Attempt at runout reducing drill chuck arbor....

M

Makintrax73

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H-M Supporter - Silver Member
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I needed a stubby 1/2" straight shank drill chuck for my round column mill (same shank as a center/edge finder, if you have a round column you probably understand why this is helpful). Bought a NOS Jacobs 32 off E-Bay for $25. It has 1/2-20 threads. Started to think "I should make an arbor myself, and make one that reduces runout in the chuck." I believe I was _mostly_ successful at doing so, and therefore figure the group might get something out of this, or possibly add some ideas how to do this easier or better.

Steps........

1) Cut 1/2-20 threads in a piece of 3/4" 1144 stressproof. Mount chuck in situ on the lathe and check runout with a ground rod......about .009" to .010" TIR

2) Turn a piece of 3/8" scrap. Mount it in the drill chuck in a 4 jaw chuck. Dial in the 4 jaw so the rod, not the drill chuck is running true. Center drill the 3/8" scrap and LEAVE IT IN PLACE AS IS FOR ALL REMAINING STEPS.

20230908_132135.jpg

3) Cut off arbor, mill flats for 5/8" wrench in the 3/4" collar. Face and center drill the back of the arbor. Mount the arbor on the drill chuck.

4) At this point I have center drills on both ends. I then turn the 3/4" shank down to 1/2" between centers. I check for taper, adjust tailstock, and cut the shank down to 1/2" I should say.

20230908_103437.jpg

The hoped for result being that the 1/2" shank will be concentric to the jaws of the drill chuck, NOT to the threads on the back of the chuck.

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The result: With various sized ground rods mounted in the chuck in an R-8 collet on my mill I measure between .0015 to .003" TIR. So I think I actually made a substantial improvement. My lathe bed has some twist so possibly the TIR is due to center drilling the temporary center slightly off due to the twist, or possibly drill chuck jaws just don't repeat no matter what you do. In either case I turned a piece of leftover 1144 into an arbor........:)
 
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I reckon it worked. I would have expected a worse result. I wonder why chucking on the moveable sleeve, and measuring TIR on a rod held in the drill chuck jaws was successful. Seems like you introduced considerable opportunity for compounding errors at the start at least.
You said you did your original TIR examination with it mounted in the lathe. Wouldn’t the appropriate first test have been to test TIR as you did at the end, in collets on the mill?
 
jwmay said:
I reckon it worked. I would have expected a worse result. I wonder why chucking on the moveable sleeve, and measuring TIR on a rod held in the drill chuck jaws was successful. Seems like you introduced considerable opportunity for compounding errors at the start at least.
You said you did your original TIR examination with it mounted in the lathe. Wouldn’t the appropriate first test have been to test TIR as you did at the end, in collets on the mill?
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You're correct that would have been better. I could have mounted it in a 3/4" collet. At that point however the end of the original 3/4" rod had been turned down and threaded in 1 setup. The threads were about as exactly concentric to the lathe spindle as you can get.

The reason chucking on the movable sleeve worked: I dialed in the rod held in the jaws of the drill chuck. The only point of that entire part of the setup was to get a temporary center concentric to the drill chuck jaws. The plan was to turn it between centers. It is always a straight line between two points (or centers). Therefore my figuring was that as long as the temporary center in the chuck jaws was exactly centered in the chuck jaws this method would insure the 1/2" shank would be turned exactly concentric to a drill bit held in the chuck jaws.
 
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Thank you for the great post with pictures and explanation.

I have been struggling with this very same thing except a Jacobs 36 with 3/4" threaded arbor. First chuck was a $10 gamble. The jaws are in pretty bad shape but the body looked good. New jaws are available for $110 but I found a new chuck for $50 so now have two where I barely needed one.
I also did the turning between centers thing, but only on the arbor before installing on the chuck. Your method shows me a better way to do it.

In my case I have an ER32 adapter in the mill and a 3/4" collet. There seems to be many places that run-out can creep in.
Mill spindle
Collet adapter
Collet
Arbor
Chuck threads
Chuck body
Jaws
Jaw nut

Even if the chuck body has low run-out the repeatability seems to be a big factor. I have been experimenting with clocking the collet in the adapter and the arbor in the collet. There is a great deal of variability no matter what I try. The best I can come down to is about 0.0015 TIR but it is not consistently repeatable. This side project has been shelved until winter when I am stuck inside anyway but I will save this thread for future reference.
 
jwmay said:
I reckon it worked. I would have expected a worse result. I wonder why chucking on the moveable sleeve, and measuring TIR on a rod held in the drill chuck jaws was successful. Seems like you introduced considerable opportunity for compounding errors at the start at least.
You said you did your original TIR examination with it mounted in the lathe. Wouldn’t the appropriate first test have been to test TIR as you did at the end, in collets on the mill?
Click to expand...


OH WAIT! Ah yeah, I see what you mean now. Whether there is any slop between the sleeve and the chuck body. I think I got lucky because it is a NOS chuck, and there really isn't any slop. I should have put the arbor in the drill chuck and mounted the arbor in the 4 jaw. That would have eliminated the slop you are thinking of. Man, I guess it's better to be lucky than good sometimes!!!
 
I’m still digesting your reply, but I’m glad at least one of us understand what the other was saying. Lol I’m a little slow, so I’ll keep thinking on it.
I just sent a drill chuck to the big scrapper in the sky that Id have liked to keep. So thanks for posting.
 
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A drill chuck is not a precision tool holding device.
 
I did a similar thing with my Wohlhaupter boring head. I bought it on eBay and it came with a slightly bent 9/16" arbor. I made a sleave for the arbor that I fastened with Loctite a flathead screw clamping the sleave at the end of the arbor. I then turned the sleave to 3/4" while holding on the body of the boring head. Now it runs true and faces square!IMG_9262.JPG
 
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