# Chuck question



## jwmay (Sep 26, 2019)

Does anybody know if anyone makes new 3 jaw scroll chucks with internal threads? I recently mounted a brand new chuck with threaded backplate to my Atlas and have immediately lost all confidence in this little machine being able to deal with all this leverage. Really looks dumb too imo. I know they used to make them, but I haven’t seen any new ones advertised.


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## TonimusMaximus (Sep 26, 2019)

Taig Tools does, but they only make a couple of sizes. What machine/threads are you looking for?


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## jwmay (Sep 27, 2019)

1 1/2 - 8


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## RobertB (Sep 27, 2019)

Gibraltar does: https://www.mscdirect.com/product/details/93220754

Many thousands of backplate mounted chucks in use with no issues. I would just try the one you have, it may surprise you, aesthetics aside.


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## markba633csi (Sep 27, 2019)

Are you concerned the chuck hangs out too far? I wouldn't worry, especially if your Atlas has roller bearings
Mark


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## jwmay (Sep 27, 2019)

Yeah, that’s my hang up. The chuck is 4 inches deep at least. Then the backplate for another 2 1/2” probably. This is all just guessing.


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## RobertB (Sep 27, 2019)

2 1/2" for a backplate?


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## mksj (Sep 27, 2019)

Bison makes a 5" direct mount 3J scroll 7-805-0552. Most likely there is a Gator equivalent which is a bit cheaper. I am assuming on the back plate that the chuck mounting plate is bit over 1" and the threaded portion makes up the rest., so it would be quite a bit wider with a back plate. Direct mount is about 1.5" shorter. You might call Ajax Industries  to see what they have or check a few other vendors. Around $500 for the 5" with two piece jaws.




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						Bison Semi-Steel Lathe Chuck -5" 1-1/2-8 Mount, 3-Jaw 7-805-0552
					





					www.ajaxtoolsupply.com
				





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			Welcome to CDTooling.com  - Carbide Cutting Tools Precision Measuring Equipment and Abrasives


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## jwmay (Sep 27, 2019)




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## jwmay (Sep 27, 2019)

Ofc this is me eyeballing the 0 inch mark, but yeah, about 2” to where the check is bolted on.


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## jwmay (Sep 27, 2019)

I guess I was way off on the chuck depth though. I’ve seen a different backplate the looks less like a flange, and more like a flat plate with internal threads. I’ll seek one of those out.


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## RobertB (Sep 27, 2019)

Where is the end of the tape measure, are you measuring from the headstock or from the spindle flange?


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## jwmay (Sep 27, 2019)

No tape measure here, but maybe it’s more informative.


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## jwmay (Sep 27, 2019)

I was measuring from where the backplate begins. I may be confused when you say flange. I would say this backplate looks like a flange. A smaller OD barrel that’s internally threaded, leading to a larger OD section is bolted to the chuck.


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## chippermat (Sep 27, 2019)

Why not trim it, something like this


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## chippermat (Sep 27, 2019)

That's what I did with mine here


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## RobertB (Sep 27, 2019)

You could make a thinner backplate, but I think the fact that the flange on the backplate is smaller in diameter  than the chuck makes the stick-out look worse than it is. (see how chippermat's is the same diameter as the chuck)


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## jwmay (Sep 28, 2019)

Thanks for all the replies. I won’t be buying a 500 dollar chuck for it, but at least I know the option is out there.

I may try to thin the backplate. I think I understand what you’re saying RobertB.  I’m of the opinion that it sticks too far away from the headstock, but if you all say it’s ok, Then that’s good enough for me. I’ll run it as it is. I don’t have confidence that separating and machining the backplate would turn out well to be honest.  There are certain jobs I’ve just really failed at so often that I am reluctant to risk it. Making anything to a precision standard is still fairly elusive for me. And one too long chuck seems better than one brand new wobbly piece of metal attached to the spindle.


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## chippermat (Sep 28, 2019)

Your backing plate was pre-mounted, you didn't have to cut the register to fit your chuck?


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## Nogoingback (Sep 28, 2019)

lathe chucks
		


These guys have a 6" Bison for a bit over $500.00.


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## pontiac428 (Sep 28, 2019)

What's the big deal? Sorry, I measured from a different spot.


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## jwmay (Sep 28, 2019)

chippermat said:


> Your backing plate was pre-mounted, you didn't have to cut the register to fit your chuck?


   True. I bought it that way. 


pontiac428 said:


> What's the big deal? Sorry, I measured from a different spot.


 Well I don’t actually know if it’s a big deal or not.  Sometimes I look at something and say to myself,”self, somethings not quite right here.”   Perhaps it’s me that’s not quite right. It just seems like a lot of overhang. I don’t know that it is.  I guess I’ll find some different thing to worry about for now.


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## chippermat (Sep 29, 2019)

I think it matters, especially with the little 1" spindle shaft and bearing on my 6" Atlas, to help minimize chatter and work climbing the cutter.


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## jwmay (Sep 29, 2019)

Yeah I kinda feel like the first indication it did matter will be a bearing failure, or maybe just chatter.  Time will tell. I’m getting used to the look of it now. Wishing I hadn’t sold off everything from my previous basket case Atlas now.  Gonna have to bolt something to the compound and try out a cut!


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## jwmay (Sep 29, 2019)

Well that worked pretty well. I’m stoked about this thing!


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## wa5cab (Sep 29, 2019)

There are several reasons why chuck "stick out" should be minimized if possible.  The obvious situation is that the farther out the chuck sticks, the shorter your workspace is.  The common way to characterize spindle accuracy is to measure and quote the TIR (commonly just "runout") usually measured on the register area on the spindle nose or on a precision ground test bar gripped in the chuck.  However, there is really more to it than that one figure (unless it is zero, which it never is).  

The spindle runs in two bearings, not just one.  Suppose that the runout measure at both ends of the spindle is 0.0020".  Further suppose that at the time you measured them, the two runouts were exactly in phase.  And that the headstock is exactly lined up with the vertical surface of the rear way.  As long as the largest diameter that you turn the work piece to is smaller than the original diameter by an amount greater than the runout, everything should be OK.  But if the two runouts are 180 degrees out of phase, the farther away from the front bearing you are, the worse the part becomes.


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## pontiac428 (Sep 30, 2019)

I realized I have been running my relatively heavy 6-jaw Pratt-Burnerd with the Burnerd 1" mounting plate on it for a year and a half as my primary chuck.  I have been "proud" of my babbit bearings for having very low runout, and the indicator still shows it, but I measured a bit of "nod" in my head stock the other day.  Like, a lot of nod, on the order of .001" per 1" of carriage travel.  I see two possibilities, one, my bearings are just worn out, or two, the heavy chuck might not have helped.  I still have shims to remove from the bearing caps, so I'll check the outboard bearing for that.  I'll probably have to bite the bullet and mount up the Timken head I have on hand.  With roller bearings, I would be much less concerned about the weight of the chuck.


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