Trouble with cut off operations

[Luiz Fernando Pinto]

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 Fernando Pinto]

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.

 

[Arnak]

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

 

[ShopShoe]

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

 

[Luiz Fernando Pinto]

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

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.

 

[Luiz Fernando Pinto]

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

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

 

[Luiz Fernando Pinto]

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.

 

[XD351]

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 .

 

[Luiz Fernando Pinto]

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.

 

[XD351]

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 ?

 

[goldstar31]

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

 

[Charles Lamont]

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

 

[xpylonracer]

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

 

[kvom]

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.

 

[goldstar31]

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

 

[tornitore45]

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.

 

[ShopShoe]

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

 

[petertha]

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.

 

[accelo]

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.

 

[tornitore45]

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.