Right wood for mandrel / jam chuck?

[Matt NQ]

About to start on my adventure of making Celtic whistles. Something I need to do first up is make a couple of mandrel / jam chucks. I'll be using them after a 200-400mm length of square stock is bored, and my idea is just to make a cone to fit into the bore - doing it at both ends will centre it. Maybe even just one mandrel with a live centre at the other end inserted in the bore in the same way.

I have three lots of wood on hand I can use: Merbau, Cadaghi and Tas Oak (here in NQ probably Messmate? It's a bit dark). Which of these three would provide the best stability and grip as a mandrel / jam chuck?

Also, how rough or smooth should the finished mandrel / jam chuck be?

Thanks in advance for any help :)

[Colin62]

I’ve not made a Celtic whistle, but if I’m thinking of the right thing it’s got a fairly wide bore and a thin wall, and I’d be a bit worried about a conical fit causing it to split if too much pressure was applied, and I’d be afraid that enough pressure to get friction to cut may also be enough to cause a split. A mandrel that passes through the bore would be safer, but a real pain if each whistle has a different bore.

As I say, I’ve not done it, so my thoughts are probably of little practical use.

[dubrosa22]

I use Jarrah or PNG Rosewood for my jam chucks. Something tough and hard grained to withstand regular use and stabile.
Mine have so far had a very slight taper with a small rebate to rest the edge of the tenon socket against. Just enough to drive the piece and support it in its final finishing.
I would advise against turning a square bored/reamed stock with a jamchuck or mandrel. Best do rough turning in a chuck held on sacrifical ends (20-30mm) and then finish the instrument with the jamchuck.

V

[Matt NQ]

Thanks Colin62 & dubrosa22, very helpful advice. I will rethink and avoid jammed in conical mandrels turning from square, as we are indeed talking wide bore and thin walls (2.5 to 3.5mm). Sounds like the Cadaghi is the best I've got for this - very heavy, hard stuff.

Looking forward to the weekend :U

[Mobyturns]

Timber for jam chucks needs to be stable and have a little give but ideally be tough enough to last a long while in regular use.

One of the issues of using a hard wood is that if you experience a catch or a loss of friction between the work piece and the jam chuck mandrel the work piece stalls however the mandrel still spins resulting in overheating of the work piece. For thin walled items such as your flutes it can cause problems with oily woods like PNG Rosewood or worse case splitting etc.

Best to design the jam chuck mandrel with straight sided tenon to match the flute bore with a just snug fit and drive the work piece with end friction from a haunch on the tenon.

Sanding the mandrel to 120 grit should be OK to give a trouble free surface but leave the end grain on the haunched drive surface with an "off the tool" finish. The jam chucks can be driven between centres with a spur drive & live centre; or shaped to incorporate a #2 Morse Taper, or as a plug to fit your chuck for the drive centre end / headstock; with the tailstock / live centre either supported with a standard live centre or a "live centre system" such as https://www.carbatec.com.au/woodturning/lathes-and-accessories/centres/nova-centre-system-vendor-code-5015.

[Matt NQ]

Thanks for this great details advice Mobyturns. I assume by "straight sided tenon" you mean cylindrical (rather than the jammed in conical mandrel I was thinking of using).