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Joining Back Panels
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Author:  Sailor025 [ Sun May 03, 2009 7:14 am ]
Post subject:  Joining Back Panels
I'm trying to join the two back panels. I created a shooting board and very carefully planed the two edges but, no matter what I do I cannot eliminate light completely from between the boards. I cannot shave anymore from these two plates. This is my first guitar so my guess is it is a newby thing and I will improve on subsequent guitars.

I bought a piece of inlay with the idea that I would join the two sides then put in the inlay to cover the seam. Then I began to wonder if the seam would be strong enough.

Can someone tell me:

1. Will the seam be fine even though some light (not much) gets through?
2. Will the seam be strong enough? (I am using hide glue).
3. How do I cut the groove for the inlay?

Thanks

Rodney
Author:  Alexandru Marian [ Sun May 03, 2009 7:32 am ]
Post subject:  Re: Joining Back Panels
Well, I think it is time to move along. and it should be better on your next. It really depends on your plane. it has to be perfectly sharp and set to take the lightest shavings. What comes out should not even be a real shaving, but more like a very fine dust. There is also some hand technique to learn: push the toe when you start, and then as you move along, slide the pressure towards the tail of the plane.

As for cutting the groove, i don't know. I would simply join everything together. Simpler, and I've seen it done on some big$ guitars, going back to Torres.
For the strength of the assembly, I think most of it come from the reinforcing strip on the back, and the transverse braces.
Author:  Mark A Thorpe [ Sun May 03, 2009 7:43 am ]
Post subject:  Re: Joining Back Panels
yea I've encountered the same thing with the plane. What I do now is use the plane to get it real close, then I have a piece of Hard Maple about 18" long that is flat with 80 grit sandpaper stuck to the flat side, a couple swipes with that does the trick, makes for a nice tight joint that I have a hard time finding when it's glued up.
Author:  Sailor025 [ Sun May 03, 2009 8:30 am ]
Post subject:  Re: Joining Back Panels
Thanks Alejandru and Mark.

Alejandru, what do you mean by you would simply join everything together? Are you just refering to the back panels? That is what I think you are saying which is what I'm about to do. I'll let you know how it works. I was getting beautiful thin shavings instead of dust. I'll work on getting just dust from my next one.

Mark, I like the idea of the sandpaper. I might try that before I glue up.

Thanks

Rodney
Author:  jordan aceto [ Sun May 03, 2009 8:50 am ]
Post subject:  Re: Joining Back Panels
I think Alexandru means sandwiching everything together, instead of inlaying the backstrip some people glue it in full depth at the time they glue up the back. If you are concerned about your plates getting narrow because of repeated jointing it is a pretty good idea, it will spread the plates out by 1/4" or whatever your backstrip width is

To inlay a backstrip i use the first straight piece of wood, plywood or mdf i can find, clamped to the back acting as a fence for a laminate trimmer to ride against. I make fine adjustments to the width of the channel (if a stock 1/4" endmill does not provide a perfect channel) by adding layers of tape to the part of the trimmer base that contacts the fence.
Author:  Alexandru Marian [ Sun May 03, 2009 10:26 am ]
Post subject:  Re: Joining Back Panels
Yes I was suggesting sandwiching the inlay/purfling strip instead of really inlaying it. For me it is simpler because I don't use power tools, chiseling the groove would really be a lot of extra work for not much gain (imho).

Since I am too lazy to make a "tourniquet" system with wedges and rope, I use an improvised wedging system. I plane a bit of slope on the outer edge of 1 of the halves. I clamp the other half to the bench (a neck blank is good for this), position the second half (and potential inlay/purfling), clamp a stop against the other outer edge (i just pick another neck blank from the pile), take the mobile wedge half and the inlay out, apply the glue then hammer the half in. Unfortunately I can't find a pic now, but a very similar operation will do - it is a headstock plate with a wedge insert, it works on the same system.
Author:  truckjohn [ Sun May 03, 2009 1:16 pm ]
Post subject:  Re: Joining Back Panels
Maybe too late for my advise....
I will share it anyway....

I think it might be time to stop working the "Good wood" and take some time out for Jointing practice on cheap throwaway wood.

Cut out thin strips of 2x4 wood in the 2" direction -- say like 1 1/2" wide x 1/8" or 3/16" thick and 2' long. Use those for jointing practice. You can get a big 'ole stack of these strips from 1 2' section of a 2x4.

You can get pieces of 2x4 wood for free out of Construction dumpsters -- so the only cost is the time for resawing them down.... and the glue.... and if you wreck a piece... throw it out and grab another one.

Here are pix of my jointing practice -- 2 15 piece "tops." I ended up sawing about 2/3 of the joints back apart and re-jointing.... so what you see there is probably 40-50 jointing go rounds. It helped me a HUGE amount... as there is no $$$$ penalty for sawing the joint back apart and re-jointing.

Attachment:
Jointing 1.JPG

Attachment:
Jointing 2.JPG


I didn't have any luck jointing with planes at first -- the planes must be absolutely true on the soles or you won't get a good joint. The joint will follow the contour of the bottom of the plane.... so if the plane is a little convex, the joint will be concave.

What I eventually found was that I needed a good straight edge (not a ruler... a machinists straight edge) to check the joint edge. I also had to use 120 grit sticky back Sandpaper on MDF to do the final truing -- as my planes weren't that true.

Good luck

John
Author:  truckjohn [ Sun May 03, 2009 2:02 pm ]
Post subject:  Re: Joining Back Panels
Somehow, the Edit timed out while I was editing....

So back to your original questions....
I think you may be able to use your back set as is -- it depends on what kind of problem you have. See rough sketch. I think the worse problem to have is the joint cut on a taper front to back that shows up as a gap on one side when you lay it down flat. This gap looks like a V when you look at it on edge.

Attachment:
Jointing.JPG


A normal D sized guitar body is about 20" long, and most back sets are about 24" long... so you have some extra on the ends to cut off.

As others posted -- the wide centerseam inlay strip will cover the outside of the joint, and the centerseam reinforcement strip will cover the inside of the joint -- so it will sandwich it pretty well.

On how to do it -- use a straight piece of wood or metal as a router fence. Clamp it all down together and use the router to cut a channel ~ 1/2 the depth of the plate.
Author:  Wes McMillian [ Sun May 03, 2009 2:48 pm ]
Post subject:  Re: Joining Back Panels
Sailor025 wrote:
1. Will the seam be fine even though some light (not much) gets through?
2. Will the seam be strong enough? (I am using hide glue).
3. How do I cut the groove for the inlay?


1. No
2. No
3. Laminate trimmer and straight edge works for me

Continue to work on your jointing technique but, since you said you can't afford to shave any more from these two plates, just use the sandpaper method to finish up this one. I have had to do that myself while building my jointing technique. But I would sand the joint with more like 320-400 grit when I did it. The joint is plenty good and, since this is a back seam, you'll have plenty of extra reinforcement, anyway. Just stick some sandpaper to a good, true surface (like a straight 2' level) and get this joint done. Remember, you can go just a touch shy of full width, too, as the box will still be bound.
Author:  Dave_E [ Sun May 03, 2009 6:49 pm ]
Post subject:  Re: Joining Back Panels
Hi All,

I suffered the same thing for years (to stuborn or stupid to buy a quality iron :oops: but found something that for the price was right! AND, it really works. So simple. Have to recomend this. [:Y:]
http://www.luthiersuppliers.com/products/p11.html

Dave
Author:  Alain Moisan [ Sun May 03, 2009 10:57 pm ]
Post subject:  Re: Joining Back Panels
Todd Stock wrote:
A very slight amount of light in the center of the joint (.002 or less) is OK, but open at the ends is a no-go.


I feel the same. If you can close the gap by using slight hand pressure, then your ok.
Author:  bluescreek [ Mon May 04, 2009 6:38 am ]
Post subject:  Re: Joining Back Panels
Sandwiching the inlay is fine as long as it is wood or wood fiber. Plastic or pearl , no. There should be a cross grain spruce reinforcement strip along the back join inside so that will help with the strength and stability. Gaps in the joint will take some filling as the finish will sink in them. As Todd points out .002 is okay. The glue will fill that.
As for a perfect join , one point that was missed was how sharp is your plane. Many people have planes and chisels and if you can't shave with them , they are not usable. I am in total agreement with Todd , that a good plane will do the job easy and efficiently. I don't use a shooting board . I use a jointer . That is just a different technique. It matters not what you use but your technique is more important. You want to be square and straight. You are using 2 axis X and Y. Practice a bit more . Are your gaps from not being straight or not being square.
Learning to set up a plane is as important at learning to sharpen one. If your edge is not true , your edge won't be either. Learning sharpening skills is as important as learning to set a neck. So as you see there are many little steps to learn. That is why apprenticing takes so long. It isn't just to learn to build a guitar , but to learn to use and take care of the tools that are used.
As a machinist , it take a little while to learn to make a true square block. Often , even when checked something may seem square when in reality it is a perfect parallelogram . If you are off square 30 seconds on the plane , that will equate to 1 degree as the difference can be doubled. As pointed out above , is the sole of the plane is not true that arch will pass into the joint . Once mastered the set up of a plane is not that difficult.
Author:  Sailor025 [ Mon May 04, 2009 1:17 pm ]
Post subject:  Re: Joining Back Panels
I never expected so many responses. I'm going to try each one to see what to do before I joint the sides. I actually tried to find something to sandwich between the sides but no luck at the local Woodcraft store. I will check Rocklers or maybe order a strip. The inlay I finally purchased is 1/4" wide and very very very thin. Almost paper thin. It was just going to be used to mask the seam.

Rodney
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