Rack and pinion or ACME?

[ratrace2]

Originally Posted by Glidergider How long is your screw going to be? That's a key design point. If you are greater then 4 feet, then the rack in pinion is probably your best bet. Longer then 4 feet and your spinning rod will develop a significant wobble. I didn't look in detail at your other build thread. That's why I don't know how long your table is. How fast do you want to jog and cut? Most guys are going with the 1 inch diameter. Enco.com sells a 1 inch 10 tpi single start acme for $10/6feet. I bought a 1 inch/8 2 start acme for $60/6 feet. You can jog a bit faster with the 2 start. Dave

Can you tell me how well the Roton ball screws worked out. I'm looking to get some 5' ball screws for my machine. The price sounds great.

[ratrace2]

Originally Posted by Darren Sweet! That is an excellent price, looks like I'll be considering ballscrews. How will you turn them down to fit the bearings for mounting etc?

It looked to me like the roton screw had a shaft cut on the end for motor/spider gear mounting?

[Glidergider]

Joe, 5 Start? You mean 2 start right?

[Glidergider]

Sorry, I can't help you. I don't have that hardware.

Originally Posted by ratrace2 Can you tell me how well the Roton ball screws worked out. I'm looking to get some 5' ball screws for my machine. The price sounds great.

[ratrace2]

Originally Posted by Cartierusm What's your price range???? I started out with McMaster Carr Acme Screws and Dumpster Anti-Backlash nuts and just recently discovered Roton..dirt cheap, if you don't buy the mounting flange. The dumpster nuts are like $18, the Roton ballnut is $22.50 for 5/8", and the ballscrew is about $1 an inch, that's cheaper than Mcmaster for the acme screw. So in my opinion go with ballscrews, I just ordered mine to convert.

Off the top of your head, could you get the Roton's, say, 8' ft. long?

[joecnc2006]

Originally Posted by Glidergider Joe, 5 Start? You mean 2 start right?

No 5 start, two turns per inch, trust me it is very smooth and dumpster nuts work great with it.

McMaster-Carr Part Number: 99030A704

Joe

[Darren]

Ok, so do I need any sort of reduction with my servo's or will 5 start give me what I need to keep the servo RPM up?

[LeeWay]

Personally I think it may also depend on the type of bearings you use, but at two turns per inch, that sucker should fly. You may need reduction to just gain torque though.
The screws I am using on my mill are 1 turn = 10 mm. That is a pretty high helix as well. I have chain drive gears on the Y and have tested that and quit at 120 IPM. For an 8 or 9" axis, that is plenty. No need to go higher, but will likely set it at about 80 IPM rapids. The gearing on it is 3 to 1. Probably way to much, but I will let the machine cut new parts when it is done, then change it to a belt drive about 1.5 to 1.
I got to work on my X this afternoon and just need to mount the motor now. May do that in the AM.

[ger21]

If you go back to your other thread, Jeff said you should run those servos at about 2500rpm. 5 start 1/2-10 screws are 2 turns per inch. You need to pick a target top speed, and gear to that. If you want to go 250ipm, that would be 500 rpm at the screw, and 5:1 gearing.

[Glidergider]

Originally Posted by joecnc2006 No 5 start, two turns per inch, trust me it is very smooth and dumpster nuts work great with it. McMaster-Carr Part Number: 99030A704 Joe

Wow, I'll bet that really moves out. Yes, very smooth. What jog speeds do you get, 200ipm?

[ahren]

I have the 5 start 1/2-10 with Dumpster nuts on my machine. I'm using 3' screws on both axes. I get rapids of 300 IPM on my Y, and I've gotten 600 IPM (that's no typo) on my X. They're wicked fast, and help a lot with whip.

Ahren
www.cncrouterparts.com

[csrc]

Darren, I am building a machine using the 5/8-.200 ball screw set up. My long axis is 48". I am using 12mm ID 6201rs ball bearings (dirt cheap from VXB). This is just less than the root of the thread so it cleaned up nicely on the lathe. The OD will press fit into 1.25" with some forgiveness (1.2594" in theory). I combed CNCZone before I spent my dough and the majority say that ballscrews are the way to go. Lots of commercial machines use R+P, but the 5/8-.200 ballscrews are cheap! You must factor in the cost of a tap for the ballnuts, however, as the 15/16" - 16tpi tap is pure unobtanium except from Mcmaster ($58), unless you pay the premium for the prethreaded flanges. I think it is worth it to eliminate backlash and wear.