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I attempted to glue on a maple bridge patch earlier today and couldn't keep the the bridge plate in position without it sliding all over the place. I'm using a go bar deck thats 34.5" between the base and ceiling. The bridge plate caul is 1/2". and the bridge plate is 2-1/2 mm. The rods are 35" with rubber tips, and I'm using titebond original glue. I took a inch off the 36" go-bars so that the tip of the bars that are in contact with the caul is positioned upright instead of being slanted, but the plate continues to slide.

I also held the the bridge plate in place for about 30 seconds before applying the go-bars.

Is there a technique for arranging the go-bars to keep braces, bridge plate, etc... from sliding all over the place? Thanks for any help.

Ron M.

Part of your issue is that the go bar pressure is not being directed straight down .. any lateral force will cause things being glued to move. In order to counteract this, place go bars pointing in from both directions,(ie on an X brace, I place them pointing in towards the centre on each arm .. thus they are counteracting the forces that may cause the brace to move). this will balance the pressure and directional forces, thus keeping things ligned up better. You could also use some stops/cauls, placed dry on the soundboard and held with go bars ... these will align the piece being glued inside the stops.

I glue my X brace first, then fit the bridge patch .. by using the directional force, I place the go bars to make the patch move slightly towards the brace, thus keeping it tighter against it. Use it when you can !!!!

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Often there is too much glue. Sometimes you can clamp temporary dry pieces of wood around the piece to be glued to hold the glued piece in place until good contact is made and the piece holds. Then reomove the temporary pieces before they get glued into place. You can also protect the temporary pieces by wrapping the edge towards the glued piece with Saran Wrap.

What Tony said!!
ya!!

Mike

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Mike Collins

Another good technique for keeping the bars in place is to tack some carpet to the top inside of your go-bar deck. This will keep the bars in place at the top. But you still need to follow the advice from others for keeping the braces from sliding on you. Good luck!

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Tracy
http://www.luthiersuppliers.com

Ron,

I do what Tony does, and I use hot hide glue, which doesn't let the part scoot around.

From your post, it appeared to me that you shortened the go-bars so that they would have less curve. If so, you needn't have worried about the curve causing the bar to put horizontal forces on the workpiece and causing it to shift. What matters in the bars is the x/y relationship between the top of the bar and the bottom of the bar where they make contact. The force involved actually works in a straight line between those two points, not along curve. In other words, if the top of the bar contacts the top of the deck directly above where the bottom of the bar contacts the caul over the workpiece, there will be no horizontal forces on the caul regardless of the amount of curve in the bar.

Hope this helps rather than confuses.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

Thanks TonyKarol for the quick and informative response. And thanks to everyone for your responses. I've learned quite a bit.


Actually, that makes a lot of sense. And you're right, i did shorten the bar to reduce the curve. Thanks for the detailed explanation.


Thanks Todd for explaining deflection and spring energy.

Ron M

You can also let the glue tack up just a touch before you put the parts together. That helps too.

BTW, LMI white "grabs" a little faster than titebond.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

One thing I've done that works is to cut some pieces of sheet metal and place them along the edges of your piece. They can be taped down with the regular blue painters tape which will help keep the piece from sliding as well as make sure your alignment is perfect before adding glue. They're really easy to work with and do a great job holding the work in place.

I started out gluing the bridge plate first but never solved this problem in a totally satisfactory way and finally went to what Tony does. I'll dry clamp the bridge plate, fit the X and mark it with the bridge plate in place. Remove the plate, glue the X, and then glue the plate using the go bars so if they do want to move it, it's against the X. Like Pat said, hide glue does make it a lot easier.
Terry

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Thanks everyone for the addtional tips. Brock in addition to letting the "glue tack up" as per your suggestion, I clamp some stops in place as suggested earlier, and it worked out fine.

I'm guessing that the above tips ( caul stops etc...) can be applied to braces as well.

Attached is a photo of the glued bridge plate. Thanks for all the help.


Ron M.

Ron, You've got way to much bow in those go-bars. You should shorten the go-bars so they are only about an inch longer than the gap, as someone previously mentioned.

Also, it does not look like you are placing the tops of the bars directly over the bottom. This will cause a sideways vector of force that is the reason you are getting slippage.

Hi Barry,
Could you elaborate what you mean when you say "an inch longer than the gap"?

Also, should I have used a bridge plate caul?

Thanks,
Ron M

He is saying that your go-bars need to be no longer than the distance from the top deck or surface you use to the top of the part you are clamping plus 1"

In other words when in claped position if you draw a sting from end of go-bar to end of go-bar there should be no more than 1" of bow in the rod when clamped.

Once you cause the go-bar to bow the least little amount you have reach the max clamping pressure. IE max colum loading. The more bow added does not increase the clamping pressure it adds only a restraind spring load. This spring load will often case a shift in the position of the go-bar in the path of least resistance causing it to come loose and fly out.

Your picture show what looks to be over 4"

Michael, thanks for taking the time to draw the illustration. I understand now.
And thanks Barry for pointing that out.

Actually the picture is deceiving, I should have posted a better one. The distance between the top and bridge plate and the ceiling of the deck is 34-1/4" and the rods are 35-1/8" so the rods are actually 1/8" short. I'll post another pic.

I'm still glad that Barry pointed that out, because i was trying to figure out how to determine the length of the rods for clamping various parts. Now i know, Thanks

Ron M.

just for info.

As your rods get shorter for various use the amount of bow needs to decrease as well to keep the spring loading down.

Like I said earlier, any length past the clamp length plus a tad of bow is excess not being used to generate clamping force. I personally only induce 1/2"-3/4” of bow to my long rods for brace clamping. My short rods for top and back to rim clamping I induce about 1/4" to 3/8" max bow. As the rods get shorter, the greater the spring loading per inch of bow.

Thanks again Michael for the all the good info. I'm sure I'll get a lot of use from the go bar deck that I built, now that I have been told how to properly use It.

Ron M.

Thanks Todd for all the useful info.

Ron M.