It is currently Sat Nov 18, 2017 9:44 pm

 

New diy table

Share and learn with other DIY members who have built their own plasma tables and accessories.
ianhem
Posts: 3
Joined: Thu Jul 06, 2017 1:53 am

New diy table

Postby ianhem » Thu Jul 06, 2017 10:09 am

Hello every one and thanks in advance for any help you can offer me.

I'm looking to build my own table and have collected some parts together somewhat by chance.

I'm already experienced at fabrication. But I've never built a cnc machine before.

I have collected some linear rack about an inch wide and 5/32 (4mm) pitch on the teeth.

I have also collected some lead screw, bearings and stuff.

Also these large motors!

So I thought there are a couple of ways I could use the rack with a pinion on a stepper motor I guess one at either side of the table.

Or I could use the lead screw with a stepper driving it maybe with a belt, that lead screw is 3/4 diameter though.

I don't know a great deal about the electronics what drivers should i use, are those cheap chinese ones workable, whether to use a break out board or a motion controller any advice is very welcome ??
Ian

You do not have access to download this dxf file.
Become a Contributing Member to gain access to the thousands of files shared by our members. Click Here


tcaudle
Posts: 788
Joined: Tue Feb 28, 2012 6:47 pm

Re: New diy table

Postby tcaudle » Thu Jul 06, 2017 11:17 am

Those motors are servos with encoders(?) on the back. Hopefully you have the matching drivers . I can't read the encoder label but they could be digital encoders, resolvers, or tachs. Its not possible to see if they are DC brushed or BLDC or some other type. It appears they MAY have gear reduction on the front which would make sense for the course ballscrews. The good news is that they are course and should be able to spin fast enough without whipping to give you speeds up to the IPM you need for plasma. All ballscrews have a max RPM they can achieve and its dependent on the You have not picked an easy route but if your goal is a learning experience and to pickup some new skill sets it will work well for you. Building a working CNC plasma table out of bits and pieces can be a fantastic journey from which you will emerge with a lot of new knowledge. You also will have to figure out a lot on your own because there are hundreds of possible combinations for hardware and software and you won't have many users that will be able to mentor you on a specific build. Keep posting and myself and others can give you general suggestions and advice along the way.

ianhem
Posts: 3
Joined: Thu Jul 06, 2017 1:53 am

Re: New diy table

Postby ianhem » Fri Jul 07, 2017 2:58 am

Thanks for your reply. I haven't really chosen any route.
I bought a couple of CNC punching machines, colossal things they were and removed these just in case they were useful.
I kept the lead screws because they are nice quality items but I was surprised at how coarse the threads were.
I also have lots of this rack and a couple of pinions.
20170707_075328.jpg


I wonder if they would be easier?

You do not have access to download this dxf file.
Become a Contributing Member to gain access to the thousands of files shared by our members. Click Here


Rodw
Posts: 87
Joined: Sun Aug 21, 2016 1:49 am

Re: New diy table

Postby Rodw » Fri Jul 07, 2017 3:59 am

Best of luck with your build. As Tom said, building from scratch is a big undertaking and yes, there are so many decisions and alternative ways to do something. Its taken me 12 months and I am hoping I will have the last home and limit switches in place this weekend. I have said a couple of times in jest what I have built is Version 87!

There are various levels of DIY table building and I've done it the hard way building everything from scratch but there are many shortcuts you can take and Tom has some great options.

I zoomed in on your photo and it looks like you have Servo Dynamics DC servo motors and they are still in business which is a start. See http://www.servodynamics.com
I'd try and use the servos if you can get compatible and reasonably priced servo drivers for them. I might be biassed but I'd run with LinuxCNC as there is a good range of hardware to control your servos such as the Mesa 7i77. You might even be able to talk Tom into sorting out a packaged solution!

ianhem
Posts: 3
Joined: Thu Jul 06, 2017 1:53 am

Re: New diy table

Postby ianhem » Sat Jul 08, 2017 5:06 am

The servos look great i agree
I dont think ill use the leadscrews as they are too coarse, but beautiful quality.
I will use the rack and pinion I have

tcaudle
Posts: 788
Joined: Tue Feb 28, 2012 6:47 pm

Re: New diy table

Postby tcaudle » Sat Jul 08, 2017 2:31 pm

Actually you are better off with course leadscrews. The reason they use them on a CNC punch press is you are moving around a rather light sheet of material and at high speeds....kinda like the speeds you need for thin material on a plasma. Study a little about "lead whip" and look at the max RPM curves of different lengths of spinning leadscrews.

You have several considerations with leadscrews for motion:
1. They reduce the speed and increase the torque at a rate equal to the TPI and the actual length of a thread on one inch of screw length. Each screw has a max RPM it can be turned at, which is a factor of the diameter, length and the type of end mounts. Over that RPM you get deformation of the shaft for centrifugal forces and it causes ball nuts to bind and vibration to set in. So the TPI is not the only factor.
2. The ballscrew is a precision bearing and it needs to be kept clean and lubed. Having one exposed to plasma dust (plasma smoke is vaporized metal ) will shorten its life.

It's all about matching the speed you need with the amount of torque (converted to linear force) to move and accelerate the mass of the gantry and all its bangles to numbers that work for cutting thinner sheet with plasma. You don't need speeds you can't use. Having a machine taht can hit 1000 to 3000 IPM sounds impressive but if the acceleration curve is bad you will still get marginal cuts. Its a LOT easier to build a table that cuts think material than to make one that cuts thin material well, and all of the components and control have the speed and response to do that.

plasmartist
Posts: 39
Joined: Mon Aug 07, 2017 1:31 pm

Re: New diy table

Postby plasmartist » Fri Aug 11, 2017 10:15 pm

About a year ago I was in your same boat. I had a friend that bought a ton of the old NASA scrap and I wanted to build my table with the servos and numerous others parts he had laying around his warehouse. There is no doubt the part quality was exceptional, but as I looked into it, I discovered I was opening a huge can of worms. My knowledge of computers and circuits is just enough to make me dangerous but not enough to design my own controller based on cnc scrap. After a few months of research (realizing that I was going to be buying a lot of various components such as DTHC, licensing, etc that was going to add up) I bought a bladerunner from tom at candcnc and couldn't be happier. There is the added benefit that when you do run into issues you can call one company for an answer. Just my opinion of course, and I commend you for building your own either route you take.


Return to “DIY Plasma Table & Accessory Discussion Forum”

Who is online

Users browsing this forum: No registered users and 1 guest