Lathe miling/spindle taper

OK, I'll bite. Why is it "obvious" that you musn't mount an endmill in the chuck? It might take a bushing to shim it up a bit to a diameter that the chuck will grab, but if you only have a small amount of milling to do it beats the alternatives.

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messagenews: snipped-for-privacy@m7g2000cwm.googlegroups.com...

Because hardened chuck jaws don't hold hardened end mills very well. The cutting rake tends to make them walk out of the chuck jaws. Ever see a Bridgeport table with those swimming pool divots (shallow end to deep end) in it? It wasn't because the operator was downfeeding the end mill during a traverse.

For a few light cuts you might get away with it. Or not.

John Martin

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Nice to see someone using their head rather than their wallet to solve a machining challenge.

If you have not yet done so, I suggest purchasing "Milling Operations in the Lathe" by "Tubal Cain. This is #5 in the Workshop Practice Series. This addresses problems and question you are not yet aware of. see

[about 1/4 down page] This is an australian web site, but Powells and amazon.com generally have or can get this in the US. [FWIW -- I have found all the workshop series books to be a good value and used several as texts when I was teaching]

If you use a 3 or 4 jaw chuck, this is a good way to hold an end mill, although it can be a PITA to set-up as you will have to use and indicator and adjust for runout. Use pieces of copper tubing (or a piece of slit copper tube), brass shim stock or pieces of an aluminum beer/soda can between the jaws and the end mill.

The chuck you should not use [although lots of people have done it] is the Jacobs or Albrecht style drill chuck. These are designed strictly for steady axial loads and most milling is intermittent radial or side loading. As interrupted and/or radial/side loads can cause the chuck to separate from the arbor, the arbor to unseat, and the end-mill to walk [out], this has the potential for [and has caused] far more excitement in the shop than most people want.

If this is more than a one time operation [and it will be] it will most likely be worth your while to make some end mill holders [given that you don't have a taper in your spindle].

The common style of endmill shank in the US is called Weldon (TM) and is simply a flat for a set screw to seat on. It is a simple matter to use a file or grinder to put a suitable flat on a shank that lacks one.

Use hex or round stock for a three jaw chuck and square for a 4 jaw. If you put a punch mark on the side that goes next to the #1 jaw and line this up every time you do lathe milling it will help you with alignment and runout. Keep the holders as short as practicable as extra length will result in added runout, whip, etc. However these will need to be long enough to let you see what you are doing. [i.e. Goldylocks dimensions/specifications]

6 inches long is a good starting point for 10 X 24 size lathes.

The most common end mill shank sizes in the US are 3/8 and 1/2, with a few 1/4 and 3/16, generally in carbide and other exotics where material cost is a factor. Thus on your end mill holder, you can machine one end for 3/8 and the other for 1/2 and be set for most if the milling you need to (or can) do on the typical home shop lathe.

I calipered the #2MT 3/8 and 1/2 end mill holders I use with the following results:

3/8 body end mill holder body diameter - 1-1/4 inches body length 2-3/8 inches set screw metric but about 5/16 unc set screw centered about 3/4 inch from the bottom of the holder

1/2 body end mill holder body diameter 1-3/8 inches body length 2-1/2 metric set screw but about 5/16 unc set screw centered about 3/4 inch from end.

Both end mill holders have a heavy chamfer to allow better access/visability. Holes for the endmills are about 1-3/4 deep on both holders. see

You can also fabricate a block that will bolt to your faceplate with 3/8 and 1/2 holes with set screws to hold the end mills. Most likely something 1 inch thick, 1-1/2 wide and 6 long should be suitable. the end mill will "poke" through the block and the hole in the face plate, but should be secure enough for the loads it will see in lathe milling.

If you have the reamers, I suggest reaming the 3/8 and 1/2 holes rather just drilling to minimize . Most likely it will be easier to drill & tap the cross holes first, then indicate and drill/ream or bore on the lathe. Probably a good idea to drill through and tap both sides. Then when you strip or wear out the threads in one hole just use the other. (But not both at the same time.)

Will the accuracy be as good or will they last as long as the "store bought" hardened and ground holders?" Most likely not, but if you are just starting, these will be more than adequate, and the price is right.

Let us know how you make out, and if you have a digital camera post some pictures to the dropbox.

Good luck!!!

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

Thanks for the help guys.