PDA

View Full Version : Bridge Placement/Height



mcknigs
05-28-2012, 08:17 AM
My first post here. Howdy! :)

I have a P'mico Collegiate ukulele. Not a baritone, not sure if it's a soprano or a concert. I think it's probably plywood. It has faux tiger striping painted on the top and back and faux binding in white paint. It was given to me without a bridge. I can see were the original bridge was, based on the unfinished patch it left behind, but have no idea where the bridge saddle was with respect to the bridge. I've found pictures of P'mico Collegiates, but none exactly like mine. The ones I've seen had the bridge saddle very close to the nut-side edge of the bridge. I see some replacement uke saddles on eBay with the saddle farther from the nut. So I can't just get a replacement and assume that I can glue it where the original bridge was.

I'm somewhat handy working with guitars, mostly electric. I understand that the bridge saddle should be as far from the 12th fret as the 12th fret is from the nut, plus a little extra. As I understand it, (from past experience) putting the saddle at exactly twice the distance from the nut as from the nut to the 12th fret will cause the uke to fret sharp and so the bridge saddle needs to be little farther away than twice the distance.

My questions:

1. This uke only has 11 frets, does anyone have a formula for determing scale length from 11 frets?

2. Once I know the distance to the 12th fret, what's the formula for determining where the bridge saddle should be?

3. I found this site from an archived post that suggested string height at the 12th fret should be about 1/8" above the fret and that means the height of the bridge saddle should be about 1/4" above the 12th fret. This uke has the fretboard flush with the top, so that tells me I need to sand the replacement bridge down to a hair over 1/4" tall, correct?

Many thanks. Glad to have found y'all.

-Scott

1931jim
05-28-2012, 10:14 AM
Welcome Scott,
If you measure the distance from fret 10 to 11 just add it to make up the distance from 11 to 12. Now the distance will be a little too long because the distance from 11 to 12 Should be less than from 10 to 11. That will be a good compensation for the distance from 0 to 12 being a little shorter than 12 to the saddle. I hope that is clear. You could give it another .5mm at the most on the bass side.
PS: I think you have the clearance at the 12th fret figured out pretty well. 2.5mm should be what you aim for to give a nice action.

ProfChris
05-28-2012, 11:37 AM
You could make a very simple bridge like this:

http://farm6.staticflickr.com/5448/7210488710_a3608be8fe.jpg (http://www.flickr.com/photos/76928743@N02/7210488710/)http://farm6.staticflickr.com/5312/7210498600_5c0355124c.jpg (http://www.flickr.com/photos/76928743@N02/7210498600/)
http://farm6.staticflickr.com/5456/7222759014_4030b4af9d.jpg (http://www.flickr.com/photos/76928743@N02/7222759014/)

This is one I've just completed in Yew, and it's fretted direct into the neck like yours. The bridge is copied from my 1920s Kumalae, and that bridge has worked OK for 80 years or more.

I think you can see the principle from the photos - it's simply a rectangular block, with part cut away to leave a lip which forms the saddle. The saw slots for the strings are widened at the base with a chisel to allow the string knot space to slide in.

I cut this over-height so I could plane it down once I'd seen the actual height at the 12th, not the calculated height - there might well be some dip or bulge in the top which upsets those calculations. So long as the lip is at least 1/16 or so this design works well; the break angle over the saddle portion is controlled by how deeply the string slots are cut.

If you want to match the footprint of the old bridge you need to work out where the saddle top should be, as explained above. Make the lip wide enough so that point falls on its mid point. Then you can shave wood from the back or front to adjust the intonation more precisely, even intonating each string separately!

Any reasonably hard wood will work - walnut is fine, rosewood or ebony even better. The yew I've used is a little soft but still adequate, and of course it matches the rest of the instrument. I wouldn't worry overmuch about less dense wood reducing the volume - my yew uke is about as loud as they come.

By the way, I'd expect there used to be a 12th fret at the neck/body join - do you not have an empty slot there? If so,why not replace it?

[edited to add: definitely measure the *actual* height required at the saddle using a straight edge. I angled my neck back a little to allow my bridge to be around 1/2 inch high including the saddle, and it's quite likely your builder did the same.]

mcknigs
05-29-2012, 07:27 AM
Thanks for the responses folks. To address some of them:

I had considered making my own bridge. I lack woodworking tools and skills but like a challenge. On the other hand I can get a ukulele bridge off eBay for about $15 with shipping. Given my lack of tools, if I did decide to make a bridge it might make more sense to glue two flat-ish pieces of wood at right angles to form bridge and saddle, rather than carve a bridge and saddle from a single block of wood, no?

The uke appears to have a neck that angled very slightly back.

The uke doesn't appear to have ever had a 12th fret. the neck joins the body just little beyond where a 12th fret would be.

Thanks for the idea of making a saddle broader and carving it to create a compensated bridge. I've seen pictures of people who did that by making a wide bridge, then using a rat-tail file to move the take-off point farther from the nut. I've never tried it myself.

I've taken some pictures which I'll insert below, not because I think they'll be particularly helpful, but because I know people tend to like looking at pictures. :)

3837038371383723837338374

ProfChris
05-29-2012, 08:33 AM
The 12th fret was where the body joins the neck - if you look at my pictures above you'll see where it went, as the design is similar. If you look closely at yours you should see a slot (perhaps filled with glue, as it looks as if someone has reglued the neck).

As the neck is angled, you can't work out the bridge height by maths, so trial and error is your friend. I'd do it as follows: place a 3mm/1/8 drill bit where the 12th fret should be, run a straight edge from the bottom of the nut slot (though in practice I'd rest that end on the fretboard by the nut) so it's resting on the drill bit, and then measure down from your calculated saddle location (nut to body x 2 plus about 2.5mm (say 1/8 again). This will give you your saddle height plus a fraction. Buy or make your bridge so the saddle will be that height, but with a margin to reduce it by (say) 1/16. Glue it on, string up, adjust until the action is how you like it.

But ...

If you don't have the skills to make the kind of bridge I showed you, then you probably don't have the skills to glue a replacement bridge on. The bottom surface of the bridge and the top surface where you're attaching it have to meet perfectly - glue holds these surfaces together, but doesn't hold across gaps at all well. If you just blob glue on and press the bridge into it, it's pretty certain that a few weeks later your bridge will fly off, maybe pulling chips out of the top. Plus you need to clamp the bridge in place while the glue sets, and a hardward store clamp won't fit so you'll need to make a clamp.

Why not find a woodworker friend, show him/her my picture and see if a bridge can be made and fitted? A local luthier would be even better but not free (this is a fairly cheap repair, though).

That's a fun uke, late 20s or 30s I'd guess. Worth fixing right.

mcknigs
05-29-2012, 09:57 AM
Thanks again for the response. I'll take all this under advisement. FWIW, I think my gluing skills far surpass my woodworking skills. I've glued bridges onto a uke and a guitar before and they're still holding. The intonation isn't perfect on either, hence my desire to get the placement correct the first time, and attraction to a method that might allow me to adjust the intonation a little after the glue is set. Whether I make a bridge, buy one off eBay or have a local luthier make one, I'll still end up gluing it myself, so I'll just have to plan and prepare as well as possible and hope the musical instrument gods smile on my endeavor. :)

Pondoro
05-29-2012, 03:47 PM
Are you in the US? I'll mail you a bridge (free) if you want one. I am not sure how much it costs to mail stuff to other countries, I'd consider them as well. My bridges are even simpler than ProfChris', but you need a saddle as well so the end result is at least as complex. But I agree with him, don't mess with this if you don't feel handy with tools and glue. My bridges were made to be a bit too high, you'll lower it by sanding on the bottom until it is the height that you want.

http://i176.photobucket.com/albums/w163/pondoro_bucket/NinebridgesSmall.jpg

I would also send you a couple of pieces of hard wood to make saddles. You might have to try a couple of times to get the compensation right. Once you get it spot on you could buy a bone blank and duplicate the saddle that worked best.

I leave for Ukulele World Congress in about an hour so I won't check this for 4-5 days (no internet).

mcknigs
05-30-2012, 03:14 AM
Are you in the US? I'll mail you a bridge (free) if you want one. I am not sure how much it costs to mail stuff to other countries, I'd consider them as well. My bridges are even simpler than ProfChris', but you need a saddle as well so the end result is at least as complex. But I agree with him, don't mess with this if you don't feel handy with tools and glue. My bridges were made to be a bit too high, you'll lower it by sanding on the bottom until it is the height that you want.

I would also send you a couple of pieces of hard wood to make saddles. You might have to try a couple of times to get the compensation right. Once you get it spot on you could buy a bone blank and duplicate the saddle that worked best.

I leave for Ukulele World Congress in about an hour so I won't check this for 4-5 days (no internet).

Many thanks for the offer. A bridge would be appreciated. It looks like I could use one of those bridges with a plastic or Tusq saddle, sand the botom of the bridge to fit and do final height adjustment by sanding the bottom of the saddle. I'm in the Washington DC area. I hope you have (had) a great time at the Ukulele World Congress. (I'll have to look up to see where that is.)

Looking at those bridges, how do the strings attach? Are there holes through from the front to the back, or do you cut channels, like ProfChris, as a later step?

-Scott

Pondoro
06-02-2012, 04:16 AM
I'm back, pretty busy today but please PM me your address and I'll send you a saddle early next week.

I drill the string holes straight through the saddle, then glue it down and drill them all the way through the soundboard into the interior of the uke. When I string it I feed them through, fish the end out of the sound hole, slip on a 4 mm bead and tie a stopper knot. This way the strings will never pull the bridge off.

I'll post a picture later, today is crazy.

If you want conventional slots you can add them with a drill and a tiny saw that you can buy at Hobby Lobby for about $5.

I made 9 bridges all at once because the most picky part is cutting the saddle slot. it needs to be all the same depth and have a nice flat bottom. The best way is with a table saw but on a single bridge your fingers get too close to the blade. So I cut the bridge (s) on the edge of a big plank, then rip off the entire strip and cross cut them by hand. That way my fingers are never near the blade, but you end up with a bunch of bridges. So I'm happy to send you one.

Pondoro
06-02-2012, 11:55 AM
Here is how a string-through bridge works:

http://i176.photobucket.com/albums/w163/pondoro_bucket/String-ThroughBridge.jpg

1931jim
06-02-2012, 12:09 PM
Very nicely done Pondoro.

Zenin
06-02-2012, 12:20 PM
The best way is with a table saw but on a single bridge your fingers get too close to the blade.
(Disclaimer: I'm speaking as an amateur carpenter, not a luthier)

It seems to me like a router table with a small straight bit (and a zero or close to it insert) could safely and accurately cut such a groove in a small piece like a single bridge, or even a strip of bridges, much easier then a table saw?

Pondoro
06-02-2012, 02:25 PM
(Disclaimer: I'm speaking as an amateur carpenter, not a luthier)

It seems to me like a router table with a small straight bit (and a zero or close to it insert) could safely and accurately cut such a groove in a small piece like a single bridge, or even a strip of bridges, much easier then a table saw?

A router would work and be safe but take several passes to cut a deep clean slot. The table saw goes fast. I cut a test slot into a piece of scrap pine to let me measure the depth. Then I run the whole big plank on edge to get the saddle groove cut in two passes (2 passes because my saw blade is too thin to make it in one). Then I rip off the edge and I have 2-3 feet of bridge. Then I dado cut to form the the "feet" for the big bridges. Then I cross cut them all apart (with a back saw) to make the lengths I like. It is really fast and my hands are never near the blade. Next time I'll take sequential pictures.

Those nine (the long piece at the top is big enough for two) took me less than an hour and that included figuring out what to do. I got three for a tenor or baritone, four for a soprano or concert and the long piece, big enough for two, I left longer in case I needed something weird. The one in the lower left has been finish sanded and is ready to go. I'll drill the string holes later when the uke is set up with the neck on it so I can measure exactly where I want them.

mcknigs
06-04-2012, 05:42 AM
This all makes sense. PM sent. Thanks! :)

-Scott

Pondoro
06-04-2012, 02:03 PM
Scott, I replied to your PM 3 times but it is not in my "sent items" so I have no idea if it really sent. I agree with the plan of attack that you sent to me, it is what I would do.

Mike

Pondoro
06-05-2012, 11:48 AM
I've sent Scott a bridge and suggested that he start a new thread asking, "Where exactly do I glue it?" Compensation and scale length are an interesting subject. Probably better off on the Luthier's forum than on this one though.

mcknigs
06-18-2012, 05:14 AM
39121
Following up on this thread...

I got a bridge from Pondoro and spent a while this weekend cutting and sanding it to fit. I glued it down Saturday and strung it up Sunday. The placement of the bridge appears to be perfect. I'll want to shape the bridge saddle, as it's currently flat and the thinnest strings are buzzing a little, sitar-style. I see most people shape bridge saddles in an arch. Since the intonation appears to be right on with this saddle, is there any reason not to shape it somewhat like a nut, rounded on the back side with a straight drop off at the takeoff point? IOW, is there a reason it has to be curved away on the fretboard side?

I still want to do something to seal the wood. I have tung oil that I've used with other projects but I think the brown of the tung oil will clash with the black and gold of the uke. Suggestions?

Pondoro
06-18-2012, 01:39 PM
Nice job, an historic uke is now making music again! I think you could arch the saddle from the back to the front as you said and it will sound good. How about a close-up picture?

I expect you could stain the bridge before you oil it. Dark mahogany or even ebony.