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17-06-2016 #21
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17-06-2016 #22
A square tubes looks not enough strong for me for aluminium machining.
I'm working on this frame for alu, with a smaller motors than what you want.
You should move the X ballscrow to lower. It is better between the 2 rails.
Everything looks welded. How can you do the end machining for a rails and others?
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17-06-2016 #23
Info about what specifically?
I can't see who's post you are addressing and though it's obvious to you it's not obvious to me :-(You think that's too expensive? You're not a Model Engineer are you? :D
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17-06-2016 #24
The design is kinda crude, it was a fast iteration. I'll probably get some time in the weekend to upgrade it so the details is more understandable. The i'm going to add end plates to the large gantry square tube. Most of the machine will be welded. I have planned to bolt the gantry and base together at the bottom of the gantry legs. I guess I need to remove the aluminium part in the title of the post sinse it's mostly steel now.
Originally Posted by Lee Roberts
I agree, I changed it back and forth several times. It became a compromise. Rails on the base would make sure the support is maksimum and equal at all times. However the moving base would be longer and the leverage from the longer base would put more stress on the machine. The weight of the moving part would also be higher.
Nice video, you got any info in addition?Last edited by PotatoMill; 17-06-2016 at 09:59 PM.
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17-06-2016 #25
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17-06-2016 #26
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18-06-2016 #27
The cost of servos is going to be quite high, so i'll probably for closed loop steppers instead. However the ClearPath servos seems tempting. Is there any good reason to use servos instead of closed loop steppers?
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18-06-2016 #28
Closed loop steppers don't have the speed or torque capabilities of servos and are sold as an 'economical' alternative. The only good reason to use closed loop steppers is because they are cheaper.
Some cheap servos like the JMC can be similar price to most closed loop steppers, it'll be interesting to know if anyone has tested how their performances compare.
Cheers,
Fenza
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19-06-2016 #29
Both have a feedback to driver, so both are better than a normal steppers.
A cost of the servos is higher than what you think. E.g. you have to reduce the rpm, with 1:2 - 1:3 transmission. 1x zero backlash pulley is approx £30-40, one belt can be £15-20 and you need 3 set. With steppers, you just need a coupling.
Unfortunately I started with servos, but I could get a cheap set from China.
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19-06-2016 #30
Thanks for the quick response Fenza and Remrendes
According to a quick estimate I did I dont think i'm going to need any more torque than what these closed loop steppers deliver; http://www.aliexpress.com/item/new-o...a-82b3fb4b4813
Estimates done with
-40kg weight of moving part
-130N force of cutter (excessive)
-20N friction
-85% efficiency
-10 m/s^2 acceleration (more than I think i'll need, but I haven built any CNC machines before so i'm not certain on this.)
-5mm lead
Using T = (F*l)/(2*PI*n) where F is total force, l is lead per revolution, n efficiency
I get 0.44N well within
However I do know that theory and experience dont always match up. And in real life there could be some factor that make the estimate wrong.
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