Tuning pins

Can I replace my tuning pins with pins that are .07mm larger? Or would that be asking for trouble (as in not being able to hammer them in far enough)? Unthreaded in both cases.

Probably depends on the hardness of the particular wrestplank. But if too tight, one could use a drill just a little thicker (really just a little!) bigger to make the holes work.
D

Le 22/08/2023 15:50, Dongsok Shin via The Jackrail écrit :

Probably depends on the hardness of the particular wrestplank. But if too tight, one could use a drill just a little thicker (really just a little!) bigger to make the holes work.
I’m not going to take the risk of redrilling, because I doubt I’ll find
exactly the side I need to gain .7 mm.

What is the rule of thumb when drilling for tuning pins? How much
smaller a bit than the diameter of the pins?

This is an old Hubbard kit, so I don’t know how hard or soft the
wrestplank is. The pins have already been changed years ago. What was
the official size of Hubbard tuning pins?

Dennis

Tapered or zither pins? I assume tapered if unthreaded.

Do you mean 0.07mm or 0.7mm? 0.07mm seems like a typo.

A message seems to have gone missing in this topic which is the first time that has ever happened. Strange.

Le 22/08/2023 16:21, Andrew Bernard via The Jackrail écrit :

Tapered or zither pins? I assume tapered if unthreaded.
Yes, tapered.

Do you mean 0.07mm or 0.7mm? 0.07mm seems like a typo.

No, I really mean 0.07mm. 4.94 vs 4.87.

The diameter of Hubbard kit zither pins is 5.00 mm.
I have zither pins by other makers: all exactly 5.00mm
(or well, from 4.99 to 5.01, within the measurement error).

Le 22/08/2023 16:51, Claudio Di Veroli via The Jackrail écrit :

The diameter of Hubbard kit zither pins is 5.00 mm.
I have zither pins by other makers: all exactly 5.00mm
(or well, from 4.99 to 5.01, within the measurement error).

Thanks, Claudio. The tuning pin I’m comparing those of the Hubbard with
is a Vogel 5mm pin. I only have a cheap caliper and don’t know how
precise it is, but there is this small difference between the two of
about .06 or .07mm, Vogel’s pin being a bit larger. If I try to hold the
both in the caliper’s jaws, the Hubbard pin will fall out.

I also have a Hubbard FD from the mid 70’s, and my zither pins are threaded, and vary in the same range as Claudio’s, from 4.99 to 5.01 mm.

Le 22/08/2023 22:49, James via The Jackrail écrit :

I also have a Hubbard FD from the mid 70’s, and my zither pins are threaded, and vary in the same range as Claudio’s, from 4.99 to 5.01 mm.

Thanks, James. Are these pins threaded? If so, would unthreaded pins in
the same holes need to be slightly smaller, which would explain why my
pins are thinner than yours and Claudio’s.

Zither pins by definition are threaded. And zither pins commonly used in harpsichords are 5 mm in whatever tolerance range.

A related question: what size bit would one use for 5mm pins?

The pins are indeed threaded, but the threads are so fine and shallow I cannot measure their depth, because my caliper will not fit between them. I needed a magnifying glass to verify they are spiral cut. My take on it is that threaded or unthreaded, the pins are designed to fit into the same size hole, however, the threaded ones hold better, because the wood fibers expand to fill the minute voids between the threads. Going out a a limb here, suppose that the 0.02 mm difference in size we saw between pins, or even on the same pin is not due to measurement error, but is related to the threading. In imperial terms, and being very generous, that is on the order of 1/128 inch, probably less.

In the assembly manual that came with my kit, Hubbard instructs the builder to drill the tuning pin holes with a #10 drill

Le 23/08/2023 15:29, Dongsok Shin via The Jackrail écrit :

Zither pins by definition are threaded. And zither pins commonly used in harpsichords are 5 mm in whatever tolerance range.

Ok, I got that. But my question is what size is the hole for 5mm pins?
And if you want to replace 5mm zither pins with tapered pins, would they
need to be slightly smaller to fit as well - in other words of the same
diameter as the threaded part?

A #10 is 0.1935 inches, which is 4.91 mm.

Drill size chart:

So, just under 5, to answer your question about rule of thumb.

But, this depends on the timber and hardness of the wrestplank. The empirical way is to test drill and see how tight they are. Perhaps not practical on an existing instrument.

Also, if you are trying to enlarge existing holes with a drill bit only slightly bigger it will invariably wander and make a mess of the top of the hole. The you will end up countersinking the hole to make it look OK but that actually looks dreadful. Engineers use reamers for this reason.

So what calipers are you using? Cheap plastic ones? Woefully inaccurate. Cheap digital ones? Same. For harpsichords it’s really worth investing in a decent tool. Mitutoyo or iGaging. I will note that unbelievable as it seems the ‘drop test’ is not reliable as cheap calipers can have jaws that are not perfectly parallel over the length, and worse, bend under strain (which is why you should measure at the tip, generally).

Can you post a photo of your pins and calipers?

My recollection from perusing the old harpsichord list archives is that makers usually drill 0.1 mm, and sometimes 0.2 mm, less than the diameter of the tuning pin. 0.2 mm less makes sense if the pins are on the slim side, like around 4 mm.

Le 23/08/2023 16:03, Andrew Bernard via The Jackrail écrit :

So what calipers are you using? Cheap plastic ones? Woefully inaccurate. Cheap digital ones? Same.

Yes, cheap digital ones. Which is why at first I only mentioned the
difference between the two pins. I don’t need to know their exact
measurements.

For harpsichords it’s really worth investing in a decent tool. Mitutoyo or iGaging. I will note that unbelievable as it seems the ‘drop test’ is not reliable as cheap calipers can have jaws that are not perfectly parallel over the length, and worse, bend under strain (which is why you should measure at the tip, generally).

Well, even if reverse the pins in the jaws, the Hubbard pin falls first.
So I’m quite sure it’s thinner.

I’m not going to try to enlarge the holes. The two options I’m
considering are getting 5mm pins or drilling holes in the Hubbard pins
(the only reason I’d have to change them, other than throw away a few
bucks). But drilling holes in pins is so boring ;-).

Le 23/08/2023 16:21, Borys Medicky via The Jackrail écrit :

My recollection from perusing the old harpsichord list archives is that makers usually drill 0.1 mm, and sometimes 0.2 mm, less than the diameter of the tuning pin. 0.2 mm less makes sense if the pins are on the slim side, like around 4 mm.

Thanks to all who have responded. Yet another related question: how deep
does a pin need to go into the wrestplank?

Dennis, according to your latest message this is not too late for you; here are some thoughts:

The issue is whether a “slightly” larger pin would split the wood. (I wrote this before I knew you are dealing with a Hubbad Instrument; year?)

I’ll take Frank Hubbard’s recommendation (Claudio’s and my instruments, both early 1970s) of 5 mm diameter pins as typical, we have to estimate the strain on the wood in a working situation. What strain is achieved with a 0,7 mm (=0.0027 inch) larger pin in an original hole, “defined” by Hubbard’s recommendation to drill the hole with a # 10 drill (=0.1935”)? A simple estimate of the circumferential strain (splitting the wood) would be the increase in diameter of the pin, divided by the pin diameter, which is, for your situation, 0.07mm/5mm = 0. 014, or 1.4 %. This is the increased strain on the wood across the grain at the pin surface.

Now compare that to the strain generated in Hubbard’s “new (virgin) situation”:

The pin diameter is 5 mm (=0.1968”) with the drilled hole (#10 drill) yielding a diameter of 0.1935” and thus a difference of 0.0033”. Thus, instead of dealing with a possible increase in strain of 1.4 % (in your new situation) we have an original strain of 0.003/0.1968=0.015 =1.5 %.

If one were to use a # 11 drill (=0.1910”, Hubbard’s second possibility) that original strain would be 2.5 % or possibly 3%.

Thus, by increasing the interference between wood and pin by 0.07 mm, you might thus more than double the stress in the wood locally. (I recognize that the hole dimension of a “new Hubbard instrument” and what you have in an older instrument with some permanent set in the wood, is hard to assess).

I have no information of what the splitting strain for your (or my) wrest plank material might be, and the local failure depends also on how close to each other the wrest pins are, that are to be exchanged. What I mean by this is, perhaps, readily visualized by a situation where two pins are located immediately next to each other (not in a harpsichord), versus several inches away from each other (isolated replacements). In view of the irreversible potential damage I would have to resolve that issue via a test of the following kind:

On my harpsichord the closest pins in the grain direction (e and f) are separate by about half an inch.

Take a plank of the same kind of wood your wrest plank is made of, as thick as the wrest pin is inserted into the plank (about an inch?) and about an inch along the grain and about the same in the perpendicular direction (a one inch cube?). Drill two holes ½ inch apart along a line following the grain, with a drill that is 3% (or 3.5% for good measure say a #11 drill i.e 0.191" in the US) smaller than the diameter of the pin. (Center the two holes with respect to the test specimen edges). Insert two pins in the two holes and “drive them home”. Did the test piece split? If not, you may be ok. If they do not split the wood immediately, examine, after a few days, the wood next to the pins on either side of the pins along the grain, looking for small incipient cracks. If you see cracks starting, you are likely to be in trouble with failures downstream. You may vary this test with separation of the pins, in accordance with your repair situation, if you are not replacing all pins.

Be careful with “drilling a hole slightly bigger” unless you can be sure your drill is small enough not to make the hole too big. Do you have a good means to measure the old diameter hole to a small fraction of a mm? If not, don’t.

PS: Making use of Frank Hubbard’s advice? (A partial repeat)

I “quote” Frank Hubbard: Use a # 10 drill (=0.1935” dia), if #10 makes the pin sit too loose use a # 11 drill (=0.1910”) which is only 0.002” still smaller. (The fourth digit after the decimal point is usually uncertain, especially in wood working.)

A # 10 drill is only 0.003” smaller than the pin diameter. It leads to a 1.5 % strain

Thus a 0.07 mm (= nearly 0.003 in) larger pin would lead to doubling the strain to about 3%.

If we take his suggestion to use the #11 drill (which I never needed on my instrument) that would have raised a strain of 2.5% ab origine, apparently acceptable by Frank Hubbard. Maybe you do not need the test described above, unless for great comfort?

Might one not conclude that the 0.07 mm larger pin still fits in with Frank Hubbard’s experience?

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