MIMF

I've been making archtops for years now, but only carved plates when working with wood. Like many luthier snobs (of which I admit to being ) I always assumed making a laminate plate would be trivially easy and not at all real woodworking. So then I decided to bang one out. Suddenly I realize that it is not so trivial

I know from searching that several members have made their own plates. Any tips or suggestions you would like to pass on? In particular I am scratching my head on jointing five layers of veneer and gluing it together. If I tape the seams, the tape of the middle layers will get captured. That doesn't seem right. But if I don't tape the center seam is bound to separate, right?

I could only find one Youtube of "Gretz" guitars where he glues up in pairs on a flat board and then glues the two pairs to a center veneer in the mold. But he seems to take the tape off before he makes the final sandwich in the mold. How is it possible that seam holds? Should the seams cross between layers? If I glue two sheets at a time, won't the glue make it too stiff to place in a mold? Should I only let the paired sets partially cure? What kind of glue (Gretz seems to be using good ole Titebond)?

Finally, what about the endless Internet suggestions about cutting a slight half moon into the bottom half of the sheet so it doesn't buckle when pressed into the plate. Gretz seems to be using just a regular sheet. In the Gibson Memphis factory tour videos they are clearly just pressing a square piece, but they are using massive machines meant to stamp out sheet metal, not some vacuum press.

Any real world experience or tips is appreciated!

Have you searched the MIMF? We have covered this topic in detail.

Well. I searched the active forum and didn't find much. But here is a thread from the old MIMF library that covers it extensively:

http://www.mimf.com/old-lib/laminated_a ... plates.htm

After reviewing this, let me know if you have any unanswered questions.

Thank you. I had searched MIMF and found nothing. This archived thread was very helpful.

The old MIMF Library is an extensive treasure trove. Let me know if you don't know how to find it.

Thank you. It is a treasure trove. I still have some questions that were not covered. For example, for those who cut a "dart" in the show layer, what do they do with the inner layers that either don't have seams or are rotated so the seams don't line up?

I gather there is a policy that we not go over material in the new forum that was covered in the old? That link is from posts that is 14 years old. There may be new glues, materials, or techniques that the new forum may benefit from. No? I'll let the thread die if that is policy.

Thanks!

I'm very interested as well.
I had found a number of posts from the OP on the tele forum (I think) which while helpful don't have this much solid detail.

There is no policy. I just thought all that info would give you a kick start. I will be happy to discuss this topic as much as you want.

I have built a number of laminated plates since that old discussion and did a bunch of testing to see what works best. I discovered that a dart or pie shaped piece cut out of the lower bout worked well. The size of the dart depends on the height of your arch. My plates rose about 1/2" and my pie shaped dart was about one inch wide at the bottom and tapered to nothing right at the apex of the arch. Yes, I staggered the location of the dart of the different layers to prevent a weak spot.

Regarding glues I ended up using epoxy or Uni-Bond 800, preferring the latter. I used their thickener to minimize bleed though. Clamping was done with a vacuum bag. I glued up one layer of veneer at a time. Tape was perforated paper veneer tape and it was left in the lamination on the interior layers. Like the old post in the library stated, I used a two piece form. The bottom or interior form was hand carved from MDF. And then I laid up the top part of the form with fiberglass making a perfectly fit FG layer that was about .090" thick. Without the fiberglass layer on top I got some wrinkles in the top layers of veneer.

So were the seams on the inner laminations running parallel to the show piece, just offset to the left or right from the show seam?

Also, when you say you glued them up one at a time, do you mean you mated two in the press, then after it cured some added a sheet, press and cure, added a sheet, press and cure, etc, until you had five?

Yes and yes.

Thank you. With your help and a little more research I feel like I can begin conducting some intelligent experiments rather than just attacking it blindly.

I laminate all my backs and sides, it's the preferred thing for the Selmer style guitars I make. I laminate both 15' radius spherical backs and vaulted backs ala an archtop. The degree of recurve in edges is what mostly drives the amount of darting that needs to be done.

I use three or five layers depending on the thickness I want. I use poplar for the middle layers in either .5mm or 1.0mm thickness. For the inner layer I use .5mm mahogany. I buy the poplar and mahogany veneers in widths that allow full width and length without a joint. If there is to be only one middle layer, I offset the grain 90 degrees . If two, I offset them 45 and -45. If three, I go 90 degress, 0 degrees, 90. Balancing the grain directions is important otherwise, the part will warp. An example of an unbalanced laminate would be three layers parallel at 0 degrees and one at 90, this would be likely to warp.

If the recurve is severe enough to cause puckers in spite of the darts (it happens), laminate the inner layers first, all but the outside layer, then fair it down before adding the last layer in a second laminating operation. One layer of veneer will go do with some coaxing as the vacuum is drawn even with a lot of recurve. If the outer layer insists on puckering, it will usually crack the veneer, so I test-vacuum the last layer down dry and see how it behaves. If it does pucker, it will usually stand the veneer up a bit and crack. From then on, it will always happen in the same spot, so pull the veneers out and open the crack up a bit with a sharp blade to give it some relief. In dark woods, you will seldom see it. In maple, it will be pretty obvious no matter what you do. I have rejected more than one maple laminated back. Or go for a dark edge tobacco burst in the finish.

All that said, I have started using molds with more modest recurve and height. At first, I thought this would be a sacrilege and maybe it is, but no one seems to notice. These laminate up in one shot, never a wrinkle, easy peasy.

I like epoxy, WEST 105 with fast 205 hardener. Even though it is fast hardener, there is plenty of working time. Sets up hard enough to remove from the vacuum in four hours (at 70 deg F) and fully cured in eight. I had no end to trouble with water base glues: short working time, messy, hydration, warping, finish spitting later as the veneer dried out. Epoxy is much better. Apply with a foam roller designed for epoxy application. WEST makes them but so does Woolsey (cheaper). I use 25 grams of mixed resin for each interface, so if I have a three ply laminate, it has two interfaces, 50 grams. I apply epoxy to both surfaces of the interface. With the right amount, you will get very little squeeze out, a super bond and a minimum of added weight.

The key to getting epoxy to work well is the measure it accurately in small batches. I mix epoxy using a cheap ($12 Amazon) digital scale that measures to the hundredth of a gram and I try to get to get it right to the hundredth. One drop is about 0.03 grams, so it can be done. I routinely mix 5 gram batches for small jobs.

Regarding the center line joining where necessary, I glue the edges of veneer together with Titebond. Rough cut the edges with a straight edge and veneer saw or razor, then joint edge with a sandpaper beam. Use tape to hold the edges together until the glue kicks and then pull the tape. This will hold up to the rigors of vacuum molding. If the tape ends up on the outside, leaving it on is no problem.

My molds are male. I glue a piece of 3/4" 6 pound density urethane foam down on a 3/4" piece of MDF and carve the foam down to the MDF. The MDF represents the edges. Coat the foam with a couple coats of epoxy and wax it. I use vacuum bag and coarse bleeder cloth, no top side mold.

Epoxy will squeeze out through the pore of the inner and outer layers. If you pull the part after about four hours, the green epoxy will scrap off relatively easily. I then clamp the part back on the mold to finish curing. Epoxy will darken the wood, but if you use epoxy to grain fill, it will blend in perfectly. As the veneer is thin, you don't want to do a lot of sanding to level. Even with a good vacuum, woods with curl or figure like birdseye will not flatten completely and sand it fully smooth might break through, so epoxy grain fill here is your friend and will help level the surface without break through. I use WEST 105 resin and 207 clear hardener. Fully cures in 24 hours, very little amine blush.

Final thought: you will have some failures, I certainly did. Wrinkles, cracks, splits in the top veneer, etc. Try to finesse them but if not acceptable, ditch it and try again. Sometimes you can save a bad one and add another layer sometime when you want a thicker laminate. After the first 6-8 backs, you'll work it out and gets good ones (most) every time.

Craig, some great ideas there. Here is my take away:

1) dry clamp the show veneer to see if it buckles.
2) pre-glue the show veneer center joint.
3) remove plate after 4 hours to scrape off soft epoxy.
4) use 6-pound density urethane foam for form.

I can see how the dry clamping of veneer could also be useful to determine the dart size that is needed.
What tools are appropriate for carving the urethane foam?

My experience..while limited to probably a dozen guitars...so 24 plates..give or take a few rejects..has been quite a learning experience and despite the miscues which was anticipated..pretty enjoyable. Most all of my products come from Joe woodworker. I start with the plain maple 4X8' sheet. Now, those come with like a luan or cheaper mahogany backer..so there's actually two layers of wood. You can get either cross grain backer or parallel grain...which is noticeably more flex and like to mix them up ..but for the laminate sides..I use the parallel. A plate consists of three layers of the maple backed and an outer face layer of figured maple...he recently picked up some quartered spruce which I'm using on current guitar. I use the Ultra Cat glue. In this latest guitar I'm using some epoxy and rather than three layers using a layer of nomex...think it's Steve Anderson using this product..wow..light strong plate. Anyway..

The biggest issue was the buckling of the plates and finally the seam of the face veneer...I'm sure there's a mathematical equation that claims you can't do this ..then do that ...and expect it to work out!! ...But, I'm not going there! My remedy has been ..on a rotating basis on the maple/backed plates is to slice from a wedge/an angle that begins app 6" inches from the lower bout edge..that produces app 1/8" "gap"at the edge of the plate...so slice of pie..if you will..silly ..I know. At the other end of the slice..I make three smaller cuts..I call them crow's feet..so at that point..it doesn't buckle...I also scrape that area back to make it a bit more flexible. Now these slices (one per) are on either side of the center line.. and angled ...one sheet the "slice will be left of center...next sheet right of center then again left of center. For the face veneer...join the sheet in the center with the blue tape on the face side.....fold the veneers over and with an 6" 100 grit block ...slowly and gently take about 45 swipes on the jointed edge to create that "angle" beginning app 6" from the lower bout edge. After a few plates..you get a feel for the process...and I've found that those "slices" close right up ..and no buckling. I clamp them onto another carved form to cure...

I'm sure I'm forgetting plenty...but ..seems to work out ok.

Beautiful guitar, Chris.

thanks Barry...and yes the entire sandwich gets vacuum pressed...probably a step in the procedure I should have mentioned

So the crow's feet is at the upper point of the pie slice?

exactly Barry... In my experience, I've found that area of the cut wants to "buckle" as opposed to "pivot"...if that makes any sense....and it telegraphs through to the face veneer...I do it to all three sheets of maple...crows feet barely 1/2" I also scrape a bit of the maple away at the crow's feet to make more compliant. Again, alternating to either side of the center line on each sheet..and offset the cut on the third sheet so as not to double up in one area. You can get pretty good at it..and these "slices" close right up... And in taking this pic for the thread..I noticed the slice is about 4 1/2" long..fwiw..

And, when I put the entire sandwich in the vacuum bag...I leave the lower bout seam of the face veneer...with no tape of any kind...the last 5-6 inches...it will close right up...the tape just creates an obstruction...

I also had noticed a bit of buckling in that area but had no way to deal with it. Thanks for the tip!

What about a Carbon fiber top with 1mm of wood on the top?