Thread: Parting Off!!!

I have a fit parting off! I tighten my gibs down on the cross slide and compound. I even lock the saddle. I try to have very little protrusion with the tool and be close to the chuck. I insure the tool is on center. I put oil on the cut and push in and out with the cross slide to clear chips. All will work fine then all of a sudden the belt (thank goodness) will squeal and all stops! Each time there is a chip that peels out of the kerf but doesn't cut free. What am I doing wrong?
Pictures 1-3 show the chip, 3 shows it after I use my hand to rotate the chuck backwards, not an easy task. Picture 4 shows how the slides are set up, trying not to over hang and that the gibs and saddle lock is tight. Picture 5 shows the amount of tool protrusion.

first what are you parting? speed?
if all is going well and then it siezes up, heat may be causing the trouble.

it`s hard to tell for sure but it looks like it may be a straight sided blade? if so, very prone to heat build up.

Not sure but it appears the top of the parting tool might not be flat, pushing the chip to the sides of the cut causing some friction/drag issues. Is the belt tight enough? I think the machine should have enough torque to overcome a small chip like that. The picture showing the angle of the compound setting means nothing if the tool itself is not perpendicular to the work. My $.02.

First time I ever heard of a part-off problem using an HSS blade in steel

The speed is 300 rpm and the metal is steel cold rolled. The blade has a taper on the sides and kind of a peak on the top. I'm keeping it flooded with oil. I'm perpendicular to the work, by eye.

Originally Posted by iwananew10K

first what are you parting? speed?
if all is going well and then it siezes up, heat may be causing the trouble.

it`s hard to tell for sure but it looks like it may be a straight sided blade? if so, very prone to heat build up.

you have an import holder(milled with straight sides) with a tapered blade, if you were to look at the tool from the workpiece point of view likely one side of the blade would be straight up and down and the other at an angle. take care when you install the blade to be sure it will have relief on both sides.
eyeballing it perpendicular is probably not good enough, use a parallel against the chuck or some other known straight edge to set it.
also grind the top of the blade flat if it already isn`t- if i understand correctly the "peak" you are seeing is for the lantern type holder which relys on a "cam" that wedges the blade in when tightened. grind the high side of the peak down even with the low side.

Instead of just eyeballing the blade perpendicular to the work, try loosening your toolpost and moving the blade up against the face of the chuck. Now when you lock it down you KNOW it's where you want it to be.

You need to grind the top of the exposed blade flat and 1-2° top rake so the widest point is at the cutting edge.
The front rake should be 3-4° more than the angle that the blade is tilted in the holder.
You should have curley chips, not the thick crumbly ones you have now.
I use black high sulpher cutting oil from the plumber supply.
It may take some practice to get the hang of it.

Bill

P.S. your holder normally uses the T type blade.

From the last pic it looks like your tool height is too high, if so, move it down to the centerline of the spindle

Originally Posted by Starrett_Eye

From the last pic it looks like your tool height is too high, if so, move it down to the centerline of the spindle

+1
A tool set to high on an OD cut will tend to dig in with any flex, same goes for an ID cut, set it to low and it will dig in with any flex.

Without meaning to hijack the thread: I have not yet tried parting off. I certainly understand the concept of the T-shaped blade, to reduce rubbing. But how is that set in the toolholder? My import QCTP came with a generic parting blade holder. Do better units have a groove in the bottom? Or would you set a very thin shim next to the blade? Build it up with layers of tape?

To the OP: have you watched Tubal Cain's videos? He has one on parting off, and there might be a point or two that would help.

1. Set the tool on center (Height)
2. Grind a small chip breaker grove on the top of the tool
3. Use a fine wheel to obtain a very sharp cutting edge.
4. Apply cutting oil, not some home brew with engine oil
5. Maintain a constant cut as it is easy to get a chip between the work and the cutting edge.
6. Check the center height of the tool again.
7. Happy cutting.

Set the feed rate , cross feed is usually 1/2 of the long. value (Sorry, I'm NOT a SB guy ;-))

With one hand on the feed engagement lever, and the other holding the cutting oil brush or squeeze tube.

All systems go.

This of course is after everything is set up and aligned. Making sure the part drop before the tool holder contacts the work.(Ask me why i mention that detail ;-)))

edit: What! No editing the title? it's LIKE! not lie ;-) This membrane key pad is cute, but not efficient.

Originally Posted by J.R. Williams

1. Set the tool on center (Height)
2. Grind a small chip breaker grove on the top of the tool
3. Use a fine wheel to obtain a very sharp cutting edge.
4. Apply cutting oil, not some home brew with engine oil
5. Maintain a constant cut as it is easy to get a chip between the work and the cutting edge.
6. Check the center height of the tool again.
7. Happy cutting.

Double that! NO freakin' engine oil1 Mineral oil just screws with any cutting operation.

I've become partial to CANOLA oil.pure vegetable. (Since I don't have any hogs around the place) I've been meaning to try Neat foot oil sometime though)

Your problem is that you are using the parting tool blank as it comes out of the package. It has a peak on the top as a feature that allows it to be clamped in the parting tool holder. Before you grind the end of the parting tool, you must flatten the peak on the top of the tool. I do that by holding the parting tool blank vertical to the face of the grinding wheel, pressing the tool to the wheel lightly until you clean up the top of the tool for about 7/8 to 1 inch from the cutting end of the tool. This will result in a slightly dished flat on the top of the tool with the depression of the dish being controlled by the diameter of the grinding wheel. It also produces a couple of degrees of backrake angle, which also provides a slight amount of clearance on both sides of the parting tool. This smoothly ground top of the tool will allow the chips to flow across the top without jamming up on the top of the parting tool.

The end of the tool should be ground so that there is a slight peak on the right side of the tool. This will allow the workpiece to be severed completely before the other end reaches the center of the work.

The work should revolve at about 200 rpm or less, depending on the diameter. You should feed the tool into the work slowly, keeping the cutoff groove wet with black plumbers cutting oil. If the tool is cutting properly, you should get a thin chip that curls up on top of the tool and winds itself into an unbroken disk in the groove on top of the tool.

Your tool with the unground top causes the chip to jam up on top of the tool, which will either stop the lathe chuck, and cause the belt to slip; or it will cause the tool to shatter and perhaps put your eye out.

If you can't visualize how the tool should look, ask me to draw you a diagram.

Another thing, your tool should never be above center, because when the tool jams, it causes the tool to swing down and into the work, which will compound your jamming problems.

In the words of the Bard: "Parting is such sweet sorrow."

Lord Byron

P.S. Cold rolled or hot rolled mild steel makes a poor piece to practice cutting off. It has a very gummy cutting action, and tends to produce globs instead of curls. If you want something better to practice on use leaded screw stock or stressproof steel.

Bruce - I would like to see a sketch of the tool geometry you described if you don't mind.

Thanks
Rick

Originally Posted by Rick_B

Bruce - I would like to see a sketch of the tool geometry you described if you don't mind.

Thanks
Rick

Rick, Take a look at this MACHINE SHOP TIPS #36 Part 2 Parting on the Lathe tubalcain - YouTube at about the 6:00 mark.

Frank Ford's site shows how he fixed the import toolholder problem already mentioned by iwananew10K.

Unlike an Aloris toolholder, the import's slot had straight sides, so a t-shaped tool, or one with tapered sides, couldn't be held perpendicular to the axis of the part.

I have no idea if this issue is contributing to the OP's problems, but it's worth noting.

Here's the link:

Import Cutoff Tool Holder Improvement

-Chris

As Bruce said, the problem looks like the top rake of the tool. One of the most important details in machining is tool geometry. If your tool is right, it should feel like it wants to cut .If it is too sharp it will break or wear quickly, but at least you will know you are on the right track, and can modify from there. If you google "Rake Angles ", and pick the images, there are several good ( and some bad) drawings that should help explain it. Also, make sure your tool has side clearance, because that could cause binding as well.Don't trust anything out of the box that comes from a discount manufacturer.
I usualy use a 6 inch scale against the tool and part to check height. If you are too high, it won't cut, but if you are too low, it could suck the carriage in.

I was having some problems with my lathe. I turned out that my headstock was loose. Something to check out. There is a bolt underneath the bed that locks it in.