Official Luthiers Forum!

Let me bare my ignorance. I often see jigs used to join top plates, such as the LMI "figure 8" jig. For back plates I often see wedge boards. Can tops and backs be joined by either method, or is there a reason it seems to be different? Or did i just happen to see this trend coincidentally? I just built a jig (with the figure 8 ropes) and see no reason why it wouldn't work for both? Thanks--and if theres a better way than either....I'm all ears (I use bar clamps for violin plates, but they're much smaller, thicker and tolerant of clamping than guitar wood.)

Dave F

I use Spanish Wedge system for tops and backs.

Pretty much any method should work for either if the joint is good. And nothing will work for either if the joint is bad Though softwoods are more forgiving, and can deal with a very slightly bad joint if you use a method that can apply a decent amount of pressure to compress the surface.

I use the masking tape method on both, which is low pressure, but the fastest to get from applying glue to having it clamped (just drop it), which is great for hide glue. Glue lines are pretty much invisible, and I don't think I'll be changing unless masking tape becomes very expensive But even then, you can reuse the long strip a few times.

I use the same method for both tops and backs, which is the "wedges on the side and modest weight on top" method. I like it because I use hide glue, and this method goes pretty fast (assuming you set it up with a dry run first).

I also like the tape method and use it the most. Last time I used the wedged approach and while it does apply more pressure it's way more convoluted. Has the nice ethos of everything being reusable though.

_________________
member of the guild of professional dilettantes

Yes,me to...!
Tom

_________________
A person who has never made a mistake has never made anything!!!

My first top. Maple strips, rubber bands, and HHG. Made a good straight joint.

I'm using this setup with four Bora clamps for both tops and backs. Works just fine and goes together pretty fast.

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

With a well fitting joint, pretty much any system will work as long as it lines up the two plates and applies some pressure.
Personally I use a board of birch ply with a stick screwed to one side and eccentric ply circles to apply pressure from the other side, use some weights over the seam area.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

https://www.youtube.com/watch?v=MD1Jm___E8Q

the key is to get the plates to mate. If your joinery is weak the joint is doomed from the start.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

http://www.luthierscooltools.com/Dwgs.htm#SApanish Clamp

Like Don, I use the Cumpiano method of applying pressure using little wedges tapped in between a clamped piece of wood and the edge of the plate to be joined. Use a weight on top to keep the plates down. It requires some set up but works great. almost too great. My joint lines are always invisible and I have a hard time finding the center line. Im thinking of trying the tape method.

I use the masking tape method, put spring clamps at the seam and hang the top from a hanger so air can circulate on both sides. I usually prepare and glue up 4 or 5 at a time so the joint is well cured by the time I use it.

thanks all. a couple mentioned difficulty if finding the centerline. with my violin plates I sand an ever so small chamfer (less than 1mm) and after gluing, it will accept chalk nicely to give a clear centerline at the butt. disappears as soon as you begin to hollow and arch carve, but at least gives you time to align and drill a toothpick hole.

I used to use the tape method with hide glue, but I have the LMI plate joining jig now and really like it.

I had exactly the same experience. I've moved from tape to the LMI jig. Well worth the price, IMO.

_________________
Steve Smith
"Music is what feelings sound like"

I do so few of these because I just build instruments for fun. At first, I used a cobbled together version of Jay De Rocher's method and it works fine. Later, I read about and tried the tape method. I used green tape, which seemed to have just the right degree of stretch, stickiness and ease of peel-off. I really like the tape method. Have not tried nor built any permanent jointing jigs because of my extremely limited production. For me, it would be an item that would remain in storage for most of the rest of my life.

What advantage does the LMI jig have over tape? More pressure, certainly, but that's not necessary with a good joint. And I expect it helps to wrestle bowed plates flat, but that's more of an exceptional case. And the tape keeps glue off the show face so you don't have to scrape it, and allows pressing the joint flat against the bench with your thumbs, even in places where one half is thinner than the other (though that's an exceptional case too). And with tape, you can join up as many plates as you want all in one session, rather than having to take turns with the jig. Just a couple minutes sitting flat against the bench is enough for hide glue to be safe to move (with a couple strips of tape across the back side of the plate for security)

$140 will buy an awful lot of masking tape.

I agree. There's certainly nothing wrong with the tape method. I don't know that I would say it has any advantages, but for whatever reason I prefer using it.

Not saying anything against the tape either but I'm happier with the jig. I think I'm getting a bit better of a glue line on my tops (and yes, my plates are jointed properly). Lot's of ways to skin the cat, and I may change my mind next year

_________________
Steve Smith
"Music is what feelings sound like"

When I worked for Sobell we had a stack of chipboard sheets, a bag of nails and a hammer. It's not the prettiest way to do things, but it works well. Last year I tried rope and wedges for the first time and loved it. But as previous folks have said, you can't compensate for a bad join with over clamping.

A few years back I posted a video about it on YouTube:

http://m.youtube.com/watch?v=OR6PdfvNj_U

Nigel
http://www.theluthierblog.com
http://www.nkforsterguitars.com/luthier-book/

Im just a beginner so you are forewarned.
Slightly offsetting the plates during glue-up will reveal the centerline allowing you to clearly mark it.

gregor

_________________
Wake up and smell the rosewood!

thanks again for lots of great ideas and insights. just for kicks, I joined my top and back with the jig and rope for one, and the wedges for the other. Both very easy and good results, but as many have said, its all in the joinery, not the method of clamping. I always prefer the simpler method, so I may stick with the wedges from now on. Hope to meet folks at the Woodstock show next weekend.

That's a great idea gregor for drawing the center line initially, but it will get sanded away and have to be redrawn a few times throughout the build process.

I think it is a great problem to have. I love it when the center seam is hard to find.