Keeping the Chuck on the mill

We’ve got a rong-fu mill (purchased on the reccomendation of Mr. Lavery) and we’re delighted with it. Save for one thing. It seems that no matter what speed we set it to, how fast or deep we cut, its only a matter of time until the chuck falls off, damaging our work and (once or twice) the table. The chuck, accoording to the manufacturer we just have to hammer it on the tapered drive shaft, but despite doing this really hard (and using an air-hammer to really drive it up there) it continues to fail. How do other teams deal with this. Why don’t they have a screw or something to keep the chuck on?!

Any help would be greatly appreciated!

The problem you’re having is related to whats known a “morse taper”. A Morse taper is a standerdized locking taper, two shallow angle tapers, male and female, that when pressed together form a very strong lock.
There are standards to morse tapaers and they are gaged by size, #1, #2, #3, and so on. The taper ( angle ) on the R-8 Jacobs Chuck arbor (The part that mounts in the mill) or the drill chuck itself is damaged or out of spec…
An inexpensive solution is to try and claen up the tapers. You can use a polishing stone to smooth the surface of the arbor. Polishing stones are similar to sharpening stones. They’re like hard pieces of fine sandpaper.
I would recommend something between 220 and 400 grit 1/4" x 1/4" x 6". You can get them at McMaster Carr for a couple of bucks. While the chuck is off the arbor, turn the machine on to a moderate speed (approx. 800 RPM) and
stone the taper of the arbor to remove any high spots. Move the stone up and down the taper keeping the stone flat. Next, clean the internal taper of the chuck. Stick the corner of a towel or rag in the taper while twisting
and pushing. Make sure both tapers are clean, put them together and give them one good solid hit. If this doesn’t
fix the problem you may need to buy a new arbor or chuck, or both. An arbor will run you about $45 and a chuck can run you between $45 and $100 so you’ll probably want to try and fix the one you’ve got.
Let me Know how you make out. Good Luck.

PM me off-line. C’mon by and we can take a look at it this weekend and see if we can fix it up for you. Or if that doesn’t work, I have a spare chuck on an R-8 arbor that you can have.


Are you using a drill chuck to hold an end mill?

Please don t do that- drill chucks are made to hold drills, and to drill holes. End mill holders or colletts are made to hold end mills. There is nothing you can do to a drill chuck and its morse taper socket to make it hold well enough to use for milling.

In addition, drill chucks never run dead true, so holding an end mill in one causes it to become a one tooth cutter.

I didn’t even consider the possibility that you would be trying to mill with a Jacobs chuck. Ginger is right, doing this is a very bad approach, not to mention dangerous. End mills should always be mounted in the correct size R-8 collet. I know everybody has a budget, but you can start with a popular size like 3/8"or 1/2" for less than $20, and add to your collection as funds become available. An eight piece set will run you around $160 ( 1/8" - 1" by 1/8", most std sizes ), and you can always check E-Bay. SAFETY FIRST!

As others have indicated it it a very bad idea mill with end mills in a drill chuck. The drill taper is not designed to hold with a side load. It is designed to drill (up and down) so the forces press the drill chuck onto the taper when drilling. You can get a set of R8 collets very inexpensively from ENCO (

6pc R8 collet set DD231-4606 currently on sale for $19.95
11pc R8 collet set DD231-4611 on sale for $36.95
23 pc R8 collet set DD231-4624 on sale for $77.95

The $20 6pc set should serve you well and be much safer than milling with a drill chuck.