threaded mounting on dividing head

[petertha]

I have a new vertex dividing head with 1.5x8 tpi threaded nose & trying figure out how to proceded on mounting a 4" chuck I just acquired. The chuck has integrated threaded backplate to save me machining a sepearte backplate casting & then mounting a plain back chuck.

The problem: the chuck only threads on a couple rotations & then seems to bottom out prematurely. Its flat ID segment hole (before the internal threads) kind of tightly fits (or bottoms) on the matching flat segment on the DH. I would think it should screw on all the way until its back is flush with the lip on the DH spindle. If I screw the casting plate (included with DH) on, it does this. Same for the protection ring.

So I measured:
1.515" = OD of DH spindle flat segment
1.512"= ID of 4" chuck flat segment
1.515 = ID of casting plate (accessory included with DH)
1.590" = protection ring.

So looks like the chuck is 0.003" (1.515-1.512) smaller ID & thats the hold-up. The way I suspect this is supposed to work for accuracy is thread the accessory all the way until its back face is flush against the DH lip so it snot just depending on threading to be axial with teh DH spindle?. Maybe the chuck is meant for a 1.5x8 tpi lathe nose? (its a deeper relief too).

I can probably set up the 4" chuck in my lathe & relieve the ID bore a smidge. Thought I would check first though, its hard to put metal back on.

 

[petertha]

Here is how the blank backplate casting fits the DH nose. (It was included as a spare with DH).

 

[petertha]

This is how the protection ring fits DH nose

 

[Philjoe5]

The 1 1/2" x 8 threaded spindle is common on both 10" Logan and Southbend lathes. If you take a threaded backplate for a South Bend it won't screw all the way on the Logan spindle, exactly what you're experiencing.

I recently had access to a new import dividing head with that 1 1/2" x 8 thread and the 4" backplate that came with it fits on my Logan lathe perfectly.

I suspect your backplate was threaded to fit a South Bend. One of the few vendors who recognizes this difference is Little Machine Shop. Here's a link to their backplates and you'll notice they have different part numbers for the Logan and South Bends with the same thread:

http://www.littlemachineshop.com/info/spindles.php

Those guys are the best.

Hope this helps

Cheers,
Phil

 

[petertha]

Thanks Philjoe5. I'm suspecting there are different lathe nose spindle standards like you mentioned, even though they are nominally threaded 1-1/8 threaded. Dang, I though this would be plug & play. And buying a seperate chuck & adapter plate does not necessarily solve the problem, but at least I would only be affecting the cheaper backplate by modifying vs. the all-in-one chuck.


The LMS website was semi useful. Unfortunately their sketch & corresponding table of backplates does not define the straight cut segment preceeding the thread. That would have been useful.


http://www.littlemachineshop.com/info/chuckadapters.php

 

[petertha]

Here is my (Bison) chuck 1-1/2 8 threaded chuck & backplate showing the straight segment ID dimension. Same 1.515" ID dimension either way. Its obviously made for a specific spindle nose of their choosing. Im beginning to think the oddball (or maybe less comon) is the Vertex dividing head spindle.

 

[petertha]

So I guess the million dollar question is: if I bore out the backplate ID slightly (section ahead of the 1.5x8 threads) so that it slightly clears the straight nose section of the dividing head spindle (red shade), but make sure that the back face is also machined square at the same time (purple arrow) so it bottoms square to teh bit of shoulder on the DH spindle, will that get me a correctly fitted backplate to the DH?

If so, what is the purpose of OD straight part on a threaded lathe spindle for anyway? I could see if it was tapered, the backplate would center up & mate against it as it was threaded on. But what does a parallel spindle nose accomplish? ie if it happened to be a looser or worn thread fit, the gap difference between spindle & bore wouldn't center it up anyway?

 

[Philjoe5]

I'm not sure if I'm getting what your question is but let me give it a try.

It doesn't matter how the backplate backs up onto the spindle as long as it does so the same way each time. This is most likely to happen if you have a backplate that fits shoulder-to-shoulder or machine the backplate to screw on for a shoulder-to-shoulder fit.

Then the backplate should be machined in the usual way for a plain back chuck.

It's only plug-and-play if you have a backplate that fits, even then you have to make a truing cut

Phil

 

[bb218]

In my opinion the 1.512 or 1.515 diameter straight section is what positions the chuck radially, the shoulder then squares the chuck when it makes contact. The thread is only to hold it, the pilot and shoulder position it.

Mike

 

[petertha]

I noticed Chronos in UK supplies the same Vertex BS0 dividing head. They mention "The spindle noses are threaded for a chuck ( suits Myford Series 7)".

Ive heard Myfords have different threads & nose configs depending on the vintage. But assuming its same 1.5 x8 tpi like DH, does this shed any light on the matter? Is that how Myford chucks & backplates engage their spindle? ie the thread move it in, but the radial fit controlled by the straight segment & then up against the shoulder?

http://www.chronos.ltd.uk/cgi-bin/sh000001.pl?WD=head dividing&PN=XMAS_GIFT_IDEAS_4.html#aGX45

 

[petertha]

SUCCESS!
I chucked an accurate test round into the 4" chuck jaws, then reverse mounted that assembly into my lathe, originally intending to see if maybe the backplate bore was oblonged a bit. The DTI showed it was dead concentric. I measured again & confirmed the bore was perfectly round, but about 0.002" smaller than the DH nose. I then decided to utilize this setup & just touch the backplate bore with some 400 paper wrapped on a round mandrel. I tested the fit against the DH & could see it was making progress. Tight, but slowly coming up the nose. Wasn't long before the dull finish gave way to a nice shine & it screwed all the way to the back. It now fits perfect. Almost like... maybe this is the way it was intended to be in the first place!

Now that I better understand whats going on, I think I'm going to get a few cast backplates for the DH. I can see now these would come in handy for mounting different variations of chucks & accessories.

 

[petertha]

Does anyone have some pics/links of setups using the DH MT dead center & the dog/clamp accessory?

Call me a simpleton but... the included clamp has a tightening bolt to lock it onto the MT dead centre. Presumambly I also need a dog that connects/locks the work piece to the clamp notch on one side like a lathe setup. But do I not also need a similar bit connecting the clamp back to a DH face plate? (ie otherwise what is stopping the MT dead center from rotating in its seat & losing the indexing setup?)

 

[chipenter]

What's needed is a 90 degree drive dog , a zip tie will have some movement but may do for light work , haven't seen dogs in catalogues for awhile .

 

[Krutch]

The unthreaded area is the register. It is there so the chuck or faceplate locate the same each time it is mounted. You will have to make the chuck fit the register.

 

[kf2qd]

If you expect to use that chuck on your lathe, I would modify the indexer to match your lathe. That way any chuck you have now, or buy in the future would work on both. Never know when yuo might want a different chuk for a different job.

 

[petertha]

If you expect to use that chuck on your lathe, I would modify the indexer to match your lathe..

Good suggestion but my lathe is D1-4 mount & this particular chuck is an integrated type, meaning the 1.5x8 tpi threaded backplate assembly is kind of hard-fixed to the chuck body, intended to stay put to preserve alignment. Also, its only 4" diameter, so a bit small for my particular lathe & I already have 6" setup for that. One redeeming quality is the chuck centering appears to be dead nuts on. I tried a variety of ground pin diamters I use as test bars & the DTI just sits there at 0.0000" under rotation.

This chuck kind of came my way at a discount, but in hindsight, I think maybe a better utility option is to select plain back chucks, ideally with front mount through bolts & then variety of less expensive back plates for other applications. That way chucks can be registered on varoius low cost mounting plates & so find a home on a lathe, dividing head, rotary table etc. Every one of these can potentially be a different animal to mount a chuck to
- threaded spindle on the DH, not much you can do about that
- threaded or any number of D/A/? mounts on a lathe, but variety of casting plates commercially available to mount up & machine the lip to depression diameter of the chuck (that was my headache on my D1-4 lathe)
- MT type hole in rotary table. Depending on the number of slots & other layout issues, this usually requires yet another interface plate to marry chuck to table.

When I was digging into 'specs' for 1.5x8 tpi spidle noses, I noticed a lot of links & pics to older lathes like Myford & US models where they could swap threaded chucks from one machine to another with ease. That just seems so logical & effortless, but somehow the world has gotten more complicated.

 

[chipenter]

1.5 x 8 is Boxford , South Bend 9" , Smart and Brown and Viceroy , you can buy ready machined back plates for these lathes , but they will be the same as yours needing a touch on the register , it's cheaper to buy a machined back plate than a plane casting .