Mill Collet Holder Attachement

Well in the middle of a job today the collet holder on my mill detached from the spindle - luckily with just a thud onto the table and not sending it flying across the room. Looks like I didn't secure a grub screw sufficiently when I put it was restoring it, I had tried to remove the collet holder previously but couldn't get it off and had give up and just left it.

So anyway, now that it is off I have the opportunity to change it.
(The collets that it uses seem to be some proprietary type as I cant match them to any standard size so I'm stuck with the limited sizes that came with the mill (6, 10, 12 & 16mm) and making sleeves for any other size needed, plus they are a right pita to remove. They jam in almost flush with the holder and you end up having to 'tap' the endmill until they loosen and release. I have already snapped one carbide endmill when it was particularly stubborn to remove. I had resorted to using an ER collet holder with a 16mm straight shaft installed into the original 16mm collet and holder to make it easier to use.)

The spindle left on the machine is 25mm diameter and has about 10mm protruding from the quill.
The original collet holder seems to be a shrink fit into a larger Ring (that's what I'll call it for lake of a better term) that has a 25mm hole at the other end (with a grub screw) that attaches to the spindle.

Spindle and Ring/Collet Holder - the top of the Ring has a fillet on the top ID which extends into the quill section and may be some sort of spindle grease control


Ring/Collet Holder, Collet and Retaining Nut


My plan/thoughts are to:
1. remove the old Collet Holder from the Ring (may need heat as a couple of sharp taps hasn't budged it)
2. bore out the Ring to a shrink fit of the OD of a ER32 Collet Holder
3. shrink it onto the ER32 Collet holder with the shaft cut off it - may also add a grub screw for safety
4. reinstall it on the spindle

This assumes the outside of the ER32 Collet holder is concentric to the taper which I will have to check first.

Questions are:
Is there a trick to keeping the collet holder perfectly aligned to the spindle when installing it?
How are they attached on other machines, I don't have a lot of experience of different mills.
Is there a better way I should be approaching attaching a new collet holder to the spindle?

Any suggestions/recommendation/observation greatly appreciated. This is not something I have every done before and a see a large number of opportunities to end up with a collet holder that has horrendous run out if it doesn't all work out.

btw Mill is a CME F900 (Spanish manufacturer) horizontal mill with a separate vertical mill head .

Is there a possibility that there could be/used to be a drawbar, securing anything (collets, tool holders, such as an R8 system inside the bottom of the quill/spindle? What's it look like up inside?

Another thought, is that thing on the end of the spindle removable? (looks like mounting screws). If so take it out and make a new ER style collet holder to replace it.

Tom,

The spindle doesn't appear to be hollow. At the top there is a short section of internal threaded for the bold that holds the pulley cluster on but nothing that goes all the way through. It's not shown in the photos above but the Ring/Collet Holder doesn't have a hole all the way through either - the Collet Holder portion ends in a blind hole. So I don't think there was ever a drawbar, and that is one reason I want to go to an ER type collet that is automatically removed with the retaining nut.

The more I look at the end of the spindle the more I'm getting the impression that it has been modified to take this collet arrangement at some time in the past. There are a couple of extra slots/holes in the spindle end that this arrangement doesn't use and the hole that the current grub screw goes into just doesn't look 'factory'.

Rather than shrinking a holder into your spindle could you modify the existing holder to accept the ER32 collets and screw an Er32 nut on it? I made a ER40 holder and nut for my lathe, you might be able to do that to your holder. Yeah, it has to be concentric, but it can be done.

The existing collets are a lot smaller that ER32 so I don't think the existing holder would be large enough to be modified. Maybe for ER25, but I already have ER20 and ER32 collet sets for my lathe and the horizontal spindle on the mill (which is an iso30 taper) so was trying to avoid getting/maintaining another set.

That being said ER25 would be the most suitable size for my uses of the vertical mill. The ER20's top out at 13mm which is a bit limiting and the ER32's go up to 20mm which I can't ever see myself using in it.

Could you make a new holder to replace the one that's there? What is the diameter of the existing adapter?

T Bredehoft said:

Could you make a new holder to replace the one that's there? What is the diameter of the existing adapter?

Click to expand...

Yes I could do that - at least I think that would be within my abilities/available machinery.
Still leaves the original problem/question - what is the best way to fit it to the diameter 25mm x 10mm long spindle end that protrudes from the quill, and have it all align with minimum run out.

Ok, after pulling the quill apart I decided a new spindle was in order - there just wasn't enough left at the bottom of the old spindle to reliability adapt to. So out with the old (top) and in with the new (bottom)


The 'new' is a brought ER32 Collet Chuck with a straight 20mm shaft, to which I fitted an extension shaft and turned to be parallel to the shaft that came on the ER32 collet chuck. As a backup I have ordered an ER32 chuck similar to this but with a 150mm shaft, 150mm would be long enough to cover both the bearings and I would just need to add the drive splines. But that is probably a month away from being delivered so on with the experiment.

I'm pretty happy with the way the replacement spindle turned out, only thing left to do is the splines. I had considered cutting up the original spindle and attaching those splines but I'm reluctant to destroy the original part until I'm sure the replacement works.

So how do you actually make splines? Looking at them I'm thinking each groove will take three passes with the mill (one for each side and one for the bottom) as the sided of the groove aren't parallel - the sides of the tooth are.


Off to do some searching on the web as to how to mill splines (another first for me), but if anyone has some tips it would be appreciated. I will have do them on a horizontal mill (as this is the spindle for my vertical mill so it's out of service), and I don't have a rotary table so will be looking for a simple way to index the slots - luckily there are 6 slots so I'm thinking of using a nut attached to the shaft in some way to give me the index for the six sides.

Best way, a mill cutter formed for the grooves, but I'm not at all sure these are readily available and quite sure the cost for one time use would be too much.

There's a thread on the "Daily" discussion on which the OP illustrated cutting a knee mill driver. This is nearly the same as your splines, but off in a different dimension. You could to them in two passes, one down each side of the spline, rotate 60º repeat 5 times.

MozamPete said:

I don't have a rotary table so will be looking for a simple way to index the slots - luckily there are 6 slots so I'm thinking of using a nut attached to the shaft in some way to give me the index for the six sides.

Click to expand...

That should work. Just clamp the nut in your vise and rotate it to index. I'd center drill the splined end and insert something in it for support.