Thread: Rotating Ballnut - design ideas
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14-01-2018 #171
Here's a vid of an Igus solution for supporting long screws - https://www.youtube.com/watch?v=Duq163m59TU
And I'm struggling to find a video of the system magicniner mentioned, but I'm sure I've seen one at some point.Avoiding the rubbish customer service from AluminiumWarehouse since July '13.
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14-01-2018 #172
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16-01-2018 #173
Boyan, If you could look at this, I would appreciate any feedback. thank you
MutzyNewZip.zip
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16-01-2018 #174
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The Following User Says Thank You to Lee Roberts For This Useful Post:
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15-02-2018 #175
Hi Iam new here and also my English is poor too. I just need to know where can I find such a code (Firmware Version 1.2 Type1.) I can find it in zip file but not download. so much thanks if some one could help me any help will be appreciated.
my Email is: [email protected]
best regards.
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15-11-2019 #176
hello im thinking to make a new cnc router for size 5x10 so my question is im going to use rotary ball nut,do i need 25mm or 32mm ballscrew for 10 feet axis and do i need high pitch screw such as 25 or 32 since im thinking rotary ball nut doesnt have critical speed maybe i can use 10mm pitch and just spin it 3000-5000 rpm with 1:1 ratio belt,
and im going to pair it with 750-1kw 3000-5000 rpm servo for it i already.
i already got quote for my supplier
rotary ballscrew 3232 10 feet=350 usd
rotary ballscrew 2525 10 feet=300 usd
my target rapid is around 1500-2000ipm
thanks
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29-11-2019 #177
Hi,
I'm just finishing a 10x5 machine with rotating ball nut so it's good timing to ask this question.
The first thing to mention is how much the screws sag under there own weight at 10ft long. With NO tension on the screws, it's massive but even with tension on the screws which you must have, there is still more Sag than you would probably expect.
So when the machine is at Rapid feeds and when axes are near the ends it leaves a long length of screw unsupported, so the screw can still vibrate.
On the machine I've built it uses a 25mm diameter with a 25mm pitch with a 1.5:1 ratio. I'm using 220V closed loop steppers spinning which spin between 1500-2000rpm. The machine is tuned at 30mtr/min(1200in/min) and will reach 40mtr/min((1575in/min) however I wouldn't suggest that speed and here's why.
The ball nut was never designed to spin at those rpm's so while you havent got the critical whip factor to deal with you still do have to consider the nut speed and what it was designed to spin at. Most ball nuts expect to be fixed and are designed for low spinning screws. So with Servo's spinning at 3000rpm or higher then you will have trouble with premature wear. Also, the alignment will be much more critical with higher RPM's.
My advice is to use a higher pitch then apply a ratio to lower the rotation speed of the ball nut while still getting the rapid feeds you would like. You will also get the advantage of increasing torque so you can lower the size of servos.
Now, where it gets tricky is with the Ball screw size. The larger Diameter screw will probably Sag more under its own weight so more tension will be needed. So you will need to design strong brackets that allow for the screw to be adjusted for alignment.
My suggestion is to go with a 32mm pitch and ratio of 2:1 that will give the equivalent of 16mm pitch and 1500rpm at the nut with 3000rpm motor. Giving just short 1000in/min which could be pushed up 1575in/min with 5000rpm giving 2500rpm at the nut which I would suggest is pushing the limit.
Hope this helps. Oh and this machine is vertical but that doesn't make any difference.
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29-11-2019 #178
I've read this recommendation several times but doesn't the increase in pitch cancel out the increase in torque so that the maximum linear force that can be applied to the gantry without stalling the motor remains the same? Or are you more concerned about the moment of inertia of the ballscrew itself?
KitLast edited by Kitwn; 29-11-2019 at 09:58 AM.
An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.
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29-11-2019 #179
Kind of yes but no, or should say maybe your misunderstanding what's being said or maybe I'm not putting it over clear enough..
Yes, 32mm pitch with 2:1 ratio will give the same linear torque as 16mm pitch 1:1 so torque is canceled by pitch difference like you say.
However, when I say Torque is doubled so the smaller motor can be used, what I'm referring to is that if 1:1 the 32mm pitch would require a larger motor to give the same linear force as 16mm pitch. So the ratio doubles the torque and allows the smaller motor to have the same linear force as 16mm pitch.
The trades off's and gains are that 32mm linear movement halves but so does rotation speed of the nut. So the pay off is that you get the same feed and torque as 16mm at 1;1 but with half the rotational speed of the nut or screw. This is the main goal to reduce whip and stress on the ballnut.
Hope that makes more sense.!
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29-11-2019 #180
HI JAZZ thanks for your insight regarding my question just talk with my ball screw supplier he suggest me to use 4040 for 3.2meter axis and 3232 for 2 meter axis..and i might follow their suggestion regarding that if budget is not constraint..anyway maybe i opt for 3232 all axis 4040 is really expensive
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