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Cauls for clamping a bridge
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10137&t=49758		 Page 1 of 1
Author:  Conor_Searl [ Tue Sep 26, 2017 10:49 pm ]
Post subject:  Cauls for clamping a bridge
Hi, I was just getting ready to do a dry run on my clamping set up to re-glue a bridge onto a Yamaki acoustic I'm repairing, and realized the x-braces run right under the wings of the bridge.

I was planning on using 3 Ibex clamps, one in the middle of the bridge with a caul over the top of the raised part of the bridge and a small caul underneath on the bridge plate so the clamp clears the x-braces, as well as a clamp on either wing of the bridge with a small caul on either wing, this is where my plan hit the snag. The braces run right under the wings. Can I put the clamp right on the brace or is this trouble waiting to happen?

Conor
Author:  johnparchem [ Tue Sep 26, 2017 11:27 pm ]
Post subject:  Re: Cauls for clamping a bridge
Make a caul that can fit over the xbrace. It you do not have the brace pattern, you can put a light inside and trace how the x brace crosses. Transfer that to the caul. You can use a razor saw and a chisel to cut the channels for the brace. I currently use a vacuum clamp, but when I used clamps I would make a caul for each guitar type I make.
Author:  Conor_Searl [ Wed Sep 27, 2017 12:06 am ]
Post subject:  Re: Cauls for clamping a bridge
So what do you mean by putting a light inside? Do you mean you put the light inside the guitar, it shines through the top and you can see the silhouette of the x brace?!?

It's late and I'm confused...

Conor
Author:  johnparchem [ Wed Sep 27, 2017 1:55 am ]
Post subject:  Re: Cauls for clamping a bridge
Conor_Searl wrote:
So what do you mean by putting a light inside? Do you mean you put the light inside the guitar, it shines through the top and you can see the silhouette of the x brace?!?

It's late and I'm confused...

Conor

Yes! You can see the x brace through the top even a good flash light will work.
Author:  Hesh [ Wed Sep 27, 2017 4:20 am ]
Post subject:  Re: Cauls for clamping a bridge
You can make as John said adapters that get attached (masking tape) to the lower, interior jaw of the clamps that go on the wings. Cutting board material cut in a small block with a matching "V" in it and then attached to the clamp works well. I often just tape leather to the lower brace jaw for something where there is no chance of glue hitting it. If there is any chance of the lower jaw getting glued in place say for a crack that goes through the body tape some waxed paper on the lower jaw too.

FYI the Stew-Mac bridge clamping caul is frequently used to clamp bridges (obviously...;) ) but with no support under the wings where they cross the X legs. You do have to be mindful with this style clamp that as you tighten the wings you can raise the center section inadvertently.

Consider making a masking tape well of sorts top side to locate the bridge quickly when it wants to be skating on wet glue.

Also consider using HHG for bridges and learning to preposition clamps, preheat the bridge and patch, work quickly and have the ability to properly locate the bridge and snug the clamps in the 15 seconds or so that HHG likes for open time. It takes some thought, practice and a desire to use an excellent choice of glue for bridges, HHG but it's worth it. Titebond original works too but I greatly prefer HHG. To be clear I would not use the bottled, rasta impasta Franklin hide glue for bridges but instead actual hot hide glue mixed properly, fresh and heated to 145F.

Lastly we like to expand the wood-to-wood gluing area to just short of the bridge perimeter, perhaps .005" short of the perimeter.

Lots of great threads here under "bridge reglue" for the asking. Learn about rabbiting the bridge perimeter, using a scraper to fit the bridge to tops, how to clean the bridge patch and how much torn up wood is acceptable and how much is not.
Author:  Bryan Bear [ Wed Sep 27, 2017 10:13 am ]
Post subject:  Re: Cauls for clamping a bridge
I have a bunch of thermo-plastic from an old job that I use to make cauls. It is not unlike "friendly plastic" so I assume that would work too. When bracing the top, I make a (or use an existing) caul that fits roughly with the bracing and bridge plate then put some thero-plastic on and press it in to make a good fitting caul. Remember to put plastic wrap between the top and the plastic so it doesn't stick. The nice thing is, you can still do this even if you forget to make the caul before you close the box DAMHIK.
Author:  Freeman [ Wed Sep 27, 2017 10:21 am ]
Post subject:  Re: Cauls for clamping a bridge
Even tho I'm a very small volume repair person I do see a fair number of bridges that need to be reglued so I built a special caul for the inside. It is made of UHMW (an industrial plastic) so glue that goes thru the pin holes won't glue it to the inside of the guitar. It has two slots that I put 3/16 bolts thru, they are further slotted so I can thread a nut on them and adjust for the spacing of the holes. It is also thick enough that there is no danger of crushing a brace with my clamps. I've actually made a couple of them for different spacing of the X brace - they look something like this

Image

Image

The bolts align the bridge with respect to the existing pin holes and applies some clamping pressure - I usually use three deep clamps in addition.

Image

I do have a simple CADD drawing of the caul - you could take that to a machinist and have them make one for you.

ps - if you use wood or something else for the caul face it with waxed paper - glue will run thru the holes and make it permanent. With my caul you still have to clean the glue out of the holes and re-ream them - sometimes the bolts will get glued in place and I have to reach inside with a small box wrench and unscrew them - the head of the bolts stands proud of the UHMW so I can do this.
Author:  Conor_Searl [ Wed Sep 27, 2017 11:25 am ]
Post subject:  Re: Cauls for clamping a bridge
Freeman, that's awesome, thank you for the pictures. So is your caul sitting on top of the braces inside the guitar, or does it fit in between on the bridge plate? And if so are the outside clamps sitting on braces inside the guitar?
Author:  Pmaj7 [ Wed Sep 27, 2017 12:24 pm ]
Post subject:  Re: Cauls for clamping a bridge
Freeman wrote:
Even tho I'm a very small volume repair person I do see a fair number of bridges that need to be reglued so I built a special caul for the inside. It is made of UHMW (an industrial plastic) so glue that goes thru the pin holes won't glue it to the inside of the guitar. It has two slots that I put 3/16 bolts thru, they are further slotted so I can thread a nut on them and adjust for the spacing of the holes. It is also thick enough that there is no danger of crushing a brace with my clamps. I've actually made a couple of them for different spacing of the X brace - they look something like this

Image

Image

The bolts align the bridge with respect to the existing pin holes and applies some clamping pressure - I usually use three deep clamps in addition.

Image

I do have a simple CADD drawing of the caul - you could take that to a machinist and have them make one for you.

ps - if you use wood or something else for the caul face it with waxed paper - glue will run thru the holes and make it permanent. With my caul you still have to clean the glue out of the holes and re-ream them - sometimes the bolts will get glued in place and I have to reach inside with a small box wrench and unscrew them - the head of the bolts stands proud of the UHMW so I can do this.
Once you have your middle clamp in place, you could probably just take out the bolts before it's dry. Basically just using them for positioning.
Author:  Freeman [ Fri Sep 29, 2017 2:40 pm ]
Post subject:  Re: Cauls for clamping a bridge
Conor_Searl wrote:
Freeman, that's awesome, thank you for the pictures. So is your caul sitting on top of the braces inside the guitar, or does it fit in between on the bridge plate? And if so are the outside clamps sitting on braces inside the guitar?


It sits on the bridge plate in between the X. Clamping the ends of the wings is always a fit and fiddle proposition. Most of the time the extend over the X and sometimes a bit beyond, as in this case. Those outside clamps have fairly long adjusters on both sides of the clamp - I think in this case they are actually resting on the top outside of the X (which is why the are barely on the wings). I have also made little cauls that extend out from the two bolts and push down on the wings - sorta like the StewMac thing does. Sometimes I have (gently) clamped against the X but I don't like doing that.

Its not a perfect design - one obvious flaw is that it can't be used on a new guitar that doesn't have the pin holes drilled until after the bridge is on nor on a pinless bridge.
Author:  BradHall [ Sat Sep 30, 2017 12:15 am ]
Post subject:  Re: Cauls for clamping a bridge
Instead of waxed paper I use clear cellophane packaging tape on cauls. I have yet to find any glue, hide, tightbond, or c.a. That will stick to it. I also use the tapered end of cheap artist brushes to position the bridge. (Found a bundle of about 20 at a craft store for a buck.) They end up about 2" long when cut flush with the top of the bridge pin hole. A little wax insures the hide glue won't stick to it, and it's easy to push up from the inside after the glue sets. And the brushes are more usable with shorter handles.
Author:  Freeman [ Sat Sep 30, 2017 8:54 pm ]
Post subject:  Re: Cauls for clamping a bridge
I get some kind of interesting repairs. This is a Mexican vihuela with a loose bridge. There is no bridge plate so the big hunk of UHMW will be my inside clamping caul (it just fits inside the sound hole), there are three shaped cauls for the bridge itself

Image

Image

This one is even bigger, a guitarron (bass guitar used in Mariachi music) - my 6 inch clamps won't reach the bridge so I'm going to have to come up with something else. They already tried putting some screws thru from the inside but its only the top so that failed almost immediately. I think I'm going to fit a bridge plate and then use some studs to help hold it one. I'm just trying to figure out how to jury-rig some 9 inch clamps

Image
Author:  sdsollod [ Sun Oct 01, 2017 10:39 am ]
Post subject:  Re: Cauls for clamping a bridge
I have been using the LMI Fox bridge clamp and have been happy with it...
http://www.lmii.com/products/tools-serv ... dge-clamps
Author:  Pmaj7 [ Sun Oct 01, 2017 11:42 am ]
Post subject:  Re: Cauls for clamping a bridge
Freeman wrote:
There is no bridge plate so the big hunk of UHMW will be my inside clamping caul

Are there any braces?!
Author:  Conor_Searl [ Sun Oct 01, 2017 5:14 pm ]
Post subject:  Re: Cauls for clamping a bridge
So I reglued the bridge, after fixing a cracked brace, regluing two loose braces, and gluing and clamping a couple spots on the bridgeplate that seemed to have no glue. The repair looks good, and seems to be holding fine. But the guitar doesn't really sound very good. I'm feeling a little lost as I have no idea what the guitar sounded like before I got it. The bridge had lifted to the point where there was no tension on the strings when I got my hands on it.

It's a Yamaki with a really thin cedar top. There's no buzzing, I have a little over .010" relief, the nut is comfortable, but the saddle is a bit on the high side, we're at around 7/64 at the 12th fret. My D-18 is just over 3/32 so that seems pretty close, (although maybe luthiery land 1/64 might as well be the grand canyon.) I noticed the saddle leans forward, which seems like it might be the culprit if the pressure is pushing the saddle forward, the saddle can't be transferring much energy into the top of the guitar. So the guitar sounds kind of brash, tubby, and uninspiring. I strung up with phosphor bronze strings, which seem like they may be a little overly bright for this guitar, and the tone might settle down once the strings mellow. Also I typically am not a fan of cedar topped guitars, so perhaps what I'm hearing is simply the sound of an old thin cedar top.

I realize much of what I'm asking is subjective, but since I've never re-glued a bridge or fixed braces before, and have no experience with this particular guitar in working order I'm wondering if there is something obvious I've missed in this repair that other more experienced luthiers may hear in my description and say "no it sounds like you missed another brace or your glue joint is bad or such and such..." or "nope that just sounds like an old yamaki guitar..."
Author:  Freeman [ Sun Oct 01, 2017 5:56 pm ]
Post subject:  Re: Cauls for clamping a bridge
pat macaluso wrote:
Freeman wrote:
There is no bridge plate so the big hunk of UHMW will be my inside clamping caul

Are there any braces?!


One ladder just below the sound hole. Top is laminated, some sort of mystery wood. No other braces.

Many of these Mariachi instruments are very cheaply made and the kids in the HS Mariachi program are pretty hard on them. I get to fix a lot of cracks and sometimes a cracked headstock. Some have tied frets which I get to replace too (the guitarron is fretless).

I believe strongly in this program and do the repairs for the school pro bono. Besides, how often do you get to work on something that looks like this

Image
Author:  david farmer [ Sun Oct 01, 2017 6:44 pm ]
Post subject:  Re: Cauls for clamping a bridge
Did you get it clamped?
If you need an excuse for acquiring vacuum here's your chance!
Author:  Freeman [ Sun Oct 01, 2017 7:39 pm ]
Post subject:  Re: Cauls for clamping a bridge
Conor_Searl wrote:
... have no experience with this particular guitar in working order ...."


That is a significant statement. You don't know if the sound changed so its really not possible to answer your question. However, a couple of thoughts. Your guitar seems to have suffered a lot of fairly major failures - bridge, bridge plate, three braces, hazy finish, loose saddle. The action is slightly high (you don't say which string that is or how much saddle is sticking out of the bridge) - so we don't know what the neck angle is or whether the neck block is tight. Is the top bellied (or sunk)? Are all the other glue seams tight?

Has this guitar been thru a serious traumatic event (hot car trunk, high or low humidity, hurricane...)?

The repairs you talk about are difficult to do - its darn hard to fix a brace or bridge plate thru the sound hole - so yes, there is a change you missed something or just plain screwed it up. In order to get good gluing you need to separate the parts, clean every bit of old glue off, spread a layer of the new glue (and use the right glue) and apply enough clamping pressure.

I'm not familiar with Yamaki guitars - its very possible that they simply weren't great sounding in the first place.

Remember that most people feel that cedar topped guitar have a warm or mellow tone, and most cedar topped guitars are smaller bodies or classicals. If you are used to a big boomy Martin mahogany dread then it might simply be that the guitar doesn't sound like you like. It might have always sounded that way - particularly if you didn't hear it before.

Your setup specs are a bit high but probably won't change the sound that much. However your tilted saddle is a cause for concern for two reasons - it needs to sit snugly in the slot for optimal transmission of the string vibration to the top and you risk the very real chance that the bridge will split. Make a new saddle

Many people think PB strings are more mellow than 80/20, not bright. However that is a quick and cheap thing to change

So many little things affect the sound of a guitar, its pretty hard to evaluate on an internet discussion forum.
Author:  Conor_Searl [ Mon Oct 02, 2017 12:36 pm ]
Post subject:  Re: Cauls for clamping a bridge
Freeman wrote:
Conor_Searl wrote:
... have no experience with this particular guitar in working order ...."


Your setup specs are a bit high but probably won't change the sound that much. However your tilted saddle is a cause for concern for two reasons - it needs to sit snugly in the slot for optimal transmission of the string vibration to the top and you risk the very real chance that the bridge will split. Make a new saddle



Thanks Freeman, the old saddle was pretty loose, it wouldn't have fallen out on its own, but I could wiggle it back and forth with my finger while it sat in the slot. I carved a new one this morning that fits nice and snug, and is a bit lower than the previous one, the guitar plays better now, and sounds great.
Author:  Freeman [ Mon Oct 02, 2017 2:11 pm ]
Post subject:  Re: Cauls for clamping a bridge
Conor_Searl wrote:
Thanks Freeman, the old saddle was pretty loose, it wouldn't have fallen out on its own, but I could wiggle it back and forth with my finger while it sat in the slot. I carved a new one this morning that fits nice and snug, and is a bit lower than the previous one, the guitar plays better now, and sounds great.


Just curious, if the action is what you would consider playable, how much saddle is sticking out of the slot?
Author:  Conor_Searl [ Mon Oct 02, 2017 3:55 pm ]
Post subject:  Re: Cauls for clamping a bridge
Freeman wrote:
Conor_Searl wrote:
Thanks Freeman, the old saddle was pretty loose, it wouldn't have fallen out on its own, but I could wiggle it back and forth with my finger while it sat in the slot. I carved a new one this morning that fits nice and snug, and is a bit lower than the previous one, the guitar plays better now, and sounds great.


Just curious, if the action is what you would consider playable, how much saddle is sticking out of the slot?


I'd say about 6/32 - 7/64...
Author:  Freeman [ Mon Oct 02, 2017 4:23 pm ]
Post subject:  Re: Cauls for clamping a bridge
If you are saying it goes from 0.1875 at the low E to about 0.110 at the high, that is quite acceptable. The rule of thumb is that IF you have acceptable action (whatever that means to you) AND at least 1/8 inch of saddle sticking out of the slot THEN your neck angle is OK. The other test is the straightedge on the frets should just touch the top of the bridge.

I was worried with all the other things wrong that you could have neck angle problems too which could contribute to the tone issues. Sounds like this is OK.
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