Internal collets

Good morning all:
I was reading through Lawrence Sparey’s classic book ‘The Amateur’s Lathe’, and also the rather quaintly named ‘A Man and his Lathe’, and noticed in the latter a project he entitled ‘inter collets’ - effectively expanding mandrel that he used in his Lathe spindle collet set.

As a user of Er16, 25 & 32 collets (just finished a spindle holder for the last mentioned) I wondered whether the application of the ER principle - of multi-splitting the collet combined with 16deg included angle taper socket - might not be used in reverse to create a number of internal collets (as he put it) on one or more tapered arbours.

I realise that this is clearly producing expanding mandrels (I’ve never got the right sized one when I need it!) and whether it is feasible in the home workshop.

Using a slitting saw to cut four slots in one end is fine, with indexing gear, but how easy would it be to securely, and sufficiently accurately, hold the now split end to slit the other?

Has anyone ever tried this? If so could you share your experiences please?

Thanks
Mike

Expanding mandrels are useful, but i'd think that accuracy could be an issue, With the ER system, the concentricity is maintained by the 16 deg. taper solidly mounted on the machine spindle. With the expanding system, keeping the taper concentric with the machine spindle would be more difficult.

Clive

Edited By Clive Brown 1 on 03/07/2019 11:47:32

Posted by Mike Waldron 03/07/2019 11:25:25
Using a slitting saw to cut four slots in one end is fine, with indexing gear, but how easy would
it be to securely, and sufficiently accurately, hold the now split end to slit the other?
Has anyone ever tried this? If so could you share your experiences please?

Hi Mike,

The collets seen here in the photo are for grinding 4 facet drills
on a Quorn grinder,they are an adaption of Derek Brown's four
facet system that was in the model engineer many years ago.

They are similar to what you have in mind for these internal collets.

As you can see these have 8 saw cuts ,after all of the turning
was completed a short piece of round material is placed
in the bore and the job held in a 4 jaw chuck on the dividing head.
The jaws of the chuck are at about 45 deg to the horizontal to miss
the slitting saw ,the saw is fed in close to the chuck and the cutting
is done away from the chuck ,this is particularly important when the
job is turned around and reset to do the second set of
four saw cuts.
The short piece of round material provides enough stability and
clamping force for the chuck to hold the work securely.

The material is silver steel unhardened,the largest is about 3 1/4
inches long and will hold up to 1/2 inch drills ,the smallest about
1 1/2 inches long and will hold a .5 mm drill.

John

John:

thanks for that.

Mike

Somewhere I have seen what you describe, either home-made or as a product, afraid I can't remember where.

Aha!  Our friendly universal supplier.

https://www.arceurotrade.co.uk/Catalogue/Expanding-Mandrels/Straight-Shank-Expanding-Mandrels-Tap-On-Tap-Off-

Edited By John Haine on 03/07/2019 14:58:34

Hi Mike,

If you mean "collets" for an expanding mandrel, like this:

They are not difficult to make. When the topslide is set for taper turning I use the same setting both for turning the taper of the mandrel and the collets in the same setting. I turned the taper in more collets than I needed so I have some spares. For slitting I just used a small hacksaw.

Thor

Edited By Thor on 03/07/2019 16:07:46

Thor:

thanks for that.

Can you recall what angle you made the taper?

Also what sizes do the collets / arbor sleeves cover?

Thank too to you others for you input also.

Mike

Edited By Mike Waldron on 03/07/2019 21:40:25

You can buy sets of the expanding mandrels.

Stub claims he's on a diet so he's a shrinking mandrel at teh moment.

Neil

Expanding collets are made. Here is an example for a watchmaker's lathe:**LINK**

At one time I had a similar collet in 5C size. At the time I didn't have a lathe so I gave it away.

Hi Mike,

I made the mandrel many years ago so I don't recall what angle I used, but the "narrow" end is 14.2mm dia., the "big" end is 22.3mm, the length of the tapered section is 85mm. The thread at the narrow end is MF14 x 1 since I happened to have a MF14 x 1 tap. I have got a smaller expanding mandrel as well, I have a tapered reamer that I used to crerate the taper in the small collets. The mandrel itself is made from a high carbon steel (0.8 to 1% C) and mild steel for the collets. I hope that helps.

Thor

Edited By Thor on 04/07/2019 05:52:44

I wonder if one could use MT tapers? Could form the "collet" bore with an MT reamer, and use an off the shelf arbor for the "chuck".

I would think that using an MT reamer is one way to make the "collet" bore, good idea John.

Thor

Would that not cause a jam up?

Is that not the whole purpose of a morse taper?

Mike

The mandrel I made has a taper not far from what you find on Morse tapers and the sleeve will hold even if the nut isn't used. I use a brass drift to knock the sleeve off. I have used the sleeve to finish turn gear wheels and pulleys so I need a good grip.

Thor

Bell Chucks are, or were, available, in both internal and external forms. Probably more used by clockmakers, but very useful for holding thin material, such as washers. Not really suited for holding material that hangs out far, since the length to grip is short (circa 1/16"or 1.5mm for the modernists )

Expanding mandrels have to be the way for longer workpieces, within reason.

For one offs, just turn up a suitable arbor. Wish that I could remember what some of mine were made for!

Howard

I have often thought of buying a set of the expanding mandrels for odd jobs such as bushes. I believe they require pre-setting very slightly over the size of the workpiece bore and then skimming to size to ensure a good fit and also to run true.