I need help with my machine

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18 Oct 2021 14:27 - 18 Oct 2021 14:32 #223456 by PhilipME
I decided to have bt-30 spindle but not clear on the motor

AC- servo or induction motor. The induction motor seem heavy and I have 16 mm ball screw on the Z-axis

The other thing do I need to sink the frame inside concrete to be able to mill mild steel with 8 mm tool

I will appreciate any critiques

Philip


Edit video : obviously the x-axis solid bars are 30 mm in diameter, not 30 meters


 
Last edit: 18 Oct 2021 14:32 by PhilipME.

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18 Oct 2021 14:55 #223461 by OT-CNC
Replied by OT-CNC on topic I need help with my machine
You can add an air cylinder as a counter balance for the weight of the spindle. If it's sized correctly you can dial it in with air pressure to get it balanced. You can always add a larger stepper / servo or gear reduction if the performance is not good. For possible lack of overall stiffness, mount an indicator and push/pull on the frame to see what flexes the most. Add bracing where need if needed. I would add a thick spoiler plate to your table or some T-slot table if you can find it. At first glance, the table looks a bit thin to me. Also, the round rail will be the limiting factor for overall stiffness. I would measure their deflection first.
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19 Oct 2021 09:37 #223540 by PhilipME
Many thanks OT-CNC for the valuable comments

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19 Oct 2021 11:06 #223548 by andypugh
Induction motors (especially aluminium-frame ones) are lighter than they look. They have about the same copper weight as a servo, but the rotor is a hollow cage rather than a bunch of magnets.

This one is 2.2kW and 15kg: inverterdrive.com/group/Motors-AC/Universal-UMHA-90L-2-B14/
This servo has approximately the same rated torque, it is about half the mass, but rather expensive: inverterdrive.com/group/Servo-Motors-AC/...otor-SSD-Drives-ASB/

Of course, itf you are not buying new then you can probably get the servo cheaply.

Also factor in the price of the drive.

I don't think that you will be needing low speed torque?
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19 Oct 2021 14:51 - 20 Oct 2021 05:32 #223563 by PhilipME
Hi Andy
Thanks for the usefull post


What do you think about this from ebay
www.ebay.com/itm/172713911589



I opened acount with universal motors. I like the 3-phase induction motor in the link. It should work with the Huanyang VFD.

the ac-servo as you mentioned, I still have to buy a driver(Not sure how to spec the driver). And I am woried also about the complexity of the AC servo motor feeding the encoder signal to the driver and making sure the signal volt matches the input-pin of the driver.

15 kg is not bad.


Thanks

Philip
Last edit: 20 Oct 2021 05:32 by PhilipME.

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22 Oct 2021 16:11 - 22 Oct 2021 16:40 #223929 by PhilipME

You can add an air cylinder as a counter balance for the weight of the spindle. If it's sized correctly you can dial it in with air pressure to get it balanced. You can always add a larger stepper / servo or gear reduction if the performance is not good. 

 


This guie in the attachment is counterweight with springs. Never thought of the counterweight untill you mentioned it. Not sure this spring arrangment will work, because there will be position along the Z where the full weight will still be on the Z-screw balls, and partialy on the motor torque.


 
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Last edit: 22 Oct 2021 16:40 by PhilipME.

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