lathe cut off tool not true

[Dave P]

I was trying to cut a very thin washer off a steel rod and I noticed my cutting tool would start exactly where I wanted it to but then would immediately move to the right. I'm using a Sherline lath with their standard cut off tool. What am I doing wrong? Thanks in advance.

 

[David Robertson]

By moving to the right.. do you mean the tool holder is rotating to the right or that the blade is flexing to the right but the tool holder is staying fixed?

A flexing blade means you have too much of the blade sticking out. A rotating tool holder may need to be slightly relieved in the center of the bottom to improve the contact pattern. If this is the problem and you need more explanation, I can provide it.

 

[Jerry Kieffer]

I was trying to cut a very thin washer off a steel rod and I noticed my cutting tool would start exactly where I wanted it to but then would immediately move to the right. I'm using a Sherline lath with their standard cut off tool. What am I doing wrong? Thanks in advance.

Dave
You are probably not doing anything wrong assuming the tool is properly set up with the cutting tip centered to the spindle. The Sherline standard front mounted cut off tool is a poor design. Because of the length that the blade extends in front of the holder, it is unstable and will wander when cutting. This can be corrected by purchasing Sherlines rear mounted cut off tool with the horizontal blade.

http://www.sherline.com/3018inst.htm

This allows the cutoff blade to be set so that only the amount of blade required will need to be extended in front of the holder. This makes the system far more stable and will allow the cutting of small thin washers well under .005" if desired. Of course this assumes the material will support such a thin washer.

Jerry Kieffer

 

[Scottie-TX]

This' a GREAT topic but one I believe may be better postured in the, "TOOLS" forum. Hope ya don't mind if I move it there.

 

[Mike Phelan]

As Jerry says, all parting tools (UK name) are better on a rear toolpost - much less flexing.

Also, better, if the size of the lathe allows it, is to use a parting tool with a replaceable blade; for parting a large diameter, you can extend the tool from its holder in stages.

Good parting technique is not that easy to master.

 

[Dave P]

Thanks all for the help. Being relatively new to using a lathe I couldn't understand why the blade was extended out so far. I'll have to get a rear mounted block. Why doesn't Sherline just increase the angle in the front mounted block so there is less blade sticking out? Thanks for the help. DAVE

 

[Kevin W.]

I believe you may also be able to work closer to the chuck, if cut off tool is mounted in rear.

 

[Jerry Kieffer]

Thanks all for the help. Being relatively new to using a lathe I couldn't understand why the blade was extended out so far. I'll have to get a rear mounted block. Why doesn't Sherline just increase the angle in the front mounted block so there is less blade sticking out? Thanks for the help. DAVE

Dave
You would have ask them that question, however the most efficient method would have been mounting the blade horizontal. In the mean time you could put spacer washers under the cut off tool block that in turn would shorten the blade when adjusted. Large diameter fender washers with the correct size center hole will prevent cross slide warpage from over tightening. A longer 10-32 mounting allen screw can be purchased at any hardware store.

Or of course re-machine the holding block to hold the blade horozontal.
This can be done with the lathe by mounting Endmills in the headstock and spacers if required under the mounting block. It would be an excelent learning project.

Jerry Kieffer

 

[Joe D.]

Also make sure your tool is sharp. If one corner is rubbing instead of cutting the blade will wander to the other side.

Joe

 

[StephanG]

Rear mounted parting tools often work better on small lathes.
It has something to do with the way the load it taken by the head stock bearings especially if there are any joins or splits.
By bringing the tool in from the rear the load pushes the spindle down instead of trying to lift it up which may not be as rigid.
Same applies if you are using a form tool.
I made my own rear parting tool and as well as coming in from the rear the tool is set an an angle.
This provides 2 additional advantages.
I get less chatter because the tool can flex away from the work if the need arises.
It is easy to get the centre height just right by moving the tool in and out of the holder till the cutting tip is in just the right place.

 

[Dave P]

Dave
You would have ask them that question, however the most efficient method would have been mounting the blade horizontal. In the mean time you could put spacer washers under the cut off tool block that in turn would shorten the blade when adjusted. Large diameter fender washers with the correct size center hole will prevent cross slide warpage from over tightening. A longer 10-32 mounting allen screw can be purchased at any hardware store.

Or of course re-machine the holding block to hold the blade horozontal.
This can be done with the lathe by mounting Endmills in the headstock and spacers if required under the mounting block. It would be an excelent learning project.

Jerry Kieffer

How do you mount the blade horizontal?

 

[Jerry Kieffer]

How do you mount the blade horizontal?

Dave
Machine a new and deeper horizontal slot in the holder block. The slot should be machined so that when the blade is locked in place the top cutting tip is centered to the spindle. The new slot will be very close to the blade locking screws but you should have just enough space.

Jerry Kieffer