Thread: Ballscrew Thickness!
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15-08-2009 #1
Hi guys im in the middle of building my machine but i would like to know your thoughts on what thickness ballscrew i should be looking at to span over 1829mm ( 6ft ) without none to much "whip" and another thing is the pitch as on zapps website they do a 5 or 20mm pitch in the 20mmOD screw, the machine im building is for precision work mainly but with it being a 6x4 bed i was thinking that a 5mm pitch would take all day get to the other end? :confused:
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15-08-2009 #2
I used 25mm OD ballscrew with a 25mm pitch for mine, and with the motors I've got, I get 18m/min, which for about a 1.4m run gives ~4.7 seconds for total travel. However, you will need to worry about whip.
Gary (from Zapp) gave me a website which allows you to calculate the whip speed based on the diameter and so forth - unfortunately, I've only got the link at work, but Gary may come on here before I get the chance on Monday to get it.
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16-08-2009 #3
Use this link.
http://www.nookindustries.com/ball/BallCalculators.cfm
use the root diameter that is normally about 2-3 mm lower than the outside diameter and select the mounting type you are using, and it will calculate the max speed before it will whip.
If you have any question, or need help give me a ring on monday.
Gary
Visit Us: www.automationshop.co.uk
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15-08-2009 #4
thanks tribbles for that info, 25mm OD is some fair chunkey stuff!
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16-08-2009 #5Gary (from Zapp) gave me a website which allows you to calculate the whip speed based on the diameter and so forth
You havent said what you are cutting or what accuraccy you require. But if you are using steppers when 200 steps per rev at 5mm pitch gives 0.025mm resolution. With a 25mm pitch you get 0.125mm resolution.
Also given that for your 1829mm travel you will probably need 20mm + dia. then motor torque will be an issue, lots of mass and inetia to control.
I may be corrected by others but you are probably in Servo Motor terratory for the distances and speeds you require.
See the attached pdf that I got from Cnc-zone.( hope its ok to repost it. cant remember who its from. {Lee any probs just remove it}
Goes in to detail about designing motors, screws and feeds.Last edited by Ross77; 16-08-2009 at 01:22 AM. Reason: Bad speeelaing as usual
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16-08-2009 #6
Sorry. Gary and your self posted whilst I was writting...
30mins to post. Must be time to go to bed....:heehee:
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16-08-2009 #7
Well i was planning on cutting woods and none ferrous metals!
Ive been looking at the 25mmOD ballscrew and im leaning towards that! as for the motors being not power full enough i can gear them to something like a 5:1 or more and get a 20-25 pitch ball screw!
What do you guys think!
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16-08-2009 #8Well i was planning on cutting woods and none ferrous metals!
Ive been looking at the 25mmOD ballscrew and im leaning towards that! as for the motors being not power full enough i can gear them to something like a 5:1 or more and get a 20-25 pitch ball screw!
What do you guys think!
If your using belts then you might also want to check the 5:1 ratio, sounds a bit high. the small pulley will not have enough teeth in mesh if the bigger pulley is to large. Ive got a calculator at work so if its any help I'll post it tommorow.
Hope you dont think I'm being negative but I had to make the same decisions for my build. I chose Slow and accurate because Im only using it to build the fast machine :heehee:
Have you concidered rack and pinon? its cheaper and very fast.
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17-08-2009 #9
Ok I've had a rethink, Have you already got your steppers and drivers yet?
If not then the better drivers have micro stepping. if you get the correct size motor then u can direct drive it and use the micro stepping to get the accuracy/ resolution you need.
Give gary a ring. Im sure he will help you and is much better qualified then me. Im just trying to cover all possibilities to help you make the right decision.
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16-08-2009 #10
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