Drive Systems for Dummies (eg. me!)

[Metalfab_101]

OK, so i've been doing a bit of reading and can't really get my head around why one drive system is better than another.To put things in context I am looking at building a oxy/acet table to cut a sheet approx 900x1200.

Firstly i'll start on the gantry. Initially I thought a rack & pinion would be good way to go, but I am sure I read somewhere that this will be a bit noisy. Is that true? I watched Apple's test run of the road runner print and it didn't seem that noisy to me. But what about belt drives? Assuming I can come up with a design that protects the belt from slag during cutting is there anything else to consider? How do they compare in terms of cost & accuracy?

Cheers,

Damo.

[aaronpentz]

Rack and pinions will work great and should give you the cut tolerance you need. I work for Komatsu Cutting Technologies and we use Rack and pinion drive systems in all of our machines. We also use software correction for the distance in each gear tooth. that brings out tolerance to aroung +/- .004 with a plasma. The belts that we use are a standard rubber belt but it has steel cords to help stand up against the slag. Try to design your machine with the drive system as high as possible. Try to get it above the cutting table

Aaron
Komatsu Field Service
http://www.fineplasma.com

[CJL5585]

Metalfab 101

You might want to talk to a member here from Australia with the handle of Apples.
He has built a rack and pinion plasma system, and can give you some pointers with his experience. There are others also.

Jerry

[JerryFlyGuy]

I to am interested in Rack & pinion drives, I'm wondering what the best pressure angle to use would be [20 or 14.5] I've looked at boston gear but not sure which is the best. Also should a person plan to gear the drive down to the pinon to keep some decent resolution? Whats the best way to keep back lash out? Is belted better than a steel system? newby questions.. but.. Haven't found much reading mat'l that I understand as I know very little about gearing and gear theory.

JerryFlyGuy

[Al_The_Man]

I use 20deg pitch, to reduce backlash and for tensioning I found this way fairly cheap using a Rosta product. This was a retrofit on a large Linde table.
http://cnczone.com/forums/showthread...ighlight=rosta
You pretty much have to gear down using a rack and pinion. Here is a usefull tech sheet.
http://www.linngear.com/faq/techspecs/tech_specs.pdf
Al.

[JerryFlyGuy]

Al, Thanks for the recommendations. I'm liking these rack/pinion style setups the more I think about them.. I priced the L2012-6 rack w/ my local supplier and came back with $119 Cdn which is a bit more than I'd like to spend so.. I got looking into the nitty gritty details and I think I can pretty much half the size of the rack and still be ok w/ what I'm using. My plan is for a fairly large foot print Mill for milling foam molds 20' x10 x 5' [ and possibly some MDF which could be concidered its hardest cut] So I'm thinking I'll get the L2020-6 rack w/ a YA50A spur. My other question for you is this, I looked up bayside's planetary gear reducers and think that I'll end up w/ a Px90-010 as long as it meets what I need. I've been excited about going to a servo style drive [ vs stepper] however I'm worried that setting up the servos will he harder than steppers so.. a bit leary of this. I looked at the Nema 34's in a stepper w/ 450 oz-in torq. I also noticed that the max listed torq. for these gear reducers is 500 in/lb [8000 oz-in. so I would be ok there. I'm thinking 200IPM rapids would be enough, so.. 300RPM stepper /10 [ 10:1 reducer] =30 Rpm X (2.25 pitch dia X pi)=212 IPM travel speed. Also 450 oz-in x10 would be ~4500 oz-in torq. The gantry will be around 150-200# after its finished [ ya may be a bit heavey but.. I like to build heavy] Am I in the range here? Does it look like this would be opperational or under-powered? I forgot to mention I'll be putting a drive on either side of the gantry. Any got-ya's you can see from this? I'd like to go for the Rex w/ Ge-320's and wait for Mach 4 but this could add up to be pretty pricey in the long run..however if I was confident that I could set it all up w/ little to no hassel I'd be interested in waiting and spending the money to do it right the first time. Opinions welcome. And last question for now, how fast do you think a guy could run while milling foam [ipm]? It's going to be all 3d work for the most part.. Hard questions I'm sure as I'm being pretty vague here but.. as I've said before.. opinions welcome.

sorry this covers so many topics... probably not the proper place for all of them.. but they seem to all tie together so..

JerryFlyGuy.

P.S. where in Canada are ya from?

[Al_The_Man]

I generally use the highest reduction that will still give me required max. top travel rate. This will also allow the highest accel/decel. rate.
This is the Rosta type tensioner fitting that I adapt for the pivot point of the servo mount carrier. http://www.rostainc.com/PDFs/KAP00_EN.pdf
Al.