View Full Version : Must drill chuck adapters be hardened?

11-04-2004, 12:53 PM
I have a question for the group. Does a Morse taper to Jacobs taper adapter for a drill chuck need to be hardened? A little background. I am a learning hobbiest and subscriber to HSM and MW and lurker on this forum and others. I have a 1950's vintage SB9A and a 1960's Clausing 8520 mill with MT2 spindle. The mill came with a 3/8" capacity keyed jacobs chuck on a 1/2 inch threaded arbor (actually a 1/2" bolt with the head cut off) and about 0.030 TIR measured on a center drill held in the chuck and a 1/2" collet to hold the arbor. Spindle TIR is 0.0005" It's so bad the table shakes when I tried drilling with it. I ordered a Rohm 1/2" capacity keyless chuck with JT33 mount and a JT33 to MT2 adapter with a tang on the MT2 end as I couldn't find an adapter to mate with the 3/8-16 drawbar on the mill. I drilled and bored an aluminum cylinder to accept the JT33 end of the adapter so I could part off the tang end and drill and tap it on the lathe. Darn those adapters are hardened! I had tested it with a file and the file cut it but I was having a very hard time cutting it on the lathe. I was able to get about half way through with a carbide tipped parting tool until I broke the tool. Got the rest of the way there with a Dremel abrasive cutoff wheel. Drilling was just as difficult. Since tapping would have been a real nightmare I decided to anneal the adapter befor proceeding. I put the adapter into a piece of copper pipe and closed off both ends. Built a charcoal fire in my chimney charcoal starter for the grill and burried the pipe in the coals and let it go until there was nothing but ash left of the coals. The adapter came out a nice uniform blue-grey color with no fire scale and dead soft. Cool! I went this route after trying to heat a 1/2" diameter cutter I made from O1 with two propane torches in open air and getting so much scale it looked like an artifact from some archeological dig. I finished drilling and tapping the adapter to match the drawbar with no further trouble. Now after mounting the new Rohm chuck to the adapter with a couple sharp raps with a wood mallet it mounts in the 8520 nicely. I now get 0.009 TIR measured on a center drill in the Rohm and drilling is a dream on the mill. I was a little dissapointed at the 0.009" result but in use it's miles ahead of where I was. For hobby use *I* see no need to re-harden and temper the adapter but thought I'd get opinions from the more experienced on this forum. I post here as this group is knowlegable and I learn a lot reading the posts as well as the magazines. Thanks for reading this long winded post. I tried to keep it short.


11-04-2004, 01:01 PM
For occasional use it should make little difference whether hardened or soft though
dead soft is pretty soft. I can recall being bedeviled by trying to find MT stuff for my
3n1 spindle and very little for mills (drawbar threaded) versus lots of adapters with tangs intended for tail stock lathe use. Some was sold as hardened with soft tang, and these were easily machinable.

Now I have a similar problem with finding
Jacobs tapers in 5v collet size for my Van Norman mill. Steve

[This message has been edited by sch (edited 11-04-2004).]

11-04-2004, 01:25 PM

I'm surprised to hear that the arbor was that hard. I have done some light machining on arbors, and have found them easily workable with HSS tooling.

In any case, maybe you could consider a straight shank arbor on a drill chuck that could then be held in a collet with your drawbar. I have one that I use with a 5/8" collet on my R8 spindle, and it works nicely. Just some food for thought.

11-04-2004, 01:27 PM
I wouldn't worry about it. When it wears out (if it ever does) just repeat the process and make another one. You should probably show a certain amount of restraint in how you bang the thing around...but being in a home shop, you'd probably do that, anyway.

That 0.009" is pretty severe runout, but it sure beats 0.030"! Eventually you may want to repeat the exercise and see if you can do better.

Arbo has a good idea on using a straight shank in a collet, by the way. That's what I do, and it works fine.

[This message has been edited by SGW (edited 11-04-2004).]

[This message has been edited by SGW (edited 11-04-2004).]

11-04-2004, 02:43 PM
No. you absolutely don't want it hard! You don't want anything that goes into an arbor harder than the bore because the taper will lose accuracy. For the same reason the end of a drill that fits in a chuck is soft.

11-04-2004, 06:43 PM
A hardened precision ground shank positioned for best accuracy will give the best results. A standard grade shank can be expected to return results in the +-.o10" (What were you expecting for under $20 anyway? http://bbs.homeshopmachinist.net//wink.gif) It is a lot of work to get that pesky JT33 and MT concentric and parrallel! Yaw, Pitch, and Wobble - you are lucky if your chepy shank does not have all three defects. Not bad for a production part.

Better means more time and attention to details.

Note too that hardened shanks are only hardened on the skin, they are usually dead soft on the inside (this is because of the RF induction hardening process used to harden them). Even the odd beligerant shank can be tamed with a powdered metal tap for harder tough materials.

11-05-2004, 10:12 AM
Thanks everyone for your replies. I will leave the shank soft for now as my hobby usage doesn't put great stress on things. As SGW mentioned I try to show restraint in how I bang things around. I really don't have a very good way to heat up that large a chunk of steel anyway. Putting the shank in the tube to keep oxygen away while the thing was in the fire worked but quenching would have been a problem as I would have had to just dump the shank out and into the oil then reach in with tongs to swish it around.

According to THRUD I seem to be doing OK for under $20 in terms of runout. I don't recall if this was from MSC or ENCO but the box was marked CHINA. I didn't think to check TIR before I started.

I wish that the shank had been hard only on the surface but it was hard all the way through. I suppose it's possible I tweaked it a little out of truth after I annealed it as well.

I will run as is for now. When my 0.009" TIR becomes a problem as I improve my skills I'll revisit the setup. Hopefully I'll have learned enough by then to improve the situation.

Thanks again for the great resource!


Paul Gauthier
11-05-2004, 12:03 PM
Generaly such arbors are not hardened, I have a couple of new ones in the shop now and they are not hardened.

Paul G.