Wire Tensioning

[nichanderson]

Hello

I just finished building my first CNC hot wire cutter. I used the same plates that Foamlinx does, with 3/4" guide rods, Igus linear bearings, 127 oz-in vexta step motors and linisteppers for the drivers.

The mechanical aspects of the are rather crude, lots of flex in the rods because they are 3/4", no way this is as accurate to .01" as the manufactuer claims, but its good enough for what I need and use it for.







I have tried cutting swept shapes (independent x axis movement) and had used a spring to attempt to control wire tension well allowing for independent movement. It didn't work, at all. The spring totally strecthed and runined the cut.

What do others use ? Just stronger springs or what ? I am thinking of mounting a few pulleys, with a sliding mass on a bar (to prevent swinging) to allow for constant wire tension, but I'm worried that the 5-10 lb of weight I can hang will be enough tension for the wire. Or put weight on both sides, maybe 10-20 lbs, and use a block and tackle to amplify the affect of the pulleys ?

Thanks,

Nick Anderson

[Mcgyver]

cool. always wanted to make a foam cutter, don't know what i'd cut, but the idea is cool.

[2muchstuff]

Are your rods actually bending or is it because the unit is not screwed to the table, 3/4" rod is pretty stout stuff. Otherwise the only other thing would be too low of a wire temprature or moving too fast, either of these two would cause the wire to bow.

[nichanderson]

No we have not screwed the axes down yet. Obviously once I get it set up, I will screw it down. I am still trying to find a place in our dept to place it.

The 3/4" rods flex somewhat, when a force is applied at the top of the y axis (say a 36" long moment arm). 1" or bigger would have been a lot better.

We can control wire temp and speed good enough, I just am trying to visulaize ways to allow the two towers to move independent of each other to allow swept to be cut.

Nick Anderson

[vulcom1]

On the cnc foam forum most of the setups use a bow that is mounted on the uprights. This way the tension does not change and there is individual movement for each end. The bow is insulated from the mounts by clamps but still has room to slide. Using pulleys and other means might work but to me the idea is to keep as much weight off the posts as possible other wise they may be pulled into the centre.
John

[nichanderson]

I have considered using a bow, but I cannot figure out a method to mount the bow, yet still allow the towers to move. Any pictures or ideas?

[vulcom1]

I went to the other site and got a few pics. The wire is supported on the insulated posts. Hope this helps and hope the guy that made this one doesn't mind as it is nice looking.
John

[GAWnCA]

Originally Posted by vulcom1 On the cnc foam forum most of the setups use a bow that is mounted on the uprights. This way the tension does not change and there is individual movement for each end. The bow is insulated from the mounts by clamps but still has room to slide. Using pulleys and other means might work but to me the idea is to keep as much weight off the posts as possible other wise they may be pulled into the centre. John

Vulcom1 - Can you give a link to this cnc foam site? Thanks

[vulcom1]

It is a yahoo forum like this one.
groups/yahoo.com/group/cncfoamcutters/ I tried putting the full url on but it keeps changing it. You may have to do a search.
There is lots of info there also and I have gathered the parts to start on mine.
John

[GAWnCA]

Check out this Foam cutting machine:

http://www.cnczone.com/forums/attach...chmentid=16625

Thanks to rceebuilder for the photo. It looks like this would be a very sturdy 4 axis foam cutting set up.

[foam27]

nichanderson ,

Did you solve you wire tension problem?

PM me your email, and I'll send you pix of mine.

No springs in the way, no bow(hehe)...

You basically have two vertical springs on each arm at the top, hot wire end goes to spring, down, around the meeting point of two bearings, out a little hole, across and the reverse on the other end.

The beauty of it is, no springs in the cutting area, no loss of wire end position when arms go opposite directions, and NO alligator clips of the wire.
The electricity passes through the bearing and supplies the wire with juice, even when the springs stretch and the wire travels.

It's all very SIMPLE, and took me forever to figure out.

Like I said, I'll send you pix, those are worth more words than what I typed.

Regards,
Justin in AZ

[garrick]

I have an observation and a question. I have cut a good bit of foam (by hand). The wire would bend more when I was moving the machine fast and if it was not hot enough. The first thing I would do is make sure your wire is hot enough and make sure it is moving slowly enough.

My question is where did you get the "same plates that foamlinx uses". The machine I wish to build will only cut through 2" think material (mostly) and I think this set up is a good one for my needs.

Thanks for your help.

Garrick