Tool bit grinding

A friend of mine has just aquired a southbend lathe that has the lantern post tool holder. The tool holder holds the bit at 60 deg angle. I cant find any information on what angles to grind the tool bits. Can anyone help me. I have done a lot of searching on the web. There are a lot of information on grinding bits that are at 90 degrees but I cant find any on the 60 degrees.

thanks

Get the book "how to run a lathe" by South Bend Lathe. Thats the best lathe book I have seen. on Ebay all the time and from Linsay books as reprint. It has good info on bit grinding.

Sixty degrees from what? Is it one of those "Tangential Diamond Toolholders", where the square bit is held in a nearly vertical position?

Like this:



If it is, then I can't offer much help, since I've never used one. I think Home Shop Machinest had an artical about them one time. If that's not it, then just remember that the tool angles that the workpiece "sees" should be more-or-less the same, regardless of the angle of the toolholder.

Paula

Best book I ever saw on toolbit grinding was by W&S for the turret lathes. Tons of info not just on cussing but controling direction of chip & chip breaking.

Ted

Clearance, Rake and Angle of keenness. That's all you have to know about tool grinding angles.

Now, South Bend's "How to Run a Lathe" as mentioned above goes through tool bit grinding quite well.

Since the book is written for South Bend users, the angles reccommended are suitable for tool bits held in Armstrong type holders in American style tool posts. They favor rather sharp rake angles which ease the cut for the rather low powered, slow speed South Bend machines.

JimK - Yes HTRL is good, but I tell ya the W&S books goes into much more detail. I think I'll add it to the 'To Be Scanned' pile as proof.

Ted

Mr. Williams:

I have both books and I have offhand ground a tool bit or two.

My point is to avoid subjecting a novice to information overload.

Paula:

That rig up shown in your post employs the same trick as the Warner and Swasey bar turners.

The idea is that you only have to take one grinding cut to sharpen the bit. To make things nicer, you grind those in a simple fixture on a surface grinder.

The idea is that you use tool bits like inserts. Have several sharp ones around and change the bits out quickly when they get the least bit dull.

In the bar turners the tools have a good bit of rake and standard clearance plus they turn a square shoulder on the piece.

In turret lathe work the above characterisitcs work to a great advantage in reducing tool changing and resetting time.

If that kind of tool holder made a real Ding How difference in engine lathe work, I would have been using them long ago.

WalterSV, there's been a great deal of discussion
here but nobody answered your exact question I
think.

I'm going to paraphrase it so if I get it wrong
you can call out:

"How does one grind a lathe tool if it is to be
mounted in an armstrong lathe-type (not shaper)
toolholder, that goes into a lantern toolpost?"

The key to the question is the fact that
tool holders like that hold the long axis of the
tool *up* at a considerable angle with respect
to horizontal.

So you need to compensate for that build in
angle by modifying the various grinds, to allow
for the needed front clearance, and to compensate
for the inherent back rake the tool holder adds
in.

Basically you grind the tool as though it were
being used for horizontal mounting, but simply
put in extra front relief so the tool does not
scuff when brought to bear right on center of
the stock.

The tool holder angle will impart back rake for
you. If for example, you wanted to make a
brass turning tool, with a dead flat top, you
would need to grind negative rake on top of
your toolbit, equal to the angle that the
toolholder points it upwards.

Now this having been all said, I will make a
comment or two.

1) Set the armstrong tool holders aside for now.

2) if you wish, you can keep using the lantern
toolpost - but simply place the tool bit
directly in the toolpost, with suitable spacers
underneath to bring it near center height. The
rocker can still be used to 'fine tune' the
height.

You will find that instead of, say, a 1/4
inch square toolbit, you can now employ a
3/8 square one, and the overhang has been
drastically reduced. The setup will become
very much more rigid as a result.

I myself do not ever grind back rake on tools
even when they are mounted flat horizontal. I've
found that this really is not needed in my
estimation.

A quick-change toolpost is a very nice addition
to any lathe, that is certainly true - but the
lantern toolposts do work fine if care is taken
to keep things rigid as possible. For a small
lathe this really means eliminating the old
fashioned tool holder.

Jim

JimK -
I did not mean to imply otherwise. Yes, your are right about the W&S book being a great deal for a novice. My point was it was the most complete work on toolbit grinding I had ever come across.

Ted

Jim:

Chapter IV, "Lathe Tools and their Application" is a full and complete answer to Walter's question. There are nine pages with pictures and diagrams and examples of various tool bit shapes and reccommendations of tool angles for use on different steels.

If you use an American style tool post you should be using the Armstrong holders. They give a good amount of back rake without having to grind away a lot of metal from the top of bit. That back rake assists in chip control, it forces the chip to curl away from the work and out of the way.

When I started working with the Aloris type tool post I had problems with the chip curling towards the work and marring the finish. I wondered why I could get a better finish on a South Bend than I could get on a Hardinge HLV-H.

I hadn't noticed that I had "lost" all my back rake.

The overall shape of the cutting edge is different when using the Armstrong holders than when using the Aloris. You can swing the Armstrong holder around in the post and set the tool in a wide range of positions.

If you choose to leave the Aloris post stationary, as you should, then you won't be able to swing the tool point around. You have to have a variety of different bits, each in a different holder.

Truth be told, I favor the American style tool post and the Armstrong holders, I never lost my knack for getting a killer finish even on nasty steels with that tooling.

I almost exclusively use the Aloris now because the American post and a cut off tool holder absolutely stinks.

I am also lazy, the switch over to a boring bar is so convenient that I won't take the Aloris off the lathe except for the real problem jobs.

Someone just starting out in lathe work would do well to learn the American style tool post and holders. Unless there is a need for production work, there may not be the need to go to the Aloris post at all. My 9 inch SB catches all the nitsy-picksy small work around here. I don't have an Aloris for it and may not ever get one.