 4 mm cut on them? 

Oz


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## Luiz Fernando Pinto (Dec 27, 2019)

Ozwes007 said:


> Parting off is relatively simple. Set tool height at centre, keep your spindle speed at around 2/3 of your turning speed(don’t slow it down to much, that will make it worse) and power feed or hand wind in the same feed rate you face with. Parting through with a hole , use a small loose fit drill up the centre, no hole: leave a little , then saw it of.
> In 40 years of machining, I can count on one hand the number of times I have had a failure, and always it was because I was going to slow! Or the tool wasn’t setup properly. ALWAYS USE A LUBRICANT, except for brasses and cast irons. If this doesn’t work your machine needs to be made rigid, or mounted rigid. Vibration is caused by job rigidity, turning to slow, or machine rigidity. I have seen countless blades or tips destroyed by people that have the speed to slow. back mount is purely to eliminate rigidity problems in the machine, also don’t  use a 4mm or even 3mm on a Taig or similar really small Lathe, try a 2mm. It’s pure mechanics with these lathes, how often do you take a 3 or 4 mm cut on them?
> 
> Oz



I am still learning some lathe operations. But I've learned a lot here from you. I am still setting up my workshop and have done a lot of tools. But soon I want to make my first models. If you are interested in following my evolution you can see in my Instagram @luiztools.

But this Instagram profile is more related to my daily life in the workshop, so don't expect any models there.

Thanks everyone for the answers. I am very grateful for your attention.


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## Wizard69 (Jan 5, 2020)

A little late to the thread but I’m not sure that people are stressing the importance of setting center height enough!!    Setting your height via a live center is not good enough.  The tool needs to be on center or a few thousands lower.   

I actually learned this at work on a machine bigger than most hobby lathes.  If your tool isn’t set right no amount of trying to get it to feed properly will work.  

Other points to consider is that the tool must be square to the axis of rotation.  Oil absolutely must be used on steel.   Note I said oil there, a lot of water based “coolants” don’t work that well in cut off operations.  And lastly feed rate must be even and at a rate that keeps the tool cutting.  

I’ve never tried a rear mounted tool post but I’ve heard good things about them.   Frankly I don’t see any reason why one should be better than the normal tool post location.  However if the tool post is crappy to begin with an improved tool post can help.  

By the way on these small lathes or even some larger ones, the compound  can be an issue.  If the compound is rigid or shifts position under cutting loads you will have problems.  On my 9x20 I remove the compound for most work, putting the tool post on a riser block.  Frankly this helps everything done on the lathe.  

By the way sometimes one is better off just setting the cut location and pulling the part to hack saw or band saw through.   Sometimes it is the quicker solution.   This especially if you don’t want to loose tool position.  

I will stop now as the list is getting long but I suspect that the number one issue is center height setting.


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## Wizard69 (Jan 5, 2020)

goldstar31 said:


> Perhaps others may correct me but I see this as an extremely dangerous practice.
> 
> I would be using either a catspaw or a bell chuck in these circumstances.


I have to agree putting ones hands into contact with a rotating piece is asking for trouble.   It will likely work fine until the day it doesn’t and blood gets loose.  

Now that being said sometimes it only takes a little pressure to remove nasty harmonics.   In that regard the end of a wooden hammer handle can muffle those harmonics and keep hands away from the part.  

In any event I believe the majority of lathe accidents involve somebody getting tangled up with a rotating part and pulled into the lathe.  Often that involves hair or clothing.   The goal of every lathe operator should be to avoid the common way people get hurt or die on these machines.


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## Cogsy (Jan 5, 2020)

Wizard69 said:


> A little late to the thread but I’m not sure that people are stressing the importance of setting center height enough!!    Setting your height via a live center is not good enough.  The tool needs to be on center or a few thousands lower.



I see this advice a lot but when I search an authoritative source (such as Sandvik) they suggest virtually on center, or slightly above center on deeper cuts to allow for tool flex. Setting the tool low leads to rubbing and possible part climbing over the tool as diameter decreases. Based on the usual lack of real rigidity in most hobby lathes, I would advocate for slightly above centre (+0.1mm/4 thou) for best results.


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## Richard Carlstedt (Jan 5, 2020)

One thing I do not see here is how to set your tool height !
If you do not have a 6" aluminum scale, get one.
Steel scales work ,but tend to be slippery when used and drop into the chip tray
_This works for any Lathe Tool_
Place the scale between the workpiece and the toolbit and gently bring the tool into contact capturing the scale.
If the scale leans into the work ( away from you) , you are too high.  So lower the tool 
When the scale is vertical, you are on center !
If the work piece is not available, use the tailstock barrel for setup, but a turned surface is more accurate.

Last suggestion from an oldtime machinist ---Tool height becomes more critical as diameter decreases !
Chuck up a 1/4" (6mm) dowel and do the above setup and you will see how sensitive you can be 

Recommendations to set tool cut edges high are a function of the front relief angle -beware !

Rich
PS
Straight aluminum strips  like .040 (1 mm) x  1/2 ( 12mm) x6 (150mm) work can be substituted


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## goldstar31 (Jan 5, 2020)

In the words of the late Professor C.E.M.Joad, a participant in the Programme  'Brains Trust' along with such International Worthies as Jacob Bronowski( The Ascent of Man), 'it all depends on what you mean by '*******"

Do you mean the tool in front or aft and upside. down or in forward gear or reverse? 
The argument for a relatively flimsy lathe was postulated by the late George Thomas who was the winner of many awards for model machining as an addition to running his own successful engineering works both in the UK and the USA. I am gratified in the knowledge that many here have wisely ascribed to not only his designs but his long researched developments and arguments and discussions with other experts both in teaching, in industry and , of course, model engineering. One of them was 'no slouch' being involved in the Manhattan Project' If one is unaware of that 'it ended World War 2 in no uncertain manner!

By utilising  a rear inverted tool post, he was able not on to solve one problem  which has beset model engineers for decades. Almost every second hand Myford which I have encountered has the tell tale hacksaw marks of--- some one -who didn't choose to listen.  The cost was a couple of copies of Model Engineer( Volume 142 et seq) a couple of hss blades of different thickness on the rotatable turret-- and laughingly, the scrap box.
Amongst other things, Thomas removed the constant 'loss of height; in re-=grinding blades by tilting them at at angle of 7 degrees and then sharpening the front edge of the blades att 75 degrees. To add icing on the cake, the rear inverted tool  minimised the going in and out of cut with the almost inevitable snapping a relatively pricey blade( s) but went on to grind a positive 'vee' on the from cutting edge but grinding a 140  'negative' vee which successfully narrowed and rolled the swarf in diameter to again minimise a slightly off centre positioning.

It was only a kerf of an inch or so and perhaps baffled some who did not have a tool sand cutter grinder nat the time( me) and I moved aware from  the Propositions of Euclid and Concepts of Pythagoras by the simple expedient of using nothing more  ethereal than a worn angle grinder disk instead. 

This was all in the Days of the Dodo- and I still have not replaced one of the blades from then.
As I have said earlier, I have swopped and changed the rear inverted tool post onto several varieties of lathes.

Amongst the many users, one was the editor of both George's books. He graduated in dentistry along with my late wife. 
Simple- well reasonably simple applied geometry.  Most of this stuff- I recalled the other night dates back to the 'real' TubalCain and worthies like Hiram Abiff , King of Tyre and and the building of the First Temple of Solomon 

Regards

Norman


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## goldstar31 (Jan 5, 2020)

Richard Carlstedt said:


> One thing I do not see here is how to set your tool height !
> If you do not have a 6" aluminum scale, get one.
> Steel scales work ,but tend to be slippery when used and drop into the chip tray
> 
> ...



GHT also made a rather pretty little tool height gauge -with two knives one for ordinary lathe tools and t'other for the upside down variety. vis .  Model Engineers Workshop Manual

If you want to retain a SHARP edge, don't use steel strips

Cheers

N


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## accelo (Jan 6, 2020)

_"Frankly I don’t see any reason why one should be better than the normal tool post location"
_
It works better because Gravity is your friend if the tool is upside down. 
I have a Myford and it uses the upside down rear mounted cutoff tool.
It works beautifully for two reasons;
It bypasses the top side as it is mounted on the cross slide directly and the above mentioned gravity assistance.
I have other lathes of similar weight and nothing out preforms the Myford for parting.
Another features are the tool is always set on center and it doesn't require resetting every time.
It is also keyed to the cross slide so it is automatically parallel. 
If your lathe has provisions so a rear mounted cutoff tool can be incorporated, I highly recommend it.
Rick


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## dazz (Jan 6, 2020)

Richard Carlstedt said:


> One thing I do not see here is how to set your tool height !
> If you do not have a 6" aluminum scale, get one.
> Steel scales work ,but tend to be slippery when used and drop into the chip tray
> _This works for any Lathe Tool_
> ...



Hi
You could make a gauge for your lathe.
http://denfordata.com/bb/viewtopic.php?f=14&t=705
Dazz


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## tornitore45 (Jan 6, 2020)

The reason for a rear tool post is that old and/or hobby lathes have a threaded spindle making it dangerous to cut in reverse with such a heavy torque imposed by a parting tool.
With a locked chuck capable to drive in reverse and placing the tool upside down one can duplicate the same advantages of a rear tool post with inverted tool set in the regular tool holder and running forward.

What is the advantage?
Gravity clearing the chip is not the reason, one may cite the cutting oil washes away as a disadvantage and would be just as wrong.
Picture the tool/tool-post sitting on the cross slide as an inverted L hinged at the bottom.  The downward cutting force flexes the entire geometry pulling the tool to dig in, the more it digs the higher the force, the bigger the dig. The structure flex and the flex raise until either the tool breaks or snaps back after it finally swallows the big bite, the latter case repeats originating chatter.
Now flip the tool upside down an run in reverse and try picturing what happens. 
Things are easier now, the cutting force pushes the tool away until the chip load balance the resisting force of the flexing tool-post assembly.

If it can be of any consolation I went from disastrous results, bone jarring chatter and white knuckle holding of the wheel to easy, relaxing, uneventful, predictable parting by just learning to set up, grinding the tool and selecting the right speed and feed.  Like swimming, is not something one can entirely learn in books; one must pay attention, sense the feedback from the machine, build experience and learn.


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## Charles Lamont (Jan 7, 2020)

A tool height gauge is the most useful little tool I have ever made. Here is the idea: http://www.hemingwaykits.com/acatalog/Centre_Height_Gauge.html

Wizard69, you say you don't see why a rear toolpost should be an improvement, and then get pretty close to explaining it yourself! The argument goes like this: a tendency to dig in causes deflection (some, no matter how stiff the machine). Part of that defelection is in the form of a rotation about the mounting. At the front toolpost the deflection is down and forward into the workpiece, whereas with a rear toolpost the deflection is up and backwards, out of the work. If you have trouble visualizing this, imagine a tower crane. In the first case a dig-in is a self-reinforcing feedback system, while at the rear it tends to be self correcting. (I didn't notice the above post by tornitore45 before posting this)


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## ALEX1952 (Jan 7, 2020)

Tomitor45 says to reverse the spindle and turn tool upside down, this will result in the tool just rubbing, if the tool is to be turned upside down the rotation is not changed. We used this method on short runs of components using form tools on a centre lathe, set so the saddle did not have to move with a plunge cut for the form and then part off to length on the same setting ,we would also use long bar stock as in capstan turning and part of without reversing which for production purpose is quicker, no stop start etc.
  I think the one big advantage of rear mounting is the tool, once set, which for most of us professional and amateur is a bit of a pain in the rear to get right, is a bit of a black art which none of us seem to agree on. I have been in the game 50 yrs and like to consider myself a good engineer/machinist and will avoid parting like the plague.


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## goldstar31 (Jan 7, 2020)

Alex- thank you for your comments but I'm not a professional anything although I was brought up in the blacksmith's shop from the age of 3 or just able to look at what my Dad did at the other side of the anvil.
Does that make 86 or 87 years--- Heaven forbid.  I WAS a bean counter but that was 35 years ago.
There is is no Black Magic in parting off though there probably is  in my survival after very early retirement.

What t is the ability to find a few pounds/dollars  to buy the book. I'm on my second one and the ability to push preconceived notions to one side and to read what someone with miles more ability than I- and get on with an open mind to create what is a relatively simple bit of machining. The Great LBSC ( Curly Lawrence) wrote about the 'Words and Music' about his locomotive building. And well he might.

You will note that I studied 'history' and have concluded that there isn't much new anyway. There wasn't much education in those grim days of war in Britain and I read whatever was to hand. Would you believe that the father of the Railways couldn't read or write. His cottage was on the other side of the river to where Dad worked.
The mystical railway gauge of 4 feet  8 and a half inches is nothing to do with the Brits- it is the width of the Roman chariot ruts that were worn on the Roman Wall. Who preceded it all seems to be a guessing game.
Incidentally, I'm still teaching or mentoring as a wend my stumbling way into my 90th year. With one eye almost gone and the other desperately in need of another 'shot', I'm still struggling to improve my knowledge( between tots of whisky)
 Get a hold of GHT in the Public Library or wherever and put a quick end to the so called horrors of parting off.
So my kindest regards for the future-- and do some thing far more demanding


Cheers

Norman - but not from the Norman Conquest


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## fcheslop (Jan 7, 2020)

Had to part four bits of round 65mm dia alloy today and using Geo Thomas rear tool post it was a walk in the park unlike the butt clenching memories pre rear tool post days
Buy the book and a whole world of well designed tools will be available including his tool setting gauge and most canbe made for very little cost and in some cases little effort
I know it may seem old fashioned to make youre own tooling as you go but the lessons learned and the knowledge gained  is pure gold
Using his boring tools in a modified form I can bore down to 1mm all from some bits of mild steel and a few bits of drill rod/silver steel total cost probable less than £10 for the small set and about £20 for the larger tool post set up that bores from 6mm up 
Just my two bobs worth
Good luck and cheers


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## RonW (Jan 7, 2020)

Hi Dazz,
      Ironically I have an identical square to the one you show. It must be more than 60 years old having been bought form my mother's shop in Northern Rhodesia, now Zambia, while I was in the model making phase of my life. I will have to dig it out  and use it as you suggest. Never thought of that. Thanks,
Ron W


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## goldstar31 (Jan 8, 2020)

I've been trying to assist in finding Mini-Bonelle drawings etc  which is a far more difficult tool to make than than the modest little GHT rear parting tool.
My mind did wander off almost blinded with hullabaloo about ' Much a Do about Nothing- or not a lot' 
GHT DID publish two smaller books himself called 'The Universal Pillar Tool' and 'Dividing and Graduating' which  were after his death, joined and considerably expanded in a companion book entitled 'Workshop Techniques' 
Amongst other pursuits, I made the UPT with the Mark2 castings after obtaining  a quite useful  fabricated and welded one which was almost given to me- for few coins.   Again, not having the temperament to make and tolerate the construction of an electrifying  dividing head, I made up a GHT Small Dividing Head with- seemingly the ability to do wondrous things with a one hole division plate but with two Acme threads. The boring(?) was done with the delightful GHT little precision  boring head albeit from the main book.

With impish glee, I made a 360 degree attachment for my Quorn using a borrowed GHT headstock dividing thing for the Myford - and Jack Radford's  division cutter thing only to find that  I have the only Quorn with 359 set of divisions. 

How, why, what and when but I have a unique  tool and cutter grinder!

Norman


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## tornitore45 (Jan 8, 2020)

[QUOTET]omitor45 says to reverse the spindle and turn tool upside down, this will result in the tool just rubbing, if the tool is to be turned upside down the rotation is not changed.[/QUOTE]

Nothing could be more wrong that this.


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## ALEX1952 (Jan 8, 2020)

tomitor45 I have just re-read your post several times to find out where we are at odds, I now think I understand your method. Are you using the front tool post, rotation in reverse and tool inverted which I agree will cut, good bad or indifferent on which I can't comment, however at the end of Para 2 you say "and running forward" which I find very confusing, am I correct in my understanding of Para 2. and if so please explain "and running forward.
Regards Alex


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## tornitore45 (Jan 8, 2020)

> With a locked chuck capable to drive in reverse and placing the tool upside down one can duplicate the same advantages of a rear tool post with inverted tool set in the regular tool holder and running forward.



"With a locked chuck capable to drive in reverse and placing the tool upside down"
AND actually running in REVERSE

one can DUPLICATE the same advantages of a rear tool post with inverted tool set in the (regular) replace "regular" with Rear tool holder and running forward.

My bad, hope this clears it.

The whole point is the reason to mess with rear tool holder is because the chuck unscrews if one tries to run in reverse BUT if one CAN run in reverse just flip all your parting tools and remember to part in reverse.


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## ALEX1952 (Jan 9, 2020)

I  understood the unscrewing bi,t it was the tool post and direction that was making me think I was more daft than I actually am. As an aside on the subject of screwed chucks I have seen some Chinese type machines with set screws to lock the chuck on the nose which I think is a suspect method if for no other reason should it slip you are probably going to Kna*****r the nose. As an apprentice I was taught on Colchester Student lathes which has a keyed nose with a large screwed collar to lock in place, I have seen this undo when the brake was used and the chuck bounce up the ways, probably not done up tight enough but it happened causing major distress to yhe apprentice.


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## goldstar31 (Jan 9, 2020)

Why unscrew a chuck when the lathe can perfectly well cut off parts whilst running in forward drive?
Which is what George Thomas understood-- having had a long history off using threaded spindles as well as other machine tools in his works. I doubt that few , if any has been the principal/owner of your own workplaces.

Perhaps a moderator would lock this as it is not getting anywhere .


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## tornitore45 (Jan 9, 2020)

There are reasons to part in reverse if BOTH conditions are met
1) The machine has a chuck mounting method that allows it
2) For any reason that is not really important the tool holding system is not very rigid and can not be improved.

Those conditions are rarely seen together in one machine because most industrial grade (not hobby toys) are very rigid and generally have moved away from a threaded spindles.

Still if one has a rigid machine and the chuck does not unscrew there is no harm in parting in reverse.
Saddle lift considerations are in order if one plans to hog down with a heavy hand.


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## Richard Carlstedt (Jan 9, 2020)

The main reason a rear Toolpost functions well is that the load is supported "within " the cross-slide ways.
This is important for newbies to understand 
Rich


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## Shaun free (Jan 9, 2020)

Luiz Fernando Pinto said:


> I am in trouble with cut off operations. I tried with a 3mm tool, then with 2mm tool (see photo). I don´t know if it the rigidity of my lathe. I´m lost. Could you help me? Even when i try to cut alluminun or brass.
> troubles that i found in the operations:
> - lougth noise
> - it don´t cut
> ...


Its never a good idea to cut between centers. I always get the cut as close to the chuck as I can and part there. If you have your live center it will cause the part to bind. Also sharpen the tooling before every cut.


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## petertha (Jan 10, 2020)

Richard Carlstedt said:


> The main reason a rear Toolpost functions well is that the load is supported "within " the cross-slide ways.



Hmmm.. But you have substantially reduced the tool post footprint area mated to the top of the compound in order to orient the cutting tool that way.

Several people who (temporarily or permanently) replaced their compound slide with a solid base and additional tool post detente/support have noticed substantially improved rigidity in all cutting operations, including parting. I don't think there is much flex in the cross bed casting laying across the ways. Or at least relative to the top end stack-up assembly which have substantially less mass, sectional area & many more inter-contact areas: the cross slide dovetails, any lead screw float, the tool post, the tool post dovetail, the tool holder, the insert within the tool holder....


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## Richard Carlstedt (Jan 10, 2020)

Peter, the point I was making was keeping the cutting load centered on the support provided by the cross-slide AND tool-slide areas.   Removing the tool-slide function as shown in your pics is also a great help as it removes another "Flex" joint in the assembly . No doubt a lathe without a tool-slide is much more rigid in operation.
I had a 1943  14" LeBlond that had a tall cross-slide ( and no Tool-slide) and it was extremely rigid. Tool-slides are not a necessity for Lathes but most lathes have them for thread work or micro taper boring , so you work within the means you have .

Rear tool posts also have disadvantages , but lack of rigidity is not one of them
Rich


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## awake (Jan 11, 2020)

I'm not sure if it has been mentioned - I might have missed it - but there is another subtle difference in the upside-down parting (whether at the front with the spindle in reverse, or at the rear with the spindle in forward): The forces from the cutting action pull the cross slide up, wedging the cross slide dovetails against the carriage dovetails, and thus increasing rigidity.

Of course, for parting right-way up, the corresponding thought it is to be sure the cross slide gibs (and compound gibs, if using the compound) are snugged up properly. Also be sure the carriage is locked and can't shift left or right.

Another point worth mentioning: If you are using a chuck that is at all bell-mouthed, it can let the part flex just enough to catch. DAMHIKT!


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## holmes_ca (Jan 11, 2020)

I have a Taig Mini Lathe and I scaled down a copy of an old fashioned spring parting off toolholder it really works great, 

Edmund.........Alberta


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## Tim1974 (Jan 12, 2020)

Why not all just get a decent lathe and be dun with all this bickering


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## Peter Twissell (Jan 12, 2020)

I choose to persevere with a Drummond round bed lathe which my grandfather bought in 1926.
I take pleasure in working out ways to perform operations which would normally be considered beyond the machines capacity.
For parting off, I find the traveling steady very useful. The loads from the tool are reacted through the steady directly to the saddle, eliminating chatter and producing a smooth, straight cut.


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## Wizard69 (Jan 12, 2020)

Cogsy said:


> I see this advice a lot but when I search an authoritative source (such as Sandvik) they suggest virtually on center, or slightly above center on deeper cuts to allow for tool flex. Setting the tool low leads to rubbing and possible part climbing over the tool as diameter decreases. Based on the usual lack of real rigidity in most hobby lathes, I would advocate for slightly above centre (+0.1mm/4 thou) for best results.



Lately the only parting I've been doing at work has been either hardened Thompson rod or a bit of 4340.      Hardened rod absolutely requires that you be either exactly on center or a tiny bit below.   If not the tool rubs.    Now different materials will deliver different results so I will not dismiss Sandviks advise completely.    It should also be noted that I suggested no more than a few thousands lower, you can certainly run into issues going too far.


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## Wizard69 (Jan 12, 2020)

Charles Lamont said:


> A tool height gauge is the most useful little tool I have ever made. Here is the idea: http://www.hemingwaykits.com/acatalog/Centre_Height_Gauge.html
> 
> Wizard69, you say you don't see why a rear toolpost should be an improvement, and then get pretty close to explaining it yourself! The argument goes like this: a tendency to dig in causes deflection (some, no matter how stiff the machine). Part of that defelection is in the form of a rotation about the mounting. At the front toolpost the deflection is down and forward into the workpiece, whereas with a rear toolpost the deflection is up and backwards, out of the work. If you have trouble visualizing this, imagine a tower crane. In the first case a dig-in is a self-reinforcing feedback system, while at the rear it tends to be self correcting. (I didn't notice the above post by tornitore45 before posting this)


I have no trouble imagining this sort of operation.    What I see is the tool working against the mechanics of the machine.    Instead of compressing the various parts of the machine together you are effectively pulling them apart.


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## goldstar31 (Jan 12, 2020)

Tim1974 said:


> Why not all just get a decent lathe and be dun with all this bickering



Tim




Peter Twissell said:


> I choose to persevere with a Drummond round bed lathe which my grandfather bought in 1926.
> cut.



Well Yes but I bought my first RB Drummond for £9, eventually gave it away and bought GHT's book for £30-- and then wore it out and bought a replacement

I don't think that I want to meet challenges in either another RB or have another damned nuisance of a bell mouthed chuck.

Perhaps the one thing that stuck in my mind in all my years is that 
this is Big Show for one life only and it is not the dress rehearsal.


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## tornitore45 (Jan 12, 2020)

> Why not all just get a decent lathe and be dun with all this bickering



Because a decent lathe use too much room and then I can not park my Roll Royce next to the Maserati next to the wife's Bentley.
Isn't obvious?


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## tornitore45 (Jan 12, 2020)

About tool height.
A tool that is high, even a few thousands, is not going to cut until it deflects enough to bring the cutting edge into contact is just plain geometry.
A tool that too low adds a bit of negative rake to the cutting angle.
This reduce the positive rake if the tool has any.
The rake angle reduction will increase as one moves to center.
As long as the tool is not going to leave too large a pip in the center is fine.
How large is a pip too large.
If the part is sturdy enough not to climb over the tool you can be 0.030" low and nothing happens.
If you are parting a 1/4" bar  1/2" from the jaws then better be no more than 0.010" low, the 0.020" pip is not strong enough to cause problems.
Being 0.005" high you may push the bar before the tool deflects enoug to start cutting.   Beside, tool/tool holding deflection is what causes chatter.


No wonder parting is so troublesome and controversial given the amount of misunderstanding of the physic and geometry of the subject.


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## awake (Jan 13, 2020)

At the risk of beating a dead horse ... I have a HSS parting tool, T-shaped but also with a U-shaped relief in the top to help curl the chips for clearance. It works very well (at least, when sharp - the other day I was thinking the material was awful, but the tool just needed to be sharpened). But here's the odd thing - the U-shaped geometry changes where it wants to be positioned. If positioned in the usual way "on center," the tips of the U are in the right place, but the bottom of the U is too low. I have to position it a bit higher for it to cut correctly.


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## Peter Twissell (Jan 13, 2020)

Provided the tool is ground with any clearance on the leading face, it can cut when set above centre height. The limit case occurs when the clearance is tangent to the surface of the work. When using old machines, it may help to have a geometry which forces the work to lift slightly before the tool begins to cut. This will take up any vertical freeplay in both the workholding and the slides, reducing the opportunity for chatter.


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