Plasma table build, first question....

Hi all,
looking to build a small table for my plasma, before getting in too deep with plans I have one question...

My torch is a contact start, the head can be dragged or used at a small distance, is this unit suitable?

its an R-Tech 30A unit but as I only want to cut stuff up to about 5mm it's worked ok so far.

It's a bit of a deal breaker so is it any good or not?

I dont know much about Plasma heads but i do remember seeing one being used where the head would come down and touch off the metal and then start. So i think you could use it this way as well ?

.Me

Hmm, just checked the website again, it states it has "HF arc start", this is the unit... P30C Plasma Cutter, 240v, R-Tech Plasma Cutting Equipment So hopefully it will do the job, I was looking at manual torch height for simplicity/cost. Dave

Hmm, to save time and money I thought I'd ring R-Tech as they have been very helpful in the past. It seems my torch would not be good for CNC as it is a contact-start head and CNC really needs an HF Pilot arc. He said it "might" work but the arc may not always strike when told and that would waste the work-piece. Sounds like my project is not going far unless i sell my plasma and upgrade the unit which would blow most of my budget.

Thinking on some more, I could likely build the table first then upgrade my plasma later on to one with a pilot arc, that should work better.

next question is, can this be done without torch height control?

adding this seems to be very expensive and would blow all of my budget on that part alone, is there a manual height option that works?

Upon doing some more web searching, I found a couple of excellent pages... Home Page And Scratch Build scratch build cnc table (plasma and router) - bit-tech.net Forums Both show budget builds and the last one is so amazing that it practically says "Just bung it together and it will work". The first thread uses a drag-torch as well although he does mention it's limitations. So in light of these discoveries I think I will proceed to the fag-packet stage and start drawing up some ideas of frame and motion methods. I'm using 44mm structural aluminium for the chassis as i have tons of it, might run the carriage bearings direct onto the frame rails or possibly fit some plate to each side and use V-rollers top and bottom. My criteria so far are... Cheap, Small, Light, Table-top. I'm looking at T5 belt drive to both sides of the gantry via a main drive shaft with one stepper driving it via a reduction system. Again the X axis will be T5 belt drive as i have a box full of useful T5 pulleys Probably 3Nm Nema23 motors, drive gear from ebay, mach3, sheetcam etc Anyone wants to throw ideas in please feel free.

I seem to have lost control of paragraph formatting????

Its a problem with IE10 & IE11.

Use Chrome?

or something else...


edit: this looks ok in Chrome

Attachment 11280

I lashed together a frame today today to get a grip for the size I can build...
http://www.davekearley.co.uk/LinkPics/CNC1.JPG

Its about 4'6" x 2'6"

im thinking of mounting some 75x6mm steel along the long sides to use as guide rail for the gantry carriages, I'm driving it from both sides so the carriages can be quite small, will be using T5 belt and sprockets to drive the gantry with a cross-shaft along the short edge.

Rough calculations, with a 3:1 reduction on my gantry drive motor, 1 step of the motor will give me 0.16mm of travel, if using micro-stepping as recommended, then 8 micro-steps will give me 0.02mm which seems very fine for a plasma cutter??

If I can reach 500rpm on the shaft, I should get around 16m/min of speed but that's a guess as I have no idea of acceleration curve yet, I'm looking to keep the gantry light by mounting the drive motor on the main chassis and driving through the belt along the side-frames, I think that makes more sense than mounting the motor on the gantry and using to "rack" its way along a fixed belt.

I have two 3.1Nm motors, 3 x 5A drive boards, a breakout board and a 36v PSU coming.

Have also reloaded XP onto my target PC and have been playing around with the demo mach3 plasma install, downloaded a manual too. Just waiting for material to arrive now.

BTW, I have had to reduce the size of my intended machine as it wouldn't fit in my workshop :( so it's now got a cutting area of 2' x 2', not as good but easy to expand later on.