How could that possibly work?

Clearly it does work, not properly nor producing the desired result! Robert Butler

I'd say try it with the blade the other way for sure. I have another type of parting blade holder though, and both 1/16th and 3/32nd blades. The 1/16th blade always leaves a convex end to the chucked stock. The 3/32nd is much better.

I use a similar tapered blade in a home made holder. The thick side is the cutting edge, which ever way the part is rotating. Blade should be held so that the side tapers are clear of the part groove produced. Mine does tend to cut with a dome face unless I cut a groove with a double cut to widen the groove, I accept this as the blade is quite thin and only 10mm high. This is on a mini lathe also.

Hi

One of the most difficult things when using a lathe that causes blue words and puts the fear of God into people. Those of a nervous nature may consider brown trousers. I know of a third year apprentice who did that when parting off on a Bantam many moons ago.

Good quality holders had a groove in the bottom of the slot so that the thin part located in it. The clamp then pulls it tight in to hold securely. Sometimes it needs packing out with a fag paper or two to get it perfectly upright. The widest part is on top to give cutting clearance. Your photo does not show any top rake??? Only have sticking out enough blade to stop chattering. The front should be ground at about 30 to 45 degrees, the direction depending if you want the pip on the stock in the chuck or on the component. I can not recommend a speed as it depends on the lathe, state of bearings, material and diameter but 50% of your normal turning speed . Try and lock the carriage to the bed and tighten up the cross slide – and top slide – gibs to eliminate chatter.
Set the tool to a couple of thou BELOW centre height – no more – to prevent the tool or work “climbing” Remember tool square To the axis of the work and SIDE CLEARANCE which you must grind yourself. Most breakages occur through build up of swarf and lack of lubrication.

good luck

grinding the end at an angle also produces a chip which is wider than the kerf (fancy name for slot!). This makes it more likely to get wedged with predictable results

I have very few insert tools but my Glanze parting tool is one I wouldn't be without. Batten down the hatches , power feed on the crosslide and little Drummond does it's stuff. All that's logical says this is a risky thing to do but I think that it's the steadyness of the feedrate and me concentrating on the cutting oil that does the trick.

Edited By Lee Rogers on 20/07/2020 18:08:55

I use one of these RDG bladed parting tools all the time. I've got a couple of specially-ground 1/4" HSS parting tools for specific job, but the blade thing gets used for about 95% of parting.

Convex/concave effects are usually due to an out-of-square cutting edge causing a deflecting force that increases with the extension/depth of parting. Parting tool mounting out-of-square will produce similar effects. Of course, in the extreme you'll snap the tool, but things can be pretty bad before that happens.

Minimise the protrusion of the blade consistent with reaching the partoff depth required – if there's a hole through the centre of the piece you can reduce it further.

I think the wider edge of the blade should always be on the clamp side of the holder, because the support is sloped to bolster the disengaged (narrow) edge of the blade there. If you use a rear toolpost that whole holder with the blade fitted should be inverted.

I certainly can't say it never gives any trouble, but it does generally get the job done even if I have to fiddle about with settings partway through – and I never have so many bits to part off as to justify paying out for one of the very good carbide insert tools I sometimes use down at the railway.