[Jzint]

Just joined the site today and would like to say hello fisrt of all. I am looking to build a combo table for plasma and routing. I have many questions, but for the first. What is the consensus on the type of drive system that is best used. I have looked at rack and pinion, direct drive, gears and belts. My problem is I have to much information in my head to make a decision about my design. I have also looked at 8020's linear slides. They slide directly on the extruded aluminum channel. This is diffently the cheaper way to go, but that's what I am affraid I'll get is cheap. I do not want something that is going to wear out in a few weeks but at the same time I am trying to save a considerable amount of money by doing this myself. I am a very avid DYI person and will not have any problems taking on this task, just looking for the experiences of the pros.

[krazycnc]

Well I'll give this a stab - this is how I described it to my girlfriend and why she hasn't seen hide nor hair of me for the last three months - it's kind of like driving a car sweetheart - I did the research on new units and thougth they were "too expensive", came up with my own design researched the parts, put the mechanical parts of the table together, that was easy, built the controll box : stepper controll board, parallel port breakout board, stepper board power supply, breakout board power supply, shielded cable to the motors, geared stepper motors, Campbell THC300 torch height controll, connected that to the plasma torch put all that together, put together a clean dry air supply, bought a computer and coreldraw,sheetcam,mach2/3, learning that not easy at all, designed a floating head Z-axis for the THC300, and am just now getting ready to test everything and see if it will work together - yes honey I just got in the car and started the engine and I think there is more to this driving than meets the eye, excuse me while I design and build this differental and mount it while i'm at it! Other things to think about - home and limit switches, radio noise interfearence, 230 volt power, oil vapor free air, swarf and dust, the cost of metal and finally your own sanity! You got to really love DIY to do this and be ready to do a lot of research and ask questions. I now think the ready made machines aren't such a bad deal after all. Good luck.

[ViperTX]

krazycnc...other then the emotional cost....what do you calculate this cost you...can't tell what you used for the aixs....is that 3 inch square tubing?

[krazycnc]

I have spent 4750.76 so far, that includes - metal, electronics, thc300, hypertherm 380 plasma torch, computer, software, compressor filters and air regulator and hoses, upgraded electricity, custom cabinet and a hundred trips to home depot. I used two 2 x 2 in thin wall welded together with the rack tacked on top for the Y-axis gantry and 4 in square for the table body.

[ViperTX]

Are you using v-groove bearing riding on some angle iron?? I think you said you were using rack & pinion...is that true?

[krazycnc]

I use patio door rollers, they fit nicely on 1/4 round or 2 x 2 - 1/4 angle. They have to be taken apart and loc-tited without warping them as they will come apart. They're available at any home improvement center.

[DSL PWR]

Ahh, patio door rollers, I'm impressed. If you get the green loctite, you won't need to disassemble them, as the green stuff is made to seep into assemblies.

[speedster]

I understand that building a cnc plasma cutter would be quite a task, but what ready built table would you consider and at what cost? I am also interested in building a table. I am just in the information gathering stage right now. Do you know of any resources for plans or detailed info on building a table? Thanks.

[krazycnc]

From what I have seen the Shopbot looks really good, it can do router or plasma. As a router theirs a lot more dynamics and stresses than a plasma table which has almost no weight or resistance. What I really recommend is a THC or Torch Height Control for the plasma table. Bob Campbell has the THC300 which gives you everything but the floating head Z-axis, you have to build that yourself. You will have to ask around a little more, I really don't know about all the aspects of buying like warrantys, follow up, free help with questions and such. Good luck!

[Torchhead]

To answer the first question of the combo plasma/router: Been there done that. There are a multitude of reasons not the mix the two. Beside the obvious ones of flames and sawdust, the engineering of the machine has to be a series of compromises. The size, weight, speed and construction of the two types are radically different. Kinda like a combo car/airplane. You need 300 or 400 inch cutting speeds with plasma on thin stuff. You need 30 to 60 IPM speeds on a router. On the plasma you need high speeds and lower torque on the router just the opposite. You need a heavy rigid gantry with lots of force for routing but a small light one for plasma. For plasma you need a water tray and negative (under the table) dust/smoke extraction over the entire cutting area. For wood you need a focused dust extraction at the tool. I could go on but you get the picture. I ran my router on my table for the first month then I cut my first steel and watched the flame slice through the material at an astounding speed and the 45 minute conversion from plasma to router has not been done since. I have not given up on having a router and I have all the stuff (but time) to build a much larger plasma and convert this table back to a full-time router.

I know all of the logic about not enough space and getting the most out of your dollars but you may want to rethink those positions.

The second question about "commercially" available machines:

There are several (more are starting to show up) of good well built machines that don't need a second mortgage on your house to buy. Google for DynaCNC and take a look at their machines.

If the shopbot uses the same motor drives and software they have in the past you should be aware that the machine runs rough (makes jagged cuts on arcs) does not have Constant Velocity (essential in my mind for good plasma cutting) and will not run MACH2/3 so the lower cost THC300 is not usable. Maybe their newer machines have fixed that (maybe not).
We just helped a shop with two ShopBots retro fit his machines with Gecko's and MACH2 and the difference was astounding in smoothness and cut quality.

[ger21]

You need 300 or 400 inch cutting speeds with plasma on thin stuff. You need 30 to 60 IPM speeds on a router.

I'll agree with you on the rest, but not this. On our router at work, The slowest I ever cut is 120ipm, with 1/8" bits. Most of our routing is done in the 300-400ipm range. But you'll need a lot more power to routes at 400ipm than you will to push a torch around.

The new shopbots use a closed loop stepper system, and are probably a lot better than the old ones. For the older ones, Campbell Designs is working on retrofit kits that run Mach3 and Geckos with the existing motors. http://www.campbelldesigns.com

[Torchhead]

That's the problem with making general statements I guess. Using a conventional router (off-the-shelf PK or Makita) and materials like Oak and Walnut (even some yellow pine) things went downhill for me at 45 to 60 IPM. I would venture that your machine at work is not a $1500.00 home built unit with a typical home-owner router. I'll be the first to admit that my time using a CNC router has been limited to home built units.

The conversion I referred to on the ShopBot was the one Campbell worked on.

[ger21]

[QUOTE=Torchhead]That's the problem with making general statements I guess. Using a conventional router (off-the-shelf PK or Makita) and materials like Oak and Walnut (even some yellow pine) things went downhill for me at 45 to 60 IPM. I would venture that your machine at work is not a $1500.00 home built unit with a typical home-owner router. I'll be the first to admit that my time using a CNC router has been limited to home built units.
QUOTE]

No, it's more like $140K. (7 years ago) If you want to cut that fast (300+ipm) on a homebuilt machine, with a handheld router, you'd probably need to take pretty light cuts. But 150ipm is really not that fast. I've seen material fed through router tables much faster, probably close to 250-300ipm, removing a lot of material, with a PC 7518.

A good commercial router today can cut at 2000-3000 ipm, btw.

[Timon II]

Has anyone know someone who has build cnc plasma table from Shopbot plans ?

[Torchhead]

What "plans" are you talking about? They currently do not appear to sell just the plans. If the design is based on their older tables I would have to advise not to use them as is. Their older designs suffered from a combination of problems (mostly motor drive/software) issues. If you can find a used 'Bot machine that you can pickup cheap Bob Campbell (www.campbelldesigns.com) is working on a cost effective retrofit kit for their older stepper driven tables. The main complaint from the owners I have talked to was jerky perfomance, slow speeds and ragged cuts on curves. Bob's retrofit uses the existing motor and gearbox but provides better drivers and control software (MACH2/3).

Keep in mind your target speeds for plasma can be as high as 400 IPM on thin material so the design needs to take those into consideration. Just taking a design for a router and snapping on a plasma is always a compromise.

[Timon II]

That is what i meant the designs of their older tables , so that is the problem , but what you think for the construction of their tables .

[eqreservoir]

Hi krazycnc

Just found and read thru this thread. Your plasma table build looks great. I would like to know how the patio Door Rollers worked out for you?

[krazycnc]

They actually work quite good. The forces involved for a plasma table are small. My typical speed for 1/8 in steel down to 20ga is 35 - 65 Inches per minute, I find no need to go faster, dosen't generate much moment of inertia. I go a little faster for the thinner stuff and just reduce the amps to 20 or so. The torch head weighs very little and has no resistance as compared to a router. I found the more important aspect was using good Torch Height Control - typically Bob Campbells, but you have to design the "floating" Z axis yourself. Good luck!!

[eqreservoir]

Thanks for your response.

By what I read the patio door roller work good on a light gantry application, but probably would not work for a router gantry.

[chris trublic]

where did you get all the wiring diagrams from to put it together, what are you using gecko drivers and bob campbell breakout board. would you have a wiring diagram to get me started.