Chuck mounting: m38x2.5, or 1.5″ 10tpi

[jaCK HobsonParticipant @jackhobson50760]

I took a punt on a very nice dividing head. I’d like to find a chuck backplate for it.

i don’t really know what I’m doing when measuring threads. I think it has a 1.5″ 10tpi or M38x2.5 chuck mounting thread

I measure about 39.65mm or 1.563″ register diameter (so that gives an idea of my margin for error) … neither seem close enough to a standard?

Any ideas?

I’m probably going to have to make one… about time I learnt how to cut threads.

[bernard towersParticipant @bernardtowers37738]

doesn’t the manufacturers name help you?

[FulmenParticipant @fulmen]

It’s obviously not 1.5″ or 38mm, but M40x2.5 fit’s the bill. Don’t get caught up in standard threads, components like this will almost always be a custom thread. If it’s US or UK mfg it’s probably inch, if not it’s most likely metric. At least if it’s made after WWII.

[Martin ConnellyParticipant @martinconnelly55370]

Some thread gauges sound like a good idea for Christmas. You need to know the thread form as well as its TPI if it is an inch based thread. It might be a UN thread or a Whitworth thread, slight difference between 60° and 55° will cause problems achieving a good fit.

Martin C

[duncan webster 1Participant @duncanwebster1]

Why is it obvious? 1.563″ is 1 9/16 register, so 1.5″ thread is perfectly reasonable.

[FulmenParticipant @fulmen]

Threads are never larger than their nominal size (lets ignore pipe threats for now). As you point out it might be 1 9/16″, but it’s not 1.5″.

[JasonBModerator @jasonb]

But the plain register is quite often larger than the thread OD

Typical Myfors has 1 1/8″ thread but a 1 1/4″ register

[Tony Pratt 1Participant @tonypratt1]

jaCK, please measure the outside diameter as carefully as possible and the pitch, if your haven’t got any thread gauges atm a tap can be used to give you an idea. Also the manufacturers name is helpful.

Tony

[DC31kParticipant @dc31k]

The spindle nose thread cannot be the only threaded item on the whole dividing head. Remove a few fasteners and see if they are imperial or metric. That would give you a very good indication of what the spindle is likely to be.

Measure the centre height. That will also be another piece of evidence.

Upload a picture of the head. Someone might recognise it.

At that course pitch, you could potentially use a ruler to determine whether it is 2.5mm or 10tpi. The difference over 25mm of threads is nearly 0.5mm.

[FulmenParticipant @fulmen]

Please disregard my comment, I missed the “register” part.

 

As others have said, more data needed.

[jaCK HobsonParticipant @jackhobson50760]

thanks for trying to answer.

The register diameter is larger than the thread diameter.

I have thread gauges. 10 tpi is amazingly similar to 2.5mm… obv if it was 2.54 then it would be same. But over 3 threads, cheap gauges, and my eyesight…

60 degree, not 55.

38mm external thread diameter on the dot as far as my eyesight allows which encouraged me to consider metric. 1.496″

Horizontal dividing head with tailstock. MT2 in head, MT1 in tailstock. 4″ centre height.

I think it is pretty well made… so tolerances might be high.

Cap head screws take a 3/16″ allen key. 20tpi. .24575″ diameter (using digital mic instead of vernier caliper). So pretty convincing on the imperial bolts?

Green.

No markings that I’ve found.

 

[jaCK HobsonParticipant @jackhobson50760]

40:1 worm drive with 60 index holes in the head gear.

[Tony Pratt 1Participant @tonypratt1]

Elliot dividing head so British.

Tony

[peak4Participant @peak4]

Have a read of this thread; Elliott maybe??

Elliott dividing head

See also near the bottom of this page
https://www.lathes.co.uk/elliott-omnimil-00/

Bill

[jaCK HobsonParticipant @jackhobson50760]

Nice, so I’m just missing the mill part… Wonder where I can get one of those. TBH, I’ll probably just use a chuck adapter on an MT2 if I need one…

[bernard towersParticipant @bernardtowers37738]

If reading 38mm on the dot its not metric but your 1.496 is right for imperial if you take off 10% off thread depth which is what most people do when screwcutting.

[old martParticipant @oldmart]

One problem with simply screwing a backplate for a chuck onto the spindle is that it would be unlikely to run straight. I would remove the elliot spindle and use it as a gauge for making the backplate, then turn the spindle around and in a four jaw independent get it running true in the lathe. Screw the backplate onto the spindle and finish turn the side that the selected chuck will fit on. Then the chuck would have a better chance of running true. The Elliot pictures show a drive plate for between centres and there may have never been a chuck option envisioned by the makers.

Try your thread gauge in the female thread, that may be longer.

[old mart]

On old mart Said:

One problem with simply screwing a backplate for a chuck onto the spindle is that it would be unlikely to run straight…….

That’s why it has a close fitting register and abutment face. The thread only holds it axially, and should not be a tight fit.

[mark smith 20Participant @marksmith20]

If its an elliott the smaller dividing heads have a 1.5″ x 10 UNS thread

[not done it yetParticipant @notdoneityet]

As an aside (if determined to fit a chuck) a 3 jaw is likely to have run out, so a 4 jaw would be better.  A drive plate, and using the centre for between-centres mounting, would be easiest for most things?  And most accurate.

[Martin ConnellyParticipant @martinconnelly55370]

I have looked at metric thread standard and UN threads in Machinery’s handbook and the thread Mark suggested is the only one I have found that matches. The 1981 BSI metric standard lists 2.5mm pitch in the dimensions of the thread form but completely misses it out everywhere else, jumping from 2mm to 3mm.

Martin C

[Author]

Posts