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side bending jig
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=29029		 Page 1 of 1
Author:  alan stassforth [ Sun Sep 12, 2010 11:28 am ]
Post subject:  side bending jig
okay. i'm tired of bending on the pipe,
and i build the same shape,
so i'm gonna build a bending jig.
i don't want a big contraption, and don't got any bread to spare.
i'm going to use 3/4" ply for the shape,
lined on the inside with sheet metal so it don't catch fire.
the curves will be slightly exagerated for spring-back.
then screw heavy galv sheet metal over the top.
then put 2 light bulbs inside at the upper and lower bouts.
i would bend the waist with the pipe first,
then let that jig heat up to do the upper and lower bouts,
using a heat gun to speed up the heating process.
sound good?
any suggestions?
oh, i'd use eye hooks with wing nuts at the waist and ends of the jig,
with wood blocks to snug the side to the jig.
Author:  John Killin [ Sun Sep 12, 2010 1:18 pm ]
Post subject:  Re: side bending jig
That is sort of how I made my uke bender.

The one thing I did differently which was cheap and easy was instead of using sheet metal on the inside to keep it from burning, I used that aluminum tape that they use to hold AC ducts together. It worked great and is still on there.

Good luck.

John
Author:  meddlingfool [ Sun Sep 12, 2010 1:51 pm ]
Post subject:  Re: side bending jig
Also you can use heat resistant spraypaint like for bbq's which also comes in reflective silver
Author:  alan stassforth [ Sun Sep 12, 2010 4:46 pm ]
Post subject:  Re: side bending jig
thanks guys.
i was thinking drywall to line it as well.
we'll see what happens.
Author:  unkabob [ Sun Sep 12, 2010 8:44 pm ]
Post subject:  Re: side bending jig
I always line my molds with aluminum foil and fasten it with thumb-tacks. since it has almost no contact with the sides there is almost no heat transfer to the sides.

I use aluminum flashing for the bending surface but you need cross bracing (3/4"X 3/4") every 4 or 5 inches to avoid oil-canning. Springback is not much of a problem if you leave the side clamped to the mold (without heat) over night.

I use flashing aluminum over the side to protect the foil that the side is wrapped in.

I use 2 X 300 watts for heat but for a Wiesenborne you might need a bit more. My bulbs are mounted on a separate base so that I can use it with several molds. Be careful with aluminum foil and electrical wiring.

Bob
Author:  Pat Foster [ Sun Sep 12, 2010 9:06 pm ]
Post subject:  Re: side bending jig
I tried the wingnuts thing and went to clamps. Simpler and faster. I had these cheapo Harbor Freight clamps that aren't any good for anything else.

Attachment:
l13.jpg
Author:  Michael Smith [ Sun Sep 12, 2010 11:49 pm ]
Post subject:  Re: side bending jig
I would suggest getting a 15 minute timer so if you screw up and forget to turn it off you are not likely to burn your shop down. 1/4" tile backer board (the white stuff would make a good fireproof liner for sides. I don't think you will need to bend the waist on a pipe first. You could just put some tin foil at the waist so as not to lose heat in that area before the bend for the waist press I think you would be happier using a large deep throated clamp if you are not going to buy a press type screw. Regular threaded rod requires too many turns to get anywhere. I tried it.
Author:  Michael Smith [ Sun Sep 12, 2010 11:53 pm ]
Post subject:  Re: side bending jig
I would suggest getting a 15 minute timer so if you screw up and forget to turn it off you are not likely to burn your shop down. 1/4" tile backer board (the white stuff would make a good fireproof liner for sides. I don't think you will need to bend the waist on a pipe first. for the waist press I think you would be happier using a large deep throated clamp if you are not going to buy a press type screw. Regular threaded rod requires too many turns to get anywhere.
Author:  alan stassforth [ Mon Sep 13, 2010 6:10 pm ]
Post subject:  Re: side bending jig
thanks for the ideas.
it's building itself in my head with some of these improvements.
Author:  Hesh [ Mon Sep 13, 2010 6:42 pm ]
Post subject:  Re: side bending jig
Alan buddy the problem with bending the waist by hand is that the way a bender works is to sandwich the wood between metal slats. The slats can be stainless or spring steel and the way that they work for us is to help contain and direct the heat on and to the wood. In addition the slat on top of the wood helps support it not unlike a splint of sorts providing some protection against blow-outs of the wood and cracking. Slats help but are only part of the equation.

So this concept of the sandwich with the wood in the middle would be more difficult to put in place possibly if the wood does not start flat, get placed in the bender with slats and then the bending begins. That's my problem with bending the waist by hand. Many of us will touch up sides on the pipe and by hand after taking them out of the bender as necessary.

Also I heard ya about funds but even though light bulb benders have bent lots of sides very few if anyone I know uses bulbs. A heating blanket is not only far faster and more effective it may cost less than the price of one medium priced set of wood. It's insurance against cracking sides but not the magic bullet - that does not exist or at least I don't know what it is...

If you have budget for say $150 in wood get a blanket instead and I would suggest Blues Creek as a source for great blankets. Also ask the sponsors for practice sides which are a great aid in learning to successfully and effortless bend sides.
Author:  John A [ Mon Sep 13, 2010 6:50 pm ]
Post subject:  Re: side bending jig
but for the $150 in blanket - you have to add $ for slats too.... what else is needed ? timer / regulator ?
Author:  Jody [ Thu Sep 16, 2010 8:26 am ]
Post subject:  Re: side bending jig
I would use three bulbs.. If you use a stainless steel slat for the curve of the form, you can scrap all the bracing rods most plans call for.I lined the inside of my form with aluminum flashing, then sealed the seams with hi temp silicone gasket material ( comes in a tube at your auto parts store). the lightbulbs worked great in class supervised by a master builder,( using walnut) , it didnt work so well for me on some thin mahogany sides I attempted to bend .. so I just ordered a blanket, to heat the top side, and I will still use the bulbs for the underside . Jody
Author:  Rick Davis [ Thu Sep 16, 2010 10:16 am ]
Post subject:  Re: side bending jig
My homemade bender is made from scrap plywood, three sockets, a dimmer and a timer. For the waist, I make a dedicated caul for each form that presses against the form -- no need to have it press the middle of the slat if it conforms along the edges. Threaded rods rather than an Acme press screw. Ends are held down with simple metal bars that swing into position. For years, I used three bulbs, 100 watt for the waist, 200 watt for upper and lower bouts. Works fine if you're careful. I've gone to a heating blanket and it's better but not foolproof and I had to upgrade the dimmer to handle the added wattage.

The biggest money-saver is going to your local sheet metal supplier and buying 6" X 36" strips of the thinnest stainless stock he has. I used to get mine at a HVAC supplier outside of Burlington VT for about $5 each (and a six-pack for the guy who cut the strips).
Author:  Mike OMelia [ Thu Sep 16, 2010 9:31 pm ]
Post subject:  side bending jig
I gotta give a +1 to Hesh's comments. I recently rebuilt my fox bender with mdf instead of plywood. The base section is plywood still. The bending shapes are mdf as well with poplar separator spars. Not expensive, prolly not a good idea for light bulbs. Save money, use mdf (good in tension) and put your money in a blanket. Absolutely stunning at how easy wood bends with the blanket.
Author:  alan stassforth [ Thu Sep 16, 2010 10:27 pm ]
Post subject:  Re: side bending jig
thanks again all.
i will get a blankey.
don't need a bender right now, so i can take my time.
i have a variac that i intend to use for temp adjustment,
and will try some scraps of wood.
thanks again,
you rocccckkkk!
Author:  murrmac [ Fri Sep 17, 2010 7:40 am ]
Post subject:  Re: side bending jig
Hesh wrote:
Alan buddy the problem with bending the waist by hand is that the way a bender works is to sandwich the wood between metal slats. The slats can be stainless or spring steel and the way that they work for us is to help contain and direct the heat on and to the wood. In addition the slat on top of the wood helps support it not unlike a splint of sorts providing some protection against blow-outs of the wood and cracking. Slats help but are only part of the equation.

So this concept of the sandwich with the wood in the middle would be more difficult to put in place possibly if the wood does not start flat, get placed in the bender with slats and then the bending begins. That's my problem with bending the waist by hand. Many of us will touch up sides on the pipe and by hand after taking them out of the bender as necessary.




But if you are using a form heated by lightbulbs, which already has a stainless steel strip screwed to the bending form, surely then you will only need one slat on top ? In that case, wouldn't you have to bend the waist first, prior to screwing down the waist caul ?

Or am I totally missing something ?
Author:  Markus Schmid [ Fri Sep 17, 2010 4:36 pm ]
Post subject:  Re: side bending jig
Hesh wrote:
[...]
Also I heard ya about funds but even though light bulb benders have bent lots of sides very few if anyone I know uses bulbs. [...]

Not too far from now, virtually nobody will bend sides with a light bulb bender because normal light bulbs will disappear: in the US some years later than in Europe. Here in Switzerland, within the last year traditional light bulbs virtually disappeared. So if you really want to rely on lightbulbs, buy your lifetime stock now or you'll have to upgrade later on to another heating source ...or run the bender with energy saving bulbs... :lol:
Author:  Chuck [ Sat Sep 18, 2010 5:30 pm ]
Post subject:  Re: side bending jig
So can I use MDF for the sides of my bender? I was planning on using 3/4 and then cutting the slots in the MDF with the router. Maybe I need to used 3/4 inch plywood for the sides of the bender. What do you think?
Chuck
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