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Final Thickness (Read 7338 times)
Heidi
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Final Thickness
Mar 3rd, 2010 at 6:18pm
 
Hello, Can anyone tell me their thoughts on final thickness of sides, backs and tops?
I have had many different numbers regarding sides for example before bending at anywhere from 1.8mm to 1.1mm.
Also when bending sides, do you put your blanket on top or below? Do you soak or just spray with water? Do you use a metal sandwich, a foil covering or wet paper towel? Just want to know what the norm is for KOA. I realize it does depend on the individual piece but just generally?
Thanks, Heidi
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Quine
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Re: Final Thickness
Reply #1 - Mar 4th, 2010 at 10:17am
 
Bending thickness depends on the builder alot.  Most use 1.5mm to 1.9mm.  I usually keep it around 1.8 to have enough room for final sanding.
Soaking or spraying is a choice too.  For koa, I would just spray it.....koa is fairly easy to bend
The blanket is below.....bending form, heat blanket, wood, metal.  I don't use a top metal strip...don't see the need
Wrapping in foil or paper is good to keep the wood resin from burning on the blanket and staining everything
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Heidi
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Re: Final Thickness
Reply #2 - Mar 4th, 2010 at 2:13pm
 
Quin,

Thanks for the info. You had written that you did'nt really feel the need to put metal on top but you wrote it as being on top, did you mean that we did not need the metal on the bottom?
Also what is your final thickness for your top and backs?

Cheers
Heidi
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Quine
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Re: Final Thickness
Reply #3 - Mar 5th, 2010 at 6:23am
 
I don't use metal on top or bottom.  Just the blanket. and maybe paper or tin foil. 
Some builders swear by using the metal straps on the top.  I never tried using one and never had a problem.
My top and backs depend on the wood.  hardwoods like koa or mahogany are 2mm.  spruce would be a bit thicker at 2.4 or 2.5
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unkabob
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Re: Final Thickness
Reply #4 - Mar 5th, 2010 at 6:53am
 
I use a lightbulb bender and I use a metal sheet to protect the sides from damage and to spread out  the load of the bending caul.
Using a bending-blanket, the only reasons that I can think of would be to retain the heat and any steam generated by the blanket and to protect the blanket itself from the moving cauls.

Do whayever works for your setup.

Bob
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Don_Orgeman
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Re: Final Thickness
Reply #5 - Mar 5th, 2010 at 12:40pm
 
Heidi:

Heat blanket on top or bottom is your choice.  If you've allowed for the thickness of the blanket when you made your bending form then put the blanket between the form and the sides.  If you only allowed for the thickness of the sides in undersizing your bending form, then put the blanket on top.

You want to use steel slats to help support the sides as they are bent.  Use both one below and one above.  You want to crank down the waist first but leave a gap of about 1/2 inch between the sides and the form.  Then bend the lower and upper bouts and tightly clamp the sides to the form.  Lastly, tighten the waist clamp to pull the sides tight against the form.

A little spray of water is a good idea to keep the wood from scorching from the heating blanket.

There is a great series of YouTube videos by Blues Creek Guitars on bending sides that should help you out.  Give them a look.  Actually, a lot of John Hall's videos on guitar making can be used with ukuleles including radius sanding of the sides (what he calls "driving the bus").

It is wonderful to see someone posting questions on Hana Lima again.  Keep posting questions and hopefully more of us amateur builders will come back to help you along.

Don
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Heidi
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Re: Final Thickness
Reply #6 - Mar 8th, 2010 at 1:42pm
 
Thanks Everyone.

I have tried out my bender but I have not been very successful. I built my own bender but did not adjust for blanket thickness and therefore I have put the blanket on top. I used "flashing" to cover my bender and also using two pieces of "flashing" for putting the side into after wetting with a spray bottle. So bender, metal flashing, side, metal flashing, heat blanket is the order I used. I tried once without flashing and scorched my sides.  I thicknessed my mahogany sides to 1.8mm. Maybe not getting hot enough with the metal flashing? I have cracked 3 sets at the waste and upper bout. Any help would be appreciated. I would love to add some pictures but can't figure out how.
I am enrolled in the luthier program with Robbie OBrien and presently building a classical guitar, but it seemed really easy to bend the guitar sides, the angles are not as harsh. I have my ukulele back and top braces and my neck carved ready to go, just have to get over this side bending hump. I am saving my pennies to take the summer intensive with Hana Lima  'ia. I love the spanish heal and I think it would be the only place to learn properly. The course is a great price, it is the plane fair and room costs that I am saving for. I would just love to get a couple sides bent right now though.
Heidi

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unkabob
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Re: Final Thickness
Reply #7 - Mar 8th, 2010 at 6:03pm
 
Heidi:
Check out www.discounthotelshawaii.com , I have used them for several years and Hector usually has the best prices or at least the best value. Make sure that he understands what you are looking for.

When you are in a hotel, seek out the maintenance shop. You might be able to do your homework there.

Allegiant Air are starting flights to Hawaii this year and Hawaiian has cheaper flights.

Bob
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Don_Orgeman
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Re: Final Thickness
Reply #8 - Mar 9th, 2010 at 3:59am
 
Heidi:

Your sides at 1.8 mm (0.070 inch) appear to be thin enough, so I suspect a heat problem.  You want the wood to get to a temperature where it bends to the mold with little pressure.

Harbor Freight sells a Cen-Tech Automotive Multimeter (Item 95670) that has a temperature function and includes a thermocouple.  You can put the thermocouple under the blanket to monitor the temperature you are getting.  The current price is $36.99, but I found them on sale a couple of weeks ago at $30 and I had a 20% off coupon, so the price was really good.

I would suggest asking Robbie to help you with the bending.  I have always found that luthiers are the most generous people when asked to help another struggling builder.  That's why Mike teaches his classes at Hana Lima -- he wants to teach others to do what he loves.

I envy you being able to go to Hawaii for the intensive class.  At least you are going at a great time for hotel prices.  Many of the hotels have been sending me emails with fantastic rates.  Agua has one hotel in Waikiki that they were offering at $55 per night with a free upgrade to an ocean view room.  That may not work for you because you may want to be closer to Hana Lima to avoid long bus rides.

Good luck with the bending.  Keep us posted on how it is going.

Don
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Heidi
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Re: Final Thickness
Reply #9 - Mar 9th, 2010 at 12:14pm
 
Thanks for the info everyone.

I sure hope I can go, won't know for a couple months.
Thanks for your help.

Heidi
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stewpot1
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Re: Final Thickness
Reply #10 - Apr 6th, 2010 at 7:09am
 
Hi,

Most of the discussion on this topic has been on side thickness.
What about soundboard and back thickness?
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Don_Orgeman
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Re: Final Thickness
Reply #11 - Apr 7th, 2010 at 3:34am
 
Heidi:

I just got an email notification from the Continental Surf Hotel in Waikiki that they are offereing a free double upgrade to an ocean view room for $55 per night (plus taxes).  The price is good through June 30.

So, if you are going to take the intensive course and want to stay in Waikiki instead of closer to Hana Lima in Honolulu that might be a good option.

Let us know what your plans are.  We are all hoping you can make it.

Don
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unkabob
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Re: Final Thickness
Reply #12 - Apr 7th, 2010 at 4:37am
 
Stewpot1:
I tend to work in mahogany and thin my back and sides to 70-80 thou. Spruce is softer and so should be thicker. I use 85-90 thou. Quine, above, uses 95-100 thou.
Be sure to use the cross-grain graft behind your center butt-joint.

Bob
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stewpot1
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Re: Final Thickness
Reply #13 - Apr 7th, 2010 at 2:20pm
 
Thanks Bob, that's the info i needed!


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