Expanding mandrels

[Peter Wood 5Participant @peterwood5]

How do I make them?

[Peter Wood 5Participant @peterwood5]

My latest stationary engine project by Anthony Mount needs a couple of parts to be mounted and turned on expanding mandrels of 8 and 11mm od.

I cannot justify purchasing commercial items but I believe they are quite easy to make.

However the only info I can find is on American forums and refers to the use of ‘pipe plugs’, whatever they are.

Can anyone give me a pointer to how to make them pls.

 

Peter

[Michael Cox 1Participant @michaelcox1]

Sparey in his book “The Amateurs Lathe” suggests a very simple form of expanding mandrel. Take a piece of bar and turn it down to the correct diameter. Now drill and tap the end using a taper tap. Slit the end of the bar into four quadrants using a hacksaw. If the part is pushed on the end and a screw is tightened on the hole then the mandrel expands when the tip of the screw reaches the taper section of thread. I have used this method works many times and it works very well.

 

If concentricity is very important then all the operations to prepare the mandrel can be performed on the lathe without romoving it from the chuck. Slitting the mandrel is the most difficult part but it is possible.

 

Mike

[JasonBModerator @jasonb]

Ramon may well be along later but have a look at this recent post of his detailing simple expanding mandrels. By slitting then doing teh final machining you keep things concentric

 

Another method is to turn a bar end to a good fit in the hole and then put a slight taper onto teh chuck end, only needs about 1deg you can then just push the part onto the taper.

 

J

[Ramon WilsonParticipant @ramonwilson3]

Hi Peter,

 

Jason points out a good
alternative and it is one I frequently use but the fit has to be just
right and the materials compatible if picking up is to be avoided.

 

 

Personally
I much prefer the expanding type which are so easilly made and work so
efficiently -there is not the worry of similar metals picking up either

 

Here are a few pics from the Racer build which though seen before by most may help you and someone else too at this point in time

 

Most of mine are made from steel but that is not
critical. They are all expanded by a normal cap head screw that has had
the head turned a 60degree taper to match a centre drill Rough the
mandrel to with .5mm and drill and tap and centre deeply. using a
parting tool relieve a portion at the front of the mandrel.

Remove from the chuck and make two or more cuts with a hacksaw down into the main part. Deburr then return to the lathe
and screw the caphead in until it just nips then turn the od to a
finished size to suit your bore. I’m sure you will find it quite
surprising just how little torque you require on the screw to hold the part firmly for turning.

 

These are great little aids, very quick and easy to make and work extremely well.

 

Hope this helps

 

Regards – Ramon

[David ColwillParticipant @davidcolwill19261]

That’s a neat trick, will have to remember that. Thanks

[Peter Wood 5Participant @peterwood5]

Jason, Ramon

 

Following Jason’s posting I popped into the workshop and knocked up an 8mm mandrel in about 10minutes using the tapered socket head screw method.

I then used it to hold the pair of cranks on which I had to turn a small boss. Worked like a dream.!!

I was surprised how little tightening the screw needed before it had a very firm grip.

 

Since then I have read Ramon’s posting and will refine the construction of future mandrels with the deep centre drilled end and the relief in the middle.

 

I now have the confidence to move onto the larger item.

 

Thank you both very much.

 

Peter

 

 

 

 

[Sub MandrelParticipant @submandrel]

I turned the flanges on my loco wheels today. I normally use the taper tap method, but I wanted 100% accuracy, so I took a length of 1 1/4″ bar (only because it had a 1/2″ mandrel at the other end) and turned a parallel stub a close fit for the reamed wheels (3/8″) but slightly short. Drilled and tapped M6 and used a thick brass washer to hold the wheels in place for turning them.I didn’t have any slippage – the wheels are 2 1/4″ diameter.

 

Neil

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