How to make expanding mandrels?

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GlennM

Aluminum

Joined

Aug 14, 2004

Location

Kingston, WA

• Jun 27, 2006

• #1

Several times in the past I've needed expanding mandrels. I could have used the between-centers type or the single-ended type seen on 5C collets. The need was never quite great enough to get me to part with the $$$. Until now.

I think I see how to make the single-end type that can be held in a chuck or collet: turn the mandrel body, slit the end in an X pattern, then drill and tap the end using a taper tap. I'd tap to a shallow depth, so that when the screw is turned in it will reach the unfinished threads quickly and wedge open the slit quarters. It only has to expand a couple thou, but concentricity is important.

If I can dream up one way to do this, there must be about fifty more ways. I'd like to hear how other people make mandrels, particularly the between-centers style. I'm not talking about taper mandrels there; I mean the type that expand concentrically.

All ideas are welcome, especially if accompanied by a drawing.

Thanks!

- Glenn M

 

bluchip

Stainless

Joined

Jun 11, 2005

Location

OH

• Jun 27, 2006

• #2

Not very complex nor accurate, but in FAST situations I have made blind mandrels using 1/4NPT plugs. They expand the split mandrel quite nicely. I'll make them with a straight shank then grip with 5C.

 

Forrest Addy

Diamond

Joined

Dec 20, 2000

Location

Bremerton WA USA

• Jun 27, 2006

• #3

Pretty hard to beat a stub mandrel (spud) slit into quarters or sixths and expanded with a pipe plug. They're convenient and simple. I was introduced to them in 1962 to finish the back and addendum angle of a set of miter gears and I've been making and using them ever since.

If you bore the threads and clean them up with the tap you can make them very repeatible in a few thou grip range. You can also re-chuck them and dial them back into concentricity as close as you wish. You can also key them for positive drive or for work requiring a specific orientation like an eccentric.

I've seen other expanding mandrels where a taperpin or the shank of a busted drill is used for an expander but pipe plugs come in a large range of sizes so there is really no competition for them in this application.

 

G

GlennM

Aluminum

Joined

Aug 14, 2004

Location

Kingston, WA

• Jun 27, 2006

• #4

The NPT plug is so obvious...now that you mention it. 1/4" or 1/8" npt plugs are perfect for my purposes. Done deal - I'll use that idea.

Thanks.

 

T

T. Overeynder

Aluminum

Joined

Aug 30, 2004

Location

Arlington, TX

• Jun 27, 2006

• #5

We used to make expandable arbors for second operation work in the aircraft industry. chuck or collet on the turned shank, rough turn an indicating ares for future use, rough turn the diameter, split 4 to six places, releave a groove behind the shoulder about .100 to a fairly deep depth to allow for a little flex, rechuck drill and bore the I.d. and tape, form a 15 degree taper on the i.d., turn an allen bolt with the same taper on the head holding concentricity with the pitch dia. Preload the screw for about .002 or .003 expansion, finish turn the o.d. to the bore size of the part,this allowes for full contact of the bore surface along its length, true the indicating area. Lossen up the allen bolt load the part and part should run very true. Arbors made this way can be reused if care is taken to indicate it in.

Tom

 

Tom Lg

Cast Iron

Joined

May 1, 2006

Location

Laguna Beach CA USA

• Jun 27, 2006

• #6

I do pretty much exactly what T. Overeynder does but I use one of those knurled plastic knobs that you moosh onto the head of SHCS; that way I don't need a hex key to load/unload parts.

 

D

donie

Diamond

Joined

May 17, 2003

Location

Walla Walla Wine and Wild Turkey

• Jun 28, 2006

• #7

Here is an expanding mandrel to fixture difficult to hold connecting rods.
The expanding part cut into 3 pieces, held together with 2 orings is forced over the same tapered stud by the nut on top.
There are a couple of quad rings and steel spacers at the bottom to effect release when the top nut is loosened.
It was worth while making this fixture and it proves to be accurate as well.

http://www.clubchopper.com/photopost/showphoto.php?photo=18012&cat=500&ppuser=1763

 

A

alwyn

Cast Iron

Joined

Mar 3, 2005

Location

UK

• Jun 28, 2006

• #8

Made plenty of these over the years,just like T,Overeynder makes them,but a 30 deg taper,because the center drill cuts the taper.

 

J

John Stevenson

Stainless

Joined

Apr 30, 2001

Location

Nottingham, England

• Jun 28, 2006

• #9

Some very nice stuff coming out of China at the moment.

http://www.arceurotrade.co.uk/en-gb/dept_218.html

These 5C's at the bottom of the page are nice as you can use the allen screw in the end to expand them or slacken the separate 5C threaded bit off and use the lever closer to release them.
very hand on blind bores.

John S.

 

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John Williams

Aluminum

Joined

Jul 29, 2005

Location

Austin, Tx

• Jun 28, 2006

• #10

How would you make one that holds a flanged 3/8 id oilite bearing? Need to shorten one from 1" to 3/4"-5/8" for a lathe replacement. Thinking turn crs to .375, bore a pilot hole and tap it short, prob 10-32, then slit it once. Need bearing length exact so I can fit dead nuts perfect.

John (newbie lathe guy)

Maybe I need to buy that machine shop tricks book that I keep hearing about?

 

Mud

Diamond

Joined

May 20, 2002

Location

South Central PA

• Jun 28, 2006

• #11

Like you are thinking, use Forrest's technique, but use a 10-24 setscrew. Tap the 10-24 threads with a taper tap, not a plug tap, and not very deep. When the setscrew enters the tapered threads, the mandrel will expand. Split it twice (quarters).

 

B

boucher

Aluminum

Joined

Dec 24, 2004

Location

Burnet, TX

• Jun 28, 2006

• #12

For the ocasional use don't overlook the Bizmuth low temp expanding alloys. I insert a undersized mandrel pour the Cerrosafe type material in the annular space and chuck the mandrel in the four jaw or six jaw chuck and indicate in machine and melt the part of the mandrel.

 

G

GlennM

Aluminum

Joined

Aug 14, 2004

Location

Kingston, WA

• Jun 28, 2006

• #13

Interesting ideas, thank you.

The NPT plug seems unbeatable for quick, no-fuss fabrication, but the Cerro metal idea is good too. Very interesting, that one, because it would be easy to use a stock piece of drill rod for the arbor.

The paraphernalia needed to melt the alloy is a drawback, though. However simple it may be, it still has to be stored and space on the bench has to be cleared for it. Tools to make the npt plug arbor are always handy.

The tapered SHCS is interesting but seems like too much fabrication effort for an arbor that will be used for just a few parts. And if you plan to make a bunch of parts on it, time is money so you'd generally buy a commercial item with all the nifty features John mentioned.

Mudflap: Great idea!

Donie: Nice fixture. For your use I'm sure it was well worth the effort, and besides it is obviously a nice piece of work in its own right.


GlennM

 

Mud

Diamond

Joined

May 20, 2002

Location

South Central PA

• Jun 28, 2006

• #14

Thanks. I was answering John Williams who didn't seem to catch your description. Maybe I was being dense. A flathead screw, socket or otherwise, will work too if you don't need much expansion force.

I've also used a tapered draw pin, that's a tapered pin with threads on the end so you can draw it out with a nut. That requires that you ream the hole with a taper pin reamer, but it gives you better controlled expansion over a longer length. I did it on a 1"dia splined mandrel and concentricity of the finished parts was very good. If you can't find draw pins, just drill and tap a taper pin for a screw.