Acoustic Guitar Construction

I am using 3 @ 150 watt white bulbs and getting up to 300 degrees in 15 minutes. I started out with 200 watt bulbs and they would burn out after one use....maybe it was a bad batch, but I put in the 150's and found that I still got plenty of heat.
I think the trick for you is going to be to trap the heat inside the mold, and yes, eliminate as much of the "heat sink" as you can.
Then you should be good to go. I got my bathroom countdown timer off amazon for about $25 shipped. I couldn't find them in the stores that went more then 15 minutes....I wanted longer. Mine goes to 45 min if needed.

Kevin

We use Sylvania clear 200 and 300 watters -- can't remember the last failure and the benders are used daily. I stupidly casues a bulb to explode by having one of the aluminum cross bars on a smaler mold ("L00") sitting right on top of the bulb (touching) --- stupidly bcause I did the same thing twice!! The mold now has "change bulb written on the sides" a 150 fits OK

Bender reworked

Very much appreciate all the expert input. Good suggestions all. I reworked my bender by adding aluminum tape all around edges of roof flashing aluminum profile. Changed out the 3-150 w bulbs for 3-200 watters. Got rid of the 6 half-inch bolts for attachment points in favor of dowel rod, and added heat shield under bulbs from more aluminum roof flashing (.015” thk). All of which appeared to be the path of least resistance.

Without loading in a side, I put my oven thermometer on the lower bout and it showed 170 F after 5 minutes, 215 F at 10 minutes, 240 f at 15 minutes, 260 F at 20 minutes, and 275 F at 25 minutes. This looked workable without having to tear it all apart to remove the 1/2” EMT ribs on 2” centers under the roof flashing.

I pre-bent the waist on a piece of the final plain-sawed soft maple surfaced at .085” the other night with the hot pipe and it bent nicely on the modified bender. Just need to do one more.

In the long term, I think I'll build another male bending form to sit on my light bulbs, utilizing 24 ga. sheet metal as the profile, but without all my EMT ribs on 2” centers, maybe just using 4, similar to the bender at http://www.dickeyguitars.com/dickeyguitars/Bender.html.

My base for the unit measures 9-1/4” x 19-1/2” which works out just right for an unused base I had on hand, Central Machinery (Harbor Fgt) Item #7769, Tool Stand Universal (150# max).

For the next male form, I plan to use a cover sheet of 24 gage sheet metal above the side being bent, attached on both ends to a rope going under the bending unit that I can hang weights on to pull the cover down, rather than having turnbuckles at the ends. A better method might be to use one of my nylon webbing load binders with ratchet to draw the cover down, or just hand weights on the ends.

Meanwhile I took the two practice sides I bent with the original 200 F bender configuration, jointed maple on one face, bandsawed on the interior, and glued them together with PW end blocks. Added some practice reverse kerfed linings from white pine, 1/4” x 3/4”. Did this quick and dirty on my old Sears radial arm that I bought in 1966 with my last check from the C&O Railroad, using a way-too-wide carbide 80-tooth blade from a chop box, making almost an 1/8” kerf.

Way to go Will!

I would caution that galvanized can cause nasty stains -- I alway recommend distilled water, but even then I've had some bad experiences and now only use aluminum and/or SS.