More Parting Issues

Matt in TN

Matt in TN

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Nov 2, 2014
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I've read and read about parting, but have a new issue I haven't read about before. I noticed today while parting, the rod/material being parted gets pulled slightly forward out of the chuck. At first I thought my tool post was moving to the left, but it's actually the workpiece moving to the right.

I've got everything locked down tight, just barely enough of the parting tool sticking out of the holder to cut the depth I need, touched up the parting tool with a stone before cutting, and tried to set the tool as perfectly midway up the part and perpendicular to the part as possible.

I'm guessing what I thought was perpendicular really wasn't, so I induced some axial force on the part? My 3-jaw chuck was hand tight, but the part pulled forward anyway. This was with 4140 steel, using dark sulfur cutting fluid.

Any ideas how to set the tool more perfectly perpendicular, or is this indicative of some other issue I'm missing?
 
Lock your carriage and compound, and make sure your parting tool is perfectly perpendicular (at a right angle) to your work.
 
I have found that setting the blade against the chuck face is a quick way of aligning it making sure the holder doesnt touch the chuck whilst doing so.
Its not quite perfect with tapered face blades but seems to work ok.
I set a square against the chuck face to ensure it was square to the cross slide some time ago when I was just checking everything out.
 
As is the case with nearly every work shop job, there is more than one method. You could set up a dial (magnet on the bed or even stuck to the chuck) and the indicator point on the mounted parting blade - then travers the cross slide. Should be no issue getting it square.

I struggled with parting off for years. Finally started to get consistently good results when I switched to a 1/8" carbide insert blade.

Recently, I have started using the parting blade in the rear holder (upside down). Works fantastic (okay, just on one job - 3 cuts in 316SS material).

I attempted to post a picture in the photo album (first try at that??).

http://www.hobby-machinist.com/gallery/dscf5102.94789/
 
Andre said:
Lock your carriage and compound, and make sure your parting tool is perfectly perpendicular (at a right angle) to your work.
Click to expand...

Carriage was locked, but there's no lock (that I know of!) on my compound. I did put an indicator on the tool holder and the carriage while cutting because at first I was convinced it was moving - but it didn't budge.

I may have to try the upside down and backwards method -
 
Chipper, I envy your rear post. My little 6 x 24 Atlas type has a rounded cast compound, no way to mount it.

Matt. I keep an Allen wrench handy to snug down one or two of the gib screws on the compound when I need a bit more rigidity.
 
tighten your chuck or put something grippy (brown paper?) between the work and Chuck jaws. you shouldn't have anything pull out of your chuck. once you sort that, then you can worry about what's causing the problem. my guess would be either a non perpendicular parting blade or one that's ground with less relief on the side facing the Chuck. i need to fix that problem on one of my blades - you can actually see it bending in the cut.
 
Often when things pull out of the chuck the issue is

1) the chuck jaws are worn more at the tip than the base; they may need to be ground

or

2) the work is not centred or is being pushed off centre by the parting tool. When this happens the work gets pushed backwards, then it rotates, and it gets pushed back again. This causes the work to "walk" out of the chuck.

-brino
 
+1 on what brino said. A good chuck should hold the work securely. Bell shaped chuck jaws hold with point contact father than along the full length of the the jaw. The tool pressure causes the part to twist in the chuck with the twist rotating with the chuck. This would be similar to trying to chuck a tapered piece in a chuck.

Squaring the cutoff blade and locking the carriage may prevent the part from walking out but that is not the root cause of your problem.
 
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