Trouble with cut off operations

[Charles Lamont]

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.

 

[XD351]

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 .

 

[MikeG]

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

 

[goldstar31]

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?

 

[tornitore45]

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.

 

[goldstar31]

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.

 

[ignator]

- 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.

 

[Richard Carlstedt]

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

 

[Luiz Fernando Pinto]

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 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

 

[Luiz Fernando Pinto]

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.

 

[TSutrina]

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:

 

[kwoodhands]

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.

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

 

[Gerald Pierce]

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.

 

[XD351]

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 .

 

[Ozwes007]

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

 

[Luiz Fernando Pinto]

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.

 

[Wizard69]

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.

 

[Wizard69]

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.

 

[Cogsy]

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.

 

[Richard Carlstedt]

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