Shortening A Drill Chuck

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I have a Chinese 1/2" drill chuck with a MT-3 taper. The end does not have a tang, but is tapped for a drawbar. I have never used this, but wish to turn the taper to 3/4" to use in my er-40 collet. I chucked the chuck in my three jaw, and indicated the taper, close to the chuck end. I t was .004 grand off. I used a .002 shim and the taper is within mere tenths...
Wondering how anyone would hold this to turn the chuck true, ie. insert a 1/2" dowel pin in the jaws and insert the pin into a collet chuck? Would we think that the chuck body is in relationship to the female taper? How would we know if the jaws are true within the chuck body?
How would you turn the taper to attain a degree of accuracy?
 
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I'd put a 1/2" dowel in the chuck, put that dowel in a three jaw, or even better your ER40 collet, and put a live center in the end of the MT3 taper (if I could), about what you said. Aside from convention, there's no logical reason the OD of the chuck would have any relationship to the ID of the jaws.
 
First off I would use the 4 jaw chuck. Chuck the 1/2 inch pin in it and indicate the pin without it drill chuck. Get the pin as close to ")" as possible. Now you have a place to start.

Tighten the drill chuck to the indicated pin abd use the center in the draw bar end. Indicate to "0" anywhere on the taper. It should already be there at "0" but a slight adjustment could be called for.

With all that done turn the arbor to your desired measurement.

Could be way off base but that is how I would do it. Your call.

"Billy G"
 
I did it using the method presented by Bill. If you don't have a four jaw chuck, put a pin in the three jaw and take a light pass to true it up to the spindle axis. this takes care of any runout in the three jaw. Then, clamp the drill chuck jaws down onto the pin.
 
Is the arbor removable from the chuck? If so, it might come apart while you are turning it to size, from the side loading. A removable arbor can also be replaced with a nice, accurate, store bought one pretty easily and cheaply, and your existing arbor will still be usable down the road for other tasks. The advice in the posts above is good if you want to turn it down anyway. I would not even try it if it the chuck is a separate part from the arbor.
 
Bill Gruby said:
Indicate to "0" anywhere on the taper. It should already be there at "0" but a slight adjustment could be called for.
Click to expand...
It seems to me that, having indicated the pin to 0 and clamped the chuck onto it, any runout you see in the taper is runout in the chuck. Indicating the taper to 0 will preserve it.
 
Are the tapers typically hardened on drill chuck arbors? If so, what type of tool would you use to turn it down? HSS? Carbide? Unobtanium?

Tom
 
By indicate I meant only to check it John. My bad. You are correct, once the drill chuck is tightened moving the original "0" at the pin will throw the whole set up off by whatever the run out is.

"Billy G"
 
O.K. Guy's...
I do believe that we're all on target here. I (myself) would use a dowel pin to turn the arbor, in a collet chuck, thus keeping a closer degree of accuracy in the axis of the chuck.
I posted this for two reasons. 1) to check my thought pattern in conjunction with y'all. And 2) I thought that there may be individuals not quite as experienced as those who have posted here. Meaning it would be a good thought train for some of the newer Hobby Machinists coming into the trade.
I thank you all for the advice, AND, for aligning our thought patterns to the same degree of machining accuracy!
And, yes, I always use carbide inserts when turning...(mostly)
Toolroom
 
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