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Hello,

I am binding my first guitar and using a binding jig with a cradle. In Robbie O"Brien's course he emphasizes that the guitar needs to sit perpendicular to the cradle so the channels will be 90 degrees. He demonstrates this by measuring the same distance from the table to the top of the guitar at multiple points. I've got the measurements matching between the heel and tail block, both sides of the waist and the lower bout. The measurements are not all the same (IE the waist sits higher than the tail/heel blocks.) Is this ok? Is it even possible to have the measurements match being the top has a 30 foot radius?

Thanks for the tips!

Jordan

In my world the sides of the body need to be perpendicular to the bench. The top and back will be all over the place as you noticed. As long as the sides are perpendicular to the bench you are good to go.

I personally use a square between the sides and the bench to set up my cradles. I use 2 cradles, one for cutting the top ledges and the other for cutting the back. That way I'm only changing the bearing and depth once per body.

M

Well, for one, there is a bit of leeway. You want to be as close as you can get, but there is some wiggle room.

I have a vertical line drawn onto my binding bench backstop at right angles to the bench top. I adjust the jigs holders until the sides are square to that line, or as close as I can get.

What you are seeing is correct because of the radius of the top or back. What matters is that the measurements from the benchtop to the top for the heel and tail blocks match each other and, separately, that they match for the bouts on opposite sides.

Also, if your guitar body has significant taper in the back from the tail to the neck, don't make the mistake of measuring from the benchtop to the back when setting up to rout the binding channels for the back. I did that once but caught it before I did nay routing.

You can verify your setup is correct by placing a square on the benchtop against the sides to see how close to vertical they are.

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Michael I wonder if you could elaborate a bit on the use of two cradles...? Is that because the radius of arching is different on top an back?

Anything to avoid too much time setting up the router depth would be welcome.

Dave

At the very least most guitars are thinner at the neck joint than at the tail. The top is hopefully pretty perpendicular to the sides but the back rarely is. By using 2 cradle you can adjust for this issue. The guitar is simply swapped between cradles to cut the binding ledge, then swapped again for cutting the purfling ledge. You only need to change the bearing and depth one time per body. I do wedge bodies on almost every guitar I build so having 2 cradles is pretty essential.

Thanks all! Glad to know i wasn’t loosing my mind.

Assuming the binding jig and carriage are both on a level, flat surface, the zero setting for the carriage holders still needs to be set to provide a level, top-facing-down body. We adjust that zero with a 3/8-16 x 3/4" nylon set screw on each of the adjustable sections of the carriage support fixtures, using a dummy body (a guitar-shaped piece of 3/4" scrap plywood). The screw sits just flush (18mm plywood plus 1/16" cork), and is adjusted with a flat-tip screwdriver.

If only one carriage is available per body, a set of gauge blocks can be milled - these slide between the fixed and adjustable sections of the carriage arms to quickly level the body when top-up in the fixture. I'd like to say we are diligent in the making and use of these gauge blocks, but once a carriage is zeroed, it is perhaps 10-15 seconds of work with a 24" level (my Stabila is accurate to about 0.010" over that distance, but less expensive big-box Chinese-made brands are just as accurate, if perhaps a bit less rugged) and a set of offset blocks to level the top-up body.

As we usually mill channels for 2-3 guitars per iteration, and nearly always of two or more sizes, dedicating two carriages per body is not practical, so we make do with one carriage per body shape and spend the extra half a minute or so per guitar to adjust things, versus a few minutes to make up what are essentially custom gauge blocks. For someone working through the first few iterations of milling channels, some sort of system to ensure a true level seems desirable. Once some degree of mastery is reached, it seems like builders move on to bigger, more complicated mistakes and can 'wing it' with the binding jig.

The other point worth considering is that both jig and carriage should be aligned to a common reference plane, so placing the binding jig cutter and the carriage such that they are in parallel but vertically offset planes avoids creating a systematic error in the channel.

Any jig which uses the top or back plate surface to control binding channel depth will have some variation in channel depth on tapered bodies, with that error determined by the configuration of the guide (larger, more stable 'reference' flats create more error; narrower flats make for less error, but can be less stable. We see about 0.015"-0.020" error in the depth of the back's upper bout binding channels on 18"-22" long bodies using a Williams-style jig.

Some factory guitars and about 1/3 of the small shop built guitars we see come through the shop show noticeable variation on the back binding depth at the neck block or cutaway, but it is easy to correct with a cutting gauge set to channel depth at the widest part of the body...we use a sharp Titemark cutting gauge and usually see the gauge start trimming material somewhere near the waist, with the deepest cut at the neck block area.

If the variation off the jig is under 0.010", it seems to me that correction may not be worth the effort, given that we see that sort of variation in many carefully-crafted instruments between back and top binding depth, perhaps due to the cleanup process of leveling and flushing the binding and purfling. Most owners will not be able to see that variation, although we have seen our share of 'super-players' , which is to say those owners that - though remarkably reluctant to actually demonstrate they can play the instrument beyond a slowly formed, poorly strummed cowboy chord - are happy to demonstrate that there is a nearly imperceptible buzz which can be generated on the low E string at the 19th fret using a 2mm pick applied to the string as John Henry's hammer to a railroad spike.

Purfling is equally affected, but with the binding hiding the depth variation, not that much of an issue (although for Style 45 shell work on the upper bout of the back, veneer shell may be thinned to the uglier, core layers).

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