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  #61  
Old 03-26-2016, 10:34 PM
LouieAtienza LouieAtienza is offline
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Depending on how you construct your top, you may want to wait before sanding the bottom of the bridge. If your top is domed, or you effect a dome by means of bracing, then you'd want to shape the bridge bottom to that dome, which is usually done by taping sandpaper to the guitar and running the bottom of the bridge to match the contour. You can scrape the sand lines off once you're done. If you require a flat surface for a flat top attach sandpaper to a known flat surface.

Of course, without the neck attached to the body, unless you made drawings, you may not know the geometry of he neck/body interface and then you may find your bridge is too high or too low, so it may be better to wait.

On another subject, there is a school of thought on keeping some stiffness in the wings of the bridge. The wings are tapered such that they do not distort as much as a traditional bridge, but tapered (as yours) to reduce the overall weight, basically giving a higher stiffness to weight ratio.
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  #62  
Old 03-27-2016, 02:02 PM
rogthefrog rogthefrog is offline
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Quote:
Originally Posted by LouieAtienza View Post
Depending on how you construct your top, you may want to wait before sanding the bottom of the bridge. If your top is domed, or you effect a dome by means of bracing, then you'd want to shape the bridge bottom to that dome, which is usually done by taping sandpaper to the guitar and running the bottom of the bridge to match the contour. You can scrape the sand lines off once you're done. If you require a flat surface for a flat top attach sandpaper to a known flat surface.
Yes, the bridge is "done" until I have a box, for sure.

Quote:
On another subject, there is a school of thought on keeping some stiffness in the wings of the bridge. The wings are tapered such that they do not distort as much as a traditional bridge, but tapered (as yours) to reduce the overall weight, basically giving a higher stiffness to weight ratio.
Interesting. In my case, I'm just not practiced enough with hand tools to thin the wings in a traditional way (an L shape drop from the saddle to the tip), so I had to do a taper.

I'm hoping to join the top and back today. There's a community wood shop in my town that's willing to thickness sand them for me, so that's pretty exciting.
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  #63  
Old 03-27-2016, 06:01 PM
rogthefrog rogthefrog is offline
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The back has been jointed and glued, and the top has been jointed as well. I'll glue it tomorrow. I don't have enough clamps to do both at the same time.

I read somewhere about ensuring the jointed edge is "fresh" before gluing, i.e. not too much time should pass between the edge planing and the glue being applied. Something about not letting the edge oxidize. Any truth to that? Can a quick scrape right before I glue the top take care of it?
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  #64  
Old 03-27-2016, 07:04 PM
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murrmac123 murrmac123 is offline
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I don't have enough clamps to do both at the same time.
Roger, you don't need clamps to join the top (or the back for that matter).

Just match the two sides , s t r e t c h several pieces of masking tape across the joint then fold the sides back and apply the glue. Close when the glue has been applied and the masking tape will supply all the clamping pressure you need. You do need to weight the top down flat when doing this of course.
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  #65  
Old 03-27-2016, 07:10 PM
rogthefrog rogthefrog is offline
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Roger, you don't need clamps to join the top (or the back for that matter).

Just match the two sides , s t r e t c h several pieces of masking tape across the joint then fold the sides back and apply the glue. Close when the glue has been applied and the masking tape will supply all the clamping pressure you need. You do need to weight the top down flat when doing this of course.
Thanks--the clamps are just holding boards on top of the joint to keep the plates flat. I'm clamp deprived.

I do like the tape trick--will try with the top!
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  #66  
Old 03-27-2016, 09:33 PM
charles Tauber charles Tauber is offline
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Originally Posted by rogthefrog View Post
I read somewhere about ensuring the jointed edge is "fresh" before gluing, i.e. not too much time should pass between the edge planing and the glue being applied. Something about not letting the edge oxidize. Any truth to that?
Yes, but it probably makes no difference on a joint that is pretty freshly machined.

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Can a quick scrape right before I glue the top take care of it?
If it is a close fitting joint - ideally, what you want - then no. The scraper will ruin the mating of the joint. If it is a good joint, leave it be.

Getting an invisible seam in a top is an art unto itself and can drive someone new to the process crazy in the pursuit of that joint. Getting the joint invisibly tight all along the length of the joint can be like a dog chasing its tail.
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  #67  
Old 03-27-2016, 09:50 PM
LouieAtienza LouieAtienza is offline
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I personally use the tape clamps (green automotive painters' tape). I tape both sides to put even pressure, and it doesn't take a lot. If I join the boards right they stay flat and straight, and I just put a binder clip on each end of the joint and hang it on a rope I have running across the shop for hanging stuff.
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  #68  
Old 03-27-2016, 10:50 PM
rogthefrog rogthefrog is offline
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Originally Posted by charles Tauber View Post
Yes, but it probably makes no difference on a joint that is pretty freshly machined.



If it is a close fitting joint - ideally, what you want - then no. The scraper will ruin the mating of the joint. If it is a good joint, leave it be.

Getting an invisible seam in a top is an art unto itself and can drive someone new to the process crazy in the pursuit of that joint. Getting the joint invisibly tight all along the length of the joint can be like a dog chasing its tail.
I spent about 3 hours on the top joint this afternoon and thought I would go crazy.

The back joint didn't turn out well. The joint is solid, but the two halves didn't mate in a perfectly level fashion, so one plate is higher or lower than the other in a couple of spots along the joint. I'll cut the glue joint tomorrow and try again, using the tape techniques suggested here so I can keep an eye on the action before the glue sets.
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  #69  
Old 03-27-2016, 11:08 PM
charles Tauber charles Tauber is offline
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It is difficult (impossible?) to have the two halves glue together so that they are exactly flush along the entire joint. Usually, one glues the halves together prior to final thicknessing to allow for that misalignment. Join first, thickness sand/plane to final thickness afterwards.

Variations on the masking tape method work. My preference is the traditional rope and wedges method.

This is the Rolls Royce version of it: nice, but overkill. A simple version - six lengths of 1x2's, some rope and three wooden wedges - is about $10 to make yourself. (Don't forget to wax the faces of the 1x2's so they don't get glued to the top or back.)

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  #70  
Old 03-27-2016, 11:20 PM
LouieAtienza LouieAtienza is offline
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Originally Posted by rogthefrog View Post
I spent about 3 hours on the top joint this afternoon and thought I would go crazy.

The back joint didn't turn out well. The joint is solid, but the two halves didn't mate in a perfectly level fashion, so one plate is higher or lower than the other in a couple of spots along the joint. I'll cut the glue joint tomorrow and try again, using the tape techniques suggested here so I can keep an eye on the action before the glue sets.
It's tough if the boards are exactly the same thickness, let alone not. After you tape you should feel the joint, then use a small hammer and a block of wood to flush it. It doesn't take a lot of force. Just get one side flush. It's possible to sand it out with a thickness sander, but my experience is that the wood can move later on if you try to flatten a joint that has more than a couple unflush spots, and have to take it down thinner than wanted.
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  #71  
Old 03-27-2016, 11:55 PM
rogthefrog rogthefrog is offline
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Charles: I was thinking thickness planing would take care of the back, but it feels wrong. My first two joints actually turned out a lot better and flat, even though the first back wound up warping a lot. I think I should do better. Plus it's an opportunity to practice my shooting board technique.
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  #72  
Old 03-28-2016, 06:13 AM
charles Tauber charles Tauber is offline
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Charles: I was thinking thickness planing would take care of the back, but it feels wrong.
"Feels wrong" is what way?
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  #73  
Old 03-28-2016, 10:38 AM
Pat Foster Pat Foster is offline
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Originally Posted by charles Tauber View Post
<snip>

This is the Rolls Royce version of it: nice, but overkill. A simple version - six lengths of 1x2's, some rope and three wooden wedges - is about $10 to make yourself. (Don't forget to wax the faces of the 1x2's so they don't get glued to the top or back.)

Here's the simple version of what Charles showed. The black cleats come from a sailboat, not necessary, but convenient. The surfaces of the tourniquet that contact the glued seam are covered with clear tape so they don't stick. The cords are crisscrossed and secured, then the wedges are pushed in with a couple of slugs from the heel of the hand, which probably yields hundreds of pounds of clamping force on the joint.


Pat
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  #74  
Old 03-28-2016, 11:34 AM
rogthefrog rogthefrog is offline
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Originally Posted by Pat Foster View Post
Here's the simple version of what Charles showed. The black cleats come from a sailboat, not necessary, but convenient. The surfaces of the tourniquet that contact the glued seam are covered with clear tape so they don't stick. The cords are crisscrossed and secured, then the wedges are pushed in with a couple of slugs from the heel of the hand, which probably yields hundreds of pounds of clamping force on the joint.


Pat
Great!

I saw a YouTube demo by a Scottish luthier who just has a channel routed in the bottom bars where the glued joint goes, so the glue doesn't make contact.
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  #75  
Old 03-28-2016, 04:20 PM
rogthefrog rogthefrog is offline
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So back to square one with the back. I cut through the joint this morning.

After watching a bunch of YouTube videos on shooting boards and plate joining, it struck me that my "workbench" and shooting board arrangement are part of the problem. The "workbench" is actually a bathroom vanity frame I built a while ago that didn't wind up being used. It's very small (20x24 or so) and wobbles.

So I busted out the table saw and started making a number of jigs that should help. A properly sized shooting board is done, as are wedges and sticks for joining. I also cut the materials to make radiused dishes for the top and back. I should be able to do the joining again tomorrow.

Thanks everyone again for the invaluable knowledge you're sharing with me.
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