KM200S Setup / Bridge Height

[Sue Rieter]

So I've got my Rob Meldrum E-Book and I finally got my feeler gauges, blue tape and files (shipping from Harbor Freight is slow right now), and so I'm starting to look at my mandolin setup. (I bought this mandolin used online.) I moved the bridge toward the neck some, because everything was flat at the 12th fret; that seems to be good now. I have some new strings, but didn't put them on yet.

Next I spent some time making some measurements under the strings with the feeler gauges. It's a little tricky to do, a little hard to hold them straight and see whether there is still any clearance. Anyway, I ended up with about .115" at the 12th fret. Pretty high, it seems. The thumbscrews on the bridge look to be about as far down as they can go. Rob suggests sanding wood off the center section of bottom of the top part (saddle), if I understand correctly. In my case, I can't see as how this would make any difference. Maybe if the thumbscrew is limited by that center wooden section, but that doesn't seem to be the case here.

I saw elsewhere someone suggested sanding some off the top of the base.

Rob suggests subtracting .045 from the initial height to determine the amount of wood to take off - this would be .115-.45= .07". That seems like way too much to sand off there. What is my best approach? Do I need to sand the bottom of the base?

After I had my mandolin a couple weeks and did some reading, I was worried about neck relief, but holding down the g string at the 12 fret I get .006 under the 6th fret, so I am less worried about that right now.

I also think the nut might be a little high, but one thing at a time.
I appreciate any advice. I'm not (too) afraid to work on it (to a certain extent), but this is my first and only mandolin that I have to learn on during these lockdown times.

Sue

[belbein]

Funny you should mention all of this, because one of the next steps in my reconstruction of a ukemando I'm rebuilding is to set the bridge. And unfortunately, I don't believe that the bridge height is going to be standard. It's going to be a bit short, because the universe has been very unfair to me on this (re)build. So what I'm going to do is to shave down the bridge pedestal: the bottom of the base that sits on the top of the instrument. That will lower the string height (the "Action").

There are a couple of limitations on this that I have learned from bad experience. One is that you can't shave down the top of the bridge, because the pins for the wheels don't have much clearance in their holes. If you shave down the top of the top, you can cut right into the channel for the pins. The other is that you can't shave down the bottom of the base a whole lot, because the base of those pins doesn't have a lot of clearance either. So you need to measure carefully exactly where the ends of the pins are and then leave them enough support to not pierce the remaining wood.

The other solution, if all of this doesn't work, is just create a one piece wooden bridge. You can very precisely measure height necessary for the bridge based on how high your strings need to be. Of course it's not adjustable. And it's not exactly standard. But heck, make it an objet d'art by carving a bass relief into the sides of Helen being kidnapped to Troy, or Napolean retreating from Moscow. That'll wow 'em on the Cafe. (Well, it won't, but I'll appreciate it.)

[Richard500]

Sue, for that much decrease, you might consider just taking the knurled wheels out, leaving the screws. This drops the bridge without weakening it and is reversible. If too low, washers as shims will bring it back up. I once, before getting comfortable with woodworking, sanded too much off the upper part of a similar bridge, and it went (and still is) concave from string pressure.
There are all sorts of options and you should be done all too quickly for this internment, which will not.

[Marty Jacobson]

Yep, that's about like the one I just made a YouTube video about. You have a few options.
1. Make or buy a new bridge that's designed to be where you need it to be (somewhere between 1/2" and 5/8" if yours is like the one I set up) - Cumberland, Brekke, and others make specially designed "low boy" bridges
2. Make a one-piece non-adjustable bridge
3. Replace the saddle with something sturdy, like a reproduction Gibson aluminum bridge cap, which can be a lot more slender while still being strong enough. But that's weird.
4. Hack the bridge. It might last a while, it might last forever. Since it's your instrument you can decide for yourself whether it's worth the risk. I was doing it for a customer, so I had to be confident that the fix I employed would be a lasting one.

To hack this bridge, you'll need to saw, file or sand off material from the bridge cap/saddle where the thumbs screws meet the top of the bridge, as well as the "beam" element on the top part of the bridge. The screw posts will now stick up, so you'll have to file or sand those down, hopefully without making them wobbly in the spongy rosewood base.
You can also remove material from the bottom of the bridge, which is pretty straightforward if you're going to be fitting the bridge base anyway. That's the safest place to remove your .070" -- though from looking at your action, I think you should aim to remove more like .100".

Removing that much material from the bottom of the bridge base will leave it essentially identical in its structure. Just be sure you don't scrape the top with the bridge posts if they stick out the bottom, they can have a tendency to rotate and extend when sanding, which can tear through the sandpaper and scuff the top. Just go slow and it'll be fine.

[pops1]

Looking at your bridge I would remove material from the bottom center of the bridge saddle, you will need to do that any way. Then I would remove the knurled nuts and the screws and take the area where the screw goes into the bridge foot lower to allow the saddle to adjust lower. There is plenty of material there to do what you need to do. Watch when you put the screws back in that they are tight and not out the bottom. There are many ways to do this and they all work. If you like this mandolin then as Marty says you can get a better quality "low boy" bridge, then you can learn about fitting a bridge foot.

[Sue Rieter]

Thanks guys, for the help.

Marty, I saw your videos, and was thinking, "Uh oh, that looks a lot like mine." As carving/making something new is beyond my woodworking skill at this point (even without the classical ornamentations (ie. Helen or Napoleon ), I think I will embark on modification what I have, with the idea of if I totally mess it up, I will get a new, shorter one. I don't have that much into this mandolin at this point (and I guess now I know why - It falls under live and learn!)

So both Marty and belbein had mentioned watching out for the posts, and I was wondering if you could take them right out while working, and pops1 answered that question, so that is great.

If I understand correctly, pops1, you are suggesting approximately the same as Marty's #4 hack suggestion. Overnight I was leaning toward taking the material off the bottom, even though I think it would be harder, given the curve on the bottom of the foot, the amount that needs to come off, and the need to keep everything perpendicular. Also the bottom fits pretty nicely against the mandolin at this point. So maybe I am rethinking it and will try taking it out of the middle (top and bottom). Overall, I might have a greater chance of success and less chance of messing up the only bridge I have at this point.

If I go for .100" as Marty suggested, should I do it half and half (ie. .050 from the center of the saddle and .050" from the top sides of the base, or is it better to take a little more off the bottom for stability? Is it worth going for less than that to start, and seeing how it is, or do you think that would be a lot of extra stringing and tuning for limited potential benefit?

I have a couple non-musical things to do today, so I think I will practice until my fingers hurt later and then embark on this project tomorrow morning.

The last question I have right now, is why do you think this situation is so extreme? Inadequate manufacturing tolerances or something happened in the interrim time? Just curious, but given my relative ignorance, I'm suspecting manufacturing.

Thanks again for sharing, you guys are great

Sue

[Sue Rieter]

I'm continuing to think, and I guess I have to take whole amount off both so that they fit past each other the whole way. I wasn't picturing it correctly in my head. So I guess I answered one of my own questions.

Sue

[Marty Jacobson]

Well, you have four surfaces you could remove material from:
Top of bridge base, bottom of bridge base, top of bridge saddle, bottom of bridge saddle.
I'd take .050" off the bridge base for sure, and then another .050" off the bottom of the bridge saddle. I would avoid taking material off the top of the bridge saddle or the top of the bridge base.

[pops1]

Marty, curious why you wouldn't remove material from the top of the bridge base. If you take .050" off the bottom it is a lot of work and it is easy to take it off where the posts screw in. Taking it off the off the top doesn't alter the fit of the foot, and losing .050" off either place leaves the same amount less for the post. I have done this many times and not had a problem.

[Nevin]

This is coming from my background in the upright bass world. If you take material off where the post screws in you are leaving less wood for the post, making it more likely to bend or fail. I know there is less tension on a mandolin but I would remove from the bottom.

[Richard500]

This is coming from my background in the upright bass world. If you take material off where the post screws in you are leaving less wood for the post, making it more likely to bend or fail. I know there is less tension on a mandolin but I would remove from the bottom.

The aspect ratio — height versus thickness at the foot, for a bowed instrument is huge compared with the very low bridges on mandolins (modern ones anyway). That is, there’s a big lever arm putting torque on those adjuster screws so you have to be careful. I don’t think mandolin bridges fall over very often.
However, ignorant twit that I am, I didn’t know adjusters had wormed into the double bass world, so, being aware of the extreme acoustic design aspects of violin or cello bridges, I’m surprised that adjusters wouldn’t make audible changes to a double bass.

[jim simpson]

It seems like the nut height is very often sent out too high. I've seen this on many higher end guitars.

[Sue Rieter]

I've been working on my bridge. It is slow work. I took it apart, looked it over and did some measuring. Because I have so much to take off, and because I a) didn't want to risk having the top crack, and b) the top of the base only has about .07" till it would be flat all the way across and c) I wanted it to still be adjustable because I really have no idea where I want a bridge to be (other than lower than it was), I finally decided to work on the bottom of the bridge, at least initially. I measured and drew a line about .09 all the way around, and started shaving with an exacto knife. 6 blades and many hours later (taking Marty's advice to go slow) I have about .07-.08 off the bottom. It doesn't look too bad and I think I am almost ready to go to sandpaper. If I need more after I finish, I will take the rest off somewhere else.

I held it up to the mandolin, and there will be a fair amount of sanding to do. The big sanding challenge, I think, will be keeping it perpendicular. Would this be easier to do if I put it back together, or do you think I can do it with the posts out?

I miss my mandolin.

[pops1]

I like the posts in, and make a piece that goes over the posts to hang onto. I would not use the adjusting wheels, just the post. A little lean, very slight, toward the tailpiece is preferable to straight perpendicular.

[Sue Rieter]

Thanks that is very helpful!

[Richard500]

Sue, if I were doing this, I’d want to prevent any fore and aft rocking during the sanding, so I’d attach the piece Pops1 suggests, but firmly, maybe with a temporary (paper membrane) glue joint and have it stick up, say 2”. Using some sort of an accurately right angle, like a piece behind it (unattached), a small piece of board, say, would help you keep the sanding process accurate. There are, of course jigs for this, but that’s less fun.
Apparently, the luthier people don’t simulate string downforce during this process, so the top of the mandolin must not deflect enough to matter. Deflection would alter the fit.

[Marty Jacobson]

Marty, curious why you wouldn't remove material from the top of the bridge base. If you take .050" off the bottom it is a lot of work and it is easy to take it off where the posts screw in. Taking it off the off the top doesn't alter the fit of the foot, and losing .050" off either place leaves the same amount less for the post. I have done this many times and not had a problem.

Removing material from the top of the bridge base, for a first-time job, is a lot more work (assuming you need to fit the bridge anyway) and involves checking the compensation and re-establishing the bridge slots. So while it's an option in general, not a great option for Sue IMHO. Thanks for the clarification.

[pops1]

Removing material from the top of the bridge base, for a first-time job, is a lot more work (assuming you need to fit the bridge anyway) and involves checking the compensation and re-establishing the bridge slots. So while it's an option in general, not a great option for Sue IMHO. Thanks for the clarification.

I was not wanting to remove material from the saddle, but the bride foot only where the post goes and the bottom of the saddle to allow for a lower action. Sue said the foot fit well to begin with so I thought that an easier option.

[Sue Rieter]

So my mandolin is all put back together with new (light gauge) strings, and the difference with the sanded down bridge foot is pretty substantial. I feel like the bridge fitting went real well for a beginner, although it took a lot of time. Here is a picture of the jig I made for sanding, with the piece on top to hang onto suggested by pops1 and the piece behind it suggested by Richard500. We made it with a table saw and drill press. It's pretty rough, but seemed to do the job.



Anyway, in the interim time I got one of those 6" mechanical rulers, and my measuring has increased in accuracy. I now have about 5/64" or .078 between the G string and the fret at the 12th fret. So, although I plan to play it for awhile as it is now, I feel like there is still some room for improvement, especially since my thumbscrews are still adjusted all the way down.

I'm not going to mess with the bottom any further if I can avoid it, that was alot of work.

I am still not clear from the discussion above where the best place is to continue working. So here is my (not fully awesome) sketch of the bridge with the posts and thumbscrews out and all the surfaces labelled:



I understand why A would be a bad idea.

Marty said

To hack this bridge, you'll need to saw, file or sand off material from the bridge cap/saddle where the thumbs screws meet the top of the bridge, as well as the "beam" element on the top part of the bridge. The screw posts will now stick up, so you'll have to file or sand those down, hopefully without making them wobbly in the spongy rosewood base

I believe he is suggesting B/C and that is what Rob Meldrum describes in his ebook as well.

pops1 said

Looking at your bridge I would remove material from the bottom center of the bridge saddle, you will need to do that any way. Then I would remove the knurled nuts and the screws and take the area where the screw goes into the bridge foot lower to allow the saddle to adjust lower.

I believe he is suggesting C/D.

This seems like it would be easier, because there is a slight angle to surface B, which I am not sure if you would need to maintain.

But then Marty said

Removing material from the top of the bridge base, for a first-time job, is a lot more work (assuming you need to fit the bridge anyway) and involves checking the compensation and re-establishing the bridge slots. So while it's an option in general, not a great option for Sue IMHO.

I would like to understand the difference between B/C vs. D/C and how it would affect the geometry of the string slots on the top of the bridge. I did spend some time looking around online but didn't really find anything.

Thanks to all of you experienced folks for your help and your patience with a beginner.

Sue

[pops1]

B/C will weaken your saddle, D/C will not. The screws are most likely now screwed to the bottom of the foot, and can you won't need to take much more off the get where you want to be. As I said before, and you were correct, D/C is where I would take off wood. Good job so far Sue.

[HoGo]

I guess I'm a bit late here but I've setup quite a few of these mandolins and my general rules for bridge are these:
Never ever remove wood from areas A and B (top of saddle and above the wheels). These weaken the structure of saddle and especially with this GOK dark hardwood the saddle is prone to splitting under load of strings. Sadly they more often than not come to me with too much wood removed and sometimes already split or starting to split.
First area to remove wood would be bottom of base often down to "full contact" and then the "D" marked areas below wheels and also the protruding "C" area so it will fit between the wheels when fully lowered. Sometimes I would completly flatten the "D" level with "E" to allow lowering the saddle enough.
The saddle of this mandolin is already compromised by cutting away quite a bit of wood from "B" and deepened string slots so I would consider replacing the top of saddle with new strip of ebony (after shaving top 1/16" off) and shaping it and to compensation steps. I often saw off the "C" away with thin japanese saw and add some good ebony piece 1/16-3/32" to the bottom of the saddle to strengthen it and glue the "C" part back and work on the rest of the bridge afterwards. That is typically also enough to stabilize saddles that split after gluing the split with good CA and clamping.
Od course I could order a new quality bridge (or make a new one) but that would take weeks to deliver and cost more than these simple steps, some of which I would have to perform on new blank as well...