Official Luthiers Forum!

Hi, just wondering if anyone out there has had any expierience/ tips with the universal binding machine from LMI.
I'm about to router my binding/purfling channel but can't seem to get a consistant height
around the contour of the guitar. I have a 30' radius on the back. 50' for the top.
I'm not sure if i'm just overly terrified about this step or over analizing it !

cheers!

Scotty my friend here are some tips for you and no worries when I got my Williams jig I was scared to use it too but it all went very well.

1) Position the guitar in the holder so that the neck and tail blocks are as vertical as you can make them. The top or back of the guitar is not supposed to be level with these jigs. If you did level the guitar the depth of the binding cut would be inconsistent.

2) Use "climb cuts" for the first pass. Climb cuts help avoid tear-out and here is an illustration compliments of Stew-Mac as to how to make your climb cuts:



Notice that the second pass is when you go all the way around the guitar in one pass and also note the direction.

3) When setting up the router and binding cutter bit test on scrap for depth of cut and height of cut.

4) If you have the LMI router bit you can cut either the purfling channel or the binding channel first. Older versions of the Stew-Mac binding router bit set require that you cut the purfling channel first or the bearing will fall into the binding channel, if it is cut first, while cutting the purfling channel. Stew-Mac has a mod/spacer available for those of us with the older sets.

5) Most importantly - wear safety glasses.

I hope this helps. The LMI jig "floats" in terms of it's height so this is why the guitar top and back don't need to be level and it is more important to get a consistent cut all the way around anyway.

Hey I just found this too and it's excellent! OLFer Chris will answer all of your questions and show you how it is done too:http://luthiersforum.com/forum/viewtopic.php?f=10117&t=19654

If you are using the UBM with the UHNW donut as the reference edge that rides on the body and getting an inconsistent channel depth then the first thing I would check is to see if the body is in the cradle with the sides true perpendicular to the work surface you have everything mounted and squared to. Because the router moves up and down freely the depth of the cut should be constant if all is squared to the work surface. The only thing that can cause it not to be is if the bit/ body plane relationship is changing.

If the sides are not square to the work surface or if the binding machine is not square to the work surface then the angle of attack of the bit can vary causing tilted channels. This can affect both depth and width of the cut.

Now if you built the binding machine and you did not incorporate a donut and some how you have a flat base of more than a fraction of an inch riding on the top or back, this will cause major inconsistency in the depth of your cut due to the fact that the top and back are not flat but a dome. As the router changes position around the body the height of the back of the base (part of the base that towards the center of the body) will rise and fall out of relationship to the edge of the top or back leading to changes in the depth of the cut.

To maintain a consistent depth you must have a small foot print riding on the top or back as near as possible to the edge without getting into the width of the cut. This is what the UHMW donut does for you.

As Micheal says the body needs to be squared up. I use a tall machine square and make sure the neck block and tailblock areas are squared up. I adjust until it is so. I then check the areas of the bouts to make sure squared up, which they usually are and if not, do that. Once set, it will leave an even depth channel all the way around. As noted the donut thing is needed or will have binding channel for say 1/4" binding at the rear and less at the front of the box. I guess could go around and adjust the level of the cutting depth on the router as you go, but a minute or two squaring the body is better and more accurate.

Hey Hesh that was good timing.
The only thing I would add is to make sure the donut has enough arch to it. I made my little half donut shoe and put some sand paper on the top and did some paper pulls and moved the donut over the sand paper to get a contour somewhat. I also checked to see that when routing over the taper from the Waist to the upper bout that the donut wasn't riding up on the high edge of the taper. I don't have the 1" dia. bit and bearings but have wondered if the geometry of the larger bit compared to the 1/4" bit has any effect on the depth of the cut for the binding when doing the tapered area. Anyone?

yes if your indexing edge (donut or taperd base are is touching out at a point not coplanar with the tangent point of the bit you will be cutting shallow but not by a lot unless your donut is wide.9 thick and wide). i would expect that the amout of error would be more with a 1" dia bit than an 1/4".