What tool shape?

[VicParticipant @vic]

I was given this a while back. The tool holder is a bit too tall for my lathe but it would only need a little trimmed off the bottom to put it to use. I’m wondering though what shape to grind the HSS bits that came with it. The tool seems an odd shape to me but I’m sure there’s a very good reason for it. Any ideas? I’ve got a Tangential Tool so no need to replicate that.

[bernard towersParticipant @bernardtowers37738]

Ive got one of those except that mine is a parting blade holder.

[martin haysomParticipant @martinhaysom48469]

i too have one of those. mine takes round tool bits, it came in the box of ju oops i mean useful stuff that came with the lathe. i have not used it yet. no bits

[BazyleParticipant @bazyle]

This is an Armstrong holder and they come in left hand, right hand, and straight on versions, as well as versions holding the tool horizontal or slanted upwards.
Yours is the best configuration enabling working up to the chuck and has top rake built in making grinding simpler.
If you rotate the toolbit 90 degrees you could use as is with minimal grinding.

[Paul LousickParticipant @paullousick59116]

Many blank toolbits are supplied with an end as shown in your photo. The final shape will depend on what type of cutting you are doing.

Lots of information on the internet that show the grinding angles. Do a Google search.

eg.  https://littlemachineshop.com/images/gallery/instructions/grindingtoolbits.pdf

[Clive FosterParticipant @clivefoster55965]

When welded shank HSS tools were the norm they were supplied in a range of shapes ready to be ground to appropriate angles for their intended use. Many of the older handbooks show some, or even all, of the normal range of shapes. Welded shank tooling was introduced to save money as only the business end needs to be HSS.

In the UK British Standard 1296, first published in 1946, is considered the definitive listing of shapes. My copy is of the 1961 version  BS 1296 : 1961. Unfortunately I can’t find it online. Doesn’t help that the 1296 number appears to have been repurposed for a standard covering Bitumastic Roofs 1296:2001!

BS 1296 : 1961 specifies 62 shapes, which includes several for planers and shapers.

In general tool manufacturers only supplied limited range of these along with their own specials. Any of those shapes will work fine when ground to the correct angles for the material you intend to use it on if you have the right job for it.

For normal folk the range is serious overkill. Tubal Cain reckoned that ordinary folk like us could get along just fine with 10 basic shapes, counting right and left hand versions separately, along with a bi-directional finishing tool for when you need a high finish and a parting tool.

Need to allow for the bend in the holder when grinding of course.

That style of holder was designed for use in American “Lantern” style tool posts which generally sit towards the centre of the topside so the crank is needed to help clear the chuck as Bazyle mentioned earlier.

In my view a simple one or two slot block style tool post is far better than the “never to be sufficiently cursed” lantern post as being far more rigid and capable of adjustments without loosing centre height setting. As the tool is tilted upwards in the holder simply sliding it in and out gives a nice fine adjustment to set centre height just so after shimming to get it roughly right.

I have several American books that emphasise the importance of correct tool tip angles yet within a few pages advise that the tool tip can be bought onto centre line by tilting it up or down in the lantern toolholder. Which obviously will change the effective angles. The contradiction never seems to have been noticed. The generally reliable How to Run a Lathe book from SouthBend Lathe perpetuated this contradiction for more than half a century and 30 or so editions. You’d have thought that someone would have twigged about sliding the tool bit in and out to adjust height without altering the effective angle.

The modern version of this error is advising folk to get a Quick Change Toolpost so they can use interchangeable tip carbide tooling. QC posts were introduced to make it quick and easy to reset the tip to centre height after grinding. Carbide tips are always at the same hight relative to the shank so a slotted block is fine. If shimming is needed it’s one time thing.

Nice thing about the up-tilt on Armstrong style holders is that it makes for economical sharpening as the tilt is too great for any rational tool rake so the top merely has to be flattened a bit to get the desired angle.

Tool holders of that style made to hold the tool flat, rather than tilted up, are for shapers and planers.

Clive

PS :-  Yes I do have lantern toolholder about the place.

At the last count it comes out about once every 8 years. Not often enough to be worth making a block and binning the lantern. Flipping the saucer base over to give a stable flat surface for the tool to sit on is good enough. Now if it were once a year ….

[Michael GilliganParticipant @michaelgilligan61133]

Many thanks for the concise and helpful notes, Clive

… as a result of which, I think I have identified the evolution of BS 1296

MichaelG.

.

[Howard LewisParticipant @howardlewis46836]

My temptation would be to try to measaure the angle(s) at which the toolbit is held, and then to grind the toolbit so that the toolbit finished up acting as a knife tool.

Although, having found the Tangemtial tool to be so useful, unless needed for some specific purpose, I wouldn’t bother.

(I did make up a “one off” tool holder for an 1/8″ round toolbit to cut a half round thread)

Howard

[Andrew CrowParticipant @andrewcrow91475]

I have been using these since my apprenticeship days in the 1960’s and one still has a permanent slot in the square turret of my Colchester student.

I basically have it as knife tool finishing diametres and faces, a quick rub with a slip stone soon restores the edge when needed, can’t remember the last time I actually re-ground it.

As I don’t need to remove material at industrial speeds it’s much cheaper than carbide tips.

Andy.

[VicParticipant @vic]

Thanks for the comments so far. I’ll have to give it some more thought. 😉

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