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| Flat bottom birdge on radius top? http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=28922 |
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| Author: | Lindamon [ Sun Sep 05, 2010 8:45 pm ] |
| Post subject: | Flat bottom birdge on radius top? |
Probably talked about before here, but I am new. I've done it with 4 guitars now, and can't think of a good way to put a 28' radius on the bottom of a bridge, or if it's necessary. Using titebond right now, but will be switching to hide soon. Thoughts? |
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| Author: | Donald V [ Sun Sep 05, 2010 9:07 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
Damon, Go to the tutorials section and do a search using the terms radius and bridge. There is an excellent tutorial there that will show you how to do it. Good luck! |
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| Author: | Corky Long [ Sun Sep 05, 2010 9:08 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
Definitely a good idea to radius the bottom of that bridge. The easiest way is to put a piece of sandpaper, face up, on the top, where the bridge will be glued. Hold it in place and sand the bridge using the top as your inverse radius template. Works like a charm. (Then remove the finish on the top where you'll be gluing the bridge). |
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| Author: | jsmith [ Sun Sep 05, 2010 10:52 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
To avoid risking a scratch (or more) on your finish, use Corky's method, but do it before going through the finish process. |
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| Author: | Howard Klepper [ Sun Sep 05, 2010 11:12 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
Corky Long wrote: Definitely a good idea to radius the bottom of that bridge. The easiest way is to put a piece of sandpaper, face up, on the top, where the bridge will be glued. Hold it in place and sand the bridge using the top as your inverse radius template. Works like a charm. (Then remove the finish on the top where you'll be gluing the bridge). If you can do this without your top flexing a lot, the guitar is overbuilt. Use your radius dish (if you are working with one) to make a solid wood block with the convex radius. Then sand on that. |
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| Author: | WaddyThomson [ Mon Sep 06, 2010 8:31 am ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
I radius my bridge blanks before I make the bridge. I use a 25' radius form under my belt sander, and rough sand to the right radius. Then, before I glue the bridge on, I can lightly sand on the top to make a perfect fit, but don't have to press very hard because I don't have much wood to remove. Only takes a couple of minutes to finish sand to fit. I put marks all over the bottom of the bridge, and sand till they are gone. Here is my rough sanding method. Attachment: P1030686 (Large).JPG Attachment: P1030687 (Large).JPG Here is how it sits on the top, before finish sanding. Attachment: P1030790 (Large).JPG
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| Author: | Hesh [ Mon Sep 06, 2010 8:41 am ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
Here you go: http://www.lenaweelutherie.info/page6/page21/page21.html |
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| Author: | woody b [ Mon Sep 06, 2010 9:12 am ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
I've got a hunk of spruce I sanded in my radius dish like Howard said. I love the belt sander idea Waddy. |
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| Author: | Lindamon [ Mon Sep 06, 2010 11:02 am ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
So cool! Thanks to all of you for the suggestions! Hope you all have a great labor day! Damon |
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| Author: | tim88 [ Mon Sep 06, 2010 11:05 am ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
Waddy, very cool idea with the belt sander!!! |
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| Author: | WaddyThomson [ Mon Sep 06, 2010 1:05 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
Thanks! I do it because my first couple of bridges, looked funny after I made them, then sanded the dome. It made the wings too thin at the corners of the tie block. Unanticipated outcomes. Now, I allow for that, by using this method. |
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| Author: | Howard Klepper [ Mon Sep 06, 2010 1:59 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
Hesh wrote: Sorry to read that your tops are often doomed, Hesh. |
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| Author: | Mike Collins [ Tue Sep 07, 2010 3:19 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
I use the old fashion way ! I leave the bridge block a rectangle shape and put it in my Parrot vise. Then I use a sharp scraper to remove the wood as needed. I check the bridge with the top it will be mated with and when it's a perfect match i use a sanding block to remove any scraper chatter. Then cut to shape ! A scraper can remove wood so fast . Mc 
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| Author: | WaddyThomson [ Tue Sep 07, 2010 3:21 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
So can 40 grit on a belt sander!  
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| Author: | Mike Collins [ Tue Sep 07, 2010 3:23 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
40 GRIT!!!!! Sounds like my first wives fingernails !
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| Author: | Shane Neifer [ Tue Sep 07, 2010 4:59 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
Mike Collins wrote: 40 GRIT!!!!! Sounds like my first wives fingernails ! That's too much information Mikey!  Shane |
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| Author: | jfmckenna [ Wed Sep 08, 2010 11:13 am ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
So does any one, like me for example, not arch the bottom of the bridge? In 18 years of building guitars I've never had a bridge pull off. |
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| Author: | WaddyThomson [ Wed Sep 08, 2010 11:16 am ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
Are your tops arched? Do you use a flat caul underneath when you glue the bridge? If your top is arched, does the bridge press it into a flat on the top of the dome? |
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| Author: | jfmckenna [ Wed Sep 08, 2010 12:47 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
I use a flat cork lined caul. I do arch the tops on most of my guitars. When I place the bridge on it I do indeed see that it is not a perfect fit but it only takes slight pressure to fit it. I've actually wondered about this in the past as I know that violins for example mate the bridge perfectly. But none of the books I have ever read on luthery suggest arching the bridge so I just never did it. It's easy enough to do so I'm not sure why it's not mentioned. The picture tutorial that Hesh provided seem to be backwards though. Wouldn't the center of the bridge be sanded off first on an arched top? The only thing I can think of here is that the top is actually concave. If done intentionally that would be an interesting way to anticipate top distortion under string tension. |
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| Author: | WaddyThomson [ Wed Sep 08, 2010 1:17 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
You are right about Hesh's tutorial. It does look backwards. Maybe he has them overarched to start with (I think he has them made, somewhere), and is just cleaning them up. It doesn't look like he's taking off 2 mm of wood, there. |
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| Author: | John Arnold [ Wed Sep 08, 2010 11:42 pm ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
Quote: So does any one, like me for example, not arch the bottom of the bridge? Been doing it for 29 years. No problems, so far. The only bridges I have had to reglue on my guitars were either in a house fire or left in a hot trunk until the lacquer bubbled (literally). I use a compound radius on the top, measuring about 30 foot at the bridge. I just use a flat caul under the bridgeplate. That is on my new guitars. Repair is a different story. I often shape the bridge to fit an old distorted top. It is usually the 'cave man' method....clamp the bridge in the vise, and go at it with a scraper. I also like to roughen the bottom of the bridge with 40-grit, whether the glue is Titebond or HHG. |
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| Author: | Hesh [ Thu Sep 09, 2010 6:38 am ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
The problem with a picture tutorial is that some folks won't read the text and will just look at the pictures...  Guess I had better produce better pictures that need no explanation... If you do happen to read the text it explains why Waddy is correct and that this bridge was pre-radiused but not to the exact same radius as my top and so flossing/fitting was desirable for me with my methods. "From the picture above we can see that the wings of the bridge seem to be contacting the sandpaper first. This is because this bridge bottom was radiused prior to installation. Had the bridge been flat and the guitar had a positive dome the middle of the bridge would show it’s lines being disturbed by the flossing/sanding action." John welcome to the OLF - it's GREAT to have you here! ![[clap]](./images/smilies/smiley32.gif "adulations") ![[:Y:]](./images/smilies/smiley20.gif "Thumbs Up") A question if I may please: Roughing up the bottom of bridges with 40 grit is what we might call keying and as such I always believed that HHG and even Titebond benefited more from a freshly scraped and smooth joining surface(s) and that keying was really a technique for glues such as epoxy? I'm not arguing with your results just confused about keying a joint with HHG and Titebond. Please comment? Thanks! |
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| Author: | Hesh [ Thu Sep 09, 2010 6:50 am ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
Or simply know in advance that a lightly built guitar top will flex as it's engineered to do and do not apply much pressure when flossing. Let the sandpaper do the work. Preradiusing if radiusing the bridge is your bag (see John Arnold's post) does not in and of itself ensure a perfect fit to the my tops unless you muscle it in place with clamps. My tops are radiused to a specific number but once built, installed, and have the bridge plate installed which is not radiused what exact radius my tops are varies and is probably compound being flatter in the plate area. Since I want my bridge to lay flat on the specific top that they are going to live on radiusing to the top or flossing gets me there. I could also scrape in a vice and trial fit over and over until I have it - that's what I do also on repairs. |
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| Author: | Alexandru Marian [ Thu Sep 09, 2010 7:02 am ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
I use flossing with a caul + props inside the guitar, mixed with separate scraping until a perfect fit is achieved. The arch I use is at least 15' - muscle fitting is pretty much impossible. |
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| Author: | Hesh [ Thu Sep 09, 2010 7:17 am ] |
| Post subject: | Re: Flat bottom birdge on radius top? |
Well that's exactly the point to me as well - unless you produce a top that is exactly your targeted radius (and possibly over built if it is.... since the dome of the guitar should be dynamic with RH changes, string tension, etc.) and "spec" fit bridge may not exactly fit the specific top without being forced by clamping. Relying on glue to correct a poor fit may be a recipe for failure (again unless this is your intention and John has me rethinking this) if all other things are not kosher... What I mean is that some folks reading this may not have much experience with gluing bridges, bridge reglues etc. and as you know we hear all manner of methods that may not produce decent results. A discussion that I had with an OLFer a couple of months was about a bridge lifting and it turns out that they left a bit of finish under the perimeter of the bridge but did not route a ledge in the bridge bottom so there was not wood-to-wood contact around the edges of the bridge. It was simply smashed in place with clamps and with finish under it too. It lifted - no surprise there. Sadly this is what some factories do too and why I see these reglues in my shop. Combine something such as this less than great method with forcing a bridge into place with clamps and it sounds like two strikes against the bridge staying in place over time. How many HHG users don't preheat parts or lack the speed to get clamps in place fast enough? Lots of stuff that we discuss here gets taken in part or out of context and then a few weeks late we have someone starting a post with a lifted bridge. |
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