PVC flute question

[Cork]

Given that flutes can successfully be made of PVC tubing, and given that PVC becomes malleable when heated, could it be possible to heat-form PVC tubing over a tapered mandrel, to make a conical bore flute body? That is, perhaps a smaller diameter PVC tube could be "stretched" over a mandrel, to form an internally tapered flute body?

I'm not a flute maker, BTW. I'm just curious, thank you.

[jemtheflute]

Possible? Theoretically, probably "yes". Practicable? That depends on what dimensions of pre-extruded tube are available where one happens to be. I don't think the electrical conduit to European standards I have worked with would do it, certainly not with a one-piece body, and there are obvious problems with joining body parts once you've made the tube conoid..... getting into lathe-turning tenons and sockets rather over-complicates matters - and that is supposing the stretched walls were thick enough to permit that anyway. One of the problems with factory extruded PVC is that, so far as I have been able to determine, you can't shrink it below the extruded dimensions effectively (you can expand it and shrink it back, but not beyond).

The tube available here comes in three sizes: 25mm external diameter (c 20.9mm ID); 20mm ED (c 16.5mm ID); 16mm ED (c 12.4mm ID): the EDs are nominal - the tubes are usually slightly smaller than that. I actually kinda tried it once to make a Bohm style head with a piece of the middle sized tube, though I didn't have a proper mandrel. It wasn't too happy at being stretched that far and was prone to buckling when forcing the softened tube over the improvised mandrel, though with a properly turned wood or metal mandrel and better heating equipment one might be able to avoid that. (I thought about getting a knackered metal Bohm flute, taking the riser and lip-plate off and using the head tube thus....might do it one day! You could even heat such a mandrel-tube internally to help avoid surface contact cooling and drag on the PVC.) I think it would be very difficult with DIY equipment to do a c400mm piece that would be necessary for a single body tube for a low D instrument (with separate head), and it would probably still be too wide at the foot end - and there's no way you'd do it with the smallest tube for a full size flute - the walls would be much too thin at the wide end even if you could actually do the expansion succesfully.

This problem (I could see no cheap, DIY practical way around it) was one reason I gave up on making conduit tube flutes when I had a serious go at it about 10 years ago. Making a conoid body would either necessitate using a mold insert mandrel and filling a cylindrical tube around it with something like epoxy - which would produce a clunky, heavy, very thick-walled at the foot end tube (if it worked reliably) or getting into injection molding - not a home-practicable option. The alternative to a conoid body, i.e. a Bohm head, poses much the same problem. I didn't know then about the Fajardo wedge idea that Doug discovered and uses to such good effect. Calmont (who sell on eBay) have found some economical way of producing Bohm heads in this material - I haven't handled one to examine how.

The American plumbing PVC Doug uses is much thicker walled and might be more amenable to the degree of stretching needed (though probably harder to actually heat through evenly and stretch without deforming), but I think one would still need to be looking at two or more body sections from stepped sizes of tube with a turned mortice-and-tenon joint and probably lathe turning down the external profile to avoid a step between two sizes of tube..... do-able if you have the equipment and skills, but again, quite a step up from simple home production. One might as well go the whole hog and either get into injection molding or turning and reaming from solid stock - like our various Delrin users or M&E.

For cheap and easy, matched to the material home-production from pre-extruded standard tubing, the wedge is by far the most practicable solution.

[Sillydill]

Hey Cork,

Jon C. has been there done that: viewtopic.php?f=2&t=8850&p

[drewr]

I've sometimes wondered if it would be possible to artificially make a cylindrical PVC flute conical by inserting something into the lower end, perhaps something like the Tipple-Fijardo wedge only larger and longer. Wouldn't something like this "fool" the airstream into thinking that the bore was conical?

[Doug_Tipple]

I've sometimes wondered if it would be possible to artificially make a cylindrical PVC flute conical by inserting something into the lower end, perhaps something like the Tipple-Fijardo wedge only larger and longer. Wouldn't something like this "fool" the airstream into thinking that the bore was conical?

It's a good idea. Why don't you give it a try. You could also try a series of smaller wedges placed along the length of the bore. You would need to figure out how to secure them in place. Having a 3 or 4 piece flute would make that easier

I tried putting pieces of wood through the bore of a digeridoo at nodal points to create obstructions at those points. I drilled holes in the pipe and stuck a wooden dowel all the way through the pipe. I really didn't understand what I was doing, and the experiment didn't work.

[Sillydill]

I'll confess to have made some PVC abominations in the past.

Years ago I messed about with cutting tuning cork faces at different angles and shapes. I did like the cork I once made with a spherically dished face.

But I also tried making bore perturbations, by placing PVC rings within the bore. They didn't much improve the tone, but could sure make the tuning wonky!

I especially disliked the Frankin Flute with the Boehm headjoint and PVC body.

Live and Lean!

[Jack Bradshaw]

I'll confess to have made some PVC abominations in the past.

Amen brother !

I still think mandrels are the way to go...but finding the right goop is a real problem......SiC concrete anyone ?

[Cork]

What I'm thinking is that PVC tends to revert to a "plastic" state at somewhere not far from the boiling temperature of water.

If that's so, then perhaps not only could an oil, for instance, have a somewhat higher boiling temperature, but perhaps a high temperature oil could also serve as a mold lubricant, as well. Moreover, suppose a mated set, of a tapered mandrel and a matched, tapered die, could encapsulate a length of PVC tubing, and then, along with an oil heat bath, and by means of heated plasticity, could a piece of PVC tubing be form fitted, perhaps by means of hydraulic pressure, from end to end of the mandrel/die set, or something like that.

Once the PVC has cooled sufficiently, perhaps its having been in an oil bath could then allow a taper-formed PVC tube to be easily extracted from its mold.

Unlike the forming of most metals, it seems that the forming of PVC could be done at relatively modest temperatures.

Of course, some lathe work could then be called for, to trim the PVC to length, and to make a tenon, along with some boring to make tone holes.

The benefit to all of that could be in a reduced spacing between tone holes, such that smaller hands could then more easily play, among other improvements.

Any thoughts?

[Aanvil]

Any thoughts?

Yes,

[edited because I didn't bother to read the rest of the post and see everyone had said the same thing]

My final though...

It would be far easier to buy a lathe and cut them from rod... but I think some folks are already doing that.

[Gabriel]

Acetone makes PVC tubing soft. Provided that one wears the appropiate safety equipment, sliding a softened tube onto a mandrel should be easy. With drying, the PVC hardens again and there you have your conical PVC flute-to-be.

No idea if that works, but it might. I think I'll give it a try. Just have to find out where to get acetone. And the joints might become a problem.

[jemtheflute]

These ideas are all perfectly possible conceptually, give or take a tweak or two and better scientific understanding of the properties of the raw material, as the old thread about Jon's efforts shows..... but in a fashion the costs and efforts of which would be proportional to the value of the end product? Short of properly tooled factory production, I doubt it.... And it is probably far easier for anyone contemplating that to go to injection molding for easy volume output that makes the tooling R&D and investment viable by producing uniform products with minimum handling at acceptable unit cost in the medium term. It would scarcely be worth turning (if you can do so) a steel mandrel and maybe an external die just to make a handful in the garden shed!

[Doug_Tipple]

Years ago I was the laboratory supervisor at manufacturing plant in Tucson, Arizona. We made molded rubber products for the aerospace industry. We didn't do injection moulding, but all of the moulds were hand-loaded with the raw material that was to be moulded into the finished products. If Jem had one of those large hydraulic presses with the steam-heated plattens in his backyard shed, he could really go to town with flute production, I bet.

[Cork]

I'd guess that a properly shaped set of dies made of a hardened and tempered steel could produce untold thousands of accurate, molded copies.

Yes, there could be an initial investment, including research and development, along with making such a finalized die set.

However, perhaps such dies could eventually be passed on, as a business asset, to yet another person's business.

Imagine, the definitive, conical bore PVC flute!

:-)

[jemtheflute]

definitive.......flute

Come come, Cork! Those two words simply don't go together. Even old Theo didn't manage that!

More seriously, Cork and Doug, yes, you kinda make my point again for me. It is the kind of thing that could (probably only) be done as a proper commercial thing (if market research showed it to have a viable volume market). I still think that even on that basis it would probably be better to work with the crude raw material and presses or molds, injection or otherwise, than with pre-formed tube being modified one piece at a time and needing extensive modification thereafter. The whole point - the beauty and the worth - of using the ready-made extruded pipe is that it is cheap and easy enough to do as a DIY home project producing very decently playable one-offs or small runs with very low material and tooling costs and no huge degree of skill. If you want to be more high-tech or more commercial, using the pipe is unlikely to be the best way forward.

[talasiga]

.....
Imagine, the definitive, conical bore PVC flute!

Imagine the Pakistani price ......