Installing Plastic Binding
I'm getting close to the end of these posts on building a guitar... After this entry, my focus will shift to finishing. Last time I shaped the bodies of the other two guitars, and in this I will add binding to the corners of the third.
Binding is a strip of either wood or plastic added to the very corner of a guitar. Often (usually on acoustic guitars, less so on electric) these strips also have "purfling" - which is a decorative strip or inlay on either side of the binding strip - I won't be adding any purfling here, just a simple binding strip to both front and back edges making this guitar what is known as "double-bound".
I've done some binding with wood on previous projects, but this was the first time I tried using a plastic binding.... To tell the truth, this is actually my second attempt at binding this particular guitar as I failed with the first attempt. That was entirely my fault, mostly because of my frugality - when ordering parts, I had included a couple strips of plastic cream-colored binding that measured 090" x .250" x 65" long (one for each side) and figured I would try make do with the rabbeting bits I already own to route the channels for them. I knew I owned a set that had a bunch of bearings with it, so I figured there must be one in there I can use that's close.
The 1/4" depth obviously wasn't a problem, as that's just the setting for how deep to go. The problem was with the .090" thickness of the binding. The rabbeting set I have has bearings for 1/8" and for 1/16" deep (0.125" and 0.0625" respectively) - and the .090" binding falls right between those. The 1/8" slot was far too deep, but I figured I would try the 1/16" bit and see how it worked out.
I know, I know. I know better than that - but I did it anyway. It was good practice... but that's about all. After I had the binding in place, it stuck out quite a ways/ I scraped it down (which went quite well, really) to where it was 1/16" thick, but it just didn't look quite right - and there were a couple spots where I scraped a little too much, and the binding subsequently became too thin - and at 1/16" it's far too easy to see a flaw like that.
So, I ordered a proper set of rabbeting bits (StewMac seems to be about the only place to get them) along with some new binding strips and re-routed the body with a correctly sized rabbet and went about reinstalling the new binding strips.
The plastic strips that came would never work as they came - they needed to be pre-bent to fit the guitar. So I taped the center of the strip to the bottom of the guitar and worked my way around the body fitting the strip a few inches at a time, taping the binding strip as I went.
To add a bend to the plastic is just a matter of heating the plastic until it deforms easily, then holding it in place while it cools. It really doesn't take a lot of heat - I did this using a heat gun, but I think that was really too hot - a hair dryer would probably have worked better. I don't own one though - and didn't want to spend any more money for such a thing (but now that I think of it, I could probably have just checked out a couple local thrift stores and picked one up for a buck or two).
The tight curves at the end were the most challenging. I just worked a few inches at a time, taping the binding as I went, making sure I could tape it with no gaps when it came time to do the same thing with glue.
The front will not require a splice, as the binding ends at the neck pocket. The back does, however, and I figured about the best place for a splice would be behind the neck - the other choice being at the bottom of the guitar, though I thought with all the curves it might be easier to work with the binding at the end of it's run rather than in the middle. I cut the binding strip to length where the two ends met, being extremely careful to make a perpendicular cut on each end.
Then it was just a matter of gluing the binding into place - again, I started at the bottom of the guitar with the middle of the strip and worked my way up each side, taping it in place as I went, then let it sit for a full 24 hours to let the glue cure. I used the Weld-On cement StewMac sells to glue the binding in place.
It went fairly well, at least for the most part.
When I was finished with the back, I repeated the process for the top of the guitar. There were two significant problems I ran into. The first was this:
Now how did I let that happen? I thought I was so careful when cutting the thing to length. Ugh... To fix it, I cut a thin slice of binding strip and glued it into place - the glue literally melts the plastic, so it should be a sound repair.
When the glue was dry, I trimmed off the excess and scraped and sanded the joint so it was flush. It does leave a little bit of a line, however.
I've read where you can take a small piece of binding strip and place it in a capful of acetone, which will melt the plastic giving you a little plastic paste you can fill small gaps with - this binding strip must be of a different type of plastic as I couldn't get it to do that... It's not all that obvious on the guitar, so this will work.
The other significant issue I had with the binding was it didn't always adhere as well as I think it should have. You can see it in the curve of the body in the photo where I cut the strip to fill above, and on the top I could pull the binding out here at the bottom of the guitar:
That was disappointing, to say the least... I guess you can't expect what is essentially a PVC glue to hold all that well to wood. To repair these gaps, I held the offending areas of binding out with my finger like in the shot above and wicked in some thin CA glue into the void, then held that all in place until it dried - problem solved for now, but next time I want a better solution. I tested some glues, more on that in a bit...
To finish the binding was a simple matter of scraping it flush with the body, simply enough done with a hand-held scraper:
From here, it can be sanded and treated just as the rest of the body is.
I want to do this better next time - specifically, I want a better glue. Now, some sort of plastic glue will be necessary to have on hand for purpose such as the repair above, where one is gluing plastic to itself, but for gluing the binding to the body, there has to be a better solution. A little testing was needed... First, a plastic glue or CA glue is commonly used for this purpose, so I decided to try a few different plastic glues against a gel form CA glue.
I had read somewhere that Testor's model glue was for all intents the same thing as Weld-On and could be used in it's stead - so I picked a bottle up at the local hobby store and by happenstance I was in the hardware store I noticed they had Duco plastic model cement, so I picked up a tube of that as well. I knew each would work well for gluing plastic to itself, but besides being a bit of a skeptic having not done much in the way of gluing plastic to wood in the past I didn't know how each would hold onto wood... So I set up a little test to see. I glued a short strip of binding to a piece of beech with each glue and let it set for 24 hours. The contenders were, in order:
First thing I noticed - the three plastic cements are NOT all equal. They each smell distinctly different, and carry different material warnings on their labels.
Now - this is wholly subjective, and I don't claim to be any kind of expert - my test was simply to pull the binding strip off of the wood to see how well each held on. For a rating system I'll use a 1 to 10 scale - let's say that this was a wood to wood joint done with wood glue as being the standard for a score of 10; a rating of 5 for the absolute minimum I would consider using; and a rating of 1 would be a complete failure. My ratings for each glue would be:
My rating: 5. It came off fairly easily, and while I wouldn't say it impressed me, I would think it to be sufficient enough of a hold to work (good because it's sold for that purpose!).
#2: Duco Plastic Model Cement
My rating: 3. It came off more easily than the Weld-On. I don't think I would use this stuff.
#3: Testor's Model Cement
My rating: 2. This stuff barely held. I definitely would not use it for binding.
#4: Loctite CA
My rating: 8. The CA held just about as well as I think you could expect any glue to hold plastic binding in place on a wood base. It wasn't as good as a wood to wood joint with wood glue - but the joint was very strong.
My take - The strongest was by far the CA glue - it's short working time would enable you to only glue a few inches at a time at best, but I think that's what I will use next time.
The Weld-On worked also - and while I wouldn't call it a "strong" joint, it does the job. I did end up using the Weld-On for this project, but was ultimately disappointed - I ended up fixing gaps where it just didn't hold well - using CA.
The other two - they just didn't hold nearly well enough for me to even consider using them.
Now, I had an idea of what held well and what didn't as far as those glues go, but I wanted to take it a little further - CA is a good glue, but it's working time is very short - so I decided to test a few more glues in the same manner to see what else might work. Here, the contenders are:
I didn't include hot hide glue - I didn't have any ready at the time I put the test together - but the liquid hide glue should suffice as a test for it as well, as once they are dry they behave very similarly. Neither did I include polyurethane glue - I don't allow that stuff in my shop - nor did I include any kind of epoxy, as you are just asking for trouble using that here, at least in my opinion.