Dividing Head – GHT or Harold Hall?

[David TParticipant @davidt96864]

[David TParticipant @davidt96864]

Afternoon all,

I'm sure this must have asked dozens of times but strangely I haven't found a direct answer. I must be searching the wrong terms….

I want to make an indexing / dividing head, suitable for my ML7 and BCA mill. The options I'm looking at are the simple Harold Hall design, or the GHT design sold by Hemingway in kit form. Are there any particular reasons to choose one over the other?

Thanks

[EmgeeParticipant @emgee]

Hi David

Either of those heads may be too high for use on your BCA, I thought the BCA already had a rotary table that could act as a dividing device ?
But perhaps you want to machine in the other plane.

Emgee

[Thor 🇳🇴Participant @thor]

Hi David,

I guess the GHT dividing head is more expensive than the simple dividing head designed by Harold Hall. If the dividing head has to be small Harold Hall's version could be made lower if you need more headroom.

Thor

[Mick HenshallParticipant @mickhenshall99321]

I made HH's version use it on bed of lathe here shown graduating dials for my Adcock & Shipley horizontal mill, constuction was straitforward using stock material

MICK

[BazyleParticipant @bazyle]

I think it is a case of deciding if you want the experience of machining a casting and an end result with curved surfaces that a casting provides, or a fabrication for the experience not being tied to castings provides. If you take the fabrication route you can adapt it to any height and form you need and happen to have bits for in your scrap bin.

I would suggest the most significant attribute to have is compatibility with your lathe spindle, chucks and collets so they are easily interchanged, Just about everything you want to put in a dividing head first needs to be machined in the lathe so interchangeable chuck and the precision of collets simplifies this.

[Phil PParticipant @philp]

You could do something like this which I made for my own machine. It adapts a Pultra clock-makers lathe head and tail stock to use for small dividing jobs.

Phil

[IanTParticipant @iant]

There are other good alternatives David – such as the Timmins Dividing Head – castings for which are still available from Blackgates. It was designed specifically for use on the Myford.

See: http://www.blackgates.co.uk/wkequip.html

Regards,

IanT

[Neil WyattModerator @neilwyatt]

Ultimately they all do the same thing.

It really comes down to how much pleasure you will get from making and using an elegant tool versus achieving the same practical result for less effort in less time.

Neil

[Stephen BensonParticipant @stephenbenson75261]

I can get mine to fit on my Cowells mill no problems best dividing head by far I have ever used and I have used a few including the Cowells one which is very poor, I noticed that RDG Tools was selling them with the micro adjuster which I wish I had for miine

Edited By Stephen Benson on 25/07/2018 21:35:21

[David TParticipant @davidt96864]

Thank you all for your replies, they are much appreciated.

Emgee – Yes I expect you are right, they probably are too tall for the BCA. More than likely I'll be using the dividing head on the lathe. I can (and have!) used the rotary table for dividing, but as you say there's always the "other" plane.

Thor – Yes, I never thought of lowering the centre height. Maybe make a riser block for use on the lathe in order to match the lathe's centre height?

Mick Henshall – Thank you for the photos. I find it interesting that the dividing head is clamped to the bed, but still appears to be at centre height with your engraving tool (which also appears to be the HH design). Does that mean that your dividing head sits above the spindle height if used on the crosslide?

Bazyle – As I have an ML7, the GHT castings are at the correct centre height anyway. So from that perspective there's no difference to the HH design. I quite agree on matching the nose to my lathe, I have no reason not to.

Phil P – I remember seeing your Sigma(?) and your dividing head on that "other" forum…. Very nicely done!

Ian T – I've seen someone else post up their Timmins, it looks like it fits the bill. I couldn't find much information on that website though?

One other thing, and again this is probably just me being dense….. The basic GHT kit from Hemingway comes with just a 24T wheel for simple indexing. I appreciate that 24T provides many of the common divisions, but it appears that any other number of divisions requires the full index plate + worm arrangement. Is that correct? The HH design, on the other hand, allows the index wheel (gear) to be easily swapped as required.

[Michael GilliganParticipant @michaelgilligan61133]

David,

I don't think anyone has asked the obvious question yet, so please allow me …

What sort of dividing work do you anticipate doing with this head ?

• If it's predominantly pinion cutting and small wheel cutting, then something low profile, with a tailstock, would be appropriate.
• If you intend to work on big wheels then somthing with more centre height will be needed, and you may have to make different compromises.
• Will you always be locking it at each step, to [say] cut teeth, or do you want to also have the facility to mill a groove under rotation.

Different answers will probably point you in different directions !!

I had always planned [round tuit] to build GHT's design, or maybe a miniature version of it … then thought about adapting it to stepper motor control. But I now have a little Unimat head which will adapt nicely to the BCA and various lathes; so it's time for a rethink.

MichaelG.

.

.

Edit: A more complete set is illustated here:

http://www.nielsmachines.com/en/emco-unimat-sl-dividing-head.html

 

Edited By Michael Gilligan on 26/07/2018 15:24:47

[David TParticipant @davidt96864]

 

Posted by Michael Gilligan on 26/07/2018 15:21:03:

David,

I don't think anyone has asked the obvious question yet, so please allow me …

What sort of dividing work do you anticipate doing with this head ?

• If it's predominantly pinion cutting and small wheel cutting, then something low profile, with a tailstock, would be appropriate.
• If you intend to work on big wheels then somthing with more centre height will be needed, and you may have to make different compromises.
• Will you always be locking it at each step, to [say] cut teeth, or do you want to also have the facility to mill a groove under rotation.

Different answers will probably point you in different directions !!

I had always planned [round tuit] to build GHT's design, or maybe a miniature version of it … then thought about adapting it to stepper motor control. But I now have a little Unimat head which will adapt nicely to the BCA and various lathes; so it's time for a rethink.

MichaelG.

Edit: A more complete set is illustated here:

**LINK**

 

Edited By Michael Gilligan on 26/07/2018 15:24:47

Yes, that would be an appropriate question! I confess that I typed my opening post in haste and probably missed some important points.

As of late my need for dividing has been limited to small scale PCD stuff. It was easily accomplished on the BCA, but it did mean having to remove the item from the lathe chuck and re-centering on the rotary table. Not a game-stopper, but not ideal. I also had to cut the stock shorter than I'd like in order to fit it under the BCA's spindle. A dividing head on the lathe cross slide would solve both issues. I expect more PCD work in the future, and quite possibly small wheel and pinion cutting. Any milling "around a corner" I think would be best accomplished on the BCA's rotary table.

Cost isn't a huge problem but naturally I don't want to spend more than necessary. I don't have much stock lying about so I'll have to buy in everything needed to make a HH head. It's still cheaper than the GHT kit but not by much, so it's not a deciding factor.

That Emco head is elegant in its simplicity and would do nicely, but I suspect it's availability and cost will put below the other options.

Edited By David T on 26/07/2018 16:27:12

[duncan webster 1Participant @duncanwebster1]

Posted by Phil P on 25/07/2018 18:47:17:

You could do something like this which I made for my own machine. It adapts a Pultra clock-makers lathe head and tail stock to use for small dividing jobs.

Phil

If anyone fancies making one like this I've got the headstock for you, send me a PM. I found a Myford DH at the right price, so Pultra became redundant

[Michael GilliganParticipant @michaelgilligan61133]

David,

Noting that Duncan may have already offered just what you need …

If you still want to build something, it might be worth looking at Keystone Clamps as a source of modestly priced castings. … Use an ebay search for Pegasus Industrial Key Clamp

These are, obviously, not 'close tolerance' components; but there are some useful-looking designs and it would be a simple matter to bush them. … The two I liked the look of were '144' and '146' [with suffixes for various sizes].

Hope it goes well; whatever you decide to do.

MichaelG.

.

Edited the ebay reference, to remove the stupid 'auto Smiley'

Edited By Michael Gilligan on 26/07/2018 19:56:13

[IanTParticipant @iant]

Hallo David,

Alan Timmins published his design in EIM Volume 3 (1981) and it was described as a "Small Dividing Head that can utilise Myford accessories". I was fortunate enough to recently acquire the Timmins body casting, complete with a pre-machined MT2 taper spindle – which is still supplied as part of the kit by Blackgates I believe. This item has joined the long list of other projects "under the bench" – but is likely to be kicked up the 'to-it' list soon as I need to make some gears on my small mill (which will also require the Timmins tailstock casting.. or perhaps a fabricated one?).

I did look at the other designs you are considering but decided the Timmins was about the best mix of capability vs time-to-build vs just nice-to-have – for my particular needs.

I have the original Timmins EIM articles (and the later article by Rod Jenkins) – so if you would like to research this option further, then please PM me and I will scan them and email 'em to you for your personal perusal & delectation!

Regards,

IanT

[HopperParticipant @hopper]

I made my own fabricated version of GHT's versatile dividing head to save cost on castings. Leaving the fabrication out of the equation, it is still probably more machining work than HH's modular block construction. But it looks in keeping with an antique lathe such as a Myford, if that matters at all to you.

One advantage of the GHT design if you go the full monty, is the micro-adjustment facility that allows resolution of one thousandth of a degree, so you can make your own index plates. (Only 814 small hole to drill!) or cut 127 tooth gears and the like.

Probably for most practical applications, the HH design is a simpler, more modern design, more easily made from standard materials.

[Mick HenshallParticipant @mickhenshall99321]

Sorry David for delay in answer to your question, I originally made the dividing head to index dial indicators for my lathe and old mill,the lathe bed seemed agood base to work from,sitting on the bed it is lower than centre height of lathe and it seemed a good idea to mount engraver to cross slide to be able to place it where I wanted it by using the saddle traverse and arrange it to be on centre height of dividing head. The dividing head was not built to be on centre height of lathe mounted on the cross slide but could be packed up to align if needed from the lathe bed. As always with hindsight a more adaptable set up might have been useful but it has worked ok and it was enjoyable makingt the tools

Regards Mick

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