Questions for a 5x10 build plan

[rpgdeity]

Hello everyone, I'm pretty much a long time listener, first time caller. So where do I start? I have been researching information and looking through the cnczone since Feb/March with interest to build a CNC Plasma table. With everything I've learned (and changed my design/plan numerous times) I still have a few questions. So I'd like to spell out my current design and see if anyone can help me out. I figured this was the right place to ask these questions, then I'll start another thread once I start my actual build. I am in the middle of drafting my table, I will have a complete dwg/dxf created when I'm done and I certainly will make it available to anyone here. I actually design/draft equipment where I work currently, I'm an engineering student somewhere in the middle of finishing up my degree.

So my goal is to start a business mainly utilizing a cnc plasma table. Eventually I plan on not only using the table to create finished product, but also to supply initial parts for a range of other second operations such as press brakes, mills, drills, and welding/fabrication. As a side note, where I work right now has a huge laser cutter that is capable of cutting up to 1/2" mild or stainless. We mainly work with stainless in the fabrication of food processing equipment. I am familiar with utlizing a cnc cutting table to generate parts for further fabrication/machining. If things go well, I hope to be starting to build my table ASAP.

As far as a budget goes, I don't really have one so-to-say. Of course I'm not made of money, but I'm willing to spend, to invest, quite a bit into the table so long as I beleive that I am creating a table of quality that can in turn make me money eventually.

So the table will be approximately 6x12' over all dimension, so it will be capable of cutting up to 5x10 sheets. I have not firmly decided on max cutting thickness capable with the plasma. I know I should go bigger than I think I will ever need, so I'm looking at either a Hypertherm 1250/1650 or a Thermal Dynamics 102/152 plasma.

I'll be buying a complete controls package from Tom at candcnc.com since I've not only heard about the great quality and support he gives, but I also suck at anything electrical.

For drive I am planning on going with gear rack, and using linear rails.

So my first question is regarding machine accuracy. I'm going to be spending an awful lot of money on linear rails, but how can I gaurantee or make/keep them accurate on my table? Say I take good care to weld my table frame straight and square. Then I attach this 12' long linear rail on each side of my frame, how do I check for straightness and adjust it to make it straight? I guess this all boils down to the accuracy of parts I want to make with my table. What is a realistic accuracy to expect here? I mean, I know I'm working with plasma, but how good can I get? Are we talking .030", .015", .005"? I would really like to hear from people who have a working table and see what kinda accuracy they are getting from their table. I'm not sure exactly what market I will end up catering too, but I have a feeling that I can make great money doing much more than just cutting art with my table (although I certainly will be cutting cool art stuff with it, I'm willing to make money any way I can) and so I think I'm going to need to make this thing as accurate as possible.

I have many more questions, but at this time, my first question I just asked seems to be the big thing that is hanging me up. Once I decide or figure out what and how I am going to attach the linear rail then i can move on. Any help is appreciated, thank you.

-Brandon

[Pure-Powder]

Why not just purchase a Table there are a host of good Quality Tables and or kits available... Saves piles of time , and the little extra it will cost you, will be easy to make up with the ability to start working sooner!! Just my 2 cents, I think more unfinshed projects out there than finished ones! Good luck which ever way you go...

[sunmix]

Hi rpgdeity,

It will be interesting to build your own CNC Machine. If you're talking about machine self accuracy, its better to use alumininum with slots in. It really helps you out on making a good and accurate machine.

If you're talking about XY positioning accuracy, use a servo motor. There are plenty of drivers who are great at positioning, such as Gecko's G320.

[millman52]

You might want to concider using only 1 linear rail on the 12' length of the table. 1 rail gives you all the accuracy of 2 without the alignment-binding problems of using 2. a simple CR flat bar with bearings top & bottom along the other side of the table holds up well. I'm not a big fan of "Skate Bearings" for that type of arrangement. I'd opt to use double row sealed ball bearings.

I feel that your gantry should be driven from both sides either master/slave arrangement with 2 motors or a jack shaft with 1

I am running ox/fuel on my table. I am able to hold amazing accuracy .005-.010 on thicker material 3/8"-1" I can't speak to how accurate you can maintain a plasma stream.