Bending Sapele with LMI bender

[BillA]

I'm new here, so if there is a thread about this, I couldn't find it.
Just tried bending sapele sides on my new LMI bender. After carefully watching the video, the first side broke in the middle and I suspect I cranked it down too hard at the end; also left out the waist area, smaller metal sheet. Tried bending the second side (with the waist support) and this time, the side broke at the top of the shoulder as well as the wood becoming warped. There were no scorch marks on the wood either time and there was a bit of moisture left at the end of the wood the second time. I followed all directions carefully and tried to feel the bend. Pretty impressive first try, no?
Anybody have experience with sapele and this set-up? Any help would be appreciated!

[gitnoob]

I don't use that bender, but whenever I break something (usually binding), it's because I either didn't let the bender get hot enough or the wood was too thick.

[BillA]

Well, the wood wasn't thick (about .085-.095'') as I followed the suggestions of Cumpiano and Kinkade. As for heat, it's set automatically and maintained on a thermostat. I could hear and see steam coming from the apparatus. I was thinking maybe the wood was too thin and/or the obvious answer, I just tried to bend it too quickly, even though I felt I was going slowly.

[charles Tauber]

I'm a little unsure of what device you are using. You are using this WITH heated silicone blankets?

[BillA]

That is the one. They make it look easy in the videos! I've used a more basic type before, with springs and no auto-thermostat, and bent some maple. But this was a surprise.

[ZekeM]

It never hurts to go a little thinner. I started with the .085-.095 like Cumpiano recommended. I now go to .07. Much easier to bend. Also you may want to go a little slower with the bend.

[BillA]

Thanks Zeke, I'll give that a try. What about soaking more than just spraying the wood with the water bottle? Could that cause any problems?
Also, what might have caused the rippling, warping of one side?

[charles Tauber]

Sapele is pretty easy to bend, relatively speaking. With the sides the thickness you stated, you either didn't have the blankets hot enough or you didn't allow the sides sufficient time to heat and become more malleable. The other possibility is that the sides had a poor choice of runout. I'm assuming you are not trying to bend extreme curves.

Personally, unless they are extreme curves, I would not thin the sides more than the thickness Cumpiano recommended. By the time they are scraped and sanded they will be even thinner, making them less stiff and susceptible to breakage in use.

The rippling can result from too much moisture during bending.

[stuw]

I use a homemade bender and cracked/warped a side or two.

Since I changed my bending order I have had no issues.

Mist sides wipe off excess water

Wrap in tin foil

Place between aluminum strips ( 6"flashing)

Heat blanket on top

Position side in bender

Bring waist clamp down just firm enough to hold in place

Turn on heat blanket

Wait for steam

Slowly bend upper bout first

Slowly bend waist

By this time my blanket is getting too hot I turn it down

Slowly bend lower bout.

Turn off heat and let sit in bender

As Charles said too much moisture will warp and ripple.

Best of luck on your next bend.

[Aubade Acoustics]

I got rid of the rollers immediately and added my own clamps. Did not feel like it was keeping it tight enough. Make sure and use the small spring steel under the waist section. I mist the wood, wrap in foil, heavy spring steel on bottom, blanket next, wood, small waist blanket, light metal on top. Follow instructions on video. Slow as it goes

[BillA]

Armadillo, I like your new clamps; a bit bulky, but I had the problem of the rolling clamps seeming to push the metal sheet up behind it, taking the side away from the bender and probably the blanket. Since there is a thermostat connected to the blanket, I think the temp was right, but maybe I rushed it. Too much water? I misted the sides once top to bottom evenly and wrapped them up. I thought maybe they would need more since people used to soak the wood before hand bending. I'll leave the thickness where I had it and try more lightly misting the wood. Please don't say "bending sapele is easy"! If I could break it with that much instruction and good equipment, I'd say breaking it is easy, unless you know just what you're doing! Thanks all, I'll repost my next result!

[BillA]

Stuw, several of your suggestions, while they may be valid, are completely contrary to the O'Brien videos using the LMI bender. But, I may give them a go; I couldn't have done much worse!

[Howard Klepper]

FWIW:

I use one of the old style benders that LMI sold 12 years ago. I use stainless steel slats, but actually, the spring steel ones are probably better since they will go flat again after use, while the stainless ones hold a bent shape. I do not put the wood against the blanket. I use three slats, with the wood between the lower two, and the blanket between the upper two. I recommend a three slat system; I think that metal conducts heat to the wood a lot better than silicone. I also don't wrap with foil since I don't have wood to blanket contact, and I want to force the moisture out as the wood is bent--retaining moisture leads to warping.

The old bender had a different way to apply pressure to the outside of the waist that may work better than the extra small slat on the new one. It's a bar held with springs that you can see on many benders. That pressure is important in stopping cracking, which is almost always on the outside of the bend.

I get the metal hot before putting the wood in, and check temperature with a candy thermometer that has its probe stuck between the steel sheets where the wood will go. I don't think there's anything necessary about this method if your new system is calibrated, but I would get a thermometer to check the accuracy of the new LMI system. It looks to me to be inherently inaccurate, because thermocouples vary a lot and may not be well calibrated to the readout. Digital readouts tend to promote a false impression of accuracy; they are no better than what is being input to them. They can be worse. I find that 310º is enough for almost any wood.

I turn the blanket off while I load the wood in. I turn on the blanket again while bending, since I've lost some heat while loading the wood. Since I no longer have the thermometer in, I check temperature by spritzing water at the slats. At about 275º it will start to form small beads that dance on the surface instead of just turning to steam. It's a rough, but helpful indicator.

I don't need to crank down the waist very slowly. I usually take about 10-15 seconds to make that bend. I have no idea why people need to go so slow with the new system.

Last thought: If you say that your thickness is "about .085-.095" then you are not measuring accurately enough. You should know your thickness to within a couple of 1000ths. And I think .095" is too thick. My standard is .080". Remember that stiffness is proportional to the cube of the thickness. At .095 your side is about 70% stiffer than it would be at .080.

I've found no advantage to continuing to heat after bending is complete and I have brought the temperature up to about 300º again, which only takes a minute or two after bending is done. I just turn it off and let it cool. Whatever you do, they will not come out of the bender perfect, with no springback. Get a hand bending iron like the Ibex and use it to touch them up. Hand bending will teach you things you will never learn from the bending machine, and help you to use that machine better.

[BillA]

A lot of interesting thoughts Howard. As for the last, about thickness, I only said I wasn't sure what it was between .085" and .095" because I couldn't remember, without looking, what I'd done. When I built my guitar at Galloup School, we used a spray bottle to determine when the blankets were hot enough and a timer for letting the bend set in and bending the ends. LMI recommends bending at 350 degrees, which it sounds like you would say was to hot. I followed the LMI video religiously because it seemed to work for them, so why not me? I'll try a few of your suggestions and let you know how it goes for me. Thanks for the thoroughness of your answer; everyone on here is very helpful!

[Howard Klepper]

Bill, 310º works for me by my system of measurement. From your descriptions, I agree with Gitnoob that you may be working too thick, or not hot enough, or both. If you are not scorching the wood at 350º, you don't need to go cooler. But I do think you should check the calibration of temperature with a thermometer, and make sure that you are really getting that hot.