Side Cut Angle on HSS Tool Bits

Can someone please explain to me what the Side Cut Angle does on a HSS tool bit?

Kind regards,

Jim

Nothing really, could just as easily be zero degrees though make sure the end angle is at least 1degree preferably more if side is zero to give a corner that is less than 90degrees otherwise you will end up rubbing.

Edited By JasonB on 27/06/2019 07:09:42

I grind my tools the exact opposite to that so that the side cut angle is -10 degrees, works great for non ferrous.

Lots of references to tool grinding show and mention SCA, I've never understood what it does.

Peter Wright's book on Model Engineering page 303 explains it. In effect that if taking heavy cuts, the width of the chip is reduced thus making it easier on the lathe.

Peter G. Shaw

A positive side cut angle ensures that the tool will not pull in to the work due to backlash in the crossfeed screw.

Andrew

If there's any beneficial effect, I think the main one is to create an outward vector on the forces acting on the tool, and hence the crossslide - so as to take up the backlash positively, improving consistency and accuracy on repetitive cuts.

Downside is that it limits working close to the chuck, and will leave your bar with a conical end after parting, potentially wasting (a probably trivial amount of) material.

I was told that, too, in my Government Training Centre lathe course in the 70s, but I can't see it. The cutting face is longer, and for a given feed rate it'll make the chip volume per rev greater.

Assuming that we're looking down on the tool the arrangement of side and end angles gives a stronger cutting edge. The tool shape is intended for roughing; it's the equivalent of using the obtuse cutting edge on a CCMT insert.

Andrew

That's what I think too. A straight tool takes the cutting force at a right angle to the shank, which I think makes chatter more likely. By angling the leading edge a proportion of the cutting force transfers sideways into the body of the shank. Bit like the way an arch bridge is strong because the shape transfers weight smoothly to ground. In other words the angle supports the cutting point better than a straight shank.

May not make much difference until the tool is pushed hard. For gentle and moderate cuts I suspect the performance of straight and SCA tools would be identical. Just a suggestion: if heavy cuts are the goal, maybe carbide is a better choice...

Dave

PS See Andrew made the same point while I dithered.  Must learn to type and think faster.

Edited By SillyOldDuffer on 27/06/2019 09:47:43

I agree with Andrew - it's for heavy cuts and helps strengthen the cutting edge. However, it's not a tool shape I use. My machines are all (relatively) light - so I don't take really huge cuts and my normal tool geometries (including the Diamond) work perfectly well for the roughing cuts I make.

This tool geometry can also be inconvenient in use too - as already mentioned by Mick.

Regards,

IanT

One advantage I have not seen mentioned is that grinding your tool this way will make teh piece of HSS last longer. If you grind the cutting edge straight, ie parallel to the main axis of the bit, subsequent resharpenings of the tool eventually leaves you with a small nub section on the end of the tool bit, which eventually becomes too small to be useful and has to be ground off and the process started again. The long oblique leading face shown in the OP allows you to keep touching up the whole face without creating the small notch or nub on the end. Saves time and toolbit material.

Would that not depend on how the tool is presented to the work? If the shank of the tool shown were at right angles to the lathe axis then I would agree but as the corner looks to be obtuse the shank could be angled so that the tool could be used for finishing and getting into corners

Errr, I think you mean acute. One could swivel the tool to get into a shoulder. The way my toolpost works it's easier to keep the tool at right angles to the lathe axis.

Andrew

I did mean Acute

Yes I prefer to keep mine square on too, most of the tipped tooling holders are best used that way including my two that use the obtuse corners of CC** inserts. If I were going to use a tool like that shown for roughing held square on then i would not grind the end cut angle as steep, just a few degrees to clear the turned work

If you look at a lot of the older books on tool shape one with a much bigger angle, say 20+ degrees is labelled as a roughing tool. Probably for the various reasons given above. If you do that and round off the left rear corner where it melds into the shank you can get away with using it for facing thus saving a tool change and vital seconds on piece work.

An industrial shape for industrial cuts. For folk like us using lighter lathes the main advantage is, as Hopper says, in allowing continuous regrinding of the tool without leaving a nub so saving on expensive tool steel.

Different if you are taking 1/2" or inch plus cuts on a big job. It does appear to make the cut go easier on a big machine but the gain is in volume of material moved per unit power not depth of cut per se. No I don't really understand it either but have done it.

Clive