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Gluing on the back plate
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=9106		 Page 1 of 2
Author:  Colin S [ Tue Oct 31, 2006 8:36 pm ]
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I'm just ready to glue on the back plate of a walnut OM and I got to thinking,always a dangerous thing.

I've used a whole range of methods for gluing the plates on the sides over the years, from using spool clamps on my first, roping using neoprene tubing, bolts and a clamping caul, and of course more recently in the go-bar with a caul.

Now when I'm fitting the braces into the kerfing I check it out by putting the back in the radius dish and fitting the sides in the mould over the top to check that I have a good fit all round.

I wondered why I don't glue the back to the sides in the same way? Put the back in the radius dish, then put the side down onto it and add the go-bars to push the sides onto the back, I could even add a caul and some go-bars to the centre of the back to ensure that it is firmly in the dish and held to its radius. Clean up would be easier, and checking for good contact easy as well.

Have any of you experts out in OLFland done it this way?

Any reasons why I shouldn't do it this way?

Colin

Author:  BobK [ Tue Oct 31, 2006 10:41 pm ]
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I've done 5 that way. I use a pair of bar clamps at the neck and tail block ends and a mixture of bar and cam clamps elsewhere spaced every 3-4 inches. My radius dishes are doubled up 3/4 ply and I've noticed no distortion in their shape when I'm using them as cauls. The only difficulty I've had is actually getting a good look at the body as it's sandwiched between the dishes.

BobK
Author:  Colin S [ Tue Oct 31, 2006 11:19 pm ]
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Bob, I don't mean to use the radius dish as the top caul, that's so I can still have access to the inside for clean up. Using the top dish would negate many of the advantages of being able to see inside clearly and being able to add a go bar to the centre of the back to hold it in the dish.


Colin
Author:  Colin S [ Wed Nov 01, 2006 12:42 am ]
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Hesh the stack would be 15' radius dish, back, rim (still in mould, then probably cross bar cauls that the go-bars would press on, although I have no problem putting thin cauls over the kerfing and just putting the go bars on them. We do put go bars onto 1/4" wide braces with no problem. I want to keep the top open for the reasons given.

Colin
Author:  Mark Tripp [ Wed Nov 01, 2006 12:53 am ]
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Colin:

I did it this way on my last one, and it worked out fine. If I'm not mistaken, I think Mario does it this way also - perhaps he will chime in.

-Mark
Author:  John How [ Wed Nov 01, 2006 1:04 am ]
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That is exactly how I do it colin. You formed the sides using that radius so it makes perfect sense to me to use it as a glueing cawl. I don't use the go bar but cam clamps but your idea is sound.

Since I have switched to hide glue, I've been thinking about a press sort of fixture that can clamp the whole thing with one or two motions. I have some ideas but haven't actually tried them yet. Maybe soon
Author:  Colin S [ Wed Nov 01, 2006 1:14 am ]
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Thanks Mark and John,

Yes John I use HHG as well so I wanted a way of quickly and acurately positioning the sides and back. This way you can see the inside all of the time.

John it shouldn't be too difficult to make a large cam clamping system that would use just a couple of levers to cam the rim down.

Although John, you do know the old Spanish method of gluing the back on with HHG don't you, (braces fitted to rim first) put the glue on, position the back in place then wipe alchohol over the brace and rim positions on the back then set fire to it to heat the glue up. Clamp while still hot! I'm going to try this on my current FE19 build, got to be authentic!

Colin
Author:  JJ Donohue [ Wed Nov 01, 2006 1:19 am ]
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This is bizarre, Colin!! The timing on your post is almost scary.

I was in the shop last night contemplating the same change in my method. I even started making the caul blocks for the rims on which to place the gobars. The only difference...my OM back is EIR.

As with anytime I HHG a plate, I do the dance rehearsal a few times before going live. I shoot for 40 seconds as a target time for having the glue applied and plate clamped. Any cool dance steps you find would be appreciated I plan to have mine glued up before the weekend and will also post the pics and results.

Good luck!
Author:  Dave White [ Wed Nov 01, 2006 2:19 am ]
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[QUOTE=Colin S]
Although John, you do know the old Spanish method of gluing the back on with HHG don't you, (braces fitted to rim first) put the glue on, position the back in place then wipe alchohol over the brace and rim positions on the back then set fire to it to heat the glue up. Clamp while still hot! I'm going to try this on my current FE19 build, got to be authentic!

Colin[/QUOTE]

Colin,

So what does the FE stand for then - Flames Emerging?

That would have to be a flamed mahogany back then?
Author:  arvey [ Wed Nov 01, 2006 2:29 am ]
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Colin, that is how I often do it, in the go Bar, Radius dish, Back, sides fitted and then a cork padded caul that goes around the rim. the caul is basically the putline of the guitar so it is open in the center.
Author:  JJ Donohue [ Wed Nov 01, 2006 2:34 am ]
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Any pics of your setup, Richard?
Author:  Andy Zimmerman [ Wed Nov 01, 2006 2:35 am ]
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I do it that way. I use the dish as a caul
Author:  Wes McMillian [ Wed Nov 01, 2006 3:05 am ]
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Same here. I placed my back in the radius dish, set my rim (in the mold) on top, set a go-bar in the middle of the back to press it firmly in the dish, then raised my rim set and loosely clamped in to the upper plate of the go-bar deck. I did several dry runs to make sure I would be able to glue (using HHG) and drop the rim set in and position it in time. Worked like a champ! But definitely practice the dry runs before going with the HHG.

And, yes, I used shorter go-bars pressing directly on the linings themselves. I really like how well you can see the fit up. Of course, if you have a good fit up on the brace notches, it should pretty well snap right in place with minimal slop, anyhow.

It also made the cleanup pretty easy. Once the HHG tacked good I was able to move a couple of go-bars at a time and reach inside to clean up the gelled glue, then just put the go-bars back in place until it finished setting up.
Author:  JJ Donohue [ Wed Nov 01, 2006 3:12 am ]
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The top dish makes an ideal caul except for one thing...one can't inspect the glue joint. The issue I'm after, as I believe is Colin's objective, is to see if the glue joint is properly executed as well as providing an opportunity to clean up glue squeeze-out.

My hope is that I can create enough space between the gobar rods to get a hand inside and get to the squeezeout. Ultimately, I'd like to find just the right size bead of thickened HHG to use so there is virtually no squeezeout and still have an effective joint.

I'm building a batch of three guitars presently...I hope to do all the method development work on the backs so that I have a predictable method by the time I glue on the tops... and if I'm lucky, I'll have little or no squeezeout.
Author:  Colin S [ Wed Nov 01, 2006 4:42 am ]
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Thanks guys, it's good to know so many great minds are thinking alike!

JJ let me know how it goes won't you. I'm quite happy to use my go bars directly on the rim, but I will use small hardboard cauls just to protect the edge a bit, though I'll give the cork lined outline a thought. I pretty much know how much glue for the joint, but I like the idea of removing a vouple of bars at a time to do any cleanup needed.

The fact that John How (who is a very wise man) does it this way, though not in the go-bar, is a big selling point.

Colin


Author:  John How [ Wed Nov 01, 2006 5:07 am ]
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Not mine of course but a possibility



Ya think there would be enough clamping pressure? John How39022.548287037
Author:  arvey [ Wed Nov 01, 2006 5:15 am ]
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Unfortunately I don't have a pictureof my setup for the back but here is a pic of glueing the top on after the back was glued. Same set up but the box is still open. The caul that is used on the top in this pic is simply on top of the rim when glueing the back on. Hope that helps a bit.
Author:  John How [ Wed Nov 01, 2006 6:47 am ]
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OK here is a question for all to ponder.
How much pressure does your average cam clamp or even gobar provide. Or better yet how much pressure does it take to make a good glued wood joint. Not that much I'm thinking, if everything fits. Where I'm going is, as I discussed earlier, I'm trying to find a quick and easy method of applying appropriate clamping pressure downward thru a set of sides in the mold to the top or back while it is laying in it's concaved or radiused dish. By quick, I mean instant, and what better way to do this than apply a weight on the side/mold assembly. I'm just wondering how much weight I would need. It would be a simple matter to distribute that weight all around the edge or keep it off the plate and over the rim, and how much quicker could you get than position the top or back and just set it down set it down.
Author:  Mark Tripp [ Wed Nov 01, 2006 8:49 am ]
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I saw a setup recently (can't remember where unfortunately) that had a "frame" built around a radius dish. On this frame was mounted a series of toggle clamps, with cauls attatched to them, in the profile of the body shape of the guitar. Once the fit is correct, the back is layed down, a bead run on the rim set which is then placed on the back, and the toggles clamped down. Might take a bit of tweaking to get it working right, but once it was setup it would be dead on accurate, and very fast too. Would also allow for complete access to clean up any squeeze out. One could even devise a system where the toggles could be moved in and out to accommodate different body shapes. The only reason I've been thinkng about this, is that I'm not yet fast enough with the go-bars to use HHG for gluing the back and top and want to start doing so... If I can remember where I saw this, I'll post a pic.

-Mark
Author:  JJ Donohue [ Wed Nov 01, 2006 10:02 am ]
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Hey John...good question. I cam clamped the bathroom scale to my workbench. Avg.(n=4) force is 28 lbs....range is 27-32 lbs. Not scientific but probably a good ballpark number.

The real question is how much force is required around the perimeter in order to get a good joint. I'll bet there is someone within the 1,000 members who might have good info on that question.
Author:  MSpencer [ Wed Nov 01, 2006 10:15 am ]
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Richard, I like your setup there, did you make your cork padded caul out of a practice top, ply or what?

Mike
Author:  Scooter B [ Wed Nov 01, 2006 10:15 am ]
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"I shoot for 40 seconds as a target time for having the glue applied and plate clamped. "

I think I am in trouble here.....I don't think I could even get a bead of glue around the whole rim in 40 seconds.
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