Official Luthiers Forum!

hi everyone just wanted to know exactly what i need to bend a cutaway acoustic guitar
using the fox style bender method

is it nesiccary to have 2 blankets for cutaways
is their any every day things that you could use for a thermostat or a timer ?
could this damage it ?

and gcfi connection ? dont know what that is..
which of these things do i need
and what wattage should i be lookin for
thanks
tomas

HI,

I use a heater blanket 6"x36" (1080w)
an industrial dimmer ( max 1500w) to change temperature,
and a timer,
2 inox sheets (o,5mm).


that's all

I'll take a shot at some of your questions. I haven't bent a cutaway, so can't say if two blankets are needed for a cutaway.

Many of the bending setups I've seen use a router speed controller to control the heat. They are pretty inexpensive and seem to work well. I would advise using a timer. The one that came with my set appears to be like the wind up timers available at various home improvement stores and are used for contolling heat lamps, whirlpools, etc.

A GFCI is a ground fault circuit interrupter. It is used to interrupt the flow of electricity to the electrical outlet should a faulty ground be detected. They are generally required for electrical outlets around a source of water. Again, any home improvement store would have these.

My heating blanket is 1020 watts (120v, 8.5 amps)

I just bent a cutaway, using only one blanket. I did switch over to spring steel
slats instead of stainless steel, to help support the sides and bindings better
through the sharper bends, but I couldn't say this was essential. If you search
on "blankets", or perhaps "controllers", you'll find several threads about using
a relatively inexpensive (on e-bay) industrial temperature controller to use with
the blankets. I use the countdown timer plus a variable control to control temperature,
and to allow me to go and do other things knowing the system will switch off
after a 15 minute max slow cool down period.

_________________
Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

thanks guys i was lookin at one on ebay there but its only 900 watts might not be powerful enough though
might as well get a good one while im at it
looks as im gonna try doing without the other blankey
thanks again very much guys
tomas

contact blues creek guitars...John supplies the blankets and controllers..

I do not and I repeat DO NOT use the dimmer switch. You want a VSI or a Router Speed Controller. Lowering the voltage in a series circuit will lower the voltage but not the current draw and you can burn up or shorten the life of the blanket.
just thought you may like to know

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I fail to see how in a series circuit, the voltage can drop but not the current, with the same load (the blanket - R) ??? Ohms law says its not possible - V = I x R.

In effect, most light dimmers do not drop the voltage .. they chop it up, so in effect the load sees a lower voltage on average. Turn down a dimmer and put a meter on it .. it will still show 120 volts (at least mine does, home depot, 600 watter) - the meter is not fast enough to see the chopping.

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Tomas,
I use two blankets and two spring steel slats (learned this from John Mayes' excellent side bending video) and bending the cutaway has not been a problem. I use a router speed control that has a three way switch - variable, off, full - in addition to the control knob and control both blankets with it as it is an 1800 watt (15A, 120V) controller. I checked each blanket to make sure that at a particular setting on the control that they were at close to the same temprature. I start the heating with the control in the Full setting so that the temp ramps quickly to about 220 degrees F. At that point, I switch to variable which slows and holds the temp at about 250 - 260 degrees F while I do the bending. I then switch back to full until the temp is about 300 degrees F at which point- I switch back to variable and hold at around 300 for 10 minutes or so. I then turn off and unplug the unit and let it cool for a while - an hour or so depending on what other processes I have going on in the shop. I don't use a timer - I know that I should - but I NEVER leave the bender unattended without it being completely unplugged from the power source. The whole bend only takes around 15 minutes from start to finish.

I highly recommend John's video if you're new to side bending.

Good luck,
Chuck

for a completely different approach not using a fox, watch this one .. one blanket, no slats, gloves, hand bending, full width outside mold with an internal plug, bending a fairly tight venetian in about 2 minutes .. english walnut, about 80 thou ....

http://luthiertube.com/video/453/side-bending

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Hi Tomas,
as Mike said, you can get everything from John Hall at Blues Creek. I imagine, as you're in Ireland, that you'll also need a voltage converter, which I think John Hall also supplies now.

There's also a guy called Tom Durr who will make up the whole kit for you including blankets with embedded thermocouples and controls so that you can just dial in the temperature. I seem to think this would cost you around €200. It looks very much like what the guy is using in the video posted by Tony.
http://www.docsstringedinstruments.com/
You won't find anything on his website but if you email him he'll tell you what he can supply. You can see more on the Luthier Community forum here.
http://www.luthiercom.org/phpBB3/viewto ... iac#p17118

There is a heat-blanket bending tutorial by Toddstock in the tut forum.

One blanket in this order, Top to bottom:

Spring Steel
Blanket
Spring Steel
Wood Sandwitch (on bottom)

I use this method, and bend and remove in less than one hour.

I havent done a cutaway, depending on the wood, you may need supersoft, etc.

_________________
Here is what a Parlor Guitar is for!
http://www.youtube.com/watch?v=oEa8PkjO6_I

One blanket is all you need . Heat is heat. As for current , amps in a series circuit will not drop across the circuit load. The dimmer switch if it does as you say would be good. If it is a variable resistor that is where you have a problem. You are forgetting to take the (R) of the total circuit , not just the blanket load.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

If the dimmer acts as a voltage divider, then yes, the whole load must be considered. But the dimmer then also divides the current. Some of the total current goes thru the portion of the resister that is now in parallel with the blanket. Again, ohms law rules .. the divided voltage and the load of the blanket determine how much current goes thru it. In effect, its still exactly the same, no matter how the dimmer works.

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"