Elliott dividing head worm…

[YouraTParticipant @yourat]

[YouraTParticipant @yourat]

Hi all.

I've just acquired an incomplete Elliott dividing head, mostly because I wanted the chuck that's on it and it was the right price..

To make it useful as a dividing head again though, I'd like to see if I can either obtain or make the worm to go with the gear that's mounted on the spindle.

Not so familiar with the specs of these things – is there a simple way to measure what I need, or does some kind soul either have a spare they are willing to pass on, or even know what the specs actually are?

Thanks,

Youra.

[Martin KyteParticipant @martinkyte99762]

If you are making, then I would junk the existing worm wheel and make a new worm and wheel as a pair.

regards Martin

Edited By Martin Kyte on 05/03/2022 13:29:03

[Pete RimmerParticipant @peterimmer30576]

Just measure the OD of the wheel at the bottom of the throat and count the teeth. Then you can work out what the pitch of the worm is and they are fairly easy to make.

[BazyleParticipant @bazyle]

The worm is a tad over 0.975in or a tad under 2.6cm diameter, minor diameter 0.632in, 1.61cm. However this depends on depth of engagement so crest of thread is 0.085in 2.18mm. Base of thread is about the same but my calipers don't go in that far. Pitch: 3 turns are 0.76in 1.915cm. so seems to be 4tpi. It was probably designed as 4tpi being simpler to set up than a circular pitch and the wheel designed to match as the only variable would be the diameter.

[BazyleParticipant @bazyle]

As it has lost the plate holder etc as well probably the best thing to do would be to make it into a stepper motor controlled divider.

Unless you already have another dividing head to make a new worm wheel, with suitable precision as that is what the whole device revolves around, then it is much easier to make just the replacement worm. If you make the first one out of brass it will be adequate for hobby use and if it is not the best match won't damage the wheel.

[YouraTParticipant @yourat]

Bazyle,

Yes – a stepper motor controlled arrangement was exactly my aim

I have a motor and indeed the controlling electronics, all I'm missing is the worm and the bits that will hold it all in place.

Thanks for the measurements – I will make it out of brass – I'm assuming it's a flat crested / trapezoidal thread…?

Next challenge of course is seeing if I can easily achieve a 6.35mm pitch thread on my all metric lathe….

[Terence BooneParticipant @terenceboone95423]

i have just purchased a dividing head the same as this and am trying to identify the nose thread.i am seeing 1.5 inch 10 tpi but doesnt really make any sense to me. could you possibly enlighten me

[Nigel Graham 2Participant @nigelgraham2]

YourAt–

If the head is to inch measurements the thread will probably be of Acme rather than trapezoidal form, though I don't think it's quite Acme either. Grind a cutting-tool to the wheel-tooth profile, and find the appropriate depth of cut from tables or calculations on worm-gears.

Cutting the worm thread is the reverse of what many of us face – cutting a metric thread on an Imperial lathe! I.e. needing a suitable conversion wheel if you lathe uses change-wheels. If it has a gear-box it might be capable of setting to inch-based pitches: the charts for the lathe will tell you.

Please Note: I take it you know not to use the half-nuts, but keep them engaged for cutting a pitch that is not a regular multiple of the lead-screw's. However, what is your lathe's lead-screw pitch?

Cutting a pitch close to or coarser than the lead-screw, on any lathe, puts enormous strains on the machine.You need take very light cuts, and it is often safer to rotate the lathe manually, using a hand-wheel on the end of the lead-screw.

.

Terence –

Well, it makes sense but simply does not match your chucks! It is not a standard BS or UN thread, at 10tpi, but some machine-tool manufacturers seem to have gone their own sweet ways on spindle threads.

If anyone recognises it for you as a size used by a given manufacturer you may be able to find a chuck for it. Otherwise, you may need make a backplate with screw-cut thread, and to suit whatever chuck you choose for it.

The disadvantage here of course is that you cannot transfer a work-piece from lathe to dividing-head whilst keeping it undisturbed in the same chuck.

.

This enquiry is of interest to me as I want to replace the missing worm and other parts driving the table, on a small Denbigh horizontal-mill. Its worm-wheel is still there so I can measure that.

I think Bazyle's advice to use brass, applicable in my case too!

[HopperParticipant @hopper]

Posted by Terence Boone on 01/06/2023 19:37:56:

i have just purchased a dividing head the same as this and am trying to identify the nose thread.i am seeing 1.5 inch 10 tpi but doesnt really make any sense to me. could you possibly enlighten me

The manufacturer's choice. They all did their own thing. Standard BSF etc TPI/diameter combinations were mostly used only on fasteners and the like, not necessarily on special machine parts.

If made in the UK it is most likely a 55 degree BS thread form, US will be UN form 60 degrees.

If you need tap to make a chuck backplate, try Tracy Tools, they stock a few different oddball spindle thread taps.

[Terence BooneParticipant @terenceboone95423]

thanks for your replies. I have limited knowledge / abilities . when i checked with the whitworth thread gauge it did look to be a larger angle but i will check again with my strong glasses on. interesting that they didn`t stick to known thread forms and makes sense of not being able to identify it. thanks.

[Nigel Graham 2Participant @nigelgraham2]

It may well be of Whitworth form (geometry) so still of 55º included angle and with the standard rounding by proportion of depth on the crest and root… just not a standard pitch for a BSW or BSF bolt thread, hence non-standard number of threads per inch.

If it is of 60º but otherwise all inch dimensions it is of Unified (American) form, but still of non-standard pitch.

The 60º angle is also that of metric threads but I would expect then the rest of the dimensions to be in neat millimetres.

I'd say Whitworth form most likely, so a Whitworth 10tpi thread-gauge will fit it nicely; but it is not of a standard BSW bolt pitch.

[duncan webster 1Participant @duncanwebster1]

Posted by Bazyle on 05/03/2022 14:44:36:

The worm is a tad over 0.975in or a tad under 2.6cm diameter, minor diameter 0.632in, 1.61cm. However this depends on depth of engagement so crest of thread is 0.085in 2.18mm. Base of thread is about the same but my calipers don't go in that far. Pitch: 3 turns are 0.76in 1.915cm. so seems to be 4tpi. It was probably designed as 4tpi being simpler to set up than a circular pitch and the wheel designed to match as the only variable would be the diameter.

Bazyle's tads are pretty big , 2.6 cm is 1.024", so the tad must be of the order of 0.024" (1.024-0.975)/2. Probably Imperial tads, which as we all know are better than metric ones.

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