Hot Wire Knife

[kb426]

This is a quick and dirty synopsis of the cutter I made. I used pvc pipe and steel elbows. I would have used all pvc but the lumber yard didn't have the elbows in plastic. I tried a guitar string but that wasn't a real good choice. This was the place that I bought nichrome wire for the cutter.
http://www.nichromewire.biz/
If you scroll down this page, he has a chart about required amps. I used ceramic cabinet knobs for the insulators. Unplugging the power supply is the switch. I used a left over transformer from some dead in the water appliance from the past. This thing is crude and cheap but better than nothing.  

[jaybee]

It doesn't get much more utilitarian than that. Nice work and thanks for the pics.

[butch27]

What is that used for? Can I cut foam with it?

[kb426]

Foam cutter. I would imagine it will do styrofoam also.

[wayne petty]

i love the nichrome wire temp/amp calculator on that site..

really saves a LOT of calculations...  and if you go thin.. not much current is needed...  

i just wonder how strong the thin wire is.. at temp..  more research..

there was an interesting episode on TV here.. where they visited a foam display manufacturer.. they make the foam almost half thickness human forms..

they build a panel that compresses the foam in different amounts. then drag the hot wire through it..  when released.. do to the extra pressure in some areas.. instead of a smooth cut..  you now get 3D surfaces

might make cutting seat contours in the foam easier..  as you want more compression in the foam.. so when the hot wire goes through.. it cuts a higher path... so when released.. the foam pops up higher in areas where the compression was more..

double sided forms might be possible. for seat cushion cutting also..

next one needs an old air hockey table..    switch the blower to vacuum and create a heater to heat plastic or thermal vinyl.. with a frame to hold it...   now you have a vacuum molding machine..  for recovering dashes and door panels..

[enjenjo]

How many volts is your power supply?

[kb426]

12 volts, 1.2 amps. I think it needs 2 amps to be real good but I used what I had in the left over box. It works but it's slow.

[wayne petty]

i wonder...   if this is why they build current limiting adjustable power supplies...

i am not recommending this item.. its for educational info only..  

http://www.allelectronics.com/make-a-store/item/PS-3003/VARIABLE-POWER-SUPPLY-0-30-VOLT/0-3-AMP/1.html

HQ Power # PS3003U. Compact, single output lab power supply. Dual LCD displays provide accurate, easy monitoring. Coarse and fine adjustments for voltage and current. Settable voltage and current limits with LEDs to indicate when current or voltage limits are operational.

SPECIFICATIONS:

* Output Voltage : 0 - 30V @ 3A
* Output Current : 0 - 3 A
* Input Voltage: 115V, 60Hz
* Constant voltage/ Constant Current
* Protection mode: current limiting



i personally picked up an 18 volt 3 amp current limiting version a LONG time ago.. i use it mostly for recharging deeply discharged automotive batteries..  if i can get the battery before somebody tries to charge it or jump starts the car.. i can stick it on this at 17 volts at 1/4 amp max.. 1/2 amp on BIG batteries.. and let them charge for days...  i have brought back several that were at 0.00 for months..

it will also work for deeply discharged deep cycle batteries if no body has tried to charge them after a slow long discharge..

why catch them before a boost attempt or charging at a conventional rate.. that will harden the sulfate spikes between the individual plates.. shorting them out..  charging at 16 or 17 volts at limited current dissolves any of the spikes....   but once hardened.. they will be a short.. and stop any further charing attempts.

[Beck]

These foam cutters were used in the model airplane world to cut styrofoam wing cores. Time filies so I'm guessing in the 70's this was the new thing. My father has a setup for this purpose. It took 2 people to do a good sized wing. There were numbers placed on a pattern on each end of the foam block. One of the guys would call off the numbers as they were reached. The other would match his progress. If this wasn't done one guy would go faster than the other messing up the shape of the finished part. Both sides of the wing core were cut before removing the wing from the original block. there was a channel cut into the foam to add a wing spar for strength. The styrofoam was then sheated with balsa wood or very thin plywood.