Milling spindle from existing collet chuck extension.

Hi all.

I'm looking to make a milling spindle (mostly for clock making) and want the nose to be ER20 or ER25 for a number of reasons.

I've been thinking of starting with a commercially available ER collet chuck extender on a 20mm or 25mm shaft to simplify the collet holding end of things, but I'm not sure how hard the shafts are, and thus how difficult will be to modify them, and in particular to cut a thread at the end for pre-load nut reasons. Questions to the suppliers have not resulted in particularly illuminating replies.

Does anyone have experience in this area?

Thanks,

Youra.

Edited By YouraT on 16/02/2021 10:04:47

Hi Youra

I used a commercially available ER25 holder to make and end mill holding device for my Kennet grinder, it machined quite easily, I had to turn down one end for a retaining collar and drill it through, I didn't have to do any threading but in this case I don't think it would have been a problem.

Only problem I had was that the holder ran out by .005", Stupidly I didn't check it before modifying, so couldn't send it back, came from a UK supplier, I've had better luck from China! Had to carefully set it up and re- bore the taper.

Dave

Edited By Dave Wootton on 16/02/2021 10:52:45

Youra,

I used a 12mm shank ER11 parallel shank holder. The first issue was that the shank and the bore of the angular contact bearings both measured exactly 12.00 mm. I had to use a diamond file to ease the shank for a sliding fit in the bearing.

The particular ER holder I chose did not have an adequate shoulder for the bearing so I had to cut this with a carbide tip. That was no problem

Then glue on and trim a steel ring abutting the shoulder

I was not able to cut the fine thread on the other end with a carbide tip. I wrapped a wet rag around the chuck end and heated up the other end with a propane torch. I took the temperature to something above a blue colour but not as hot as glowing red. You can see the extent of the heat affected zone in the photo below.

The pre-load is set with a hex nut and the pulley is threaded to act as a locknut

I'm very pleased with the result.

Hope this helps,

Rod

Thank you both very much Rod and Dave - that's reassured me somewhat, I'll go ahead with my plans..

Rod - curious, what bearing arrangement did you use in your spindle? I have the "Spindles" book, but can't really decide which layout will be most suitable for wheel and pinion cutting....

Thanks again,

Youra.

I’ve drilled out a number of these and the steel was quite hard on all of them. It took quite a while using a carbide drill. I think you’d need to anneal it first for cutting threads.

Youra,

I used a pair of angular contact bearings, one at each end. These from arc.

Rod

I have made a couple of spindles from these where the preload was applied using an improvised clamping arrangement push the bearings together and using a split collar with tangential clamping screw around the shaft.

One of them was on my Unimat, where the pulley was clamped against the Belleville washers to control the preload, the pulley is held by a setscrew in a flat on the shaft, then the bush pushed hard against the pulley and clamped by the tangential screw. I used a carbide mill on the shaft to make the flat but no other hard machining.  As noted above you may be disappointed by the runout on the collet taper.

Edited By John Haine on 16/02/2021 16:53:21

Thanks again Rod - maybe the slightly larger set given the ER25 size I'm aiming for, but a useful pointer.

John - yes quite possible - I'll measure, and I have access elsewhere to a toolpost mounted grinding spindle should I need to make things better.....

Converting an ER extender to replace the standard spindle has been a well known modification to Taig milling machines for the last 15 (ish) years to standard collets can be used instead of Taigs own versions.

Might be worth a Google search to see how folk have done the job.

Clive

Also Dick Stephen wrote articles in MEW some years back on making a high speed head for his CNC converted X3 mill, using an ER parallel shank chuck. Worth finding the articles as he will deal with all these issues (except perhaps the concentricity one).

John - thanks - I found the article in issue 159 which was indeed helpful !

Clive - wow - OK - *so* much more info Thanks !