Group Project: Dividing Head - Organization and Design

[extropic]

My suggestion was to incorporate "some blind holes for a pin".
The nut doesn't have to be tight, like a draw nut for a 5C does.
It just sets and maintains the axial clearance or the spindle which will not require to be "tightened".
The blind holes/pin are really for some worst case scenario.
I expect that all will have (or can make) an appropriate pin (or rod, or punch).
No uncommon tools required.

Also, regarding the brass ball vs a brass tipped setscrew.
On the commercial brass tipped screws that I have seen/used, the tips are fixed (press fit or bonded) to the screw shank.
That type is not desirable for locking a thread because the rotation of the locking screw will rotate the brass element.
You don't want the brass element to rotate (wear away, create debris). You want the brass element to be non-rotating.
I recommended a brass ball because they are inexpensive and available in multiple sizes from McMaster-Carr.
The force of the setscrew will deform the ball, creating a thread-like form to bear on the spindle thread without damage.
Make sure the locking screw tip (setscrew in this case) has a relatively smooth tip to bear on the brass element.
Certainly, the brass ball could be replaced by an appropriate slug of brass rod.

 

[Flyinfool]

I am close to that also, I have one 5C collet, a 3/16 and a vertical/horizontal collet closer that I bought for one specific job. I did happen to have one other use for a collet since then that just also happened to be 3/16.

You are correct, this nut does not need to any more than a very light finger tight or it will bind the spindle.
I will get back to that sometime tomorrow, I hope. Right now I am dealing with the aftermath of my 2nd covid shot.

 

[Shotgun]

Do we NOT have them? I would figure a 5c collet block set is so common that we'd all have one already.

I don't have 5C collets. Just ER32

 

[extropic]

I had thought about the cantilevered worm gear. Since this is a dividing head and not a rotary table, the worm should never be driving against a load, it is just doing positioning There are locks for the worm shaft and the spindle and the trunion to clamp everything solid during a cut.

Sometimes I forget that not everyone has all the same tools as I do. I have wrenches that fit those nuts, most probably don't. I am already using brass tipped setscrews for the spindle indexing plate.

To emphasize and clarify my suggestion for better support the worm shaft; I think the bold statement is shortsighted.
I think the strength of the gear mesh or a torque limiter (shear pin?) should be the weak link in the gear train, not the mounting support of the worm.
I know this is not intended to be a full industrial universal dividing head, but I would want to perform some milling operations while rotating the spindle and not be concerned about the worm shaft. It looks like such an easy fix.
Universal dividing heads are designed to have the spindle driven during a milling operations for the purpose of creating features such as spirals and cam slots.
A great upgrade (outside the scope of this thread) would be to incorporate an electronic drive along the lines of the electronic leadscrews we see.

I think I've made my point, will bow out and leave it to the participants to decide.

One thing I've already learned from this thread, If I were to ever propose such a group build, I would want a completed set of drawings in hand on day one. Not necessarily set in stone (changes to be negotiated amongst the participants) but ready to go, if agreed.
That's not a criticism of this project in any way. Flyinfool is doing an excellent and critical job. The thread has run very smoothly. None the less, it's at 200+ replies and the design is still in work.

Good luck all.

Watching with interest.

 

[Brento]

I am liking @extropic idea for the support. If it isnt alot to change i think it would be nice to have the support so in the future you can use the head during milling. Up to everyone else.

 

[Shotgun]

I am liking @extropic idea for the support. If it isnt alot to change i think it would be nice to have the support so in the future you can use the head during milling. Up to everyone else.

It would be some MAJOR rework.

You'd need a support attached to the Trunnion on the opposite side. To make space for that, you'd need to slide the Worm Gear toward the Trunnion Crank, reshape the Worm Shaft, wipe out the graduations on the Trunnion, and then add more parts for the support. As it stands, the Worm Shaft is about as thick as it is long, and and is supported by 3/4" thick steel that has a clamping/locking feature. The teeth on the gear/worm are about 1/8" deep and 3/4" wide. If you're cranking on that thing hard enough to make it warp so much it skips a tooth, you're doing it wrong. Not paying attention AND abusing the tool.

Remember: Perfection is the enemy of good enough.

Also, we did not start this build completely blind. We had a good write up of a working example from Mark_f, and the genesis of a SolidWorks model that @Flyinfool took up and ran with, doing the leg work of consulting with each participant to make sure they could make the parts. If we had started with a full set of drawings, I hardly think we'd be any further along than we are now.

 

[Shotgun]

Also, having built some complex contraptions that started with a set of plans, I can say that it is truly amazing how what first seems like an innocuous change usually results in a ripple of unintended modifications.

 

[Shotgun]

Universal dividing heads are designed to have the spindle driven during a milling operations for the purpose of creating features such as spirals and cam slots.

This statement piqued my interest, @extropic.
To make a spiral, there would have to be some sort of coordination to lock the rotation of the dividing head's spindle to the advancement of the mill table it was attached to.

First, do I have that right?
Does the mill table have to have some sort of power take off to drive the dividing head?
Do these commercial dividing heads also allow the piece to be positioned at any arbitrary angle as this design allows?

 

[Ianagos]

This statement piqued my interest, @extropic.
To make a spiral, there would have to be some sort of coordination to lock the rotation of the dividing head's spindle to the advancement of the mill table it was attached to.

First, do I have that right?
Does the mill table have to have some sort of power take off to drive the dividing head?
Do these commercial dividing heads also allow the piece to be positioned at any arbitrary angle as this design allows?

Most of the old school dividing heads I’ve seen have had the capability to do helixes if you had the gearbox. Typically that would also consist of a set of gear that mount to the x axis handwork and a 90degree gearbox of some sort. It’s a more advanced feature but a useful one.

I don’t think we need to design it with that on mind as I’m betting way too many guys have all types of mills and hard to make it work with any kind although that could be up to them.

I have thought the unsupported worm was a bit odd. Typically I also see an eccentric bearing on the worm to it can be rotated to compensate for wear. I could also imagine this being done with a self aligning or cylindrical bearing?(not sure if that’s the correct term) on the fixed end and a bearing that rides in a slot on the tail end that can be adjusted via set screw.

Whatever the case I do think compensation for backlash should be integral in the design and I also believe to achieve a low level of backlash both ends of the screw should be supported so it cannot flex.

I need to download the solidworks model and take a look better as I’ve just looked at the pictures

 

[rwm]

I know Tom Lipton has done it:

Robert