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Jigs for arching the bottom of the bridge?
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Author:  Alain Moisan [ Tue Jun 11, 2013 3:45 pm ]
Post subject:  Jigs for arching the bottom of the bridge?
Hi group.

As many of us, I currently put the arch on the bottom of my bridges by sanding the bridge over an arched plate with sandpaper stuck to it. But I find this task tidious and I'm trying to design a jig that would use a router. What I have in mind is something similar to the jigs that are used to make radius dish. But before I go ahead and start prototyping, I was wondering if any of you guys had something equivalent.

Thanks for letting me know!
Author:  Kent Chasson [ Tue Jun 11, 2013 4:08 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Have you tried making a sanding block big enough so that you can sand across the grain? If you can get an 8" stroke with 80 grit paper, sanding goes very quickly.

When I built a large batch of bridges for another builder, I seem to remember making a curved plate that went on the platen behind the belt of my vertical belt sander. I'll look around and see if I can find it.
Author:  Pmaj7 [ Tue Jun 11, 2013 4:20 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
I've been thinking about the same thing. Currently, I chisel, scrape, sand.

It doesn't need to be domed, just a straight radius and then touched up on a domed block.
Author:  WaddyThomson [ Tue Jun 11, 2013 5:32 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
I did that for my 4x36 belt sander. It's a scrap of HOG wider than a bridge and a bit longer. I tape it under the belt and adjust the tension. Takes about 2 minutes to radius a blank. I do it before cutting out the wings and such. It fits perfectly.
Author:  Alain Moisan [ Wed Jun 12, 2013 8:14 am ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Kent Chasson wrote:
When I built a large batch of bridges for another builder, I seem to remember making a curved plate that went on the platen behind the belt of my vertical belt sander.

WaddyThomson wrote:
I did that for my 4x36 belt sander. It's a scrap of HOG wider than a bridge and a bit longer. I tape it under the belt and adjust the tension. Takes about 2 minutes to radius a blank. I do it before cutting out the wings and such. It fits perfectly.

Thanks Kent and Waddy! That sounds like a plan. Much easier than the router jig I had in mind.

Todd Stock wrote:
Takes me 2-3 minutes to sand the bridge...6" x 10 plate with 80 grit...if it takes much longer than that, the sandpaper is too fine.

With a 6 inches long EIR bridge, I can understand. But I'm trying to radius the bottom of a 7 1/4" long Honduran rosewood bridge. So it is a bit more work.
Author:  WaddyThomson [ Wed Jun 12, 2013 9:20 am ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
One quick tip. When sanding the bottom of the bridge, flip it around from time to time, otherwise, you get some unevenness from all sanding in one direction.
Author:  jfmckenna [ Wed Jun 12, 2013 11:49 am ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
I used to just glue them on straight till I read some posts about it in this forum. BTW I still don't think anything is wrong gluing them on straight. But for kicks I thought I would try it. I used a scraper and eye balled it to get it close then used the double stick sand paper trick and then back to the scraper to clean off the grit marks and it really only took 5-10 minutes tops.

I guess what I am saying is that jigging up something like that seems unnecessary. The guitar top itself is the jig idunno
Author:  Alain Moisan [ Wed Jun 12, 2013 12:16 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
jfmckenna wrote:
I used to just glue them on straight till I read some posts about it in this forum. BTW I still don't think anything is wrong gluing them on straight. But for kicks I thought I would try it. I used a scraper and eye balled it to get it close then used the double stick sand paper trick and then back to the scraper to clean off the grit marks and it really only took 5-10 minutes tops.

I guess what I am saying is that jigging up something like that seems unnecessary. The guitar top itself is the jig idunno


On a steel string, where the area you will use as a sanding block is backed by two legs of an X brace and a bridge plate, it makes sense. But on a classical where the top is considerably thinner and more flexible, and trying (as I've stated) to shape a piece of hard honduran rosewood, it doesn't work too well. The top deforms too much as you apply pressure while sanding.
Author:  Alain Moisan [ Wed Jun 12, 2013 12:42 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Filippo Morelli wrote:
Good quality 80 grit paper. Won't matter what wood - couple minutes.


It takes me about 10 minutes to get the entire bridge radiused. Then about 5 minutes for touch-ups to get a good fit.

I'd like to bring this to 2 minutes.

Call me lazy! (Or efficient...)
Author:  Alain Moisan [ Wed Jun 12, 2013 1:24 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Filippo Morelli wrote:
Be lazy! I agree!


I will, promise! ;)
Author:  arie [ Wed Jun 12, 2013 1:53 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
i use 2 of these http://www.luthiersuppliers.com/products/p5.html when doing a dished top:

Image


one with 80 grit and one with 120 grit
Author:  Alain Moisan [ Wed Jun 12, 2013 2:07 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Thanks Arie, but that is already what I use (I made my own boards though...). What I'm looking for is more towards some motorised jig...
Author:  arie [ Wed Jun 12, 2013 2:18 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Image
Author:  Alain Moisan [ Wed Jun 12, 2013 2:22 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
:D
Author:  Alain Moisan [ Wed Jun 12, 2013 3:07 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Todd, I'm not looking for information on how I suck doing it manually. I'm looking for ideas for a motorised jig.

But thanks anyway.
Author:  Wes McMillian [ Wed Jun 12, 2013 5:05 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
If you already have a convex dish, as you said, mount it on something that goes roundy-round. Disc sander, drill press..........
Author:  SteveSmith [ Wed Jun 12, 2013 5:38 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Todd Stock wrote:
...key is ... and an insert to place in saddle slot...


Now that is a great common-sense idea, the kind that makes me wonder why I didn't think of it - thanks Todd!
Author:  Alain Moisan [ Wed Jun 12, 2013 6:07 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Wes McMillian wrote:
If you already have a convex dish, as you said, mount it on something that goes roundy-round. Disc sander, drill press..........


I thought of this but it's easier said than done. With the RPM that a disc sander has, unless the radiused board is perfectly centered (and I mean "perfectly"), you're in for some heavy vibrations. And although the RPMs on a drill press are slower, the problem remains. Chances are I'd be trying to sand a bridge on a flapping board!
Author:  martintaylor [ Wed Jun 12, 2013 8:27 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
arie wrote:
Image



Love it Arie, I now have a use for the old potters wheel that my wife wanted me to throw out! I knew there was a good reason for hoarding it.
Author:  Kevin Waldron [ Wed Jun 12, 2013 9:33 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Just a thought, but why couldn't you make something along the same lines to where the bridge is fixed and the radius guides are reversed to make the proper arch and you simply route the bridge to the radius.

Blessings,

Kevin
Author:  Robert Renick [ Wed Jun 12, 2013 10:00 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
A collar on the spindle sander, 60 grit. I think to avoid needing a backer, you can do the curve on the bottom first, then all subsequent shaping jigs need the shape to match the bottom.
Author:  guitarjtb [ Thu Jun 13, 2013 4:39 am ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Filippo Morelli wrote:
Todd Stock wrote:
Ebony or BRW...and i do enough repair work to have done my share of longer bridges...key is decent abrasive and an insert to place in saddle slot...


Saddle slot insert to hold the bridge while sanding? Great idea, I never thought of it! Will try on the next one ....

Filippo



I have a 2 1/2" x 2" x 12" block with a 15' radius on one side and a 25' radius on the other. Very easy to make by cutting close with the band saw and finishing off in a radius dish. 80 grit Mirka is stuck to each side. Usually, I am sanding the radius into the bridge blank before I put in the bridge slot. So, I use a 2" x 4" piece of 3/4" plywood with 2 small dowels exposed that will fit into bridge pin holes. This gives you a great handle to hold onto the bridge/bridge blank without sanding off the finger tips. Never takes more than 2 or 3 minutes to sand the radius into the bridge so I've not seen the need for machinery to do this. Kinda like fishing for bream with dynamite.
Author:  Alain Moisan [ Thu Jun 13, 2013 8:37 am ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Kevin Waldron wrote:
Just a thought, but why couldn't you make something along the same lines to where the bridge is fixed and the radius guides are reversed to make the proper arch and you simply route the bridge to the radius.

That's what I initially had in mind, but unless I have a dedicated router for this, it would take more time to setup the jig than to sand manually. So it would sort of defeat the purpose.

Robert Renick wrote:
A collar on the spindle sander, 60 grit. I think to avoid needing a backer, you can do the curve on the bottom first, then all subsequent shaping jigs need the shape to match the bottom.

Hey Robert, thanks. That's also a plan. And indeed I planned on putting the radius first, and then shaping the bridge. This is how I do it when sanding manually anyway.

James Burkett wrote:
Never takes more than 2 or 3 minutes to sand the radius into the bridge so I've not seen the need for machinery to do this. Kinda like fishing for bream with dynamite.

Like I previously pointed out, for small steel string bridges, hand sanding works fast. It's the extra 1 1/4" that I hate. It makes you remove much more material.
Author:  Robert Renick [ Thu Jun 13, 2013 8:58 am ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
That simple collar on the spindle sander was made for the operation shown, but has found many other uses. A great way to shape without any tear out on anything, and setup is just drop the throat plate in.
Author:  Kevin Waldron [ Thu Jun 13, 2013 1:17 pm ]
Post subject:  Re: Jigs for arching the bottom of the bridge?
Filippo,

Think that you would have to make a caul for every style bridge. Your radius I'd think would remain constant for most instruments, and I don't think that you would have that many different bridges, even with our cnc files we probably don't have over 20 total.......

For a caul you can use wax paper and canned urethane foam insulation ( Lowes, Home Depot ) held in a clamp while it dries.

Blessings,

Kevin
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