plastic pins?

In an autoharp, there are 37 tuning pins, made of steel. Each one is about

1.5 inches long and .2 inches in diameter. The pins are held by friction in a maple (usually laminated) block. Autoharpers are always looking for ways to reduce the weight of the instrument. My question is: is there any plastic that could be substituted for steel in this situation? I know that in violins, the tuning pegs are wood, but there is not as much string tension.

Sorry this isn't exactly a metal question :-)



Reply to
Will Self
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What about hollow steel. Probably could halve the weight and still have the same 'feel' as solid.

Reply to
Jim Stewart

Two problems with plastics for that kind of application: stiffness, and creep. A plain, unfilled plastic is unlikely to have enough of either.

A couple of composites might do it. If graphite/epoxy has the required stiffness (it probably does), it has fairly good resistance to creep. It won't maintain tension forever, but it should be Ok. The other would be boron fiber/epoxy. It's stiffer, but much harder to get and to work with.

People who make boron fly rods may be able to give you a piece to try. I haven't seen any of them for a while, but a decade ago they were the hottest thing in ultra-performance, lightweight custom rods.

-- Ed Huntress (remove "3" from email address for email reply)

Reply to
Ed Huntress

Assuming the pins are solid and at an average density for steel of 7.8g/cc then each weighs 6 grams and the total is 222g or about 0.5lb. If the pins were drilled through at 3mm it would reduce the weight to just under 4g each and have a minimal effect on the stiffness because most of that is in the outer section of a solid bar. Total is now 145g for a 35% weight saving at minimal cost.

If cost was less of a problem and you went to titanium alloy pins at a density of 4.5g/cc you would save over 40% of the weight anyway and if you drilled those at 3mm the weight would end up at 2.26 grams each for a total of 84 grams and a weight saving of 62%.

Any further saving on that wouldn't be noticeable I think given the total weight of the instrument.

You might possibly be able to use hard anodised aluminium at a density of

2.8g/cc but I think the strings would wear through the anodising in time. Might be worth an experiment though and it would be cheap to do. There are some very hard coatings for aluminium becoming more available these days so a chat with a specialist might be in order. I have no idea of cost though. Put "Tufram" into Google and see what you come up with. Hardness between 45 and 65 Rockwell C which compares very favourably with case hardened steel. Even with solid pins you'd be a bit lighter than hollow titanium and probably cheaper too.

Dave Baker - Puma Race Engines

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Reply to
Dave Baker

All autoharps that I know of use steel strings (some wound with bronze for lower pitch). Violins use either catgut or synthetics, some wound with a flat metal ribbon. The tension is greatly different.

Steel guitar strings are wound on metal tuners. Nylon guitar strings are wound on metal tuners with a sleeve of nylon (or some similar plastic) so there is more travel for a given angular turn of the tuning key.

The pins, I believe, have a shallow steep multi-lead thread on them to pull them into the block as they are turned. And they seem to be hardened -- to take the bite of the steel string, and to take the wear of the tuning key going on and off many times over the life of the instrument.

It might be possible to make the block of something like Delrin, with cavities milled where the strength is not needed -- but this will probably affect the sound -- whether adversely or not remains to be seen.

Now -- what *might* be an interesting substitution and reduce the weight significantly would be pegs made of titanium. Again, the lower mass of the pegs will affect the sound somewhat. Whether it improves it or deteriorates it (to your opinion) remains to be determined.

Actually -- the strings are metal. The current tuning pegs are metal -- and the replacements ones should also be metal, I believe.

Good Luck, DoN.

Reply to
DoN. Nichols

One thing I haven't seen mentioned is that the tuning pegs on the autoharps I've seen are square-headed and turned with a key with a matching socket. I'd think that unless one were to come up with another way of turning the pegs, the biggest problem would be knocking off the corners of the square heads - or twisting the heads off - of plastic or composite pins. Even hollow metal pins might fail if the wall in the head area is too thin.

If not for that, G-10 (epoxy-glass) might work. I think the strings are wound around the pegs quite close to the pin board, so shear may be as big a factor as bending.

My vote is for aluminum (70XX?) pins fitted closely to the tuning wrench. I haven't checked the density of the other plastics/composites mentioned, but G-10 is approx 2/3 that of aluminum.

Ned Simmons

Reply to
Ned Simmons

What about a Carbon Fiber rod? Don't know specific properties you need, but it would be much lighter and very strong.

Reply to
John Sullivan

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