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View Full Version : Advice on new table and ball screw.



D-man
25-07-2012, 02:20 PM
Hey guys, I've finished building my new table and have a couple questions.

I was going to run a R&P system in all axis but I'm not to sure. Would a 3000mm ball screw have too much flex say at 25/32mm thick?

http://img.tapatalk.com/1f695d40-e4ff-11eb.jpg

irving2008
25-07-2012, 02:47 PM
25mm dia screw if supported in fixed/fixed bearing configuration will whip at 550rpm or 5.5m/min on a 10mm pitch
32mm dia screw if supported in fixed/fixed bearing configuration will whip at 746rpm or 7.5m/min on a 10mm pitch

either way the inertia is high so a hi volt/hi current/hi torque motor is needed...

D-man
25-07-2012, 02:59 PM
What do you suggest? Stay away from a screw and stick to R&P belted system? If so you know of anyone that could knock me a couple up?

JAZZCNC
25-07-2012, 06:08 PM
Unless you use a rotating ballnut then stay away from screws for the reasons Irving shown.
Personally I'd go for the rotating ballnut over R&P anyday but it will work out more expensive and slight more work to impliment than R&P.

I wouldn't go with belts over this length and size of gantry has the tension would need to be high to stop slap and belts will stretch with gantry weight.

R&P will be the easiest to do and if your just cutting wood it will be plenty accurate enough. It will still need larger motors and drives like big ballscrews due to it not being anywhere near efficient has ballscrews so you won't save much in this department.!

My 1st choice would be rotating nut's on 25mm x 10pitch screws.! Could maybe get away with 16mm x10mm but it's a fair old length and 25MM would be stronger. The little difference to performance would be worth it IMO.

NO I CAN'T FAR TOO BUSY.?? . . .But I'm sure there's a little scrout on her that would for the right money.?

D-man
25-07-2012, 06:39 PM
Interesting I've never heard of these rotating ball nuts.... Am I right in saying that it's the but that spins rather than the ball screw ? I can see that your not going to get a whip as Irving said I will with a normal setup

JAZZCNC
25-07-2012, 06:59 PM
Interesting I've never heard of these rotating ball nuts.... Am I right in saying that it's the but that spins rather than the ball screw ? I can see that your not going to get a whip as Irving said I will with a normal setup

Ah ha ye you can spin your "but" if you like but you'll need lots of sudo cream . . Lol

Yes the nut spins and the screws are fixed and actually put under tension which helps further.

Jonathan "scrout" has made some DIY rotating nuts so just do a search on the forum and I'm sure you'll find the thread.

He'll be along soon anyway either via PM or showing his spotty face on here. .:whistle:

D-man
25-07-2012, 07:08 PM
Pmsl Jazz!! I will be greasing up the lead screws with that stuff lol

Jonathan
26-07-2012, 11:28 PM
NO I CAN'T FAR TOO BUSY.??

I'm strongly inclined to say the same...how soon do you need them? They would be the ideal solution.

D-man
26-07-2012, 11:40 PM
I'm in no great hurry tbh. I've temp fitted the table with my 4ft screws and try are working flawlessly! And the beat thing about it..... That big ass gantry is running on 2 x nema 23's lol and I still can't stop the gantry!! So this will do me for just now. When you get some time let me know and we will talk.

In the meantime you were wanting to try the rotating nut on some R2020 correct?

D-man
26-07-2012, 11:45 PM
Here is a crappy video of the Nema 23's kicking ass lol

From zero to the park position.

http://www.youtube.com/watch?v=hn_PBTq1LCs&feature=youtube_gdata_player