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.

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.