Expanding mandrel arbor taper

I have several large diameter long expanding mandrels, one doesn't have the arbor. I was wondering if expanding mandrel/arbors have a standard taper to the interface. I am going to machine/grind one I was just curious if there is a standard or if it depends on the manufacturer. I didn't see any manufacturer information on the mandrel I have.

I don't think there is any industry standard.

Back in the daywe used to make them to the Imperial** standard taper pin angle of 1 in 48

** Metric standard is a different angle

I've seen at least 2 different tapers on the arbors I have, possibly 3.

Yeah, I looked through the ones I have that are complete and it looks as if there are no standard tapers either. To the back-burner this goes, many other priorities.

SShep71 said:

Yeah, I looked through the ones I have that are complete and it looks as if there are no standard tapers either. To the back-burner this goes, many other priorities.

Click to expand...

Why not measure ID taper of expanding part and make a mandrel to fit? I have a set of these, several of the expanding pieces use the same arbor, guessing you checked that already?

That's why back in the day we used the Imperial taper pin angle, often large and long taper pins could be used as expanders / mandrels, and the expanding pieces were easy to make because we had the matching taper pin reamers.

FWIW batches of various sized blank expanders were made (a quick process in batches) ready to be machined for a given job.

Limy, you got any tips about making the expanders? Grind inside taper and outside diameter first? Slit then retain shape somehow during heat treat? Apply the collet-makers trick of leaving an unslit stub on both ends during HT to be ground off last?

I have a quite decent Chinesium set of expanding mandrels which are lifesavers on occasion, but sometimes wish I had some custom expanders (like with shoulders for a particular job).

As far as I can remember we left ours soft (I never saw any hardened expanders,) so no grinding on them, and the taper arbors were seldom ground (an old (flat belt) Holbrook lathes taper turner was permanently set at 1 in 48 crack on. the insides were reamed with taper pin reamers (that go up to 1 1/2'' Interstate HSS Straight Flute Taper Pin Reamers - 43-441-5 - Penn Tool Co., Inc)

They were then slit in simple square or hex jigs (when one end was slit the expander was turned 1/2 a flat, and as the OD's were a standard bar size, we used rings to hold them for machining to final size.

Purist toolmaking it probably wasn't, but accurate it was, ...........breakdown machining was a big part of that shops work, often against the clock (even with the clients waiting in the car park) so it was ''get her done engineering'' ....which to be fair, (and as would have been noticed in my other posts)often lacked a little finesse, .but as Big Jim would say ''twiddly bits cost money'' **

P.S. ** Didn't stop the bugger charging top $ plus though