CNC Hotwire Attachment

[Hawkeye]

Since I just got into lost foam casting and recently finished an X2 CNC conversion, it occurred to me that it would make sense to use the CNC mill as a base to cut foam patterns for casting.

I made up a frame for the wire to clamp to the Y-axis motor and a couple of support arms to attach to the mill table to hold the foam workpiece.
   

The nichrome wire came from an old crock pot that my Mom wanted to use as a planter. I've had the wire for a few years. Now I have a use for it. The wire is supported by plastic blocks with brass bolts to adjust the wire for squaring it up to the table.
   
   

I'll experiment with the arms to try different methods of fastening foam blocks for cutting. Maybe pointed bolts threaded through the sides to stick into the block or clamps to hold it down on the horizontal flanges.

I powered the wire using a 12 VAC, 50 VA transformer controlled by a dimmer switch. A test cut on a piece of 1" blue foam shows that it cuts quickly and cleanly. I'll make up a test run in G-code one of these days to put it through its paces.

[arvidj]

Mike,

I am sure you have done all the research on this but I happened to get a reference to this in an email the other day and thought it might be appropriate to share in this thread with you and everyone else.

http://www.youtube.com/watch?feature=pla...2VUmrpN1lk

Of note ... at about 3:25 we see the rather clever Gates Rubber couplers that he is using and at 4:19 it appears as though his power supply is providing about 18.6 volts and .86 amps ... obviously 100% dependent on the type of hot wire he is using.

Note also that I am not knocking his choice of couplers. (a) they seem to work in this application, (b) see -a-.

Arvid

[Hawkeye]

That's a completely different application, but if I was still into RC, I'd have to consider it.

I came across this site for calculating the requirements for any given gauge and length of nichrome wire.

http://www.jacobs-online.biz/nichrome/NichromeCalc.html

Pretty easy to use. My wire is about 0.008" diameter and 12" from contact to contact. For a temperature of 480F, I'll need 0.747 A at 8 volts. Kind of hard to get an accurate voltage out of a transformer run from a dimmer.

[Hawkeye]

I worked up some G-code to try out the hotwire. It's just plain fun to watch. I can appreciate how the guy that invented wire EDM must have felt. "Wow! It works!"

   

I forgot to get the camera until after I pushed the Start button, so all these pictures have the cuts already done. You can see the setup, though. Foam clamped to the arms. No Z-axis movements.

   
   

I set the cutting speed to 15 inches/minute. That seemed to work well at full heat (12VAC transformer). For making patterns for compound shapes like the tower for a vertical steam engine, you could cut one profile, then rotate the piece 90* and cut the other two sides.

[DaveH]

Mike,
That is quite smart

DaveH