Quick Change Tool Post Indexing

[BCRider]

OK, I think I got caught up in the posts mentioning precision. And to be fair you did ask about the idea of 29 or 29.5 which implies at least half degree consistency.

Still, you have also mentioned wanting to move the post and come back to where the parting tool is ready to go. And as we've determined already that goal alone requires very repeatable indexing. So....

[npalen]

OK, I think I got caught up in the posts mentioning precision. And to be fair you did ask about the idea of 29 or 29.5 which implies at least half degree consistency.

Still, you have also mentioned wanting to move the post and come back to where the parting tool is ready to go. And as we've determined already that goal alone requires very repeatable indexing. So....

A half degree would be about 0.017" at 2" radius.

[npalen]

For those needing fifty millionths repeatability:

https://www.aloris.com/aloris-products/aloris-tool-posts/indexable-tool-post-sets/aloris-indexable-tool-post-ca-i

[J Tiers]

A half degree would be about 0.017" at 2" radius.

And, any sort of reasonable clearance of a pin in a hole should do better than that by at least a factor of 3 even when worn a bit. Therefore, a straight sided pin at that distance ought still to do a cool 10 minutes of arc even after a bit of wear.

A tapered fit pin ought to do 10x better, easily, for 1 minute of arc repeatability at least. That is likely to be better than required for a parting off tool, at least one that is made sensibly, like a typical carbide insert type.

Is it needed? That's up to whoever wants to use the thing.

[BCRider]

Honestly? I do think it's possible to get a good repeatability. We only need one pivot point with a good degree of positional constraint. It might be a split conical bushing that self centers the tool post on the center stud as the retention nut is tightened or it might be something along the lines of that "snowman" double arc hole for the indexing pin. With either of those or some other option as the play is taken up by torquing the tool post in the right way the parts will come to rest with good repeatability. But one or the other (or perhaps both) need some way of achieving that sort of constraint to be accurately positioned. Even if both are in slightly oversize holes it likely won't be too bad. But without any wedging action there's room for some error.

The thing is that it's only a little more work to make it so there is a full control point of position restraint. Seems like if one is going to go through all the work why not do the little extra.

[npalen]

And, any sort of reasonable clearance of a pin in a hole should do better than that by at least a factor of 3 even when worn a bit. Therefore, a straight sided pin at that distance ought still to do a cool 10 minutes of arc even after a bit of wear.

A tapered fit pin ought to do 10x better, easily, for 1 minute of arc repeatability at least. That is likely to be better than required for a parting off tool, at least one that is made sensibly, like a typical carbide insert type.

Is it needed? That's up to whoever wants to use the thing.

A plate from a spin indexer would seem to be a good start to modify for an indexing tool post. The vernier indexing to one degree would be overkill, however..

Edit: It would seem that a diamond shaped pin would be needed in this mod as getting the index plate attached at a perfect distance from the two sides and the index pivot of the tool post would be very difficult without at least some adjustability.

[Georgineer]

...
I like the multifix tool posts but they are very expensive and the increments of 9 degrees (40 positions) doesn't make sense to me when 15 degrees give 30, 45 and 60 capability.

I haven't read all six pages - the discussion at times gets uncomfortably like reading some of the threads on Practical Machinist - and possibly somebody has already made the point, but it seems likely that the inventor was French or Military and used steps of 10 gradians, or "grads", which number 400 to a circle. It works neatly for divisons by 2 (quarter, eighth, etc.) but gets messy with divisions by 3 (third, sixth, etc.).

George

[npalen]

I haven't read all six pages - the discussion at times gets uncomfortably like reading some of the threads on Practical Machinist - and possibly somebody has already made the point, but it seems likely that the inventor was French or Military and used steps of 10 gradians, or "grads", which number 400 to a circle. It works neatly for divisons by 2 (quarter, eighth, etc.) but gets messy with divisions by 3 (third, sixth, etc.).

George

That is interesting! Thanks for posting.

[J Tiers]

Perhaps there is a basic conflict between the very decimal-centric mode of thought vs a more ratio oriented mode, which favors fractions.

[Paul Alciatore]

I think I was one of the ones talking about making identical parts. That was the first and primary reason why I wanted a QC tool post system. I was making some parts in small batches (5 to 25 or so) and it was just taking too long with the needed tool changes and reacquiring the numbers after each change. A QC tool post that had good accuracy with multiple tool changes saved me many hours of machining time.

I suspect that there are many others here who see that as a primary concern in getting a QC tool post. It is probably at the top of the list for the people who first developed QC tooling systems.

But I can see how others may not have had that experience or see it that way.

[npalen]

I would say that making parts for sale is the dividing line between home shop machinist and commercial operator much the same as the difference between amateur and professional sports. I'm sure that many folks "cross the line" back and forth, over time, regardless of their occupation.

[J Tiers]

I won't say I have never done runs of several dozen parts, but I do have a bed turret setup for the Logan, which can make the QCTP a lot less of an issue.

[BCRider]

It's not that unusual for a HSM'er doing this as a hobby only to need to make identical multiples. I'm working on making a dozen or so identical screws for a gunsmithing need. Somehow my supply of Remington 12 pump action 22's has led to a breeding program in the safe during the quiet dark times. And they all share a distinct lack of pump handle screws. Rather oddly shaped pump handle screws at that.

So it can happen to any of us at various times.

[npalen]

An indexing arrangement something on the order of this Incra protractor might work well for indexing the tool post. Wouldn't need to be this complicated but repeatability of the home various positions would be somewhat important. We initially talked about 15 degree increments to satisfy most chamfering needs, with turning and facing tools, and the home position for cutoff "zero".

I have an idea where the "pointer" (what's the correct term?) of the device would be held to the top of the compound via a mild strength magnet and the protractor component would simply square up to two sides of the toolpost. There would be no discrete positions of the toolpost along the t-slot but it could be positioned and locked anywhere as normal. The protractor assembly would simply follow along with the magnet holding the pointer in position relative to the protractor.

[npalen]

Interesting video of Stefan Gotteswinter resizing a hardened shank for a Wohlhaupter boring/facing head. Couldn't help but notice, at about 14:07 on the timeline, Stefan "indexing" the QCTP (toolpost) to chamfer the sharp corners.

https://www.youtube.com/watch?v=c9X3nmSbQvg