My Newb Plasma Table Attempted Build

Hi all. I'm very new to the the forum, inexperienced completely with building any type of CNC machine. I am a very experienced pipe welder and fabricator.

I used to have a side business building accessories for off road vehicles. At that time my company would use vendors to do our cut work. I quickly found that, as a small company (compared to these vendor's typical oil & gas customers) that they either didn't want my business - too small - or they were gouging me.

Fast forward to now, a few years later, and I have some ideas for stuff I want to build and sell. I don't want to deal with outside companies anymore, so I'm determined to make myself a small plasma table to do what I need it to. I'm not versed at all with Linux, any CAM software or the like, but I am very experienced with CAD (Autodesk and Solidworks).

I spent months watching videos and combing the net for information about different home-brewed tables. Unfortunately, until I started building, those searches didn't lead me here...because I believed erroneously that this forum was strictly having to do with software. Duhhh how wrong I was about that!

Ok, on to my in-progress build. After all of that research, I wasn't sure what software/THC I wanted to use. I consided just buying a Langmuir table, but that open gantry with very small cutting area and no THC lead me away. Somewhere I ran across some non-plasma openbuilds v-slot stuff. I wanted to have a 4ft x 4ft cutting area. I have very limited space for a machine, but I wanted to possibly be able to expand (lengthen) it at some point in the future. I also wanted to have the ability to cut from 4ft x 8ft sheets, saving money on materials.

I was just going to get some extrusion, then I saw some OX plates. Many state that they aren't well suited for larger machines, but most of the folks making those statements are using them for router tables. I figured maybe it would work ok on my size table, considering that it's just a plasma and there are no loads on the gantry other than the static weight and mass of mounted components.

I purchased some 20x80 1500mm v-slot for the Y axis rails, and the appropriate 20x30 1500mm material for the gantry. I like the idea of a lightweight gantey (read aluminum). Makes sense that it would be light weight and therefore less wear and tear on bearings, motors, etc.

One potential issue I saw with the Y axis rails was flexing, after all they are only 20mm wide. Rather than making the frame from more v-slot I elected to use steel square tubing. I had a bunch laying around already, 2" x .25" wall. Plenty beefy and I figured it would keep the gantry well planted with the weight below all of the moving parts. I was able to get the table frame squared pretty well, and the deviation from side to side as well as width variation is +/- 1/32in and +/- .1deg (from a digital angle finder). Best I could do with a not-so-leveled concrete slab to work on. As it turns out, this all was the easiest part! I'm hoping that getting the tolerances in as close as I can will prolong the life of bearings and such. I'm using the extreme wheels from openbuilds, with belt drive (used as rack by glueing a strip with teeth up, and laying the drive portion teeth-down over it).

I know I'm here very late in my build, however I welcome advice/thoughts whether they're good or bad! I'm further along than what's in this post, actually, I'll post more later.

Pat

I actually already have a Mesa 7i96 board and a THCAD-10 for the THC element. I agree about the potential issues with the polycarbonate wheels. With the gantry being 1500mm (59in) wide, and cutting at about 48in x 48in, I'm hoping to keep them out of harms way and clean the v-slots daily. I have a plan to mount Hiwin style rails if this doesn't work out so well, and problem will be solved.

The water pan will be several inches below the level of the lower wheels on the track, so I'm also planning to make some thin (18ga or 20ga) bold-on shields to run along the square tube to deflect splashes and sparks from getting to them. Surely won't hurt to try that out.

The idea for the Mesa electronics came from finally finding this forum. They seem so much better than the regular parallel BOB's that I was almost going to use.

Pat

I'm an old welder. Sparks flying will make me feel right at home!

I don't have everything. Going today to pick up the resistors for the voltage divider for the plasma. I have a MeanWell 5v and 48v (12.5A) power supply. I had purchased several NPN type inductive proximity sensors for limits/homing, and didn't take into consideration the need for more than 5v but less than 36v needed for those. Ugh.

At this point my water pan is nearly welded up up, I'm cleaning up the wiring on the table, I just made the brackets and mounted the proximity sensors onto the table (1 on each side of Y axis Y1 and Y2, one on the X carriage, and one on the Z). I have just a little bit of soldering connectors at the wiring on the table and whatnot, and I should be able to test the motion and dial that in over the weekend. That's the tenative plan, anyway.

I just found that CNC Plasma cutter, general ideas thread late last night and started reading through it. I wish I would have wandered into this forum several months ago! Still, the software and electronics are the biggest challenge to me and even though I've read the PlasmaC primer and Guide several times, a lot of stuff escapes me still.

I did manage to get Linuxcnc (Debian 9 RT-Preempt) master branch onto my computer a few nights ago. That was very challenging for me haha. The motion testing will let me know just how badly I messed that up...

Pat

For my Z axis, using the original style OX plates, I wanted to use the newer-than OX plates C-Beam. My reasoning was to have the channel portion of the C-Beam facing out, and using mini wheels inside it and a plate for the floating head portion. I have hopes that having the mini v-wheels inside the channel will protect them, as they will be right by the torch head.

The challenge this posed at the onset was that the OX plates were designed for 20x60mm v-slot. With the C-Beam being 80mm wide, I took some measurements and determined that there was sufficient room on the existing OX plate to precisely redrill the holes for the wheel blocks at the wider required spacing. Worked like a charm, although it isn't as pretty (had to remove length from the blocks for interference issues). Great care has to be taken to ensure the new hole array is squared on the plate. I've heard a lot of folks complain about the mini v-wheels not turning very easily, and I had some issues with this (wanting the floating head to move smoothly). I sanded the precision shim that is located between the 2 bearings inside each wheel, and this took care of it. The plate now will free-fall with nothing attached to it.

Other items in this build not previously covered are:

Stepper motors - NEMA 23 hybrid 570oz 5A (overkill, but they were on sale same price as smaller ones...)
Stepper drivers - KL 5056 x4
Power Supply - (1) Mean Well SE600-48 and (1) Mean Well RS15-5
Controller - Mesa 7I96
THC - Mesa THCAD-10
Limits - Micro switch for floating Z/NPN inductive prox. sensors for all other limits x4 (needing another power supply for voltage to those)

I also have a generic opto-iso r (4) relay board if needed, although I think the output SSR's on the 7I96 should work for what I need - please chime in anybody if this is not so, so far research indicates it'll work fine for it.

I will mostly be cutting 7ga thru 20ga material with the machine, although the plasma itself will definitely handle much thicker material.

Pat

I have everything connected up now. I have virtually no clue what I'm doing in Linuxcnc, but the damn thing moved all axis on the first try.

Gotta do some more research, most information I can find is for stepconf on other versions of Linuxcnc. I'm running the master branch so the bits look different in pncconf than what I'm finding in searches.

I'm trying to determine the stepper settings. I'm running a belt with opposing belt as a rack (can't remember the name that's referred to). Also running inches. I saw somewhere on this forum someone said a 20 tooth pulley running 3mm pitch belt (same as mine) has a scaling of 3.33. So I converted the 3mm to .118 inches, which gives me a scale of 84.75.

I plugged this into pncconf and ran test/tune axis, and it does some weird stuff. At the end of each direction movement it jitters before going back the other direction. I played around with microstepping and speed, and I can get the movement smooth - until it reaches the end of travel and pauses to change direction. Still kind of shakes around. Of course I know it's something I've done wrong or haven't done.

Any ideas? See anything obviously wrong that I'm doing or neglecting to do?

Pat

Can you post your hal and ini files?

Some versions of pncconf have setup values that can cause poor stepgen performance
so there may be some minor hal file editing required

Thanks for the fast reply (love the 7i96 board, btw).

I haven't ran all the way through the pncconf yet, so no files written as of yet. I'll complete it now and grab them, then post.

Pat