Parting Difficulty

I am not so sure that going to a wider tool is the answer. A wider tool will offer more turning resistance to the work piece, which in turn creates more downward force on the tool, creating more chance for chatter. A narrower tool would offer less resistance, in turn resulting in less downward force and less flex, provided the tool does not stick out too far. 3/32" is narrower than 1/8", not wider.

The other points that have been brought up are all good also, and gib adjustment on the cross slide and the compound are very important. I had mine where I thought they were tight enough, but I had to snug them up just a bit more for parting to go smoothly. Even then I would still have some trouble, which I was able to virtually eliminate by going to the slightly narrower blade. There are times when I need a wider cutoff tool, but most of the time the 3/32" tool works very well.

One last thing to consider is that after sharpening your cutoff blade on a grinder, it might be a good idea to hone it a bit on a stone to give it a very keen edge.
 
I became interested to check if it is possible to use a wide carbide cutter that I've got. I cant see any big use for it except if the load will be very high so thin inserts may snap. The width of the insert is 5 mm (1/5 inch). The workpiece is a 45 mm (1.8 inch) aluminium T6 rod. The gearbox was set to the strongest torque but w/o activating the back gear, which would have produced a lot more torque. I lubricated with small squirts of WD40 and it worked well with auto feed.

 
Not good to use tailstock support when parting. Make sure tool is exactly square, perpendicular to the work. Otherwise the tool binds as you advance it.
 
I agree with Terry that a narrower insert will make it easier since the load on the lathe is reduced. I normally use 3 mm (1/8's) so the test with the wide insert was just out of curiosity to see if it would work.
 
The two problems I usually run into with parting is; turning too fast and (as eeler1 says), make sure you have the tool "exactly perpendicular" to the work. It's not hard to turn a 1.5" work piece way too fast. Start slow and you can always speed up to make the process more efficient. Starting too fast is asking for instant problems. There is virtually no side clearance on a parting tool. So if the tool is not exactly perpendicular to the work turning axis, it very soon starts to drift to one side or the other causing it to make a lot of noise and eventually jam. You might also try grinding a 3 degree clearance to the left side of the cutting point, (slope away from the work being parted). This has worked for me in reducing point chatter to zero. I also use a constant coolant/lubricant flow to cool the blade and work and keep the chips moving out of the groove. As stated by others getting all the turning conditions correct is essential to parting. I would also suggest starting with smaller work pieces to get the feel of it.
 
prasad said:
I tried it again with live center mounted and at one point I think the parting tool got caught.
Click to expand...

Prasad, there's one problem!
higgite nailed it above - Never, ever part between centres!!!

It should only be done with the work mounted in a chuck or collet.

prasad said:
I will have to buy a wider parting bit then
Click to expand...

terrywerm was suggesting a thinner parting blade, as that will mean less cutting force required.

-brino
 
It sounds like you are turning too fast. I part in backgear and at the slowest or next to slowest speed on a larger diameter like that. The larger the diameter the less rpm you need. We are dealing with SFM here.
 
You've received some very good advice: careful tool alignment, slow speed, thin parting tool, lots of coolant and don't pause when feeding into the work.

The best thing that I ever did for my smallest lathe was to add this threaded support to the cross-slide. Parting with a 3/32 blade in any material (under Rc 30) is never a problem.

The support is threaded into a tapped hole in the cross-slide. A screwdriver slot was machined into the top of the support for easy removal. (When the compound-slide is in use, the support is removed.)

P1020300.jpg

Incidentally, QC toolposts are not well-suited for parting due to the long cantilevered distance between the cutting edge of the tool and the surface where the toolpost is actually clamped to the compound. If you have to use a QCTP, consider supporting the tool with a machinist's jack as I did for the boring tool in the photo below:

P1010304.jpg
 
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