How to Use Heat Blanket?

[Kim Strode]

I've just purchased a Heat Blanket from MEI and am seeking advice on how to the get the best results to bend sides.

I've built a Fox style bender with light globes and a dimmer switch for good measure. The mould is made with a stainless steel sheet bent around a custom wood frame and I have a second stainless steel sheet to lay over the top of the side or blanket. At this stage I have not connected the blanket to a thermostatic control.

Can you suggest how you got your best results?

Thanks, Kim

[kiwigeo]

Hesh is the one to ask about using a heat blanket. My method is based on his procedure.

My sandwich from mould outwards is as follows:

stainless steel slat
side wrapped in al foil and lightly spritzed with distilled water.
Staimless steel slat
spring steel slat

I get the sandwich ready on the mold and then turn on the blanket (Blues Creek 110volt job). The blanket doesnt take long to heat up so after about 3 minutes I wind down the waist caul followed by the lower and upper bout cauls. Once the cauls are all snugged up I turn the blanket off for 3-4 hours. I then turn the blanket on again for 2-3 minutes and then turn it off again and leave the sides clamped in the mold overnight.

[Allen]

I've used mine with 2 stainless slats over an MDF form.

I wrap the side in kitchen paper and get it damp with water from a spray mister, then wrap in al-foil to seal in the steam. This is place on top of the first stainless slat, the wood, then the heat blanket and finally the last slat.

I use those large metal toggle clips that you get from stationary stores to hold papers together, to clamp the "package" together. The plastic clamps that I had didn't last 2 minutes with the heat that the blanket puts out.

I just have my blanket hooked up to a domestic light switch that I turn on and off to control the heater. I use a spritz bottle to test how hot the slats are. When the water "pops and spitz" then it's hot enough to start bending. I've got the thermocouple, but just haven't got around to rigging up a controller.

I've just got a form and use bar clamps and cauls to press the slats into place. I clamp the butt into place and the slats are sticking straight up in the air. and then turn on the heat.

After 2 - 3 minutes the side is up to temp. and it starts to sag, this is when I start to help bend it around the lower bout until the slat is fully wrapped across the lower bout, and the slats are touching the top of the upper bout. I then start to clamp down the waist. Not all the way, just partially. I then start to bend the slats around the upper bout and partially clamp this in place. I then alternate between tightening down the waist and the upper bout until everything is nice and snug.

During all this I usually cycle the blanket on and off a few times based on the sound, smell and sizzle from a spritz bottle occasionally sprayed on the slats.

So far I've not destroyed any sides. The first set I did get some cracks in because they were far to thick to start with and I was just to quick to start bending. The kitchen paper has shown some scotch marks from the heat, but I''e never had any marks on the wood.

If you've got the thermocouple installed on your blanket, then be careful of where you position the blanket. I made the mistake of having the thermocouple over the very butt end of one side and the thermocouple ended up denting the wood quite deeply due to the heat and pressure from the clamping. Luckily that was the side that was too thick to start with, so I had lots of material to level it out.

Hope that gives you some idea.

[matthew]

I. The plastic clamps that I had didn't last 2 minutes with the heat that the blanket puts out.

Me too. I do it like Allen.

[Hesh1956]

Nice clamp!!!!!!

Kim my friend here is a toot that I put together a while back that details how I bend sides with a blanket and Fox style bender.

Some of this stuff is optional but still helpful IMHO like the third, spring steel slat, and the third clamp/caul.



http://luthiersforum.3element.com/forum ... l#forumTop

[kiwigeo]

I nearly forgot my most important piece of equipment....a really loud kitchen timer so I dont forget to turn to blanket off. These blankets can get to a very high temperature and before you know it youll be reaching for the marshmellows to roast on your blazing stash of tonewood.

[Hesh1956]

I nearly forgot my most important piece of equipment....a really loud kitchen timer so I dont forget to turn to blanket off. These blankets can get to a very high temperature and before you know it youll be reaching for the marshmellows to roast on your blazing stash of tonewood.

Absolutely!!! I never leave the room when using a blanket and the entire time that my blanket is plugged in is probably less than 5 minutes.

They can and have started fires in some builders shops that some of us know.

[Kim Strode]

Thanks everyone for your feedback and help - I have one further query?

I put a plug on the blanket from MEI today and turned it on. I was very surprised at how hot it got within a matter of a few seconds - is it normal for them to get very hot so quickly. I am concerned it will burn the wood - do I need to run it with a thermostat?

[Bob Connor]

That's entirely normal Kim.

I have a thermometer that is inserted beween the blanket and one of the slats.

Start with it flat out.

When it reaches 120, I'll start the bend and when it gets to 150 either turn it off or dial back the router speed controller to maintain 150 degrees if I think the wood needs to cook a little longer.

[kiwigeo]

Thanks everyone for your feedback and help - I have one further query?

I put a plug on the blanket from MEI today and turned it on. I was very surprised at how hot it got within a matter of a few seconds - is it normal for them to get very hot so quickly. I am concerned it will burn the wood - do I need to run it with a thermostat?

Hi Kim,

Yep these blankets get bloody hot bloody fast and if you leave them too long theyll set fire to your wood...and then your workshop.

A thermostat isn't essential but its useful. I dont use a thermostat with my blanket but I do keep a close eye on how hot everything is getting. I judge when things are hot enough to start bending by spraying water on the top slat. If the water breaks into dancing beads immediately then its hot enough. I also tuck a digital thermometer into the sandwich...I got a turkey basting thermometer with the blanket I bought from Blues Creek Guitars.

As already the most important thing is never to leave the blanket unattended when its turned on.

Cheers Martin

[Allen]

Did that once and the wife said, "Gee I love the smell of that wood".

Never, ever again!

[Lillian]

I have a windup 15 minute timer in line with mine. It's cheap insurance.

[Kim]

I wire myself into the loop, a man can only stand 240 volts for so long before he has to let go of the wire, you got no chance of burning you're wood that way.

(Warning: Please do not do this unless your John Howard, George Bush or Robert Magabe)

Cheers

Kim

[kiwigeo]

Mmm.....I challenge anybody to stand still with 240 volts hurtling through their nuts.

Still if it works for you......

[Kim]

Mmm.....I challenge anybody to stand still with 240 volts hurtling through their nuts.

Still if it works for you......

It takes time Martin, but it's pretty good once you get over the initial shock

[Hesh1956]

Kim my friend this would be an excellent topic for a tutorial.

I can see it now, using jumper cables with VERY strong spring clamps hook-up that 240 volts and be sure to have an assistant take pictures..... Perhaps using a macro lens......

Man is the retaliation going to hurt for this one....

My blanket came from John Hall at Blues Creek and it has a temperature adjustment and a timer built-in and already wired up. I typically set the timer for 7 minutes and kill it manually when 2-3 are left showing. This means that the blanket is only on for 4-5 minutes so this gives you an idea how fast they get stinkin hot........

Does anyone from the OLF crew remember the post a couple of years ago where someone had a fire in their shop for an unattended blanket left on?

[Paul B]

Don't remember who that was, sorta remember reading about it tho.

I know Mario Proulx had his shop burn to the ground years back, don't remember the cause. I remember him saying that he sat on the curb outside his house feeling totally powerless while the fire crew tried to put it out. I don't think it was one of the high points of his life.

Probably a good time to mention the value of even a cheap smoke detector in the shop. Mario now has one and coupled with a baby monitor you can hear it from inside the house.

[Lillian]

I remember someone charing a cherry side answering a phone. And there was someone who left a blanket on low on the work bench over night or the weekend. They left the scorch mark as a reminder to double check that it's turned off.

I don't remember what caused Mario's shop to burn, but I do remember that the lake was frozen over and he couldn't get to the water. So now he has an old hot water heater filled with water as an extinguisher of sorts.

[Lillian]

Mmm.....I challenge anybody to stand still with 240 volts hurtling through their nuts.

Still if it works for you......

It takes time Martin, but it's pretty good once you get over the initial shock

Go to your physio and ask to borrow their TENS machine. You can start the current off low and work your way up. Its a cool sensation, sort of.

Now, I'm betting that the current won't bother you, but I dare you to keep a straight face when you pull the adhesive pads off.