fine tuning intonation/compensation at the bridge

[Dan Gunderson]

Hi all, I was hoping someone here might be willing to share your general process for final adjustment of the intonation with a compensated bridge.
I'm waiting for the varnish to cure on my first F5, and am having to physically restrain myself from stringing it back up and getting it set up.
I have a cumberland bridge, and the compensation is roughed in to the saddle. When I strung it up in the white, everything sounded reasonably close, but I imagine some fine tuning will result in a vast improvement in intonation. I did some searching around, but don't have a good sense for the best order of operation in terms of fine tuning the intonation and compensation at the bridge. Is it pretty much just a trial and error process? Which string course do you try to keep closest to the "correct/intended" scale length? How narrow (generally) do you try to get the "ledges" where the strings break across the saddle (they are ~1/8 or so now).
Thanks as always.
-Dan

[dunwell]

Howdy Dan,

I don't recall off hand if the Cumberlands are pre-notched or not but I thought not. In that case it makes it easier if the roughed in areas are still flat on top.

- do your initial positioning of the bridge via the F-holes and arch of the top and just put some fine saw nicks in the saddle top to locate the strings. If it is already notched, just pay attention to whether or not your strings are being located properly. Bring it up to tune and check your octave note to the octave harmonic and tweak the bridge location as needed to get it as close on all four courses as you can. Lay some tape onto the top in front and back and one end of the bridge for location so you don't lose the sweet spot.
- take a scrap piece of E string or other fine wire and bend it into a V shape. You may want to make loops on the ends if your fingers aren't all calloused and abused.
- lift one string and slip the V wire under it at the saddle. It should stay in place with the fine notch but still allow you to slide it forward/backward as needed for intonation.
- use a good tuner that shows the cents and move the wire around till you have the open string, the octave note, and the octave harmonic at least within 2 or three cents of each other. The fretted notes will tend to want to be sharp. Mark the V-wire location on the saddle top with a fine pencil.
- repeat as above for the other strings.
- then pull the bridge and make the front edge of your pencil marks be the front edge of the break point. Make the back sides a bit more rounded and be sure to leave enough meat there so the strings won't cut into and deepen the slots. Use files to make your rounded slots again sloping the back side to ease the string over the saddle. It doesn't hurt to have the ledges large if they are smooth, I usually don't change the back side at all from the rough shape, only change the front edge to get the intonation. If you get too much drag or are getting popping when tuning then you can reduce the shelf, but this usually only happens on the wound strings.
- re-string and test again. You may need to raise the top a bit to comp for the slot depth you just cut.

As usual, this is just ONE way of doing it, I'm sure others will chime in with their processes. I always get something from other folks way of doing things too.

FWIW,
Alan D.

[Rolfe]

Hi Dan,
You gotta be patient with varnish, real patient. I make my own saddles, but things still get a little off from my standard compensation cuts. I always start setting up with one D string. When that is tuned up and the compensation smack on, I add the other strings but do not take them up to full tension. At this point I make sure the strings are centered on the fingerboard. Then I take the outer G string up to G and the outer E string up to D. Now I check my action height: I prefer .050" over the 12th for low action and .060" for Bluegrass. The reason for taking the E only to D is not over-tighten it if I need to raise the action. I then check the intonation on the E (tuned to D) and the G and wiggle the bridge around a little bit if I can improve it that way. The "wiggling" is partly why I don't have all the strings tuned up yet. If all is good, I tune up one A and check it. The A string is the most challenging, and the store-bought bridges are almost always off on the A. Remember to "set" the bridge so it is well-seated after you have done that tuning, and tune the four again. Now, with only four strings tightened, I can easily take the tension off and remove the bridge if the saddle needs modification. You will want to set up with the saddle "ledges" at your current 1/8 to give you some width to tinker with but then, when all is right, take them down to 1/16 or so from the tailpiece side (duh). Remember to do the string grooves slanted down toward the tailpiece so the strings take off at the very front of the "ledge" and cut the grooves only a half string deep on the wound strings and no more than string deep on the plain strings. Have fun!

[Pete Hicks]

I varnish my instruments, and the varnish used to stick to the bridge. I found out that if I rub a little beeswax on the feet of the bridge the varnish doesn't stick at the first string change.

[Paul Hostetter]

I have a cumberland bridge, and the compensation is roughed in to the saddle. When I strung it up in the white, everything sounded reasonably close, but I imagine some fine tuning will result in a vast improvement in intonation.

It might be, but there are so many variables with string gauges (at least if you ever stray from J-74s) and action, and string condition, and playing style, that it’s not worth getting too caught up in it. You’ll spend hours getting it right, only to find that someone else will play the setup and hear different intonation, or they’ll play it for ten hours and it’ll be wrong again. I’d spend more time getting the base of the bridge to be a vacuum fit under tension.

I did some searching around, but don't have a good sense for the best order of operation in terms of fine tuning the intonation and compensation at the bridge. Is it pretty much just a trial and error process?

Yes. I generally start with the routine bridge (which a Cumberland is) and get the E right on, then see how the others behave. In other words, adjust the bridge forward and backward until that one string course is spot on at full pitch and at the action you know you want.

Generally the routine Gibson compensation covers the A and the D when the E is right, but I often (not always) find the G goes sharp, meaning its ideal point of contact for that course is farther back. This means you have to add ebony to the back of the bridge saddle to accomplish that. (I just did this today, so it’s fresh in my mind right now.)

Here’s what I’m talking about. The upper bridge (purple) is the standard, notice that the G setback is relatively slight. In the lower one (blue), the point of contact is farther back and the G intonates better.



Whether you do this or not is only important if you actually play the G way up the neck. Few people do.

How narrow (generally) do you try to get the "ledges" where the strings break across the saddle (they are ~1/8 or so now).

Wider is fine, as long as the slot is ramped a bit so the string slides well. If it’s too thin, the string will cut down through the ebony. I think the string sounds better with a bit more contact.

PS: once in a blue moon the routine standard bridge intonates better if it's flipped end for end:



In this case, you again start by positioning the bridge so the E is dead on, and see how the others do. The whole bridge will have to be farther forward, but you have a bigger setback for the G. I usually do the standard bridge, and don't listen too hard to the G.