I thought I'd paste the text from Johnson's Facebook post here, just for the record. There are a few very interesting observations. One is that he says the delrin he gets has no grain. Another is the Proxxon model maker's saw, which seems like the dremel tool I was fantasizing about.
Here's one I found on Amazon only $129. I think it is essentially the same as what he uses (his model is K230, this is K115, which I think must be voltage).
ANOTHER APPROACH TO MAKING PLECTRA FOR A HARPSICHORD.
I get asked many times about how I go about making plectra and having just gone through the action of one of my double manuals, I photographed making the plectra for that instrument. I have put together a few words of description, not my strong point I'm afraid, but I will be glad to explain any queries you might have. Hopefully the pictures will do that for me.
There are many ways of converting harpsichord plectra from sheet delrin. Some makers punch from the sheet, some guillotine but I engineer mine to create a taper to the underside of the plectra. I find a tapered plectrum not only enables a firm final setting into the tongue, it also produces a better shape to the final attack on the string which I feel does have an effect on the tonal vowel sound.
This means the material you start with needs to be thicker than you are ever going to finally use so I start with sheet 1mm thick bought by the square meter. That sheet is then reduced for ease of storage into sections 90mm x 280mm and from 90mm width I cut strips 18mm wide that will produce a combe of approximately 100 plectra.
Delrin is manufactured in graded quality and the highest grade should be purchased. I took advice on this from the firm that supplied me, an engineering company specialising in injection moulding and lathe turning that product. The material they supplied had a perfect surface to both sides, was accurate to the fraction of a mm and showed no sign of grain or rolling. I mention this because it has been long thought by makers that delrin has a grain and that should be correctly directed down the length of the plectra. There was no trace of grain on my material and on questioning the engineer he replied he was not aware of a grain factor with the quality they had supplied. I must say in his favour that seems to be the case and I have had no ill effects of sound or durability from test I have done with my supply making plectra in both directions.
I use a PROXXON model maker's circular saw for engineering the taper on the strips that will produce a combe of plectra, an ideal tool for this job. First you need to create an accurate wood backing block that has the taper you require, for me that is 2 degrees. I have 6 blocks made from lime and after working six stripes of the delrin at a time. I use 8mm double sided sticky tape for all of the processes engineering the plectra so for the first stage a 18mm strip of delrin is firmly placed on the wooden block so the taper can be cut from the Proxxon saw. You will notice from the pictures I use a wooden fence to the blade. I was advised by the delrin engineer to create and angle on the fence away from the back of the blade so that only the front teeth on the saw blade were cutting the material, in a sort of fly cutter action. Advice that I found very helpful as no heat is created at all and the operation is achieved with great accuracy. I usually make four cuts adjusting the fence with a tap from a light hammer. When you have finished machining the angled saw cut to the thickness you need for your plectra you will need to clean the face of that tooling a little. This job I find works better using a file technique of three grades of wet and dry abrasive, 240 - 400 - and finally 800 grit. In order to assure you are going to keep controlled flatness I have glued the abrasive paper onto 7mm MDF board turning them into little very fine files.
When that work is completed the delrin is removed from the wood blocks and any remains of the double sided sticky tape is clean off. The lime backing blocks can then be re-surfaced on the shop main saw for their next use, so that set of blocks will produce a few thousand plectra.
The pictures will show the lime backing pieces I make to take you into the final stage of producing the combe of plectra. The sticky tape this time is placed immediately above the scribe line and that has been made to leave the amount of plectra length you need to fit into the tongue. That scribe line and the relief cut behind it will allow the wood to clear away as you cut each plectra, again the pictures will show that better than words can explain.
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Fred Sturm
University of New Mexico
fssturm@unm.edu http://fredsturm.net http://www.artoftuning.com "We either make ourselves happy or miserable. The amount of work is the same." - Carlos Casteneda
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Original Message:
Sent: 03-31-2015 13:14
From: Fred Sturm
Subject: Manufacturing plectra
I see Instrument Workshop now sells "pieces", 1.5" x 6" as well as strips. That seems like a better bet, much easier to figure out a way to cut it. And the paper cutter method David mentioned would seem ideal with this kind of size.The clamping was the big issue, since whatever you use to cut it, you put so much pressure on it it wants to slide, and it's slippery material. I've never been fond of pre-cut plectra, but in the past few years have just gone with it for lack of time and patience to do something else.
Oops, but now I look again and see that in these pieces, the grain is along the width (maybe that's where I got the mistaken idea about the strip grain). But maybe I could request them to be cut the other way. Or I could just cut across the width, and have 1.5" strips, enough for 2 - 3 plectra each (or 5 - 6 for 4'). That is probably the simplest solution, as making a short cut like that would be fairly easy to do, maybe just using fine shears.
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Fred Sturm
University of New Mexico
fssturm@unm.edu
http://fredsturm.net
http://www.artoftuning.com
"We either make ourselves happy or miserable. The amount of work is the same." - Carlos Casteneda
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Original Message:
Sent: 03-31-2015 12:39
From: Donald McKechnie
Subject: Manufacturing plectra
Ah Ha! You just might have something there with the mini table saw!
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[Don] [McKechnie,] [RPT]
[Piano Technician]
[dmckech@ithaca.edu]
[Home 607.277.7112]
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