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Message started by fritsauce on Jul 19th, 2009 at 9:04am

Title: Side Bending Question
Post by fritsauce on Jul 19th, 2009 at 9:04am
Hello everyone, i recently purchased a Hana Lima Tenor uke kit. So i am currently in the process of making the jigs i will need to hopefully build a uke that sounds and plays nice.

My Question is:

When using the tenor plans i recieved with my kit, do i cut the outline of my jig to the exact size of the outside of my ukulele plans or do i make it slightly smaller to take into account the wood, metal and blanket.

If i do make it smaller should i use the inside line from the plans.

Thanks, Alex

Title: Re: Side Bending Question
Post by mblue on Jul 19th, 2009 at 1:20pm
Hi fritsauce. When I made a bending form/jig, I did as you are saying here, and made it smaller, to compensate for any heat blankets, metal bending straps, etc.

Title: Re: Side Bending Question
Post by fritsauce on Jul 19th, 2009 at 5:17pm
Thanks mblue, how much did you compensate?

Title: Re: Side Bending Question
Post by mblue on Jul 20th, 2009 at 1:25pm
I measured the thickness of my heat blanket and bending strap together (about .085 inch). Then, on the plans, I drew a line .085 inch inside of the line on the plans, and used that line to go by for the jig..
It worked ok.. However, I ending up buying a luther's bending iron, and I like using it better than a bending jig. The iron takes more time. However, I feel like I had more control with the bending iron. I like being able to see how the bends are looking as I go. Also there is less chance of scorching.

Title: Re: Side Bending Question
Post by Don_Orgeman on Jul 21st, 2009 at 4:12am

Bend is not a precise science.  You will probably get some spring back after bending on the jig.

I used the line for the inside of the lining on the plans as the template line for constructing my bender and it worked out well.


Title: Re: Side Bending Question
Post by unkabob on Jul 21st, 2009 at 6:44am
I agree with Don about the springback of sides after molding. The aim is to get the sides close to correct and spring them into position on the solera.

My work may be considered sloppy but the finished instrument never quite matches the outline on the solera. If you want a perfect profile, use an exterior mold that Pete Howlett uses on youtube rather than the solera. The tooling is more geared to commercial production and is much more complicated to build.


Title: Re: Side Bending Question
Post by Jeff B on Jul 22nd, 2009 at 5:51am
Some really good ideas, guys.

I'm about to build my side bending jig and I'm thinking of maiking the mold form slightly wider than the width of two sides so I can bend both of them at the same time.

Most commercial ones don't appear to do this but I saw the idea executed somewhere. It would save time because you're bending both sides simultaneously and you should (theoretically) get the same shape in both pieces.

But I see some drawbacks in that it may make it harder to get both sides aligned properly and would certainly require more pressure from the end and waist clamps. Might be other issues I'm not foreseeing.

What are your opinions of this idea? Or should I stick with bending one side at a time?

Also, anyone have experience using incandescent light bulbs as a heat source within the jig as opposed to the heat blanket? I'm thinking of putting 3 ceramic bulb sockets evenly spaced inside the jig and covering the wood inside with aluminum foil to prevent the jig wood from being scorched. The sockets are rated for up to 600W each - though I wouldn't put bulbs of that wattage in them. Probably more like 150 watts each.

On a Home Depot trip I bought some perforated aluminum sheet to make the part of the form that the sides will rest upon during the heating process. I figure this will allow a fairly solid surface for the sides, let the heat through, and also allow the steam to escape. I'll use a solid sheet of stainless steel as the top cover over the sides as they are being bent to trap the heat and steam in the wood below it. It seems to make sense in my head, but I may be looking at the dynamics of it all wrong. Again, opinions?

I bought a neat little digital thermomenter yesterday that has a remote probe and several alarm capabilites and a BIG (2" high) readout. It can measure temps up to 400 degrees. and can sound an alarm when a specific temp has been reached or exceeded. It was just $40. Anyone interested in it let me know.


Title: Re: Side Bending Question
Post by unkabob on Jul 22nd, 2009 at 8:08am
I alway bend both sides at once. I always put the soundboard sides together and mark the high-point with felt pen and mark the mold at the high-point. I tighten the lower-bout bar to keep the highpoints in place and then slowly lower the waist-caul. This draws the waist material from the head end so work slowly.

I use two 150 watt bulbs in ceramic holders on a 1"X6" base. The mold sides slide down the side of the base and angle-brackets front and back hold the mold in place. This way you can fit other body molds on the same base.
My last build,a baritone, I built an eight inch wide mold and the bending forces caused the aluminum to oil-can, causing so-so bends.

A video on youtube from Taylor Guitar quote 285 degrees for bending. I would work in the 230-250 range but that is just a guess.

Taylor wrap their sides in paper to retain oils on heating. Pete Howlet uses aluminum foil to retain water and it worked well for me last time.

Good luck


Title: Re: Side Bending Question
Post by Jeff B on Jul 22nd, 2009 at 9:42am
Thanks, Bob.

I just saw a video of a guy using a Fox bender to bend mahogany sides for a guitar. He blanketed the wood between wet kraft paper, aluminum foil, stainless steel slats, and a heating blanket on top and set the whole sandwich on the form with the waist mark under the waist caul. He let the temp get up to 370 using a temp probe stuck between the sandwich. He watched for steam to rise then slowly brought the waist caul down to about 1/2 inch above the form, then pulled the bottom caul carefully down over the bottom of the form. Then he set the top caul. That done, he tightened down the waist caul and let it "cook" for 15 minutes.

After 12 hours, he removed the wood and had a perfect bend. Very nice process. I'm now thinking of translating that process to the light bulb heat source instead of a heat blanket. My bender will be similar to the Fox bender, designed so that different size forms - from soprano uke to dreadnought guitar - can be mounted in it.



Title: Re: Side Bending Question
Post by Don_Orgeman on Jul 22nd, 2009 at 12:49pm

I bend both sides at once.  I built my bendder using 12 inch wide heavy guage tin and used two thicknesses of 3/4 mdf on each side giving 9 inches of heated surface to work with.  I have 1/2 inch aluminum rods drilled into the inside mdf layers to act as heat sinks to help hold heat in the bender.  I use 4 - 200 watt bulbs for heat.

You do not want to use perforated metal for the surface of your bender.  You want to trap the heat from the bulbs inside the mold to get the surface really hot.  Perforations allow the heat to escape instead of being transferred to the sides.  Perforated material is good for the bands because they allow the steam to escape as you bend.

If I had it to do over, I would spring for a heat blanket and build a simpler bender form.  If you plan to build several ukes the investment isn't too great.  If you plan to build guitars in the future, maybe you would want to buy a guitar blanket now -- especially if you plan to bend both uke sides at once.

Using the light bulb bender with the heat on the bender, I like to bend the waist using a hot pipe heated by a propane torch and then immediately transfer the sides onto the light bulb bender.  That way you are not attempting to bend the waiste into the form with minimal heat.

Anyway,  food for thought.


Title: Re: Side Bending Question
Post by jack on Jul 24th, 2009 at 2:04am
I bend sides for guitars or ukes at the rate of about 1 per week.  I use a heat blanket, and make my bending forms the thicknes of the sides smaller than the outline.  Remember that it is the heat, and not the water, that makes the sides soft enough to bend.  I bend between 2 sheets of stainless steel, which I get from a commercial kitchen supply place for about $10 a pair.  Put the probe from the thermometer between the blanket and steel, as it can stain.  If I am using a really high oil wood, I do wrap in brown paper to avoid staining.
I got my bender from blues creek guitars, and block it up to handle ukes.  I just finished a kasha baritone/ cutaway in rosewood, and had no problems with the bend.  I can't imagine why you would need to bend both sides at once.  I bend between 250 and 290 F
You can see me bending a rosewood side for a guitar at my web site www.hastingsmade.com under the media section.  I built my first 2 ukes just using an iron, but it is so easy to make bending forms, that I now have forms for all the ukes I build.  I just make a single 1/2 pattern in some high quality 1/2" plywood, using a band saw, and spindle sander.  Now take this pattern, and cut 3/4" plywood close to the line, and then use a flush cutting router bit to make all coppies exact. for a uke I make 3 pieces, screm together using 1 1/4" spacers to get a bending form just over 4" wide.
Hope this helps, I find it is plenty of work to bend 1 side at a time, and do it acurately!

Title: Re: Side Bending Question
Post by Jeff B on Jul 25th, 2009 at 6:42am
Thanks, Jack.

Probably right, not a good idea to bend two at once. Viewed your video and it helped a lot.

Can you give me some details on how you constructed the waist caul? I can't discern them from any of the photos I've seen. I also noticed you have springs on the caul that are located differently from those I've seen on the Fox bender. Also, what is that metal rod that appears below teh waist in the form? How does that function?

Someone commented on my choice of perforated metal on my bender's form. I actually saw this in use on the bender pics that Hana Lima I'a uses. The perforated sheet is permanently mounted to the form and allows heat from the bulbs to penetrate the wood while still providing sufficient support. I would still sandwich the wood between wet paper, aluminum foil and then the metal slat.


Title: Re: Side Bending Question
Post by jack on Jul 25th, 2009 at 11:52am
The rod under the waste is actually a 1/2" bolt which I use on all of my forms to hold them from moving in the bender.  I move the springs arround, based on the size of the body.  My center caul is made by blues creek and I think he has applied for a patent.  It is a piece of heavy gauge stainless in a loop, and you can adjust radius by placing dowels of various diameters inside.
good luck
by the way, I had a fox bender with light bulbs (3x150) and switched to blues creek with the heat blacket, and sold my fox.  Charels Fox is a great guy, but I think some of the other suppliers, are as good or better, for less money.

Title: Re: Side Bending Question
Post by Jeff B on Nov 13th, 2009 at 4:42am
I got sidetracked on my bending jig. Recently decided to buy the heating blanket from Asa rather than fool with light bulbs.

I happened to see the automated bender that Taylor Guitars uses and it is interesting to note that they have a slight "under-bend" in the top and bottom bout areas of the form. This means that the wood is pulled farther than needed for the finish bend to avoid too much spring-back when the wood is removed from the form. I think I'll do that when I make mine.

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