Question re: crack along the grain of a side board

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Donald McMillan
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Question re: crack along the grain of a side board

Post by Donald McMillan »

Good morning, folks!

This is my first post to MIMF, and unfortunately I come with a question!

I'm building my first guitar from scratch right now - a 000 with a cedar top, walnut back and sides.

I have the top joined and braced, so now I'm working on the side preparation. The sides are currently 4-5 mm thick, and I'm hand planing them down to 2mm. I've discovered a crack in one of the sides that runs for about 15cm along the grain, near the top of the side. The crack line shows on both sides of the board, and I can move it a little when pressing on it.

At this point, I think I only have a few options, and I would really like some feedback/advice moving forward:

Option 1: Scrap this side set and start with a new one.

I would prefer not to do this because the set matches my back.

Option 2: Stabilize the crack, and continue.

I "think" this is possible, but I'm not sure how. Would it make sense to flood the crack with CA glue, etc.? Before planing or after? Comments, anyone?

Option 3: Trim the sides down to the crack.

I can do this, but it doesn't leave me with any "wriggle" room when I'm at the point of profiling the depth of the guitar. Thoughts?

I would really appreciate any suggestions or advice I can get at this point. Thanks..

Ian

Chris Reed
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Re: Question re: crack along the grain of a side board

Post by Chris Reed »

If this guitar is for you, then you can afford to risk a failure because you *will* build others!

So I'd glue up the crack with hide glue (hot is best, but the bottled kind would probably work here).

Then thin to desired thickness.

Plan to profile so you lose as much of the crack as possible.

Bend, accepting that the crack may open up, particularly if you use water to damp the side. If hand bending, a metal back strap might help. Once bent, re-glue the crack. This is why hide glue is best here - new glue will reactivate the old, so you don't have to try to clean out the crack before regluing.

With luck it will turn out fine.

Bill Raymond
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Re: Question re: crack along the grain of a side board

Post by Bill Raymond »

Remember, also, that when you have assembled the top and back to the sides, you will (probably) be cutting a bit more from the side for the binding ledge. If the crack is close enough to the edge it may be supported by the lining or cut away entirely by the binding ledge.

Donald McMillan
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Re: Question re: crack along the grain of a side board

Post by Donald McMillan »

Thank you, Bill and Chris, for your advice. I never thought of using hide glue for the crack, but that makes sense!

And the profiling will definitely get very close, if not totally, to removing the crack.

I guess that's what I'll try.. :D

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Ryan Mazzocco
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Re: Question re: crack along the grain of a side board

Post by Ryan Mazzocco »

I've fixed several a side crack with thin CA, but that was either a repair on a completed guitar or a repair on a set of sides that were already bent. Even so, my first reaction to the question was CA. I understand the thinking in using HHG for this since it will reactivate unlike Titebond, but I don't know why CA wouldn't do just fine here also. With Walnut being so dark the line would likely disappear or just blend in and look like part of the grain. I don't know what CA's failure temperature is, but I suspect it's higher than HHG. :?: I could be way off here, but that's what I would have done.
In either case, you can save this set and there's no reason to scrap it, IMO even if you were building it to sell.

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Barry Daniels
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Re: Question re: crack along the grain of a side board

Post by Barry Daniels »

Hide glue will show less than CA. Wouldn't make a difference in rosewood but you might be able to see CA in walnut.

If the crack falls over where lining will be installed then you should not have any problems. If not, then side braces might be a good precaution.
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Chris Reed
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Re: Question re: crack along the grain of a side board

Post by Chris Reed »

CA is just acrylic plastic once it has cured. It softens at a fairly low temperature, and will certainly melt during side bending. Plus it leaves a dark line.

HHG might well hold if the side can be bent dry, and allows regluing if not. This is why I suggested it.

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Ryan Mazzocco
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Re: Question re: crack along the grain of a side board

Post by Ryan Mazzocco »

Chris Reed wrote:CA is just acrylic plastic once it has cured. It softens at a fairly low temperature, and will certainly melt during side bending. Plus it leaves a dark line.

HHG might well hold if the side can be bent dry, and allows regluing if not. This is why I suggested it.
Oh okay. Good enough for me. :)

Donald McMillan
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Re: Question re: crack along the grain of a side board

Post by Donald McMillan »

Thanks again for the helpful advice...my first thought was to wick in some CA glue, too, but I wasn't sure how it would react to a bending iron. Somehow, using hot hide glue seems like a safe alternative, though.

I'm going to try that tomorrow, and give it a full day for the hhg to set. Then, planing and bending the day after. I'll post pictures then.....of my success or failure..grin. :)

Donald McMillan
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Re: Question re: crack along the grain of a side board

Post by Donald McMillan »

I thought I would give my "unofficial" mentors a look at what I've done with the crack so far.

As per advice, I mixed up a batch of HHG, and I basically slathered it on the crack area on each side. I didn't worry about being neat, since I knew I'd be planing it off. The crack is actually quite visible.
OOO Guitar build124959.jpg
Then I started planing. I'm working it down to 2mm , as per the instructions in the book I'm following. Alex Willis's book.
OOO Guitar build141218.jpg
The crack is definitely still there ;) , but I'm down to thickness and nothing has disintegrated yet, which must be a good sign!

I checked the height of the side once it's joined to the top and bottom, and the crack will be almost totally eliminated, so I'm very tempted to cut to the profile now. Is that a good idea?

I also thought of flooding the crack again with a really thin application of HHG, before bending. Any thoughts?

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Barry Daniels
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Re: Question re: crack along the grain of a side board

Post by Barry Daniels »

You should have used clamps and closed that up. A glue filled gap has no strength and will always be ugly. But even if your crack falls onto the side, it will probably be removed when cutting your binding ledge. So plan and layout the parts accordingly.
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Donald McMillan
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Re: Question re: crack along the grain of a side board

Post by Donald McMillan »

Barry Daniels wrote:You should have used clamps and closed that up. A glue filled gap has no strength and will always be ugly. But even if your crack falls onto the side, it will probably be removed when cutting your binding ledge. So plan and layout the parts accordingly.
Thanks for the reminder about gluing, Barry.

I didn't clamp the crack at all, and your "should have" makes sense....now :).

I guess that's the good part about my first scratch-built, it's all a learning experience!

Thanks for the input.

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Bob Gramann
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Re: Question re: crack along the grain of a side board

Post by Bob Gramann »

It's hide glue. Moisten it, heat it up, and clamp it.

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Barry Daniels
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Re: Question re: crack along the grain of a side board

Post by Barry Daniels »

What Bob said. The quicker you do it the better it will work.
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Donald McMillan
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Re: Question re: crack along the grain of a side board

Post by Donald McMillan »

Thanks, guys...

I'll do that.

Todd Stock
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Re: Question re: crack along the grain of a side board

Post by Todd Stock »

CA is often used to treat cracks and other flaws in rosewoods and ebonies before bending...you can paint the stuff on Brazilian and - provided you exercise reasonable care - the repair will likely stay intact through either pipe or Fox bending. I've repaired light colored mahogany and maple prior to bending with CA, and while both pick up some superficial staining, it scrapes and sands so as to be unnoticed under finish. Keep the CA on the repair surface (the mating surfaces of the crack) and avoid making a mess on the show surface of the side. Use a disposible micropipette and medium CA if in doubt about ability to control things.

If bending on a Fox or similar, I don't think the glue will matter much - hide and fish will liquify again (heat + moisture...go figure), and Titebond will soften, but because everything is held in registration, the adhesives will harden up without critical loss of strength. If worried about the crack moving, try taping the side in that area with 3M blue - works surprisingly well to hold under bending heat in a Fox bender.

If pipe bending, don't expect hide, fish, or TB to hold the crack together without some help - back the bends with a strap. CA works better here than more heat and/or moisture-sensitive glues like epoxy, fish, hide, or AR/PVA.

Todd Stock
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Re: Question re: crack along the grain of a side board

Post by Todd Stock »

Also - think seriously about substituting a bolt on or dovetail for Willis's Spanish heel. I think a lot of what he suggests in terms of technique is valid, but you WILL screw up neck angle on one or more of your first builds (DAMHIKT), and the ability to reset the neck without a slip or other major surgery. Realistically, as a custom builder and repair guy, I've seen enough messed up necks on factory and custom guitars (from experienced builders that should have known better), that I don't even include Willis in the loaner package of books that new students get before their time in the shop. Cumpiano's revised bolt-on design will have minimal impact on your order of build at this point and allow you to make a few mistakes without paying too dearly for them.

Donald McMillan
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Re: Question re: crack along the grain of a side board

Post by Donald McMillan »

Thanks very much for the advice, Todd.

Your comments about the Spanish heel are noted. I'll stay with it this time, because I want to stay the course with the book and I already have neck built. But, I've already started thinking about my next one, and a bolt-on is definitely going to be the way I go.

Thanks again.

Donald McMillan
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UPDATE re: crack along the grain of a side board

Post by Donald McMillan »

I thought I would post to let my mentors know that I've made progress with my cracked sides.

I did everything as suggested, using hot hide glue along the seam of the cracks, then compressing the area with clamps. After it dried and settled, I started planing the sides down to 2mm (ish). I did a lot of planing the old-fashioned way, using a #4 Stanley, and the cracks were very stable except for one little spot. Since I got a little worn-out from that and everything looked fine, I ran the sides through my my drill press safetyplaner attachment, and got them down to 2+mm.

Then I scraped them until I got to final thickness. Everything looked good to go!

Todd Stock recommended taping the cracks when bending, and that is what I decided to do. Here's a picture of the sides with layout and tape on one.
IMG_20160331_122346.jpg
So...now I've bent 1 - count them - 1 side so far. My bending iron decided to be fussy today, and the construction site next door brought all our power down for 2 hours! Either way, 1 bend today...another tomorrow! When you're retired, there's no rush! :D

Here's my first bent side in the form cooling off.

Thanks again, folks. I'll post a true build record in a day or so.
Attachments
IMG_20160331_160459.jpg

Todd Stock
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Re: Question re: crack along the grain of a side board

Post by Todd Stock »

Good! Never let a setback stop your forward progress!

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