[t0m]

I am making a plasma table. i was planning on a 4' x 8' but am deciding to scale it down to either a 4' x 6' or a 4' x 4'.


i have decided to go rack an pinion over ballscrew. I am stuck on which spur gear and racks to get.

From what I have read the 20 degree pressure angle is prefferred over 14.5.

so I now know that much.



from what I have read i will want to stay between 12 and 20 for my diametral pitch.

so I now know that much.

but for the exact pitch and number of teeth thats Ideal for my application, I am clueless. ie - I dont know what I need.

I want to directly drive the gear rack by the spur gear( drive along the gear rack if you will) without any belts or other mechanical gear reductions.

so My thinking is, for this to work and to get good control and resolution, Id want the motors to turn at a relatively high speed with a low IPM travel.

I would rather the motor have to turn more times than usual to make an inch of travel, than to have a motor that a 1/4" of a turn would create an inch of travel.

i am mainly going to be making turboheader flanges out of 1/2" steel and stainless. as well as aluminum endtanks pieces from 11 gauge aluminum and gaskets from 16 gauge copper.

I really dont know what ipm is Ideal for my application.

I have been searching and searching on this site and have gotten this far but am not finding any more information thru search
any help would be greatly appreciated.

tom

[Switcher]

I'm very interested in this also. I was looking at this same product earlier today. I also wander If the width of the rack & gear matter, what would be best (5x5 cutting table)?

I know they should be the same width, I'm thinking about the contact area.

[aaronpentz]

You will have to buy very high torque motors if you want to go with a direct drive system. You will save yourself a lot of time if you go with a reducer using belts and to spring load the pinion gear against the rack. (self compensate for wear) You would have to have a pinion gear with the least amount of teeth as possible for a direct drive setup.

[2muchstuff]

I have 16 pitch rack/pinion on my x-axis. With a rack/pinion system you will need to reduce the output motor RPM, whether it is done by timing belts or an expensive zero backlash gearbox. The reduction will give you the torque needed to move things around. You are contradicting yourself when you say you want a direct drive and then later on say wanting the motor to make several turns.

It is just the nature of a rack system needing to have some kind of reduction. I'm not saying that it can't be done but on the size that you need, 4'x6'. I can see if you were building a table 4"x6", then you could get away with a 64 pitch rack or smaller.

[Brian Kidd]

With all the reading lately of drive systems for a CNC Plasma table I think I want to go with belt drives instead of going rack and pinion. I am thinking about putting together a 4' x 8' table and use steel for the base and aluminum for the gantry. One question I have is with the recommendation of using 2 motors for the 'X' axis should I still have a shaft going across to the other side to still help keep everything in line or would that case more problems?

B.Kidd

[2muchstuff]

You can use two smaller motors, one will be slaved, but it would be better to use one larger motor. On a table that large I would use a shaft that would link both sides to keep things in line. Out of curiosity are your motors going to be mounted on the gantry with a stationary belt or the motors mounted on the table with a moving belt. The belt clamped to the gantry.

[Brian Kidd]

You can use two smaller motors, one will be slaved, but it would be better to use one larger motor. On a table that large I would use a shaft that would link both sides to keep things in line. Out of curiosity are your motors going to be mounted on the gantry with a stationary belt or the motors mounted on the table with a moving belt. The belt clamped to the gantry.

Actually I am not 100% sure yet, I think I've seen both ways done. I've read through so many posts now it's kind of hard to keep everything straight and to remember where all the good pictures and drawing are. Is there a recommended way?

B.Kidd

[2muchstuff]

It's a matter of personal preferance, which way you feel comfortable with. I know what you mean about all the pictures and drawings, they seem to run together after awhile. That is what is nice about this site, so many ideas and thinking from all over the place.

How big are your motors.

[Brian Kidd]

Well at this point I do not have anything except for my brothers ESAB Plasma. I am actually in the middle of putting together my IH CNC mill and bench so it will probably be a bit before I get to the plasma table but I am trying to research and start designing now so I have an idea of what I am going to make when the time comes.

B.Kidd

[aaronpentz]

you could do a Gantry style machine and only drive one side. If you look at our
KPCL 300 amp machine

www.fineplasma.com

our TFPL also is a Gantry style machine with a single side drive.

On a machine that is only 4 feet wide I would use a shaft. I can give you pictures of our smaller machines if youd like. We use a shaft drive with a single motor on all of our machines except for the REV2 wich uses a dual motor system. we went that way because the machine is sectional and can be custom ordered to a width of 12 feet. Easier assembly.