My whistlemaking project is coming along well, but I am running into a rather obnoxious problem with material for the mouthpiece outer layer and fipple plug. Delrin gets “hairy” when abraded and is so squishy that even in a fitted collet (as opposed to a chuck) it is difficult to get accurate interior and exterior diameters. In search of a harder material, I ended up using some Garolite phenolic resin my friend had lying around the shop. It works great, but it’s quite an ugly color and I haven’t found any in more attractive colors. I was thinking about just using black polycarbonate, but wondered whether anyone here could suggest something that machines cleanly, is rigid enough to resist any significant deformation while cutting to size.
It would be really fun to have some dark red / dark blue mouthpieces to invoke the old Generations if the material is available in different colors…
Delrin is available in colors, primarily used in medical applications, and is more expensive. I think Delrin is one of the most machinable plastics, but requires a different attention in technique, speed of tuning, and sharpness of tools. Delrin is a homopolymer, Acetal resin is a copolymer.
Avoid heating up the material, and sneak up on it for final dimensioning.
“Delrin (and acetals) are polymerized formaldehyde but when they are heated, they turn back into formaldehyde gas which burns much like alcohol.”
Phenolic resin is the material used to make the composite models of Burke whistles.
And Mr. Mack Hoover is also using it to make his whistles.
If your whistle sounds nice, you will see the material differently.
Not really. I was indicating my belief that there IS no plastic that machines better than Delrin, and suggesting that you instead develop the techniques and use the tools that can overcome your original objections. As many others have done. Jon C., Chris Abell, Dave Copley, Desi Seery (RIP), Rob Forbes, Garry Somers, Gene Milligan - all seem to have managed quite well in working with the material. Delrin has its quirks (flexing away from tools, heating up, etc.), and some makers may not care for those characteristics, but the challenges are obviously not insurmountable.
The availability of colors that might meet your aesthetic desires was a side note. Alternative colors (to black, white or natural) are often used in medical applications, so they are available, but pricier.
Thanks, Loren. The problem mostly arises when making the fipple plug (outer diameter, as tool pressure moves it despite small cuts and sharp tools) and mouthpiece cowling (inner diameter). Getting a firm, but not seized fit is a little finicky and requires multiple adjustments in many cases. I’m looking to cut down on machining time as much as possible to be respectful of my friend’s time (he does the majority of the cutting, I do the fine-tuning, the math and the design), so more rigid materials would be better. I’m considering just casting some polyurethane resin rods in custom colors depending on the cost per foot.
As for the “hairiness” the parts fresh off the lathe sometimes have burrs as usual, but when trying to take these off with a needle file or some 1200 sandpaper, I end up with a rough surface that I’m guessing isn’t super great for airflow. It also precludes adjusting the tone with fipple block/cowling alterations.
Madman, sorry, I didn’t realize you were having someone else do the machining. That said, My suggestions were aimed at a way to make the cowling part, although other makers may very well have found different solutions the problems of flex while making that part. For the fipple plugs (or blocks, as we called them in the corset making world), is your friend using a steady or follow rest on the lathe When he turns the Delrin down?
The finish issues you talk about can be solved by using a slower feed speed on the lathe, combined with a curved, rather than straight edge cutting tool. We ground our own and found a sort of rounded boat bow shape cutter often gave the smoothest finish when lathing challenging non-metal materials.
As to your question about potential materials other than Delrin/acetal: We used a couple of different types of faux ivory for decorative sleeves and what you would call a mouthpiece cowling. One was GPS, and I can’t recall the name of the other, but its been so long that there may be better options now anyway. Regardless the stuff turned and finished very nicely, and looked great, but it does look like ivory, grain and all, and I’ve no idea if it comes in other colors etc. the pipe makers use this stuff all the time, so ask over on the UP forum and I bet you’ll get some quick answers on who’s using what and how much it costs.
Thanks Loren, I will definitely pass this on to Richard. Delrin is awesome because it’s SO CHEAP, but I did run across something else this morning while lollygagging at work. Check this out! https://www.cuestik.com/store/?DEPARTMENT_ID=106 They have really nice, attractively-colored phenolic stock (and some sweet marbled resin). Doesn’t look too pricey for the sizes we need either. I’m also considering trying to make a flute out of this stuff since I feel that delrin really eats the higher harmonics (a contentious issue, I know).
This has certainly been a fascinating project even just from a materials standpoint!
While accepting that no two flutes (even by the same maker) are truly identical, yes, I have. I suspect is has way more to do with the way the sound reaches the player rather than the audience, as well as the tactile feedback under your fingers and face. I don’t dismiss delrin flutes at all - I just feel that they’re missing something I personally would like to retain.
McCallum Bagpipes in Scotland has been making chanters and complete bagpipes out of the stuff they call “polypenco” in the UK, usually black but also in colours as seen here. They seem to have no trouble machining it.
Exactly.
OP-- how are you turning your polymer? A machine lathe as opposed to a wood lathe I’d imagine.
I’ve found that Delrin or Acetal turns best with a very sharp lathe tool and taking very small cuts, especially as you approach the final outside diameter. It’s definitely tricky stuff, but it makes a terrific whistle.
These polymers don’t respond well to sanding, which is what I think you mean by “hairy”. The sandpaper pulls up very tiny threads of the stuff but they don’t fly off, remaining attached to the piece. You can sand it WET using automotive wet/dry sandpaper in the 400 grit and up. Keep it very wet. If anyone knows a good way to buff it, post it here.
For a good finish on acetal, these methods may prove useful:
Drill and ream with an oil mist. A machinist using an enclosed CNC machine will use a flood of soluble oil; that’s good, too. One of my guys used a water mist with good results.
Use High Speed Steel or 5% Cobalt for drilling the side-holes, and for turning. These come with a sharper edge than carbide. Ask your machinist what he’s using. The service life of replacing HSS tools may cost a little, but the results are worth it.
Make sure your tools have a positive rake and a 0.015 radius. If the work chatters, you may need an internal steel arbor for support. “Reduce surface speed, increase feed” is the watchword for a better finish.
Walt Sweet
