Warco Dividing-Head: 50 Divisions Possible?

Help!

So far I have used my Warco-badged BS 0 or 1 dividing-head only infrequently and in direct stepping and protractor modes.

I now wish to engrave some 50-division dials, my first go at full dividing (from the holey plate), but it won't give them! Is that right?

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Studying Ivan Law's book on gear-cutting, I had rightly worked out the method, but the stop-fingers will not close back-to-back sufficiently for the calculated setting. My sums are:

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5 major divisions (the tens): 72º per division; 5s at 36º steps: both attainable using the DH's protractor scale and a calculated list of angles.

The 1s though (= 0.001" travel on 20tpi lead-screws) are at 7.2º increments.

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The fitting's only possible dividing-plate settings are the 20- and 15- hole circles; the 20-hole the better choice. 40:1 ratio so (40/50) full turn for 7.2º.

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So presumably set the fingers to span (4/5) X 20 = 15 holes.

No! That gives an accumulating error I found and calculated, by testing 10 division-moves against the protractor. I recalled a thread on here a long time ago that the fingers need setting in 1 hole closer than you would expect.

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Therefore set the fingers at 0 and 16, not 0 and 15. Or the 15-hole equivalent. The tool actually bounds spaces round the disc, each marked by 2 holes, not simply counts holes.

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Only they won't go. They stop against themselves before even opening the 16th hole to lead, so to speak. The other two plates offer only prime- and odd-, number circles that won't give 50 divisions.

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So what am I doing wrong, please?

Have I missed a calculation or something?

Or do I need contact Warco to see if they supply larger-count plates that will allow 50 (and greater)? Warco's web-site is not forthcoming; stating only that it offers the heads with 2 plates, and not enumerating them.

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This dividing-head is not worn-out or broken. I bought it hardly used, if at all (bereavement sale within the club), It is though, very stiff and "lumpy" to operate; not giving smooth full rotations even when disengaged. I don't know if it is grease-packed and that has hardened over the years.

I have also been unable to discover how to lock the engagement, risking disengagement and back-slipping when manipulating the fingers and a very awkward, stiff detent with a too-strong spring.

Did you set it at 16 holes or the correct 17 holes which is 16 holes as calculated plus one hole for the pin.

4/5 x 20 = 16 not 15

Edited By JasonB on 19/07/2022 11:23:15

If you have access to a 3D printer, it is not too difficult to simply print a division plate with the number of holes you need.

My cheap & cheerful (72:1) rotary table had a similar problem in that I couldn't do 25, 50, 75 or 100 with the dividing plates available. I drew a 25 hole plate, and printed it in PLA. It worked fine for a one off.

Typo

Edited By Peter Cook 6 on 19/07/2022 11:43:38

Regarding the fingers make sure you have the tapered sides facing towards your 17 holes not the straight sides as that would prevent you getting full movement of the fingers

If I understand the problem correctly the fingers will not allow the correct indexing to be achieved. I'm slightly surprised by that; 4/5 of a turn should be possible. If, for some reason it isn't, then simply index the 1/5 of a turn and move the fingers back at each index rather than forward. It helps to think if the indexing in terms of spaces rather than holes.

Andrew

With the setup here to divide 50 divisions the sector arms are set to give
an advance of 16 holes not including the hole the index pin is in.

With this set up as shown the index pin arm is rotated clockwise and
drops into the hole as it passes over the lower sector arm ,the sector
arms rotate anti-clockwise to set the position for the next division.

John

Or, if the bevelled edges of the fingers will not allow you to swing the second finger around far enough, as is sometimes the case on some DH's, you use the square edge (but of the other finger)  instead, which then allows the other finger to go around far enough. Clear as mud? Good. Play with it and you will see how to do it.

And I find it helpful to think not so much in the term of "holes" but in terms of "spaces" and each space begins and ends with a hole. So as Jason says, the required 16 spaces will mean 17 holes between the fingers. Think of the first hole as 0.

You could also do it as 12 spaces on your 15 circle. (ie total 13 holes) if that is easier.

PS, Harold Hall's book "Dividing" (Workshop Practice Series) is well worth having in conjunction with Ivan Laws' Gears etc.

Edited By Hopper on 19/07/2022 12:15:14

Edited By Hopper on 19/07/2022 12:27:37

Thank you Chaps.

I do have the fingers the right way round, bevel to the pin; indeed I had to move the spring-plate to allow it. I'd tried putting the pin against the square edge but it does not work on this make of head.

I had calculated 20 X (4/5) correctly as 15 but then thought I needed use hole 16.

It's not easy to see quite how this works, but I will try that 17th hole..

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(And if it works, the " 19th hole" to celebrate ?)

Are you sure, see my post above.

4/5 = 0.8 not 0.75

Oh yes, Jason!

Silly me! I never was right good with numbers.....

Anyway I think I've cracked it.

The fingers were not going round enough to open the last hole. Inspecting them closely I could see what looked like burrs on the contact edges. I took them apart, very carefully filed them to gain that extra mm or so of approach at the tips, re-assembled them and this time it worked!

There do seem to be slight angular errors but I think this a backlash effect as it is very hard not to overshoot or avoid pulling the worm out of engagement when moving the things round. (No worm-eccentric lock.)

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All this started when I had set up the dividing-head and its tailstock on the Myford mill for some bits on the steam-wagon and in repairing a Rothenberger tube-bending set (for making steam-wagon bits). Simple to set as I have made T-slot tenons for them.

While set I thought, "What have I outstanding that uses the same set-up?"

So I made a chuck-key to replace the bodge I'd been using on my Harrison lathe's 4-jaw chuck.

Then remembered the still-unfinished 'Stent' T&C Grinder has lots of graduations and cross-holes. It also has some parts specified as knurled but far too large diameter for my clamp-type knurler, so I'm giving them scallops instead. That separately though, with the BCA Jig-Borer, to keep the mill still with the dividing-head centred.

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Peter Cook:

No, I've no access to a 3D printer so I'd need use the rotary-table to make further division-plates. Besides, as I can't learn 3D CAD, I'd have no hope with 3D CAM whether by sticking-on or peeling-off machine!

Another option is to print off a division wheel with the appropriate graduations, (e.g. https://www.cgtk.co.uk/metalwork/calculators/divider), enlarge to A3 size, glue to a piece of plywood and use a pointer to index each hole you drill.

A3 is approx. 300mm in its smallest dimension, so the disk could have over 900mm circumference. Say you are drilling 50 holes in your plate, the marks on the disk would be roughly 18mm apart. So if you can only line your pointer up with a confidence of 1mm, the error will be small.

In addition, it has often been pointed out that errors in hole spacing on a division plate are reduced by a factor of the worm ratio when the plate is used.

This is the manual for the Vertex BS0, if you don't have one. This is exactly the same, as far as I know, as any other of this type of dividing head whatever the badge may say. The worm is 40:1.

images.machineryhouse.com.au/products/K4005/PDF/Manual.pdf

I haven't been through this particular edition but if my memory serves me correctly there are some minor errors in the tables relating to the higher divisions. I printed and laminated the tables which were corrected and are kept in the workshop.

Forgot to mention you can ignore Rows A to F in the tables as these only relate to the BS2 model. You only need to read Rows T, H & N for the basic dividing heads BS0 & 1. (I think BS stands for Brown and Sharp, although I stand to be corrected).

Edited By Chris Crew on 19/07/2022 20:04:04

Thank you for those tips!

I've book-marked the manual - I do have one I'd found on-line but it's of poor quality and does not print very well, so thank you for this version.

I have now identified the problems.

The first was my arithmetic! It took Jason two goes to point that out to me.

The second was suggested by small burrs on the fingers, preventing them from approaching each other enough to reveal the last hole in the series. I trimmed the contact areas (not the indexing edges!) back slightly, and they now open the necessary 16th of the 20 holes. Because the contact is close to the spindle it needed only a fraction shaved off to make that difference at the rim.

If I were to make a larger-count dividing-plate it's just occurred to me that I could do so by fitting the blank and a large lathe change-wheel, keyed together in some way, on a simple direct-indexing spindle to fit the jig-borer or bench-drill table. Although the jig-borer has a built-in rotary-table with worm-drive and protractor scale, it won't itself act as a full dividing-head, nor does it have a Vernier angle scale.