# Introduction and a couple of quick questions



## siscoken (Jul 15, 2017)

Hello to group...been reading for a while, but first post. 30 year mechanic ...6 yr operating engineer...now semi retired and  logan lathe owner ... a 200 I believe .
It is a mid 40s if I am remembering correctly.
It came with two 3 jaw chucks that fit machine and a 4 jaw that has the mounting threads 2 deeply recessed to reach the threads on the machine and that is my first question.
Do I just look for an adapter plate for that chuck and if so where to start.
Thnks Ken


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## Nogoingback (Jul 15, 2017)

If your 4 jaw has a flat back, or flat with a recess on it and holes for mounting bolts, then it will need an adapter.  It's possible to buy adapters that are pre-threaded for the spindle
on your Logan: you then would machine the adapter on your lathe for the correct fit to the chuck.  Adapters like that are available from a variety of sources.  If you have a 10"
Logan (Model 200), then your spindle is threaded 1 1/2-8.

When you can, please post some pictures so we can see what you have, and if you haven't
done so, have a look at the Logan Engineering sub-forum here: there's lots of good 
information on your lathe there.

Welcome to the group, and keep asking those questions!


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## Mister Ed (Jul 15, 2017)

Are the threads in the chuck the correct size 1 1/2-8 and are truly just too deep to engage the spindle? If so, you may be able to correct that.

Before determining a course of action ... pics are necessary.


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## siscoken (Jul 15, 2017)

Mister Ed said:


> Are the threads in the chuck the correct size 1 1/2-8 and are truly just too deep to engage the spindle? If so, you may be able to correct that.
> 
> Before determining a course of action ... pics are necessary.


Can post picks yet but I will
Thread are close ... but not correct....with plate taken off 4 jaw and reversed to test... will only thread on 1 turn and then bind


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## siscoken (Jul 15, 2017)

I am assuming that these threads are not tapered...which would explain them only going on 1 turn when reversed.


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## Mister Ed (Jul 15, 2017)

siscoken said:


> I am assuming that these threads are not tapered...which would explain them only going on 1 turn when reversed.


No the threads are not tapered.


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## wa5cab (Jul 15, 2017)

I don't recall ever hearing of a lathe or mill spindle with actual tapered threads.  But there may have been machines with nominal 1.5" diameter threads but a different pitch.  I don't know of any off hand but for example, the two commonly encountered 1" threads are 1"-8 and 1"-10.  Another possibility is that the threads are metric.  Around 38 or 40 MM.  And who knows what pitch.  You can easily determine the pitch with one of the coarser pitch gauges.  But the ID of the register area (the counterbored space before the threads actually start) must not be over about 1.5003" in order to properly fit the register area on the spindle.  The threads themselves are not what centers up the chuck to the spindle.

In any case, you can buy pre-threaded adapter plates from just about any of the on-line machine tool suppliers and adapt one to your chuck.  Have a look around eBay, Amazon, or do an Internet search.


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## wa5cab (Jul 15, 2017)

I'll add that the first step to determining whether or not you can use the existing plate is to determine the thread pitch.  If it isn't exactly 8 TPI already, you can't use it.  Slightly too small a pitch diameter and too deep a register area you could fix.  But you can't successfully change the pitch.


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## siscoken (Jul 15, 2017)

Yes looks like right size wrong pitch.... so new plate is the way to go...
Thnks for help


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## siscoken (Jul 15, 2017)

Well... get this ... as I was making some measurements to order a new adapter plate for my 4 jaw, I looked at my spare 3 jaw and noticed the adapter plate on it had 2 different bolt patterns. I usually don't have this kind of luck, but it turns out its a perfect fit to my 4 jaw.
Anyway thanks for the helpfull comments....I will post some pics as soon as I get all the pieces together and my shop cleaned up a bit.
Thnks again


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## wa5cab (Jul 16, 2017)

Now that's what I would call good luck!  Although with a 4-jaw, it isn't that critical, I would check the runout on the OD of the chuck body with it mounted to the back plate in each of the n possible orientations (n = the number of mounting holes, assuming that they are all evenly spaced on a single circle).  Then use the position with the least chuck body runout.  And match-mark the chuck and plate in case you ever need to remove the plate for any reason.  Do the same for the 3-jaw in case you ever need to go back and use it, except that the runout measurement should be made on an accurately ground test bar (NOT on something turned in the chuck) and not on the chuck body.


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## siscoken (Jul 16, 2017)

wa5cab said:


> Now that's what I would call good luck!  Although with a 4-jaw, it isn't that critical, I would check the runout on the OD of the chuck body with it mounted to the back plate in each of the n possible orientations (n = the number of mounting holes, assuming that they are all evenly spaced on a single circle).  Then use the position with the least chuck body runout.  And match-mark the chuck and plate in case you ever need to remove the plate for any reason.  Do the same for the 3-jaw in case you ever need to go back and use it, except that the runout measurement should be made on an accurately ground test bar (NOT on something turned in the chuck) and not on the chuck body.


Yes it's a purfect fit ....plate has a shoulder that is a exact fit into the recess on chuck....what are the odds...
thanks for the tips.
Ken


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## kvt (Jul 16, 2017)

No need to clean the shop,  Most of us with small work areas are often cluttered and a mess,   Or at least mine is, and from the pics others post many of us have that problem,   More stuff than room to put it all.  Nice that the backing plate has the holes for both of your chucks.   I would take the best 3 jaw, and keep it mounted on one,  then the 4 jaw on the other,   Unless the 2nd 3jaw is a different size where you need it sometime,   I would clean it up and keep it as a spare.   Good luck.


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## wa5cab (Jul 16, 2017)

Yep. Chance in a million.

Just for future reference, what did the thread pitch in the odd plate turn out to be?


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