Do whatever works for you. There is no hard and fast rule about the angle of the tool presentation. I often swing mine around the other way a bit, so the point is trailing the leading edge. Seems to spit the chips out better. Only about 10 or 15 degrees needed. On the ohter hand, many carbide inserts are deliberately made with a point of 80 degrees or so, so that both cutting edges are angled a bit away from the face being machined, providing clearance.

Presenting the cutting edge square on to the job does seem to generate long, straightish strarnds of swarf that are a pain to deal with. Angling the tool tends to curl the chips up more conveniently.

Also experiment with feed rates and rpm. Different combinations affect chip generation.

Angling a tool gives thinner, wider chips, which, especially with HSS, can lead to freer cutting.

A knife tool with just the end cut across at an angle is best set at about ten degrees to allow easy working into a corner and facing as Mick describes.

Angling it the other way (or grinding across the corner), by rather more (say 20 degrees or more) creates a roughing tool that may be able to deliver deeper or faster cuts but won't cut up to a shoulder.

For the best finish a rounded tip and/or small flat on the tip parallel to the work (which shoudl ideally be a bit longer than the amount of feed per revolution) will help.

'Polishing' the ground edges with a slipstone or diamond card can help too.

Neil

No, but it may not matter. I guess your grinding is a little off and – as you suggest – angling the tool provides the relief that a more accurately ground tool would have built-in.

Good tip I got off the forum (forgot who, apologies) was to put an extra 10mm (or so) on top of the grinding platform so that the wheel naturally undercuts the tool at a tangent, and then grind at a horizontal angle, say 15 degrees, to provide relief. Works for me.

As a tool wears, it sometimes helps to angle it to present a different part of the edge to the work. I usually resharpen instead.

I'm not good at grinding (facets galore, cooked steel, and burnt fingers) and prefer carbide. Even so, about 10-20% of the time I go back to HSS, usually on small diameter work where a fine finish is needed.

Dave

Edited By SillyOldDuffer on 24/06/2018 09:34:03

If you are wanting repeatability when changing between tools, better to make sure any such angle is ground into the tool, not imposed by turning the toolpost. I've gone to a lot of trouble to make a very solid toolpost base that is rigidly located on the cross-slide, and the Dickson block is dowelled to it to be precisely square. All my tools are snugged into their holders and tightly clamped, so I can be sure that it goes back into exact position. Makes CNC turning and I suspect using a DRO system much more convenient.

And then again, Lewis Hamilton's driving is of a specialised type, and tells you little of how he'd do in the Tuesday evening rush hour on the bypass.

Similarly, you'll probably find it best to suit your tools to the type of work you're going to do. Accurate repeatability isn't often required unless you're making batches of components, which hasn't often been needed in my model engineering experience. It's been more useful to me to have a versatile go-to tool I can use on a variety of materials and cutting angles, as the spectrum of both that I've encountered has tended to be broad.

That tool would be great for facing shoulders on turned work. I would expect chips leaving the tool will impinge on the just cut surface and scuff it. Rotating the toolpost 10* to 15* clockwise should cure that problem, The alternative is to grind the front face to give a front cutting edge angle of 10* to 15*.

Hard to tell from your picture Ross but the tool looks high to me. Are you aware of the metal strip method for checking it?

With the lathe stopped gently pinch a metal strip vertically between the tool-tip and a rod. If the top of the strip leans away when you tighten the pinch, the tool is too high. If the bottom leans away the tool is too low. Adjust by shimming until pinching doesn't move the strip in either direction; slightly low is OK.

Further to Andrew's comments about SoDs, I've just had a birthday. Now I'm an old sod.

Sorry about the sideways photo!

Dave

Very true. Because it's quicker I normally set tool height with a home-made height gauge.

With a fingernail you can feel amazingly small differences in height between the tool tip and the flat top of the gauge.

Main disadvantages are making the gauge accurately in the first place and having to move the saddle so the gauge can sit flat on the ways while offering up the tool.

I made the gauge from Aluminium rod which picks up dings if you sniff at it. With hindsight mild-steel would be better.

Dave

don't get too carried away with setting centre height. The main effect of having it wrong is the front clearance changes. If you're machining something 6" diameter and you've got the tool height 1/16 too high it will reduce the front clearance by just over a degree. I'm not going to get worked up about that. Obviously for small stuff it matters more, and for facing off.

There is also a very small effect on diameter, in the above example if I feed the tool in by 0.1" the actual reduction in workpiece radius is 0.10002". Again it has more effect on small work.

When I worked in a machine shop many years ago, the thinnest packing available for the 4 tool turrets was 1/16", but this means you can get within 1/32" up or down

Usually more critical on smaller diameters. You can get away with the tool set well below centre and it still cuts ok. But too far above centre on small diameter and the front face can rub on the job, instead of the cutting edge. Also, if there is any tool movement, as on a small flexible lathe, or an old worn one, a tool set above centre will dig into the job deeper, sometimes causing problems. A tool below centre will flex downwards and away from the job.

12 x 12mm index tool holder? Sounds pretty large for a small lathe. Check the tip is not sitting above centre height.

Some small lathes don't like carbide tools because they are not rigid enough. Maybe that's the problem. Some improvement might come from using the ground finish inserts instead of moulded. (eg a CCGT insert instead of CCMT etc.)

Also, you would want to have the rpm about double what you were using for HSS. And keep up a good feed rate to it. Ditto depth of cut. Inserts like to work, hard. Generally, they often will not give as good a finish as a good HSS tool because you can't take such light cuts to finish with.

I use several 12 x 12 tool holders on my 8 1/2” by 14” lathe and they work fine. I’ve actually Araldited some gauge plate to the underside of the tool holders so they’re always on centre height in my four way. I keep thinking I should have got the 16 x 16 holder and milled off a couple of mm till it reached centre height.