help: Foam cutting CNC construction ideas

[KC8QVO]

I am going to be building a foam cutting CNC. I plan on using the complete 4-axis kit from hobbycnc.com with the 4 200oz-in motors. My wire will be stainless steel .020 single strand trolling wire. The axis will be heavy duity drawer rollers (the ball bering ones, not the cheap slides) either from Home Depot or Lowes. The ones at Home Depot are about $1 cheaper. The supports for the X-axis rollers will probably be angle aluminum or steel with the rollers facing in. The Y-axis will be 2" square aluminum or steel tubing with the same rollers mounted to a bracket that is mounted to the X-axis rollers.

Now here is where my major question comes in to play. I would like to use a stainless steel ballscrew and a spring loaded ballnut for the actuators, but that is going to cost a LOT Heres my alternative. Lowes and Home Depot have VERY LONG threaded rods. The one I was looking at is 6' long and the threads are 1/2"-13. Is it going to be possible to use this? I realize there may be some backlash in the setup, but with some grease on the screw I think I can pull it off. Has anyone done this for a foam cutter or any other CNC? I am guessing that the CNC program (most likeley GMFC-PE) will be able to be set for the thread size of the leadscrew, right?? I have done the old G-code crap before so this should be a breeze. I am also proficient in AutoDESK products (AutoCAD, Inventor) so the design aspect will be a piece of cake once I figure out the program.

Steve

[captahab]

I'm sure you could use the long threaded rods from Home Depot if you want. I used a shorter (30" or so) 3/8" threaded rod from a hardware store on one my first prototypes. It seemed to work ok. I recommend a middle of the road approach however. I bought some 1/2 10 Acme threaded rods and nuts from Enco. They weren't much more expensive and the work well. They sell 3' and 6' lengths for not much, if any, more than the local hardware store. They are on sale right now for $6.99 for the 6' ones.

Also, 200 oz*in motors seems like a lot of overkill. I'm using 142 oz*in motors on the x axis and 60 oz*in motors on the y. I'm running them on about 65% of their rated amperage so I'm sure they aren't putting out nearly that much torque. My machine is pretty big too. It's got about 50" of usable travel in x and 25" in y. I haven't had any problems with low torque. GMFC is designed to melt the foam via radiation so the wire never even touches anything. The motors just have to overcome the friction in the machine and have enough to stretch the spring when cutting tapered shapes.

I tried the drawer slide approach myself but I wasn't satisfied with it. It was relatively simple but it's hard to find 50" drawer slides. The biggest problem I had with them was that they had a lot of slop in them when they were extended very far. They would probably work fine for a small machine though.

GMFC PE and Pro allow you to set the thread size to whatever you want but it's all in metric. The pro version has a conversion window that helps but you still have to put in everything in mm.

Hope this helps.

[KC8QVO]

Yes, that does help, very much actually. When I went to Lowes and Home Depot to look at the drawer rollers I found ones that were already open and extended them all the way and felt how much slop there was and it didnt feel like there was a whole lot, not enough to cause precision and repeatability problems anyway.

As of right now I just want to be able to cut 1/2A stuff and replace the wing on my .40 size trainer (it will be in two pieces, about 30" each.. depends on how I design it) so I dont need a REAL big machine. My choise on the 200oz-in motors is for expansion, if I do. I can also use the motors for other machines - besides the foam cutter. Its better to have more than you need than not enough hehehe.

Steve

[erase42]

i have a large foam cutter 57 x 40 x 100 it uses 1/2 10 acme leadscrews. i started with brass leadnuts about 1.5 inches long they worked fine for the first year of heavy use, (3-4 hours a day) but then they started to develop backlash. i cut them in half and intalled a spring between and pinned the two halves so that the lose one cant rotate. that got rid of the backlash and lasted the next year. i just replaced them all with acetal ones this week and hope that lasts another year. Anyway point is, if acme is good enough for my commercial application, im SURE it will do for your machine, and probably even threaded rod (non galv) would suffice if you make some sort of anti backlash nuts. If you like, send me an email when you are ready and ill mail you a length of .014 inconel wire. When i string my machine it takes about 100 inches of wire and when it breaks its usually still 90, more than enough to string smaller machines. Email is erase42@aol.com

[stevesplanes]

Hi

i went to ebay and bought Delrin Acme Flanged Nuts 1/2 - 10 RH. He sells them constantly. Item number: 7588292174 at the time of this posting. They are $3.00. They are cheap and self lubricationg. I have been strugling to make a large machine myself. I need to cut a full size wing 30 foot wing span by five foot chord. I am now willing to job it out. i don't expect the wing not to be sectioned off. the resulting foam wing will be used for making a mold.

[erase42]

Im interested, send me an email at erase42@Aol.com. I think I can manage it with my machine. What state are you in.