Dividing head advice

Hi: Can anyone please help me identify the Dividing Head shown in my latest album 4in Dividing Head the item I'm most interested in is finding out if anyone knows where I can find new or used pin plates to go along with the number 3 plate that came with the DH when purchased. The DH is a 4in the pin plate is 123.6mm dia. and has a knurled edge with a black plate pinned on the outside circumference saying each division =1mm the plate is 5mm thick it has a 30mm inside dia. the number 3 plate has 4 sets of drilled holes 40, 37, 36 and 29 holes. The plate is attached to it's backing piece by two chamfered screws the holes are 3.3mm dia. and have a 42mm PCD

You've got the div head can't you make them???

I've not used a dividing head, but I'm guessing the plates don't need to be particularly robust. Would a laser cut and engraved plate in 4 or 5mm cast acrylic be acceptable? I could do a run of them if they proved ok.

Robert,

You say in your post that the outside of the plate shows 1 division = 1mm, but the photo shows 1 division = 1 min. Either a misreading or typo.

Sorry, can't help with the identification. They are all basically the same internally - at least in the manner of their function - what you need to know is the worm/wheel ratio to aid with the choice, or design, of additional plates. Yours is unusual in that it is secured with only two screws. Most that I've seen use three. That, in itself may help to narrow down the manufacturer.

Good luck,

John

A couple of overall pics showing the entire assembled divding head from different angles might help ID it.

Robert,

Just done a search for images and, lo and behold, Warco have come up with a set with two hole fixing. Product number 8146. Might be worth getting in touch with them and get some dimensions?

John

From the photos in your album, it looks very nicely made Robert

But I regret that I too don’t recognise it

MichaelG.

For one off or occasional use it is possible to 3D print index plates.

Some time ago, there was an article about making Division Plates.

It suggested using scrap CDs or DVDs. The method was make the first "new" division plate, and then use it to produce a replica. and so on until an acceptable level of accuracy had been achieved. With each iteration the error would be reduced by a factor which was the ratio of the Dividing Head / Rotary Table being used to set the intervals.

With a 90:1 ratio, the third plate to be produced should be fairly accurate with errors being reduced by a factor of 8100.

Howard

If you were a manufacturer offering this facility on your dividing head, would you duplicate this feature across all plates in the set? How much would that cost you? Is it not highly likely that the other plates do not have this feature and will just have a plain edge?

In addition to the other ideas, there are numerous webpages (e.g. https://www.cgtk.co.uk/metalwork/calculators/divider) where you can print out a piece of paper with the necessary divisions on it. Print it out at A4, photocopy it to A3 (approx. 300mm diameter) and attach it concentrically to your plate blank. Line up the marks with a pointer. Assume some error in your lining up - say 1/2mm. Work out the angular error 1/2mm at 150mm radius gives (1/300 of a radian or about 12 minutes of arc).

I've had another look at your album and I see that there are 360 divisions around the periphery of the plate. That would make the worm ratio 90:1, so that 90 turns of the handwheel results in one full revolution of the table.

John

I started with that, and thought the dividing plates for Robert's machine would have the same number of holes as an HV6. But they don't!

HV6 plates have:

A: 15, 16, 17, 18, 19, 20 holes
B: 21, 23, 27, 29, 31, 33 holes
C: 37, 39, 41, 43, 47, 49 holes

Which match the corrected table supplied by Howard Lewis.

Whereas Robert's No 3 plate has 29, 36, 37 and 40 holes

Presumably, HV6 plates will work on Robert's Dividing Head providing his machine really is 90:1 and the plates are the same size. I'll measure mine and report back later.

Yer tis.

Or, forget the pin-clock attachment thingy and drive the head with an Arduino and stepper motor.

Dave

Edited By SillyOldDuffer on 14/04/2022 18:14:02

You may like to play with this calculator, Robert :

**LINK**

https://www.cgtk.co.uk/metalwork/calculators/dividing

I’ve just tried your worm ratio & available holes, and it seems to work nicely.

MichaelG.

.

Good find, John

‘though I was astonished to read this on Warco’s page :

”Please note the number of fixing holes shown in the photo may vary.”

MichaelG.

It's been pointed out to me that there are at least two glaring errors in my latest thread 4in Dividing Head - the first being that the label rivited to the outter edge of the plate says 1 division = 1 min (not 1 mm) the second is that the two chamfered holes that lock the plate in place ate 6.3mm dia not 3.3mm dia. Sorry for any confusion. I've had one reply saying that "why cant I produce the plates myself" - no reason why if I knew the combination of holes in each plate.

Edited By Robert Trethewey on 14/04/2022 23:06:47

Your dividing head is unusual in that it has the Deg and Mins on the plate. I have not seen that before. With a 1 min accuracy, you can produce the plates that you need, just have to plan what you are making and then create or get made the number of holes on that plate. No point having plates that are full of hole numbers that will never be used and just sit on the shelf. Was there any stamp marks on the dividing head or parts or plates?

Some plates are drilled from each side but are not through holes, and the other divisions are on a different pitch radius on each side of the plates.

Nice to know more about your dividing head. Was it a differential unit, or does the back shaft just turns the worm gear at 1:1

.

I think that’s the essence of Robert’s problem

He has one plate out of a set of [presumably] three or more; and wishes to put the appropriate patterns on each of the replacements.

Knowing the outside diameter of a plate, and the diameter of the indexing holes; he can probably deduce the realistically feasible maximum hole-count … but there’s a long way to go after that.

The short-cut, of course, would be to identify the device [which is where we came in].

MichaelG.

Edited By Michael Gilligan on 15/04/2022 06:29:59

The short cut, of course of course, is to use the brains with which we are blessed and work this information out for ourselves.

We are asked to ID a dividing head. The only pictures we have of it are in a fully disassembled state. We have no data on the indexing arrangement (i.e. the max. and min. hole PCD that it will accommodate) nor the indexing pin size. We do not do Mystic Meg here, we do engineering.

If identification is our aim, we need photos of the full piece. Supplementary information that also provides a good lead is the worm ratio (you do not need any plates at all to find that), the fasteners used on it (metric UN, Whit), the spindle fitting (e.g. a metric spindle nose thread would point us in a different direction to a Myford spindle nose thread).

John Hinkley provides reasoning for a 90:1 ratio. I tend to agree with him. So we go and look at something that has the same worm ratio (e.g. the HV6 given as an example). If we find any difference between the plates on that and the plate we have, we do not give up, we identify exactly what that difference is and see if it is an equivalence rather than a difference.

Below is the info. for an HV6. It has a 20 hole and an 18 hole. Everything you can do with these, you can do with the 40 and 36 on the plate above. Note that it comes with three plates with six hole circles in each, which may not be a suitable arrangement for the one above if you cannot fit six circles in the range of the indexing arm.

---

90:1 worm ratio

Hole circles=[15,16,17,18,18,19,20,21,23,27,29,31,33,37,39,41,43,47,49]
---
All divisions possible with above plates
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 45, 46, 47, 48, 49, 50, 51, 54, 55, 57, 58, 60, 62, 63, 65, 66, 69, 70, 72, 74, 75, 78, 80, 81, 82, 85, 86, 87, 90, 93, 94, 95, 96, 98, 99, 100, 102, 105, 108, 110, 111, 114, 115, 117, 120, 123, 126, 129, 130, 135, 138, 141, 144, 145, 147, 150, 153, 155, 160, 162, 165, 170, 171, 174, 180, 185, 186, 189, 190, 195, 198, 200, 205, 207, 210, 215, 222, 225, 230, 234, 235, 240, 243, 245, 246, 255, 258, 261, 270, 279, 282, 285, 288, 290, 294, 297, 300, 306, 310, 315, 324, 330, 333, 342, 345, 351, 360, 369, 370, 378, 387, 390, 405, 410, 414, 423, 430, 435, 441, 450, 465, 470, 480, 486, 490, 495, 510, 522, 540, 555, 558, 570, 585, 594, 600, 615, 630, 645, 666, 675, 690, 702, 705, 720, 735, 738, 765, 774, 810, 846, 855, 870, 882, 900, 930, 945, 990, 1035, 1110, 1170, 1215, 1230, 1290, 1305, 1350, 1395, 1410, 1440, 1470, 1485, 1530, 1620, 1665, 1710, 1755, 1800, 1845, 1890, 1935, 2070, 2115, 2205, 2430, 2610, 2790, 2970, 3330, 3510, 3690, 3870, 4230, 4410]
---
Missing divisions up to 100
[28, 44, 52, 53, 56, 59, 61, 64, 67, 68, 71, 73, 76, 77, 79, 83, 84, 88, 89, 91, 92, 97]
---
Hole circles needed to produce missing divisions
[14, 22, 26, 53, 28, 59, 61, 32, 67, 34, 71, 73, 38, 77, 79, 83, 14, 44, 89, 91, 46, 97]

.

I disagree completely

… but let’s not argue about it

We have simply interpreted the task differently.

I consider the ultimate objective to be completion of a set of plates, of which there is currently only one plate available.

MichaelG.

Edited By Michael Gilligan on 15/04/2022 07:42:08

.

John’s reasoning seems incontrovertible

… except that there are only 240 divisions around the plate.

He does have the right answer though !

MichaelG.

Edited By Michael Gilligan on 15/04/2022 08:52:23