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This is happening when routing the mortise. I’ve had this happen twice now, any ideas what I might be doing wrong? I’m using a 1/2” down cut spiral bit with a template bushing in the LuthierTool edge vise. I make sure to go at least binding depth on the first pass and then take 2-3 more passes.



After dumpster diving the dust collector bin to get the chips I was able to repair it fine, but that’s 45 mins I’d like to avoid.





Brad


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Cut the bindings with a razor saw before routing mortise…

Same here. Done this since the first time I had the problen

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Never had a problem and don’t want to. Guess I’ll start cutting the bindings with a saw first too!


Steve

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Steve Smith
"Music is what feelings sound like"

Another thing I do if I'm worried about chipout when a bit exits a cut is put a piece of tape over it (the part that you want to stay put). Even if it does pull up, at least you have better luck finding pieces!

What kind of glue are you using for the binding/purfs?

Duco seems to stay a bit rubbery and might contribute to the binding wanting to lift. Once it starts moving bad stuff can happen.

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Brian R, Wood Mechanic
N8ZED

I dont have a solution for you, but Im glad I looked at this post cuz it's happened a couple times to me too. I, too, will be presawing the mortise at the binding.

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Brad—

Pure speculation by me, but I would suspect the direction of travel is a factor. As we all know, when you are holding a handheld router with the bit pointed down, the bit is turning clockwise. So, if we assume you are standing at the top and not the back of the guitar, and if you are routing the bass side wall of the mortise, heading from top to back is a conventional cut, and heading from back to top is a climb cut. In contrast, when you are routing the treble side wall of the mortise, heading from top to back is a climb cut, and heading from back to top is a conventional cut. Using a conventional cut on the treble side wall of the mortise seems to me like a way for the bit to grab the binding and purfling and fire it out away from the guitar. I think a climb cut on the treble side wall of the mortise might lessen the chances of this. Put simpler: for both side walls of the mortise, move from top to back, and keep extra hold while doing the climb cut on the treble side. Of course, as suggested, just cutting the binding and purfling at the anticipated mortise wall location would do great, too. I hope this helps.

Several things come to mind. Are you using a plunge router? If so, are you locking it down while moving it around? Seems like there's
some flex in the system allowing the bit to get a bigger sideways bite as you go deeper. Also, is the bit centered in the bushing? No explanation needed I'm sure. Some means of backing up the binding while routing may help. Looking at the pictures, could be as simple
as lacking for glue and clamping pressure in that area. Banger job on the fix.

If you are cutting full depth in uncut head block I think a climb cut could yield you a way worse outcome than the bit of chipping you pictured. Climb cuts can be fine when just a little material is to be removed, like trimming a top after gluing to ribs.

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Tom—

Brad described taking 3-4 passes, not one full depth pass. Just making sure we all understand what he’s doing.

I bet you this was the out cut on your bit. Tape the area that little support from some masking tape may be all you need to avoid the tearout. Also be 100% sure you have a glue glue on the binding. May I ask what glue you used to glue in the binding?

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks for all the feedback. I think Don nailed it. Coincidentally I was shooting video when this happened so we can now all watch together and critic my work!

https://youtu.be/KgCgonNORc4?si=XzsiwFkt9Y97GroP

The first pass was coming into the body on the right side of the mortise.

Brad


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No criticism at all! I think I saw all climb cuts except the second pass, which was a conventional cut. In other words, you went counter-clockwise on all passes except the second one, which was clockwise. C shaped path on all passes. Nothing wrong with any of that; I just suspect some combination of factors makes the binding/purfling vulnerable to chipping out on the treble side. Maybe it's vulnerable for both kinds of cuts. Who knows? I like the idea of cutting it with a saw before using the router. Then there's no worrying about it.

I'm with Brian what glue for the bindings Brad?

We had blowouts like that years ago here reported by people binding with hardwoods and thin CA. They reported 4" pieces being broken off.

That's why I always went with Titebond original mess and all it kept my bindings on.

I do use CA for all binding jobs. I tack it in place and then go back and flood the channel.

This doesn’t happen all the time but it has happened twice now which was enough to make me ask the question.

I think I will also cut the binding ahead of time. I always do light passes, maybe that saves me the other 9 out of 10 times, lol.


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Done all of mine except one with thin CA, never had a problem.


Steve

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Steve Smith
"Music is what feelings sound like"

This is the answer all things considered. The rotation of the bit is unavoidable and is what is causing the issues, climb cutting on the treble side lessens the chances of a big blowout simply because you are starting at the problematic area as opposed to pushing up to it, but it is still and issue either way. A "bad" piece of wood is unavoidable, proper gluing certainly makes things better, but being human even if dotting one's I's and crossing the T's doesn't guarantee anything. The surest way to give yourself the best odds in this situation is to cut the binding/purfling as close as possible to the finish route location, and even that is not a 100% guarantee but I'd be very surprised if anything beyond a very localized incident happened, something like a little chip of wood blowing off. End grain routing is always an issue and when making let's say an end grain rabbet I pull out an adjustable T-square and set it to use a utility knife to score the surface before I make the route and this has greatly improved results.

Binding and routers do not get along. Precutting the binding before routing, as described above, is the safe way. I do it every time before I cut a slot with the router.

Many years ago, I got the bright idea that I could use a flush cut bearing bit on my bindings and not have to scrape them flush. There were pieces of that binding all over the shop. I had to reroute the binding ledges and bind it again. I wouldn’t have know if I hadn’t tried.

Thanks, all!

One thing I should have mentioned at the start was the chips of binding were all three the same length and in three layers so it definitely exploded with some gusto.

I wonder if the second pass where I came back from left to right was the culprit. I have been consciously trying to take the first pass at .075” or greater cut so that I’m coming through the binding in one shot. It’s possible the first pass was a little shy of that and then coming back around left to right I caught the binding just right.

Well, good news is it was fixable (yay ebony) and even so it would have been covered by the fretboard. Appreciate the help!


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Nice repair Brad…

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Why didn't you cut the mortice before binding the guitar?

That’s an idea!


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The longer I do this the less I use CA
when your glue joint has voids this happens. Thin ca can void and here is a point
when you rout your channels , especially with wood. BE SURE TO BREAK THE INSIDE CORNER
you will NEVER get a perfect inside corner cut. This in itself can hold binding off. As a machinist , this was drummed into
our heads.
If you insist on using ca your better off with locktite medium get , this can fill small voids. ME DUCO even for wood.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I've always assumed this was the bit pushing the binding outward. Even a small cut can catch enough to cause a breakout.

I do this after the binding is on and the side is dressed and leveled. I clamp on a guide jig for a top-bearing router bit, and make the saw cut in the binding along the edge of the jig. I hate to say how long it took me to figure that one out, but I've had no problems since I started doing it that way, even with straight bits, so long as I don't forget to make the cut.

If you really prefer cutting the mortice after binding the guitar you can clamp a sacrificial bit of wood to the face of the guitar flush with the side and allow the bit to cut into it before cutting into the binding. It is similar to the tape idea but holds things in place more securely.