Official Luthiers Forum!

Not that the guitar-making world needs another way to glue tops and backs together, but I saw some ideas online and I thought I would slightly improve my current way of doing it. Here is what I came up with:



The workboard is a regular 24" x 24" piece of exterior grade plywood. There is a trough in the middle (3/4" wide, ¼" deep) to let glue drip down and provide air to the glue joint for faster drying. There are 3/8" dowels, two on each end, that are anchors for the silicone rubber bands. The bands provide the anti-buckling pressure once the sideways clamping pressure is applied. There is packing tape on the workboard on both sides of the glue trough, just to avoid any stray glue causing the worst possible problem (i.e., gluing the workpiece to the workboard). The six cams apply the sideways clamping pressure.

Here are closer photos of two of the cams:



Here is a close up of the anchors:



Here is a closer view of how the bands keep the plate from buckling:



Here is a close up of the anchors and the trough:



Here is a close up of a cam:



The cams are just 4" diameter circles of ¼" Baltic Birch plywood I bought from one of those crafty types on eBay. You can make them easily enough, but for the price ($2.19 each, including shipping), buying them was an easy choice. The off-center pin is a 3/4" washer head screw, and the "handle" is a stub of 3/8" dowel. I drilled holes for the off-center pins about ¼" off-center, and holes for the dowel stubs about 1" from the outer edge.

The virtues of this design:

1. The cams are super fast to tighten after the glue is applied, and therefore great for hot hide glue.

2. It allows me lots of flexibility on where to put the cams. If they need to be moved, I just unscrew each cam's screw, put the cam where it is needed, and screw it down, backing out the screw just a smidge from fully tight.

3. It can be moved off the bench to make room for the next task.

The gluing procedure:

I put the plate halves on the workboard, under the bands, with the edges to be glued about ½" away from each other, but the edges hanging over the edge of the gluing trough. I place the cams so that they are fully open (least amount of gluing pressure), but right up against the outside edges of the plate. I use a heat gun to warm up the gluing edges, and then use a brush to spread glue onto both of the gluing edges. I close up the top and bottom cams lightly, both sides at once, and make sure everything is aligning right. I snug up both sides of the top and bottom cams, then snug up the middle cams, then move around from cam to cam and make sure the outside edges are not riding up on the cams. Within a minute, all cams are applying good pressure, the bottom of the center seam is dripping its excess glue down into the gluing trough, the top of the center seam is ready to be cleaned off, the bands are keeping the plate halves from buckling, and the whole shebang is ready to be moved off the bench.

The trough seems like a good idea, as does that cam design. I use a slightly convex-in-length piece of MDF
on top of the joint to keep it flat, but the joint is not visible that way, FWTW, so maybe the bands would be better.
Food for thought! Thanks for the ideas..

Well thought out and very compact. I like it!

I’m digging the bands. The top almost looks like it’s set up to deadlift.


Sent from my iPhone using Tapatalk

Pretty cool thinking and execution Don. Cams do lots of good work in Lutherie and I am reminded of Frank Ford's Jack the gripper which is all about cams too.

Thanks for all the kind words! I like the cams, for sure. They are SO much faster than anything that uses screws, and you can immediately feel when enough pressure has been applied.

The other stars of this show, though, are the bands. They apply just enough downward pressure to prevent the plate halves from buckling up, but they don’t interfere with the sideways clamping action of the cams. The same cannot easily be said for any system that mashes the plate halves down, top to bottom, with clamps and cauls (used on some gluing jigs). I really think the bands are ideal for what the “anti-buckling” part of the jig needs to accomplish: preventing buckling, but allowing side to side movement. Plus, the bands can be placed prior to applying the glue, so that’s one less thing to deal with after the glue is applied.

This way of positioning the parts allows the center seam to have some small height mismatches along the length of the seam. But honestly, I get those no matter how I go about this task. I just make sure there is enough plate thickness at this point so that it doesn’t matter. The corresponding benefit is that, not being mashed between two pieces of wood, the center seam has more air for the glue to dry faster.

Nice design.
A couple of thoughts-
I wonder if wedges of slippery plastic slipped under the bands across the joint would eliminate some of the height mismatches.
Lining the bottom of the trough with tape might make cleaning up the glue drips easier.

Good ideas, Clay! Some thoughts on the wedges idea: You wouldn't even need to use wedges; you could just use uniform width boards (2-3" wide), with tapered ends to make getting under the bands easier. This would make the pressure more like the ropes and wedges method.

The height mismatch is really not a big concern to me, so I probably won't go to this trouble. The fewer things I need to fiddle with during a hot hide glue job, the better. But others might want to try harder to get the heights to match up, and this sounds like something that might help in that regard.

Tape in the trough is definitely a good way to keep cleanup as easy as possible.

Nice jig. I wonder if it would work with cams on only one side, pushing the plates against a stop or ledge of some sort? That would be half as many parts to "fiddle with" during the process. Thanks for sharing.

_________________
George :-)

George--

Absolutely, it will work the way you suggest. I thought about doing that. Here is why I went with the cams on both sides instead: If both sides of the center seam can move a bit toward the center of the trough during the glue up, then that allows more space for the glue brush to apply the glue before you clamp. If one side is stationary, positioned at the center of the trough, and the "moving" side is slightly hanging over the edge of the trough, that leaves less space for the glue brush to get in there. The cams are so easy to throw that having to do both sides is not a hassle at all. So, I like it the way it is. But your suggestion can work just fine, too.

Can you move the cams around to accommodate different sized or irregular shaped plates?

Barry--

Absolutely! That was part of the genesis of this. I recently tried to glue up one of those tops that is coffin-shaped, and my prior way of gluing it did not do well. I started looking into what might work better. With this jig, you just unscrew the screw, move the cam wherever you want, and screw it down. Eventually, the workboard will be riddled with holes, but I just consider that part of the jig (just the workboard) to be a consumable with a long life. Eventually I will get a new board, cut the trough, drill the holes for the anchors (which I have not glued in; no need to), put down tape where desired, and move the cams and bands over to the new board. Easy to do, and really, a long way off. You can put a lot of holes in plywood and have it still do the job.

I sure do like the simplicity of the jig. It appears that it will work great with very little to do.

The only thing I would consider is two dowels in each cam. That way you could put a stick between them when you wanted slightly more pressure.

_________________
Joe Beaver
Maker of Sawdust

Joe—

There’s no harm in making the cams easier to throw by adding another dowel stub. If someone wanted to really crank them, I might suggest keeping the screw a bit tighter; I think the friction might help hold the increased pressure. Of course, at some point, you overcome the stiffness of each plate half, and they start buckling in the middle of the half. A weakness of this design is that, other than the bands, there is nothing to prevent buckling in spots other than the center seam. Maybe, if you need that level of pressure, you can install more anchors and bands. Two more bands per half would probably do the trick. I like that solution. Tops and backs will have different tolerances for the extra pressure, obviously. Great ideas (yours and mine combined) for those situations that need more ooomph: another dowel stub to give more leverage, and more anchors and bands to prevent buckling.

Great looking jig.

Perhaps you could have a line of pre-drilled holes along the horizontal plane of each cam and use bolts and wing nuts so that you can easily shift the cams to accommodate odd shaped plates??

G.

_________________
www.leddingtonguitars.com

Gary—

You could certainly experiment with that. A few thoughts:

A cam’s action depends on how far off center the rotation point is. If you move the rotation point further from center, the cam applies way more force sooner in its travel. At some point, the cam loses its utility if the rotation point is too far from center; it just doesn’t do the job. I recommend experimenting to see what I mean.

Also, the reason I like screws instead of bolts and nuts in this specific application is that screws are easier to move somewhere else. You just unscrew, move the cam, and screw it down again. With bolts and nuts, you have to drill a new hole, etc.

But certainly experiment and see what happens! Let us know what works for you.

Nice. Where did you get the bands?

Roy--

Here is a link:

http://www.grifiti.com/band-joes/standard-bands.html

I think you can get them on eBay, too. Just search for the brand name.

I learned of their existence, and their utility for building guitars, from this thread from David Farmer:

viewtopic.php?f=10101&t=48073&hilit=silicone+rubber+band

I plan to use them in the exact same way David does, when I next bind a guitar.

Thanks Don.

I wanted to mention a few other things relevant to Gary’s thought of putting multiple rotation point holes in each cam. At least, I think that’s what Gary was suggesting. If I misunderstood, Gary, please let me know.

I placed the rotation point hole for each cam at 1/4” off center. So, one spot on the outside edge of the cam is 1/2” further away from the center than the corresponding spot on the opposite side of the cam, 180 degrees of rotation away. If you place the cam so that it’s “short” side rests against the plate, the maximum clamping movement you can get is 1/2”, when you throw the cam 180 degrees.

You can definitely get more clamping movement out of these cams; you just move the rotation point further from center. But at some point (and I have not experimented to find out where it is, nor do I know enough about the math and mechanics of cams to compute it), the cam won’t work as a clamp. Imagine a rotation point 1/2” from the outside edge. That won’t work.

So, I opted to use a modest amount of “throw,” and I just move the cam to where it is needed, which is simple, due to using a screw into plywood as the rotation axis.

I hope that makes sense.

Don wrote:
"So, I opted to use a modest amount of “throw,” and I just move the cam to where it is needed, which is simple, due to using a screw into plywood as the rotation axis."

When I build using a "workboard" for assembly I screw wooden "L" brackets around the perimeter of whatever shape guitar I am building, rather than using the more elaborate setups that use slots and movable spool clamps. Using the ubiquitous cordless drill I can move the "Ls" in place quicker than I could move the spool clamps and position them exactly where I want them. I think the idea of using screws to make adjustments to jigs is under utilized by many.

I agree with using the screws to adjust. A belt sander, drill, deck screws and 3/4" plywood takes care of a lot of the jigs I make. I often just use em once then recycle the screws and the wood (if the pieces are big enough).

_________________
Steve Smith
"Music is what feelings sound like"

Clay--

You just inspired me to experiment with something. I normally make dedicated molds, in the regular fashion (several glued layers of plywood, bandsawed to the profile, etc.). I made one of those Jim Williams adjustable molds years ago, but I didn't like it very much. Too fiddly. I have been thinking about ways of making a better version of it, and I've been coming up short. Dedicated molds seem better in comparison. But, what if I do the following, per your suggestion:

1. Cut a decent piece of 3/4" of plywood (Baltic Birch this time; more likely to stay flat) to the shape of a normal outside mold. Maybe also cut a hole in the middle to both lower the weight and provide access through the mold. The hole would need to be significantly smaller than any anticipated guitar profile.

2. Cut a bunch of 3/4" plywood right angle L brackets that can stand at whatever heights are needed for the guitar in question. Perhaps different heights for different ends of the guitar, and/or for different stages of construction. Taller brackets might be needed for gluing on blocks, and shorter brackets might be needed for gluing on kerfed linings, for example. The leg of each bracket that sits against the workboard would need to be within a specific height range so that two screws of a specific length can go through the leg, seat well in the plywood, but not penetrate the other face of the plywood. Good planning is all that is needed there.

3. Drill "through" holes of the right diameter for the screws into the bottom leg of each L bracket, two screws per bracket.

4. Draw the profile of the guitar on the workboard.

5. Screw the brackets around the profile. Maybe at the head and tail, I use something more substantial that can better facilitate gluing the blocks to the sides. Change out brackets, shorter or longer, as needed for the task at hand.

I'm firing a whole bunch of new ideas off of this! Thanks for the inspiration.

I went through a couple of iterations of bracket making and finally decided on a relatively simple design. I haven't found a need to make various heights, but kept them low enough to fasten my linings but high enough to use spring clamps if I so choose.
Another idea I incorporated in the workboard is a removable solera. My brother gave me a large roll of rubber impregnated cork gasket material and I cut and glued several layers with various size cutouts to create a solera shape for a particular plantilla, which just lays in place on the workboard.
I sketched the bracket design I'm using now:

I found a single screw held the brackets in place fairly well and allowed for small adjustments to be made by loosening the screw a little and turning the bracket. The notch in the bracket allows an oversize soundboard to be put in place to facilitate gluing the sides on. I drew a centerline on the work board and drilled a hole for a bolt to pass through at the approximate center of the soundhole area. After the soundboard is in place I use a short stick of wood with the bolt passing through it and a wing nut to clamp the soundboard at the soundhole.
As an added bonus the workboard/ bracket combination can also be used to hold the shape of the guitar when you need to remove the back to do repairs.