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End pin physics


nathan slobodkin
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Following up on the discussion of the forces involved with pegs, peg holes and reamers. Would the folks who understand these things care to adress the forces working on an end pin? I see many cellos where the end pins don't fit well and while some were obviously badly fitted in the first place I assume that million dollar instruments at one time had decent enpins but that wear or seasonal changes have rendered the pin or hole too loose and subsequently either out of round or otherwise distorted.

My interest is in knowing whether these problems can be minimized by making smaller or larger end pins or using alternative materials for end pin sockets. I also wonder about the possibility of using some kind of rigid non-wearing non-deforming bushing into which the end pin units are installed.

Thanks for any ideas on this.

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A well-fitted endpin should last just about forever, if not longer :) The end pin plugs in the larger instruments have to be larger to accommodate the 8mm or 10 mm pin rod itself, If they are too slender the pull of the tail cord will bend them enough to cause the rod to bind. It is entirely possible to bush an endpin hole. I've never used fiber or other materials for this, but if it works on peg holes, it should work on the endpin holes as well. A stronger material will only serve to straighten out the tapered hole. It's the pin material itself and the precision of the fit that matter most.

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The stresses on the endpin (and the hole) are going to be far worse than for the tuning pegs, at least for the violin, where the endpin diameter is about the same as the peg.  The endpin has to take the load of all 4 strings, cantilevered slightly out of the hole.  I can't answer for the durability of the pin or hole materials, only to say that it is likely to be more of a problem (with creep and compression) than the pegs.

 

Reducing stress with a larger diameter should help.  And using harder materials, particularly something like a bushing, should also help a lot.  I had considered putting bushings in my fiddles, but decided that it could always be done later if the hole loosened up too much.

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The stresses on the endpin (and the hole) are going to be far worse than for the tuning pegs, at least for the violin, where the endpin diameter is about the same as the peg.  The endpin has to take the load of all 4 strings, cantilevered slightly out of the hole.  I can't answer for the durability of the pin or hole materials, only to say that it is likely to be more of a problem (with creep and compression) than the pegs.

 

Reducing stress with a larger diameter should help.  And using harder materials, particularly something like a bushing, should also help a lot.  I had considered putting bushings in my fiddles, but decided that it could always be done later if the hole loosened up too much.

Would dampening the reamed end pin hole with thin CA glue to harden the wood help with compression from the forces acting on the end pin?  Note: I am not saying to glue the end pin.

 

-Jim

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I've been adding a maple bushing to my cello end blocks for a few years now. I think, given the forces involved, that it's especially important that the endpin fit well and remain stable over time. I find I'm able to get a much better fit this way, as opposed to setting the endpin in the softer willow or spruce block.

I wrote a Strad article about my endpin bushings last year. I install the bushing before I glue the rib to the block, so it's invisible from the outside.

I have a feeling that it helps with sound, but I don't have any evidence to back that up. It makes sense that if the fit of the endpin were sloppy than some energy would be lost, but probably not very much. I like the idea that this puts strength where it's needed, without adding unnecessary weight.

I think perfect fit is more important than size. I turn all my endpin housings on a lathe after I get them so that the taper perfectly matches my reamer.

MD

post-6731-0-86841400-1471643083_thumb.jpeg

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Would dampening the reamed end pin hole with thin CA glue to harden the wood help with compression from the forces acting on the end pin?  Note: I am not saying to glue the end pin.

 

-Jim

That's the question I was about to ask. And CA glue in the peg holes as well.

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Don,

What reduces the stress if the endpin is larger?

 

Don,

What reduces the stress if the endpin is larger?

a larger surface area increases the contact area which dramatically helps displace the foot print lbs per square inch load....another type /way to think about the displacement factor is think of high heels vs flats, the amount of load displaced on the tiny point of a high heel is much more concentrated than with a flat heel....This is quite exponential mathematically where factors increase or decrease quite rapidly based on size....which leads me to think of whats going on with the diameter of the sound post, is a slightly different sized post better or worse for some violins and not others...I must admit never played with the diameter of a post much , but it's something to think about ...of course too thin a post could go through like a needle, assuming it were structurally strong enough, of course dependent on the plate thicknesses....And what about a fatter one?...sorry my middle name is Don, :lol:

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If it's slightly loose wet the wood in the block hole. 

I don't think that's a good idea. The end pin hole will return to its former looseness as soon as the moisture dries out of it. And it could even wind up worse than before because while the wood is wet it's easily dented or distorted, further damaging the fit.

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End pin.

1. A small tapered wood plug that holds the tail gut securely. 

2. If it's slightly loose wet the wood in the block hole. 

3. Cello end pins...easier to fit before gluing the top on. 

4. Violin ones cost 50 cents and if they cost more I don't buy em. 

End pin.

1.Million dollar cello

2.Sold fairly recently by one of the worlds most respected shops.

3.Very loose end pin socket and hole seriously out of round.

4. Hope this never happens with one I fitted

5. Knowledge can't hurt.

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What I like about cello endpins is that they are hollow which allows one to check the soundpost fit after slight adjustments.   Here is a endpin for a violin that is hollow.  So I assume you must adjust the hole to fit the endpin.    I use 8 mm at the collar for my violin endpins.  May try to make some hollow endpins as an experiment.

 

The sum of the string tensions for a violin is typically around 50 lbs or 23 kg.  The fact that the saddle is not a friction-less pulley means that the force on the endpin is much less.

post-24376-0-20631500-1471706338_thumb.jpg

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That's the question I was about to ask. And CA glue in the peg holes as well.

I don't think CA glue would soak into the wood fiber enough to prevent compression. I do believe a substantial hardwood bushing is a good way to go, although I would question any claims to improvement in sound. Because the rest will absorb pretty much all vibration conducted through the tail gut, the rest of the length between the rest and the endpin will be static.

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Static friction = sticktion, if you really want to get picky about it.  Both are correct enough to use in the kind of engineering I used to do, so I think it's OK here too.

 

He did not say "static friction". He said it's not a "frictionless pulley". It is a common mistake to believe friction needs a ramped force to get things going. I don't think confusing them would work in any engineering and Langragian mechanics needs a PhD for the later. It's incredibly difficult to describe "Sticktion", mathematically while it's trivial for friction even in non-linear cases.

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I've been adding a maple bushing to my cello end blocks for a few years now. I think, given the forces involved, that it's especially important that the endpin fit well and remain stable over time. I find I'm able to get a much better fit this way, as opposed to setting the endpin in the softer willow or spruce block.

I wrote a Strad article about my endpin bushings last year. I install the bushing before I glue the rib to the block, so it's invisible from the outside.

I have a feeling that it helps with sound, but I don't have any evidence to back that up. It makes sense that if the fit of the endpin were sloppy than some energy would be lost, but probably not very much. I like the idea that this puts strength where it's needed, without adding unnecessary weight.

I think perfect fit is more important than size. I turn all my endpin housings on a lathe after I get them so that the taper perfectly matches my reamer.

MD

 

Hi Michael - you've said it all. I love the insertion of the maple dowel in the end-block - brilliant.

 

I bushed my cello end-pin hole in 1998 (also sleeved my pegs, bushed the peg-holes and made a carbon fibre end-pin) and noticed a definite improvement in clarity of sound.

 

The pics are from two jobs I did in 2011. The owner of a new Palatino had a go at fitting a new end-pin. He attacked the hole with a rat tail file and got carried away. 

 

I use Tufnol rather than wood - less chance of it coming to pieces when turning a 1.5mm thin sleeve. I slipped in the boring of the sleeve just for sake of continuity - that cello wasn't a Palatino - not unless they were in business in the 1800s.

 

post-98-0-25086000-1471744243_thumb.jpg

 

post-98-0-99031900-1471744388_thumb.jpg

 

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post-98-0-47205600-1471745031_thumb.jpg

 

post-98-0-78878300-1471745224_thumb.jpg

 

 

cheers edi

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Slightly tangential to the discussion, but friction between the tailgut material and the saddle is something I try to avoid for reasons that have little to do with the endpin. I want to eliminate all upward pull on the saddle because in time the tailgut will pull the saddle away from the block. A touch of paraffin will do it, although I have taken to using a half-saddle in recent years, which also helps enormously.

 

As for bushing the endblock, it's a lot easier than replacing the end block and drilling a new hole. Some of the cello endpin assemblies require a maximum hole into which is fitted a rather substantial steel sleeve. They don't bend, but they do work loose! Maybe a good place for a little extra sticktion? Like all things with the violin, the tried and tested ways work really well, but when conditions start to decline I think a little bit of reaming and a slightly larger endpin is an excellent solution.

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- snip - when conditions start to decline I think a little bit of reaming and a slightly larger endpin is an excellent solution.

 

Hi Bob - mmm -  when I bushed my cello's end-pin hole I visited a friendly local luthier had a look at her cello end-pin reamer. I took some measurements and made my own reamer - max dia. 25.4mm.

 

post-98-0-37465500-1471797736_thumb.jpg

 

That did useful work - until I bumped into the oversize stumps that the modern end-pin seems to favour.

 

There was no time available to machine another reamer blank and cut the flutes with my angle grinder - so I did a quick and nasty wooden taper epoxied onto a steel shaft with some belt-sander abrasive epoxied onto the taper. The intention was that it would only be needed for the one job.

 

Joke!

 

It turns out that it works very much better than a reamer - no sharp edged teeth to worry about banging against other steel bits - no honing to keep things cutting sweetly. No sore wrists.

 

It's now been used for quite a few replacement end-pins.

 

The abrasive belt is showing signs of wear and I guess I'll be discovering how easy it is going to be to re-cover the tapered pin.

 

Then a real fat rosewood end-pin came in and I rapidly turned up an even fatter sanding reamer (in the background of the pic) - that has only done one job.

 

post-98-0-19505500-1471796774_thumb.jpg

 

cheers edi

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I've been adding a maple bushing to my cello end blocks for a few years now. I think, given the forces involved, that it's especially important that the endpin fit well and remain stable over time. I find I'm able to get a much better fit this way, as opposed to setting the endpin in the softer willow or spruce block.

 

Seems like a good idea, do you install an endpin bushing on violins as well? 

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