Lathe tool angles

After finishing a grinding rest I ground up some tools from the L H Sparey book using the angles for the basic tools required.

Are angles that important.

I ground up a tool for brass 2 deg 5deg 5 deg, but when I tried it I thought that tools I ground with steeper angles worked better.

The knife tool at 55 deg 5 deg 5deg actually cut brass fine, I used the same speed for all tools.

Am I doing something wrong.

Bob

I use a tangential tool - Diamond Tool Holder - ground to the standard angle for brass as well as steel, it isn't a problem. It may be a problem if the brass you are turning is a very sticky grade, but all the brass bar I've had is clearly hard brass and I've never had a dig in.

As to speed, you can turn brass faster.

The angles aren't that important but 5 is a bit low for steel. This is because it won't give much clearance so the first bit of wear will result in it rubbing. Use 10 all round for steel.

It is the top rake that really governs the cutting action and the other sides are just to give clearance and make it easier to get into corners. So 10-15 will give you a sharpish chisel edge for steel but higher values makes it weaker. For aluminium up to 20 helps and it is soft so strength is not an issue.
But for brass it cuts so easily that the chisel grabs the tool and causes a dig in. So you want and really need less than for steel, like 0 to 5.

Note and think about how moving the tool off dead centre affects the effective angles, especially for small diameters.

On our sizes of lathe, typical speeds and depth of cut really sharp trumps correct to book angle every time. In practice it seems to be harder for a neophyte to get a really sharp edge with shallower angles. Especially if finishing off by hand honing. Until you get the feel its dreadfully easy to take the sharpness off by tilting the abrasive stick or diamond hone a fraction at the end of the stroke. A degree or so on 55° probably won't make a huge difference. But on 2° most of the edge will be gone. Easier to hold against 55° than 2° too.

Book angles are derived from industrial and toolroom practice to give a good balance between tool life, rate of cut, ease of cut and protection from things like built up edges, mile long swarf rats nests and so on. For small lathe users generally whatever works works. But don't get caught faffing around with mini cuts. Should be able to take material off at something approaching book rate for the motor power. Although those of use with industrial size lathes usually don't exploit the power because its such a pain handling scarf that thick coming off that fast.

You should use the correct speed for the materials in question. Brass in particular is a proper speed demon and you probably won't be able to go fast enough with small diameters. But, as you have found, it responds well to a sharp tool.

Clive.

Edited By Clive Foster on 13/08/2018 17:18:40

I dont think I have ever measured the angles I grind on my tool bits. I just give them enough clearance to stop them fouling anything and enough top rake to give a good cutting edge. Nothing fancy,but then,I,m not too interested in making swarf at an industrial rate.

Works well enough for most jobs and what,s the hurry anyway ?,it,s a hobby,not a job ,so enjoy !!.

Too easy to get carried away by books,rates,times ect, forget them,they dont apply in our world [not in mine,anyway ]

X2 Larry!

Yes, same here. Even with other tools ground to cut steel I’ve never had any problem turning brass. I even drilled some brass on the lathe the other day with a standard twist drill and it didn’t grab. Maybe modern brass is a different composition?

What Clive said, and Larry too. And I discovered ages ago that whatever angle you quote from a book, there's another book which gives a different angle.

George

Speak for yourself.

I know from experience my lathe (3hp motor) will remove about 2.8 cubic inches of steel per minute before stalling. If the work, clamping and metal to be removed demands it that's the rate I run at. Same as in my man or mouse milling thread I've had swarf coming off dull red. If you get feeds and speeds right the swarf gets broken so there is no need to handle it. Just don't stand in the way!

Andrew

Andrew

Squeak, squeak. A piece of cheese would be really nice. Squeak, squeak.

Can do the hefty cuts'n red hot swarf thing. Have done it. But rarely need to. Generally on my work the gain from saving a couple or three passes isn't worth the candle when I can come straight down to size on normal cuts without having to bother with fine finishing cuts. Or correct for really hot work measuring oversize. Given the chance 50 thou / 1 mm is a finishing cut to me.

Clive

PS Shouldn't that have been "Squeak for yourself" not "Speak for yourself"

Edited By Clive Foster on 13/08/2018 20:09:17

The recommended tool angles are a compromise between free cutting and durability therefore maintaining exact tool angles is not necessary. Tinker with the angles to see what works best for you.

I use Sparey's standard knife tool geometry for both steel and brass/bronze. Works for me on these small (Myford/Drummond) lathes.

Single point screw cutting and angles of finished article are the only angles I particularly worry about (as in ‘measure’ them). The rest are close, if necessary, but not critical. We often don’t use ideal metals so ideal cutters are irrelevant for most of us.

I like hot chips,but not when they,re heading for me at a rate of knots.

I like cheese too,much easier to cope with !

While these removal rates are impressive,and may be required in industrial situations,I doubt if they would show up often in the hobby world.

Sparey mentioned in his book,while talking about HSS, that Armstrong Whitworth removed swarf 1 1/4" wide x 1/4" thick at a rate of 32ft per minute ! Makes no mention of how hot it was,but I doubt if anyone was standing in the line of fire. Perhaps had they used carbide tools,they might have been to produce 2 x 1/2" flat BMS.

There are times when I produce deep cuts,mostly when I dont want them ! Has anyone else been there,done that ?

Yep, more than once.

Last time it occurred because I forgot to tighten the ER collet chuck.

Andrew

Mostly, chipped CCMT0604 bits are used with the unused 100 degree corners for roughing. (Andrew would like the blue stuff coming off). Hundred thou cuts can make it chatter.

The original tips are used in a Boring bar. So the angles are already chosen. For most of the other straightforward turning, the Diamond (Tangential ) tool is used. Freshly sharpened, (Boasting!) it will take a cut of 0.0005 inch, or much greater. With a 1/4 toolbit have never exceeded a 0.050" cut.

The HSS parting tool, ( Secondhand when I got it, at least thirty years ago, and still nowhere near worn out)   is inverted in the rear toolpost has zero top rake, and gives few problems.

On the RF25 Mill/Drill with HSS cutters, rarely exceed 0.050" depth of cut.

So am looking for fresh types of cheese.

Howard

Edited By Howard Lewis on 14/08/2018 14:16:14