Bending woes, trying to improve

[Eric Knapp]

Hello, I'm sure learning through mistakes! I got the binding for the back of my first guitar bent and glued on, although poorly in some spots. Now I'm trying to bend the top binding and it is breaking and twisting so far out of alignment that it might not be usable.

The first mistake is I didn't get all four binding pieces bent before gluing. Lesson learned. Now I'm trying to figure out how to recover. Woodworking procedures require materials, tools, and technique.

My material for the bindings was a piece of rosewood. When I cut the strips they warped a lot. I think there was too much tension to be used for binding. I was hoping that the bending process could straighten out the twists and that helped. But, then they started breaking. I even used SuperSoft 2 and they still broke. If I use a different board the top and back bindings won't match. Sigh...

My bending iron is really old. I got it from LMI in the 1980s and it seems either too hot or too cold. I am wondering if I should keep trying or upgrade to a newer system. I see videos of people bending well with a steel pipe and a torch, or even a charcoal fire.

My technique is probably not good at this point. I'm learning and improving but very slowly. Not having someone to show me how to bend is making it difficult to learn. Youtube videos only help to a certain degree.

What advice do you experienced folks have for me? New tools, buy pre-made binding? Just keep practicing? I'm stumped.

Thanks,

-Eric

[Bob Gramann]

When you cut your own bindings out of boards, you have to watch for runout. I usually don’t and deal with the results. Many woods, rosewood included, can be joined with scarf joints across the face almost invisibly. When the break happens. go back before the detectable runout on the not bent yet end and cut the binding at the same angle on each piece. That way, the whole piece doesn’t have to be discarded when it breaks. Premade binding is expensive. I only use it when I don’t have the wood I need.

I usually find that bindings bend best dry often with a little more heat than was used for the sides. When I’ve measured, 300-350F seems to be good. I use a 2 3/8” aluminum pipe with a charcoal lighter squeezed inside. I use a 600 watt dimmer to control the heat. I glue the binding to the guitar as soon as I get it bent. If it cools for a while, it gets much stiffer and harder to match to the sides. Bending all four pieces before installing them takes too long—they get stiff and hard to fit.

[Barry Daniels]

When I upgraded to a Fox Bender, my bending results improved dramatically. I still use a pipe for touch up and it consists of a thick walled brass pipe heated with a propane torch. Thin walled pipes never seemed to hold enough heat.

[Eric Knapp]

When I upgraded to a Fox Bender, my bending results improved dramatically. I still use a pipe for touch up and it consists of a thick walled brass pipe heated with a propane torch. Thin walled pipes never seemed to hold enough heat.

Which bender did you get? What do you recommend if I decide to go that way?

Thanks,

-Eric

[Eric Knapp]

When you cut your own bindings out of boards, you have to watch for runout. I usually don’t and deal with the results. Many woods, rosewood included, can be joined with scarf joints across the face almost invisibly. When the break happens. go back before the detectable runout on the not bent yet end and cut the binding at the same angle on each piece. That way, the whole piece doesn’t have to be discarded when it breaks. Premade binding is expensive. I only use it when I don’t have the wood I need.

I usually find that bindings bend best dry often with a little more heat than was used for the sides. When I’ve measured, 300-350F seems to be good. I use a 2 3/8” aluminum pipe with a charcoal lighter squeezed inside. I use a 600 watt dimmer to control the heat. I glue the binding to the guitar as soon as I get it bent. If it cools for a while, it gets much stiffer and harder to match to the sides. Bending all four pieces before installing them takes too long—they get stiff and hard to fit.

Thanks, Bob. These are good tips. I’ll try to measure the temperature of my pipe again. I suspect it’s too high as I’m getting some burning. I’ll also try to repair a split with a scarf.

-Eric

[Clay Schaeffer]

Plastic bindings are much easier to fit, and may not be a bad way to go until you have more experience bending wood. A well fitted plastic binding will look better than a poorly fitted wood one.
I use plastic on most of my instruments because I think it is a better material for the intended purpose, but I do use wood for some instruments.

[Bryan Bear]

When I was first learning to bend on a pipe, I had much more trouble with bindings breaking than sides. I think I was rushing things more than I would with a wider piece of wood. Since the narrow bindings felt less stiff, I was trying to bend them before they actually relaxed from the heat. Keep the binding moving on the pipe and let it heat up slowly along a good length. Keep it rocking and sliding. Practice getting the feel for when the wood relaxes under gentle pressure instead of trying to bend it.

[Peter Wilcox]

Keep the binding moving on the pipe and let it heat up slowly along a good length. Keep it rocking and sliding. Practice getting the feel for when the wood relaxes under gentle pressure instead of trying to bend it.

I think that is the most important part. Patience.

I also put a dampened folded paper towel over the pipe between the pipe and the wood. I don't know if it's the moisture, or the better contact with the heat from the pipe, or both, but it makes the bend easier for me. I redampen the towel as needed (and when it chars I use a new one. )

[Alan Carruth]

I use a stove thermometer to monitor the temperature of my bending iron. Over the years I've crept up to higher temperatures, and gotten better results. The trick is, of course, to avoid scorching the wood.

My take on it is that the lignin 'glue' that holds the wood fibers together softens with heat, and that's what allows us to bend wood. It actually softens at a fairly low temperature; somewhere around 180F iirc, although that probably varies a bit with different sorts of wood. The trick, though, is that the softening temperature seems to vary with the moisture content of the wood, the lower the moisture content the hotter you have to get the wood to bend it. Eventually, as you drive off all the moisture, it won't bend at any temperature below the scorching point, which is often around 350-375 F, and may be lower with low moisture. So the deal is that you want to get the wood up to the bending temperature fast, and bend it before all the moisture goes out.

To that end I tend to run my iron at around 325 F these days. Use a back strap to help hold in the heat, and put pressure on the outside of the bend: the wood often seems to fail first on the outside, often by peeling where there is run out. Moisture seems to reduce the strength of the bond between fibers, increasing the peeling problem, so if you want to add moisture put in on the inside of the bend. This is especially germane with figured wood; the rule is 'more heat, less water' for curly maple.

To avoid scorching you keep the wood moving. Get it hot enough to bend in one spot, bend it, and slide the piece down, chasing that hot spot along as you go. Keep in mind that the wood will tend to retain the shape it has when it cools off, so you have to keep some stress on the part that you just bent when it's off the iron.

You control the amount of bend by how fast you slide the wood along; slower gives a tighter bend. I like to over bend by a fair amount on the first pass if I can; it's usually easier to straighten out an over bend than to get more bend in something that wasn't taken far enough. I'll over bend the whole thing, allow it to sit and stabilize over night, and pick up some moisture from the air, and then come back and correct it the next day. It is far more important that the curve be smooth rather than right.

The wood tends to remain somewhat plastic for a while after it cools off. If you sit too long on one spot, or if there's some tricky figure, you can make a corner, with a flatter spot on either side. If you try to flatten out the corner right away, and then bend the flats, the corner will re-bend, and you're back where you started, but with less moisture in the wood and probably some stress too (and not just in you!). The way to go about this is to bend the flats first, getting them as close as you can to the curve of the corner. Then allow the part to sit for a few hours or over night, and straighten it all out as much as you need.

Hand bending of this sort is one of those 'luthier' skills that not many other woodworkers develop. Once you get the feel of it it's rather enjoyable. I often use it as a demo at the local crafts fair, partly because it's 'different' and partly because it's one of the few things I can do out doors on an August afternoon. One time a bent a set of apple wood sides, which went like butter. I left the bent sides out on the bench in the tent overnight, and when I got in the next morning they were straight again. I got two demos out of one set of sides. After that they went right into the outside mold with some turnbuckles, which put an end to that foolishness...

[Eric Knapp]

Plastic bindings are much easier to fit, and may not be a bad way to go until you have more experience bending wood. A well fitted plastic binding will look better than a poorly fitted wood one.
I use plastic on most of my instruments because I think it is a better material for the intended purpose, but I do use wood for some instruments.

That is sage advice and I think I’ll do that on my next guitar. Having been a woodworker for so long made me want to use all wood first. That has really slowed me down.

-Eric

[Eric Knapp]

I think that is the most important part. Patience.

I was trying to be patient but I think it was not enough. That s a good tip and I’ll try to slow down.

I also put a dampened folded paper towel over the pipe between the pipe and the wood. I don't know if it's the moisture, or the better contact with the heat from the pipe, or both, but it makes the bend easier for me. I redampen the towel as needed (and when it chars I use a new one. )

I’ll try this the next time I head to the shop. I think my pipe is too hot too.

-Eric

[Eric Knapp]

I use a stove thermometer to monitor the temperature of my bending iron.

<snip>

Thank you, Alan. I’m going to save this thread as there is a lot of good information in it. Your comments are very valuable. You’re right about most woodworkers not bending wood much. This guitar is my first time with it and after a whole lifetime of woodworking I feeling like a total rookie. I’m going to keep practicing.

-Eric

[Karl Wicklund]

I agree that the key is just doing it a bunch. Practice.
On the other hand, however the guitar turns out, leaving you satisfied, have at!

[Eric Knapp]

I agree that the key is just doing it a bunch. Practice.
On the other hand, however the guitar turns out, leaving you satisfied, have at!

Thanks, Karl. I will be very satisfied with my first guitar. It's taking forever but I've had a few diversions along the way. It will get done and I'll start on the next one. Someday I want to make a good one. I can dream, eh?

-Eric

[Dick Hutchings]

Plastic and celluloid are the easiest and give better protection. Wood can look better sometimes but really doesn't offer the same protection from bumps. I don't buy celluloid anymore because of the hazmat fee so I'm stuck with wood or plastics that I don't like. Oh for the good old days of buying gorgeous multi-ply celluloid, 20 years ago, maybe less.

[Alan Carruth]

Celluloid is a snare, and so is cellulose acetate, but less so.

I made some celluloid back in high school as a science fair project (imagine that today!). Cellulose is rendered soluble in organic solvents using nitric acid, and the nitrocellulose that's formed can be a high explosive if it's nitrated enough. You have to get to about 18% nitration to make it soluble, so basically one molecule in six is 'explosive'. That's not concentrated enough to explode, but it sure is flammable, which is why they don't allow it to be shipped in bulk. It's unstable chemically, and breaks down over time, and it goes much faster with UV exposure. As it breaks down it shrinks and becomes brittle, and it also out gasses nitrates, that react with water in the air to form nitric acid. Cellulose acetate is made in a similar manner, if I understand correctly, and out gasses acetic acid; less bad, but bad enough. Museum conservators consider either material as 'toxic', and have to isolate them from the rest of the collection. The more nitro you have in one place the faster it breaks down.

I saw a Stromberg archtop guitar in the 'Dangerous Curves' exhibition in Boston about twenty years ago that had lots of celluloid binding, a celluloid pick guard, black celluloid for the head veneer, and all finished with a heavy nitro finish. Some of the finish cracks had gone into the wood, the binding was in pieces about 1" long that were falling off, the pick guard was curled up, and the head veneer looked as though it had been torched. It was sad. They didn't include pictures of that guitar in the catalog. You could also see when Martin switched over to nitro finish from the varnish and shellac that they had been using; the newer finish was in worse shape.

Nitro is tougher to begin with than wood binding, but over time wood wins.

[Dick Hutchings]

And I'm stuck in the snare. I want it I want I want it. But, Wood may last longer than celluloid but I don't expect to live long enough to see it degrade. When it does, it's someone else's problem. I know, that's a bad attitude but it's mine Since I can't or won't spend the money on the hazmat fee, I'll be building the modern way with plastics and wood. Now, where can I get fancy multi-ply ABS or CBS or NBC or whatever the heck it is?