A modification to the traditional clothes pin clamp for linings

Barry Daniels - 11:37pm May 2, 1999

I've never been happy with the results I get when gluing linings onto the sides of a guitar. The problem is trying to clamp surfaces that aren't parallel. The triangular shaped linings slip around on the wet glue, and also refuse to lay flat against the sides. This results in glue filled gaps under the linings which certainly compromises strength. I've tried wooden clothes pins, small c-clamps, hardware store spring clamps and office supply binder clips, but they all have the same problem; trying to clamp non-parallel surfaces.

Today I came up with a solution: use the only surface on the lining that is parallel to the guitar side. This surface is the bottom of the kerfing cut. Using a clamp with a blunted knife edge to press against the bottom of the kerfing cut eliminates the source of the problems. I made my clamps by modifying my wooden clothes pins. I took the clothes pin apart and cut a 1/8" deep slot on the head of one piece with my fret miter saw. A piece of 0.030" thick brass, that was cut into a rectangle about 1/2" by 5/8", was hammered and superglued into the slot. I then filed the protruding edge of the brass so that it would be parallel to the other side of the clothes pin when it was in use. In other words, when the clothes pin is put back together and the two bearing surfaces are separated by the distance equal to the thickness of the guitar side and the wood under the kerfing cut on the linings (a total of approximately 0.100") it needs to be parallel. (You may need to alter the other side of the wooden clothes pin to have a flat surface for clamping. I had filed my clothes pins years ago according to the instructions in David Russel Young's book.)

This may sound like a lot of trouble with little to gain. However, they work great and it only takes about an hour to modify 20 clothes pins (your results may vary). The elimination of slippage and the tighter glue joint are significant. Make one and see if you don't agree that it's a better mousetrap. An added benefit is the knife edge pushes the clothes pin apart more resulting in more spring force. Throw those old rubber bands away.

Barry, thanks for what sounds like a great solution to the problem. But I might retain my rubber bands, just for good measure.

One idea comes to mind: how about filing the metal so it has only two contact points? They would bite into the linings a little, but I think they would also bite to different depths to adjust for any slight out-of-parallel as the clothspins shift in use. They might also fit better to a lining that is curved anyway. The points would, of course, be dulled enough that they don't do damage.

Tim, Thanks for your input,

The two points of contact sounds like a reasonable alternative. The key point with this modification is to make a clamp that self-aligns and doesn't shift in use. That is why filing the blade parallel to the other side of the clothes pin is the critical step in making the clamp. Your two points of contact would also need to be parallel to the face of the other half of the clothes pin in order for it to work properly. One possible benefit with the flat blades is the ability to shift the clothes pins up and down. This may come in handy when cleaning the glue squeeze-out. Shift two or three pins up out of the way allowing you to get a damp rag in there. Then slide the clamps back into position. The smoothness of the knife blades sliding in the kerfed cuts does not appear to cause any lifting of the semi-glued lining from the guitar side.

I'm anxious to hear if the knife-blade lining clamp idea has merit with other luthiers, and results from those who try it. Or am I the only one who has struggled with this task.

Barry, just one little wrench in the works. What do you intend to do with areas like cutaways and tight upper bouts. I often have to to bevel the edges of the kerfed slots just so that there is enough space for the lining to make that particular curve. In other words there IS no space for such a clamp in that area. Perhaps you could cut 1/2" off the end of one side of a clothes pin and insert a steel pin (parallel to the other side of the clothspin)that would fit into the space that's still open when the kerfing is compressed at the outside (or inside of the instrument if you want to look at it that way). The pin would have to be just slightly smaller in diameter than the saw kerf and would also need to be fairly stiff so that it wouldn't bend easily (It'll be a pretty thin pin).

I still think it sounds like a good idea, surprising no one has thought of it before. It's got to be cheaper than the kerfing clamps made for Taylor (I'd love a set of those babys).

Julian, I was wondering how to modify the method for a cutaway. Perhaps using a thinner knife blade would work, but you are correct that sometimes the kerfs completely close up which would not allow entry of the blades. Your pin idea sounds like the perfect solution. I will make a few and test them when I get to the upper bouts in my current project.

For many years (and about 360 guitars) I have used an alternative method for clamping linings. I made a whole bunch of cauls which fit on the lining and give me a paralell clamping surface. I made these inlong strips on my table saw and cut off clamp sized pieces. I have used the same batch for at least 25 years so they are durable, and they make clamping very easy. There are photos on my web site, which I think you can find by clicking on my name.

Charlie--that's a neat idea. Made we wonder if a person could glue a segment of lining to one jaw of a closepin by inverting it such that the clamp sees parallel surfaces when doing it's job. Maybe a tiny piece of sandpaper glued to the inclined face of the kerf segment would keep it from slipping? The additional clamping thickness would let the torsion spring apply a little more force also. Wish I could come and work in your repair shop for a few months!!!

Charlie's lining page.

Charlie,

Neat tip. It appears to me that the key elements that make your tiny caul method effective is 1) there is top edge on the caul which registers with the top edge of the lining preventing slippage, and 2) you make your own lining so you can ensure that the angle of the slope matches your cauls. I buy my lining from various suppliers and have noticed that the angle can vary quite a bit (sometimes even within a single order). The knife-blade clamp is immune to this variable factor.

I'm still working on the problem Julian pointed out about using these clamps in the upper bout or in a cutaway. I checked a non-cutaway classical (currently with the back off ) that has kerfed mahogany lining supplied by LMI, and noticed that the 0.030" brass knife-blade fit in the kerfs (albeit snugly) even in the upper bout. I think the problem will mostly be apparent on cutaways, however, there is only a few inches of lining where I think the kerf will close off completely. One could revert to the un-modified clothes pin in this spot. However, I still intend to try Julian's idea where a pin is inserted in the end of the clothes pin.

I received the following e-mail which poses a question I thought worthy of posting here:

Hi Barry, my name is Alessandro and I also love to work on woods and instruments. I found on the mimforum esactly what I was looking for, but I haven't understood what's the trick that you have used to avoid the space between the sides and the kerfing (Alessandro attached a picture here which I can't include but it shows lining bent around a cutaway that only touches the guitar side at the points created when the lining does all of its bending on the kerfed saw-cuts) because of my poor english, so I will very happy if you should be so kindly to explain to me ( in the simplest way that you know, pls!) the method used. I'm planning to build a cutaway, so this information is really important for me.

You have to know that I'm living in Italy where is really hard to find information about the acoustic guitar building (have you never performed a search for italian luthiers???). Ok Barry, thanks a lot for your help!!

My answer to him was: I assume that you are referring to the small gap behind the little blocks in the kerfing, which is due to all of the bending occurring at the kerfed saw-cut (the blocks don't bend). There is no way to avoid this, and it usually is not noticeable except, as you said, at an area of greater curvature, like a cutaway. I am building a cutaway, archtop guitar right now, and I think I will shape the lining (kerfing) with sandpaper to get it to fit to the cutaway a little better. I think the best way to do this will be to use masking tape to attach some coarse sandpaper to the inside of the cutaway. I will then hold the kerfing in place and move it back and forth a few times. I believe this will be enough to remove the little points of wood behind the saw-cuts in the kerfing which will allow the strip to fit tighter against the side. This is my first cutaway, so I have never tried this technique before, but it sounds reasonable.

Are Alessandro and I being overly concerned about this minor detail?

Actually I think it is worthwhile to be concerned about the ability of linings to fit properly on tight curves such as cutaways. I use a solid on piece (non-kerfed) lining for my cutaways, and simply fit it very carefully to the curvature of the cutaway. My rationale for this is that the cutaway is intrinsicly a "weak' point in the structure of the guitar and I want my construction to be very careful there. Maybe this is a bit too compulsive, but I doubt it. Charlie Hoffman

I double cut my kerfing for the cutaways in order to get them to bend into the tight curve of the horn. I had been doing it on the bandsaw (a little rough if you're not careful), but I'm thinking of ordering some. Taylor double cuts theirs by changing the registration of the linings in their gang saw. They cut it once, move it, and cut it again.

As for kerfing clamps, you can order the Taylor kerfing clamps that work very nicely around triangular profiled kerfing.

I completed gluing the linings with the modified clothes pin clamps in my current project, an archtop with a cutaway. To deal with the issue of the kerfing slots pinching off in the tighter bends of the upper bouts and the cutaway, I made some of the knife-blade clothes pins using thinner metal. I used some aluminum flashing material which is about 0.010" thick. I was concerned about this stuff collapsing in the clothes pin but in such a small piece, it didn't seem to be a problem. The aluminum worked for the tighter bends except for about 2" of the cutaway where the kerfs were tightly closed off. So I reverted to plain clothes pins for this small area.

Overall, I think the knife-blade modification was worth the time. Installation of the linings was easier and quicker with these clamps (no slipping of glue joints and waiting for the glue to grab hold) and the quality of the glue joint was the best I have ever achieved on a kerfed lining (no visible gaps).

My first go at leaving a contribution.Around tight curves I tend to use the plastic type clothes pins,they conform well to the triangle section linings and being narrow means lots of pins can be used in a curved section.Like Charlie Hoffman ,I more often than not fit a shaped continuous lining around cutaways.

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