Cutting rocker into an eps block?

I recently posted about the board I am planning to make.

In the past, I have use used traditional “close tolerance” (I guess you could say) blanks with cedar stringers from Foam-EZ. This time around, I am trying EPS. I bought some foam from a guy in LA–the EPS comes in rectangular blocks.

What is the best way to cut my rocker into the chunk?

There's been plenty written about it here.

Thanks. I’ve never doodled with electronics, but it sounds simple enough as long as I can follow instructions!

What they said - only I use 9/8" clear cedar, which is 1" thick, lay out and cut out the rocker/foil, split with a band saw, use as hot wire guide, use one for stringer.

Heres a thread I did a while back that might help.

 

http://www2.swaylocks.com/forums/eps-epoxy-build-thread36-micro-simmons

I’ve found that 2" window screws that are threaded half to 3/4 of the way up and have a pan head work really well for attaching templates to the block.Just try not to spin the screws out and they hold good.I only use 3 per template,one at each end and one at the center.

cut out the profile twice in wood panels.

MDF is easy to sut and sand.

I usually cut one profile in MDF and one profile in the wood I want to use as a stringer.

drill small holes in the wood, so you can attach the wood to the foam using nails.

I found out that using nails is the best way to attach te profiles to the foam. This way there is nothing that blocks the wire going over the profile.

u can use a hot wire. u need 2 profile templates(i make mine from beaver board), which u screw on each side of the block on the same level. than just use your hotwire to cut the foam above and under the templates.

I created a hotwire this evening. After screwing around with the wiring, I finally got the string hot. However, it wasn’t hot enough. What kind of transformer should I have hooked up to my dimmer?

http://www.harborfreight.com/10-2-55-amp-6-12-volt-battery-charger-engine-starter-66783.html

 

 

How do you limit the current to the wire? The battery charger doesn’t blow it up?

i THINK you use the float charge setting… I know 2 guys who have that same Charger

Use the battery charger to charge batteries. Get one of these if your serious about cutting foam. http://www.circuitspecialists.com/variac-variable-ac-ps05kva.html

http://www.ebay.com/sch/i.html?_nkw=variac+5+amp&_sacat=0&_odkw=variac+amp&_osacat=0

I just posted this in the other hotwire cutter thread, but it is also applicable here. I bought something called a 24VAC 48 @ Center Tap 3-5 amp transformer. THe wire  DEFINATELY heated up this time. In fact, it heated up so much, that it burnt out 10/10 times.

Instead of using the small E string, we used the LARGE E string. Same thing. After getting red hot, we plunged the wire into the foam slowly. The wire would super heat at the exposed ends not inside the foam, and break with the slightest pressure. We tried limiting the electricity so the wire would barely cut the foam as well–still same results. The exposed inch-and-a-half would grow red hot and fry.

I’m considering buying a variac, but I don’t think this would take care of the frying wire problem. Any advice?

I use an old computer power supply. Since it doesn’t have a variable voltage output, some basic math skills are needed. But if you finished primary school and have access to a calculator or computer, you should be able to do it.

 

Edit: This math is also applicable if you use a variac, no more guessing. (You can measure the resistance/meter of your wire using a multimeter)

 

I always take 60W/m for the wire.

 

The formula is: resistance/meter = (Voltage/meter)^2 / (Power/meter)

 

e.g. if you have 12V, you want a 0.5m wire and 60W/m you need:

  • a wire with (12/0.5)^2 / (60/0.5) = 4.8 Ohms/meter      (good vendors list the resistance of their wires)

  • You also need to make sure that your PSU is capable of delivering 30W (= 60W/m * 0.5m) on the wires you use (a computer PSU typically delivers between 150W and 400W, the power per output per wire pair is always listed on the PSU)

 

With this technique you just buy a wire for every length you need, attach to PSU and you’re good to go. You never need to control a variac and risk overheating your wire.

 

Use the math in my post above and buy nichrome wire on ebay! This is very cheap!

Guitar strings are the cause of your troubles.

THANKS!

What gauge wire are you using?

I use 100# test stainless steel single strand fishing leader from walmart and a variac. The steel holds up to heat better than nicrome IMO.Any heavy test steel leader works.With a variac you just turn the nob until the wire is hot enough to cut foam. No math or education required!

HAH! I like the way you think Jesus.

I read your comment after I ordered some 24 gauge nichrome wire.

I’ll post the results after I test the new wire.