Official Luthiers Forum!

I'm building a press for gluing on tops. My carved tops are not an issue because they get glued on flat, but does anyone have any clever ideas for clamping up a drop top? I usually just do it with a million clamps, and it's never easy or convenient. I'm looking for a bit more of a reliable and simple way to do it.

Thanks for any ideas.

A drop top isn't glued flat?

_________________
Francis Richer, Montréal
Les Guitares F&M Guitars

Nope You shape the back for the forearm relief, and then bend the cap to fit. Clamping it always a pain in the butt. I have a couple of good thoughts on it, but before revealing what I've concocted (I'm still concocting, BTW) I wanted to get everyone else's thoughts on this. It's just a big pain in the butt problem that I've never seen a good solution for.

Vacuum clamping?

Just for the record, 'drop top' tends to be used for any thin (1/4" or less) top glued to a guitar body, whether or not it is contoured, bent over a curve, whatever.

It is? I wasn't aware of that, but I'll be more careful in my usage next time. My impression is that the first use of the term "drop top" was by Tom Anderson specifically referring to the bent, "dropped" forearm contour of the top.

I'm not convinced that vacuum clamping will put enough pressure on the piece to adequately bend it and give a tight glue line. If I had access to one, I would try it, but I don't and it's too expensive/time consuming for me to experiment with right now. It can probably be made to work with appropriate cauls and fixtures, but I'm definitely out of my comfort zone with vacuum. It's certainly an attractive solution, though, because of it's simplicity.

I think what I'm going to do is as follows. I'm going to make a clamping caul for the contoured part that has a couple of holes for the press screws (to hold it in place) and then threaded 1/4-20 inserts all around for bolts that will put pressure on a 3/4" plywood caul. The press and caul will do the heavy lifting of bending the top and holding the caul in place, and the smaller bolts will clamp the edge and give a nice glue line. I'm experimenting so we'll see how it works out.

I'm surprised that it doesn't seem like anyone's come up with a good solution for this yet other than industrial presses. Maybe that's why we don't see many small builders do this kind of thing? There's really just not a lot of information out there about this at all...at least not any I can find.

I think that a gobar deck and lots of bars would be a good way to go. I have never done this as I only build acoustics but it probably would work real well.

Fred

_________________
Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866

Vacuum bags are just made for that kind of lamination--with a proper bag set up, you'll get much more even pressure than you can get with any kind of mechanical clamping. I use vacuum bags to lay up backstraps on necks (with a pretty good bend to it) and get much better glue lines than I used to with cauls and clamps...

Dave

http://www.luthiersforum.com/forum/viewtopic.php?f=10123&t=34858

I don't know the correct way to post a link but gave it shot to a thread about your issue.
There is a factory tour video that's worth watching.

If the link doesn't work it's on the second page titled "3/16 Maple Top" - second from bottom
at time of this post.

Well, there are lot of votes for vacuum bags. Let me start by saying that I will not be using a vacuum at this time. The cost and time experimenting is just not in the cards right now. That said, I'm wondering if there's anyone out there that realibly builds these kinds of laminations with bags. I'm not talking thin veneers, flat top guitars or something similar. Specifically, does anyone out there regularly glue up drop tops, without prebending them, using only vacuum bags? I'm realy curious about this. It's something I may think about for the future. I just don't know anybody, or even know of anybody, that's doing this, but if someone is I would love to know all about it....or even just know that someone is doing it successfully.

I have made hundreds that were clamped with vacuum bags. There is a trick to it.
First you must thickness your top to about .100" if you want a deep bend like a stock Strat contour. If you want a lesser bend ,thickness can be in the .125" range.
Woods like Koa, Birds Eye,any.hard Maple,rosewoods, Cocobolo, etc... must be steam bent(an ordinary clothes iron and a rag works great) to help conform them to the back. Also leave a small bit of extra top wood to overlap the edge where you have a contour bent.
One rule that I never break, is to make sure you are not trying to bend over a compound curve. Sand with a hard block to ensure a smooth even surface. Use a grit no finer than 180 to give the glue better grip.
A spray bottle spritz of water on the bend area will help woods like Big Leaf Maple relax a bit and conform better.
Cook for at least 2-3 hours in the bag under vacuum. This will help dry the glue faster than air drying.
You can bend thicker tops if you kerf them before bending, but this is best done with a CNC router.
Hope that helps,good luck.

_________________
How long is that in luthyears?

Thanks, Brett. I'm currently bending a 1/4" top with kerfs cut about 2/3 of the way down. It's not a very deep contour....only about 10 degrees in my particular design...just enough that you still feel it and can rest your arm there.

Do you use any cauls to do this?

I would set up a caul for a screw press (veneer press, book press, cider press) You could probably use on clamp if you jig it right.
http://www.grizzly.com/products/Deluxe-Press-Clamp/H5510

You will find other uses for this also. I have two of them and I use them all the time.

_________________
Ken

Sorry, I have never bent a top thicker than about .180" with a vacuum bag.
Most of mine have been about.100".
I only have seen thick kerfed tops bent by a guitar maker buddy who offers them on his bodies.
I have never tried it myself.
My buddy uses cauls he made with his CNC routers, so they fit very well.

I think I will stay with Vacuum bags for my guitars since I like deep contours.

_________________
How long is that in luthyears?

What I ended up doing is making a caul that the press screws can push down on to get the basic bend. Then around the edge are 1/4-20 screws that push down and drive the top home. I'll take a picture at some point. It actually seems to be working pretty well. I'm hoping to do a glue up this week so we'll see how it goes.