Noob looking for advice from the gurus

[Rhinorider]

I have just started the planning stages for a table. I have been lurking around here for a long while and have decided to take the plunge.

I am planning to build a 6 x 10, large enough for full sheets. Mainly 16 ga to 1/4 inch, occasionaly 3/8, and rarely upto 1/2". For the table frame I am thinking 2 x 4 x 1/4 tube, maybe 2 x 6 x 1/4. I may have to go with the 2 x 6 for water table to have room for 3 inchs slats and space under slats for plasma gunk. If I do 2 x 6 would 3/16 thick be ridged enough or should I stick with 1/4? I have a source for the 3/16 that is much more reasonable in price.

For "X" axis I am planning on "V" rails. Dual drive with 600 oz steppers. As the drive system I am really confused on this one, rack and pinion or belt? I have read and read threads on here and the more I read the more confused I get. I would like to acheive speeds up to 450ipm for rapids and cut 250 ipm for light ga aluminum. Are these realistic speeds? Pros and cons on drive systems, seems to me rack and pinion would be more precise and easier to maintain, belt would be cheaper?

My gantry I am planning on using 3/8 side plates, with 2 x 4 cross member. Single drive, v rail, and again undecided on drive system. Motor size I haven't a clue yet, I am thinking I sould wait to see what the gantry weighs in first. "Z" axis I'm thinking ball screw direct driven, or maybe linear slides. Floating head with some sort of THC. I would also like to be able to expand and add an etcher on the back side of the gantry but will add that at a later date.

Now to the plasma cutter. I am convinced to go Hypertherm. Originaly planned on the 1000 but after reading many threads I am leaning toward the 45 now.

I know this has been a long thread full of NOOB questions, and I thank you all for your patience. Gurus, am I on the right track? Millman I just may hop on I-79 and run down to pick your brain a bit. Thanks everyone.

[millman52]

Rhino, I used 2 X 6 X 3/16 on my 5' X 10'. I however cut lots of 1" plate. I feel that the 3/16" wall is very little more than just what is necessary for my table. Keep in mind I have no center supports to make cleaning from underneath the table much easier.

If you are going to have legs along the rails like most people build these tables the 3/16" should be more than necessary.

If you haven't seen one of the home built tables in action it would be well worth your time to visit me or someone else tosee one in action. You'll get many ideas to help you along with your build.

If you want to come by you are welcome. Send me a private message & I'll give you some contact information so we can arrange a convienient time.

[millman52]

Richard,

It was nice having you in today. I enjoyed your visit. I hope it helped in at least some small way with your intended build. Please feel free to contact me anytime you have questions. I don't have all the answers but I'll do my best to help if I can.

I would think there would be plenty of opportunity in your area to carve out some market. Whether it be industrial, automotive or art.

I hope your ride home was plesant & safe.

[Torchhead]

I have just started the planning stages for a table. I have been lurking around here for a long while and have decided to take the plunge.



For "X" axis I am planning on "V" rails. Dual drive with 600 oz steppers. As the drive system I am really confused on this one, rack and pinion or belt? I have read and read threads on here and the more I read the more confused I get. I would like to acheive speeds up to 450ipm for rapids and cut 250 ipm for light ga aluminum. Are these realistic speeds? Pros and cons on drive systems, seems to me rack and pinion would be more precise and easier to maintain, belt would be cheaper?

My gantry I am planning on using 3/8 side plates, with 2 x 4 cross member. Single drive, v rail, and again undecided on drive system. Motor size I haven't a clue yet, I am thinking I sould wait to see what the gantry weighs in first. "Z" axis I'm thinking ball screw direct driven, or maybe linear slides. Floating head with some sort of THC. I would also like to be able to expand and add an etcher on the back side of the gantry but will add that at a later date.

.

Here are some numbers to play with:

Average RPM of steppers run under moderate load and with proper voltage/current: 800

Step UP (speed increase) of Rack & Pinion or long belt drive: PI times the diameter of the final drive gear/pulley.

Loss of torque of R & P or Belt drive: 1/PI times the diameter of the final drive gear/pulley.

Reduction of resolution/accuracy for R & P or Belt Drive: 1/PI times the diameter of the final gear pulley.

So, if you have an 800 RPM motor and use a 1" dia pulley and direct drive it to the final gear/pinion/pulley, you gain 3.14 times in speed (2400 IPM) and lose 2/3's of your torque and resolution. When you have poor torque you have poor acceleration. If you have poor acceleration you will have rounded corners. You have a blazing fast machine with reduced accuracy and poor acceleration.

The numbers are worse for servo motors since they can spin up to 4000 RPM!

While you can tune the velocity to be anything you want in software it cannot gain back the things you gave up to get too much speed.

Leadscrews do just the opposite. They reduce speed and multiply torque and resolution....often too much. A 10 TPI leadscrew with a 800 RPM motor leaves you with jobs of torque but only about 80 IPM of max speed.
Us a 2 start leadscrew (effective 5 TPI) and you can approach 160 IPM (fast enough for most plasma cutting on thicker material).

Ballscrews and leadscrews have RPM limitations over a length based on their diameter. A 3/4" dia leadscrew of 5TPI and 10 ft long will start lead whipping long before you get to 200 IPM! The final kicker about leadscrews and plasma is one of dust and dirt. Plasma cutting is incredibly nasty and the fine abrasive (and conductive) vaporized metal gets all the moving parts. Leadscrews are a plasma dust magnet.


Having the weight of your gantry (it will be pretty heavy if its 6FT wide) will help predict how much torque you will need to run at the acceleration and speeds you need. That will determine the motor sizes and gearing (belt reduction) you need. At some point you get outside the capabilities of steppers to get both torque and speed and need to consider servos.

Just some things to consider.

TOM Caudle
www.CandCNC.com
Totally Modular CNC Electronics
Lowest cost full Digital Torch Height Control on Earth!

[Rhinorider]

Neil, thanks again for the look see on your table. It was very enlightning. You definately gave me alot of food for thought.

Tom, thank you for your input. I am sure we will be talking alot in the future. I have decided to go with your system, just have to figure out what all I will need first. LOL

Yesterday I took a little ride about on my bike and rode down to see Neil's setup. I was truly impressed. After I got back last night I was doing a little more research and I believe I have my gantry figured out. I have access to some 2 x 4 x 1/4" 6061 aluminum tubing that has 2 internal 1/4" webs inside. I am thinking of making the side plates from 3/8" aluminum with some of the inside of the plates hacked out to reduce weight. I'm thinking that will still have the rigidity needed and still weigh in at an acceptible amount. Tommorow I will get some more specs on that tubing and will post it up.

Tom, Neil and I where talking and I came up with a question that he suggested I ask you. Right now I am thinking of your 4 axis stepper system. My question is, what is involved down the road to add another axis or two? Correct me if I am wrong but doesn't Mach support 6 axis? I may want to add someday a pipe indexer, etcher, or drill.

I am going to wipe out my drawings and start over. As soon as I get something I'll post them up.

Thanks again,
Rick

[Rhinorider]

Just a quick little update. The design stages are coming along quite nicely, I've been working on drawing up in CAD. I'll post them when I get them done. Just bought my first major piece for the table I got the winning bid on a Hypertherm 1000 on fleabay, just waiting on the bog brown truck to come now.

[millman52]

Rick, Everyone has to decide "how big" is right for their own situation. In my case my maximum cutting surface is about 5'1" X 10'1". Hind sight is 20/20. If I were building again my cutting surface would be more like 4'6" X 13'. I have never needed the 5' wide but could really use 12' of cutting surface with an extra foot to get the gantry out of the way to load the table.

In my case & the jobs I do I have found I can purchase 8' X 24' sheets at a much better price & the particular steel company will either shear or cut those huge sheets down to 4' X 12' or even 4' X 8' cheaper than I can buy them pre sized. But I buy a good volume of steel & buy plate in about a months supply at a time. (Cuts down on their trucking costs & that translates to less per # on new steel).

My point is If you don't need the 6' wide cutting surface I wouldn't build it that wide. it makes unloading the table harder after the sheet is cut, because you can't reach across the cutting surface. & it makes your gantry heavier.

Keep us posted & get som drawings up when you get a chance.

Neil

[Rhinorider]

I made my first purchase toward my table. I am the proud poppa of a Hypertherm 1000. The big brown truck delivered it yesterday. All I can say is WOW, I had an old piece of 3/16 that I played around on, the 1000 went through it like a Katana sword.

Another update on my design. I am going to use rack and pinion drive. I have been working on designing a belt reduction this evening, I need some one to check my math. If I have a top target speed of 600 IPM and use a 1" pitch timing belt pulley on the motor shaft, by my math I need a 4.18" pitch driven pulley. If I use a 1" pitch spur gear off of the driven pulley shaft will that give me my target speed?

[millman52]

I made my first purchase toward my table. I am the proud poppa of a Hypertherm 1000. The big brown truck delivered it yesterday. All I can say is WOW, I had an old piece of 3/16 that I played around on, the 1000 went through it like a Katana sword.

Another update on my design. I am going to use rack and pinion drive. I have been working on designing a belt reduction this evening, I need some one to check my math. If I have a top target speed of 600 IPM and use a 1" pitch timing belt pulley on the motor shaft, by my math I need a 4.18" pitch driven pulley. If I use a 1" pitch spur gear off of the driven pulley shaft will that give me my target speed?

Based on 800 RPM motor speed that is correct