where to buy ground lathe mandrels

I am building a PM research #5 Coke bottle engine and believe I need one of these for the fly wheel and drive wheel. To suit a 0.313" bore.

I have not been able to locate in the UK , loads of expanding ones for 1/2" upwards but nothing small.

I only have a mini lathe and no taper turning facility so can not make my own.

If no source do you have any clever get arounds.

I did wonder about soft solder onto a parallel shaft and then drifting it on?

Regards Clive

Just turn a spigot a thou or two oversize and put a taper on it with a fine file.

Personally I wouldn't machine a flywheel using a tapered mandrel; it's an open invitation for chatter and a wobbly flywheel. Use a 4-jaw chuck or a faceplate:

With this arrangement the rim, bore, one face of the rim and one side of the boss can be machined in one setting, so everything should be concentric.

Andrew

I agree totally with Andrew.

Tony

Same here just hold on a faceplate or in the 4-jaw which should allow outside face, one edge, hub face and hole to be bored all in one setting. Then reverse to do other side of rim and flywheel. A far more solid setup.

Edited By JasonB on 20/07/2020 13:22:47

Proper tapered mandrels are quite expensive. The instructions and examples shouldn't be taken as gospel as the builder will tend to use things they have around so unless experienced in writing for beginners wouldn't think of adapting for the less well equiped.

edit: Also you don't have to follow the sizes obsessively with things like bores of .313 (which seems to be a loose 5/16 so beware it might be wobbly on a bit of silver steel axle). You can go to a metric or round figure if it suits you as long as the mating axle (or whatever) is possible in your chosen size.

Edited By Bazyle on 20/07/2020 13:32:34

I can't vouch for the method but I have heard of the use of adjustable reamers as between centres mandrels.

I agree that it's better to machine in the chuck if you can. But if not another approach based on the "spigot" (possibly tapered as Andrew mentions) is to make a threaded end on it so you can clamp with a nut as well.

The mind boggles

Tony

Only needs a bit of a heavy cut and the job will stop rotating while the reamer reams your hole oversize, sounds totally stupid to me, but what do I know?

.

I am not for one moment suggesting that this would be an affordable solution:

https://www.ptgworkholding.co.uk/products/between-centres-mandrel

... but I suppose it’s what the ‘reamer genius‘ had in mind.

MichaelG.

Dispite it not being the best method can your topslide not be set at an angle?

If so it's easy enough to set it a degree or two over and machine a male & female part at the same setting, thread the end of the male part and saw a slot in the male. Even at 5/16 should be doable with a small boring bar or even holding a milling cutter as a boring bar.

thanks for the replys guys. The wheels are only quite small, max 75 dia, so not sure about the face plate.

4 jaw would be good setting up practice as most of my stuff to date has been simple and in the 3 jaw.

Jason , yes i can set the top over, although the range of cut travel is quite limited with any accuracy.

Sorry i do not follow your next bit. What does the saw slot do and why in the male part. What is in the female part? I may be being a bit dense but does not compute on my experience level.

are you meaning to screw the 2 parts together so that the hub of the wheel is gripped between the opposing tapers?

Regards Clive

Clive I was actulally describing making a small two part expanding mandrel where the nut drives the female part down the tapered male one and the slit allows the make to expand.

The other option for such small wheels is to make a mandrel that has a parallel spigot that is a good close fit in the flywheels hub and then as it gets nearer the chuck the spigot is tapered outwards buy a fery small amount say 1/2degree on the topslide. In use you push the flywheel onto the parallel part then give it a tap with a soft hammer and the tapered part will grip the work.

As Jason described, only not home made. 5/8" between centres expanding mandrel.

Martin C

A simpler, cruder, device can be made quickly from a piece of suitable round bar. Here's one I made for 8mm hole size.

Turn the spigot to the appropriate size and a clean area on the parent bar to make future resetting in the 4 jaw chuck easier. Drill a suitable hole, I used M6, the full depth in the spigot and tap using only the taper tap to within about half the width of the part to be held from the shoulder. Make a saw cut down to near the full size bar.

Place the part over the spigot and tighten a square ended bolt in the hole until the part is secure.

I have used the mandrel in the pictures above a few times and it is now just about worn out and will be replaced soon but that is no great problem. I also have a 10mm mandrel to the same design which has also been well used.

The design is not my idea but I can't recall who I got it from, probably off this forum.

Jim