[Mike Wood]

Hello all

I’m new to this and would like to get opinions about a round pole rf-31 clone 3 axis retro. Jeff Davis style

Dc servo size - Does it make sense to go with a little extra power? Will it make it easier to setup the mill and avoid faulting and such or will it just cause trouble? Wondering if 1100oz 90v nema23 (camtronics) or 850oz 72v nema24 keling with gecko g320 drives and 72v 20a keeling power supply is too big?

Timing pulley ratio – Jeff calls out 2:1 with 430oz servos. Should this increase with the larger servos (3:1) ?

Encoders – Assuming reid 5/8 .200 ball screw, which encoder makes more sense 200, 250 or 500 cpr.

Internal Z axis mount – When the time comes, will the camtronics 1100 nema23 servo fit inside the head? How about the keling 850 nema24

Z axis preload – What’s the thought on Z axis preloads? And does it fit inside the head?

Front mount Z axis - There’s a need to double as a wood working drill press for a short time. What about mounting the z axis ball screw assembly on the front of the head with a disconnect quill plate, keeping the spider handle till things change?

Ball screw wipers – How can I fabricate inexpensive wipers? – I saw some good posts but I just can’t find them any more. One using a door mat sweep and the other silicon caulk.

Lubrication – What kind of lubrication is needed for the ball screws and contact bearings?

Thanks

[Bubba]

Mike,
I'll throw my .03¢ in as I converted my RF31.

Dc servo size- YEP, bigger is better in most instances. My first servos were kind of wimpy and I could not achieve any reasonable rapids with them. In conversation with Mr. Gecko, he pointed out that I was running out of steam and if a flea landed on the table, it would fault out! Be careful about the "max torque" ratings, you don't want to design to those! Again Mariss gave me some formulas to go by for proper sizing of the servo/reduction ratios to use. Everything is a trade off. Higher reductions give more torque but can limit the rapids. Plan ahead for what your trying to do. Loads milling plastic are most likely a lot less than milling hardened steel.

Timing pulley ratio- see comment above, this is a trade off type of situation. Again what loads, speeds etc do you want to achieve.

Encoders – (One moment while I put on my asbestos suit)! OK, got it on. When I first set my machine up, I used 1000 line encoders on the ballscrew and it worked beautifully. I read the stuff on this and other sites where the max was 500 line encoders. Again, it depends on where they are mounted, (if on the servo then belt reduction makes a difference) and how fast you want to go. It also depends on how fast your computer can output steps! More tradeoffs!

Internal Z axis mount – Sorry can't help with this one.

Front mount Z axis - This is one I still have a problem with. The further out your "moment" arm is to drive the quill up and down, the more you have to worry about flex in the system. We all know about the backlash in the pinion drive system so again, trade off in type of system. If you make some sort of disconnect, you introduce another possible weak link.

Wipers- I used to have a link to how somebody else did it, but here is link to my page that will give you another idea on how I did it:
http://bellsouthpwp.net/A/r/Arts_home_page/DRO/

Lubrication – My solution was to install a one-shot system to lube not only the ball nuts, ways, and the bearings. I use way oil in the system. I realize some will say grease for the nuts, but I figure that oil on a regular basis is better than grease only once in a while (remember, you have to get to them!)

[dgoddard]

I'm in the process of converting a RF31 to CNC using 850 oz-in servos, 4800 max rpm, with a 3:1 reduction. Got most of the design/machining completed. Working on turning the ballscrews now. Bubba (also known as "Art") has been a great help in assisting me as I was a "newbe" to CNC. If possible would suggest you visit someone with a CNC conversion in your area. Think it will help fill in the blanks left from read-only. Bubba and I swap ideas on a regular basis.

Think you will find that the 850 servo will be too large for Jeff's Z design. I've opted to go with the basic using the fine feed first and maybe later convert to a Z ballscrew. Worry about that later.

Be glad to share my sucess/failures/tips/etc. of a newbe to CNC. I'm located near Commerce, GA

[Mike Wood]

Hey guys

Just got in. Thanks for the replies. Bubba, I took a look at your site, looks good. This is where I saw the wipers - this is the ticket. So, I suspected the larger servos is the way to go and I guess the Z axis might be a bit more involved than I thought. Can you point me to the formulas for proper sizing of the servo/reduction ratios?

So, The 850 servo being to large, do you think that is because of the nema24 foot print. Do you think the other motor might fit? I'm up in southern maine kennebunkport

Thanks
Mike

[Bubba]

Mike,
Attached is an xls file that I put together along with the comments from Mariss on how the various areas are derived.

Fill in your parameters (in the yellow cells) and the answers that you need are generally in the blue cells.

Hope it helps.

[JMcDonald]

Sorry to bump the old thread!

I am looking to retrofit this particular mill also. I was looking at this kit that includes some basic software, a Gecko control unit, and 3 1200 oz/in stepper motors, plus the cables for them, etc. What else do I need to complete the retrofit? I was thinking it is simply a matter of attaching the motors and powering it up, but is there more needed than that?

*edit*

Forgot the link:
http://www.super-tech.com/root/itm.a...M-EMC-GeckoPwr

*edit*

Just read a few 3-page threads about this. Found some good info, but nothing really definitive. Anyone have any basic advice?

[Uguessedit]

My industrial machines feed way oil to the ball nuts so nothing wrong with it. If using grease I’d recommend some Kline or something of quality. I’ve made my own screw wipers using Delrin or shoe that threads onto the ball screw and it keeps it clean as it drives back and forth.

Mike,
I'll throw my .03¢ in as I converted my RF31.

Dc servo size- YEP, bigger is better in most instances. My first servos were kind of wimpy and I could not achieve any reasonable rapids with them. In conversation with Mr. Gecko, he pointed out that I was running out of steam and if a flea landed on the table, it would fault out! Be careful about the "max torque" ratings, you don't want to design to those! Again Mariss gave me some formulas to go by for proper sizing of the servo/reduction ratios to use. Everything is a trade off. Higher reductions give more torque but can limit the rapids. Plan ahead for what your trying to do. Loads milling plastic are most likely a lot less than milling hardened steel.

Timing pulley ratio- see comment above, this is a trade off type of situation. Again what loads, speeds etc do you want to achieve.

Encoders – (One moment while I put on my asbestos suit)! OK, got it on. When I first set my machine up, I used 1000 line encoders on the ballscrew and it worked beautifully. I read the stuff on this and other sites where the max was 500 line encoders. Again, it depends on where they are mounted, (if on the servo then belt reduction makes a difference) and how fast you want to go. It also depends on how fast your computer can output steps! More tradeoffs!

Internal Z axis mount – Sorry can't help with this one.

Front mount Z axis - This is one I still have a problem with. The further out your "moment" arm is to drive the quill up and down, the more you have to worry about flex in the system. We all know about the backlash in the pinion drive system so again, trade off in type of system. If you make some sort of disconnect, you introduce another possible weak link.

Wipers- I used to have a link to how somebody else did it, but here is link to my page that will give you another idea on how I did it:
Page not found – BellSouth Personal Web Pages

Lubrication – My solution was to install a one-shot system to lube not only the ball nuts, ways, and the bearings. I use way oil in the system. I realize some will say grease for the nuts, but I figure that oil on a regular basis is better than grease only once in a while (remember, you have to get to them!)

[CL_MotoTech]

We have ourselves a necromancer.