Are you trying to cut the 5mm width in one go? in other words is it a 5mm wide insert.

I'd go with Jason's suggestion irrespective of tool width.

Also, slight angular misalignment? I square my parting-tool holders, whether HSS or carbide (I use both), to the face of the chuck.

Grinding HSS tools on a normal bench-grinder is not too difficult, with some practice, though it helps if you replace the usual tool-rest with a larger, adjustable table.

What RPM are you using?

Sounds suspicious that your tool holder is holding the blade at an angle, then the insert is also angled in the blade. Those type of cut off tool is usually held level, so the insert provides the back rake angle. The tool holder is probably designed to hold a straight HSS type of blade at a slight angle. So you probably have double the angle required. Which would cause it to dig in as you describe.

Pics of your set up would help see what is going on.

Also, lock the carriage and the topslide while parting off or grooving. Run the RPM a bit lower than you would for turning the same diameter. Low speed of 200rpm on a Myford should be ok if all else is well with carbide tooling. And keep plenty of oil, any kind of oil, on the job as you go. Dribble it on from an oil can. Setting the parting tool a bit below centre can help alleviate dig-ins too. Don't set it above. It will rub and can then suddenly grab if you put more pressure on it to make it cut..

I use an inverted rear parting tool in the Myford with good success, but opinions vary on that. You should be able to get the conventional style insert tool to work ok, certainly better than what you are experiencing.

Edited By Hopper on 21/06/2023 14:08:41

Are you using a carbide parting off insert?

If so, they are useless for grooving in my experience as they chatter badly if you don't keep the feedrate up. Which is not ideal for sneaking up on the depth of a groove. As a parting off tool they are fine, procvided you keep the feedrate going, a minimum of 4 thou per rev and preferably rather higher. For cutting grooves I use home ground HSS tools as they allow you to sneak up on a dimension without chatter and leave a good finish. Buy a bench grinder and some HSS tool blanks.

Andrew

Rather depends on the Insert, I regularly groove with my Mini-thin inserts and sometimes with a MGEH grooving tool but if it is a GTN style parting insert the Myford may not like it unless it is a sharper one intended for nonferrous metal though many get on OK with similar inserts in the "Greenwood" type holder

I did not make a suggestion. Just asked for a bit more detail.

Edited By JasonB on 21/06/2023 14:55:34

As advised, tighten the gib screws. Minimal play in all areas is rhe secret.

If the tool has no top rale, it is less likely to dig in.

The tool edge should be sharp, on the centreline and square to the tool, and to the lathe axis. An angled cutting edge produces swarf which is wider thann the cut, and likely to jam.

Best of all, is to fit a rear toolpost amd mount the tool imverted.. (In that way the swarf falls away asnd is mless likely to clog the cut. )

Feed should be slow, about 0.002" (0.050 mm ) per rev.

DON'T rush, and err on the side of low rather than high speed.

HTH

Howard

Additionally, I have rigged up a bottle of soluble oil, above the lathe, with a needle valve to provide a steady drip ontom the HSS parting blade in the rear toolpost.

This works so well that I very often use power feed to part off!

Keep the rpm low.

Chatter usually means that bthe speed is too high.

Again, rigidity, zero top rake on a sharp tool, and a slow steady feed, preferably mounted inverted in a rear toolpost, would be my recommendations.

Howard

Holding the parting blade in a separate tool holder (Explore the "Gibraltar" toolpost! ) will be more rigid that a QCTP which has an overhange, and several interfaces, each of which will lessen rigidity.

If you are going to make a toolpost specifically for parting off, why not make it a rear post, holding the blade square to the lathe axis, with zero top rake, and exactly on centre height?

A steady drip feed of soluble oil onto the blade will improve matters even further.

My parting blade is 2.38 mm (3/32" ) wide, and is always used inverted..

Howard

What rpm?

And what metal?