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Author Topic: Warco VMc /Chester 626 knee mill CNC conversion  (Read 58718 times)

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Offline Hood

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Re: Warco VMc /Chester 626 knee mill CNC conversion
« Reply #20 on: July 23, 2008, 03:50:04 PM »
Problem, book must be at the workshop after all :( gotta get the desk tidied up so I can find things LOL.
Hood

Offline Perfo

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Re: Warco VMc /Chester 626 knee mill CNC conversion
« Reply #21 on: July 23, 2008, 04:01:06 PM »
hmmm Yep I wasn't counting on micro stepping I thought 800 steps per rev would be good enough as your 20Khz on 2000 steps is correct then div it all by 2.5 gives you 800 steps per rev at 8Khz. I think my calcs and yours are the same except I didn't factor on micro stepping. Does this seem likely?
This is where I come unstuck I'm quite at home with software or electronics etc or even mechanical systems that I've got a bit of experience with (which I haven't at all with a mach3 setup on a proper mill).
As concerns how many steps to use I simply thought what's my target accuracy. I guessed 0.01mm would be a good starting place but not sure if it's realistic. I then thought if 0.01mm is my target then the electronics must have at least this level of resolution so I guessed I'd need at least 100 steps per rev. With my motor and drive combo I think the minimum I can get is 400 steps per rev so I doubled it to 800 steps per rev thinking this gives me a resolution of 0.00125mm I then multiplied or divided this with my mechanical gearing to actually arrive at a final resolution figure which in my case as I have a 3mm pitch lead screw and a 3:1 gearing on the motor I end up with 0.00125 mm travel per step. I’ve got this sneaking feeling I am missing something fundamental here so please don’t give up me just yet. Are there any advantages of micro stepping except a smaller degree of rotation per step? And thus do I need more than 800 steps ?

Offline Perfo

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Re: Warco VMc /Chester 626 knee mill CNC conversion
« Reply #22 on: July 23, 2008, 04:16:21 PM »
Your bridgeport seems a bit bigger than my 626/vmc which I'm glad about as my steppers are only rated at 305 Oz-in of holding torque (is this the same thing?) so they have a third of your stepper power.
No probs with the book thing whenever you feel like it when you have a minute is good enough for me. I'm still waiting for the base to be released from a fellows locker which I may get back next week. Then I've probably got another week on top of that to wait for my smoothstepper. At least when i get my Base back I can start machining the plates etc for mounting the steppers on.

Offline Hood

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Re: Warco VMc /Chester 626 knee mill CNC conversion
« Reply #23 on: July 23, 2008, 04:21:14 PM »
Micro stepping makes for smoother motion, Mariss says 10 micro steps is the ideal and I believe him, he knows his steppers :)
 You seem to be working arse for tit LOL, what you want to do is work from your hardware and that will give you your steps per unit, from that you can work out what kernel speed you would need for a given speed (although if SS its not an issue)
 Ok so stepper at 200 steps per rev, you get Geckos with 10 micro steps so that 2000 steps per rev, 3:1 gearing = 6000 steps per rev of the ballscrew. Ballscrew move 3 mm/rev so thats you back to 2000steps but its per unit now (1 unit = 1mm in your case). With a 2000step per unit I would think you could get 1250mm/min out of a stepper, I get 2500mm/min  with 1000 steps per unit ((200 x 10 x 2.5) / 5) = 1000 steps per unit. Smaller motors can often rotate faster so if you are using smaller steppers you may well get a faster speed.

Hood

Offline Perfo

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Re: Warco VMc /Chester 626 knee mill CNC conversion
« Reply #24 on: July 24, 2008, 09:57:16 AM »
okay cokay then that's how I'll set it up. I do like to know the inns and outs of things but will always opt for the proven tried and tested methods suggested by fellows such as yourself then fiddle and break them later once I know it's all working. :)

Offline Hood

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Re: Warco VMc /Chester 626 knee mill CNC conversion
« Reply #25 on: July 24, 2008, 04:21:25 PM »
What drives are you getting/have got?

Hood

Offline Perfo

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Re: Warco VMc /Chester 626 knee mill CNC conversion
« Reply #26 on: July 24, 2008, 09:37:46 PM »
I've got myself some fine 86BYG450B-011 from motion control products 4 phase 4 amp per phase 305 oz/in (2.16 Nm holding torque. I've only got two at the moment but need to find a third as they no longer do these in MCP but have got similar In my simplistic mind I thought I'd try the two I've got and if they work fine then get another but if it struggles on one axis then I'll get a bigger one for that axis.
To with them I've got three MSD542 Microstepping Driver (4.2A Peak)  from the same company.
I must admit though I'm not sure holding torque is directly related to driving torque.
Re: Warco VMc /Chester 626 knee mill CNC conversion
« Reply #27 on: July 24, 2008, 10:26:09 PM »
About stepper torque:
    Here is the the general summation of the following topic.
  "As a rule of thumb - the MAXIMUM dynamic torque of a motor will generally be in the order of around 70% of its holding torque."

http://www.machsupport.com/forum/index.php/topic,6466.msg42355.html#msg42355
RC

Offline Perfo

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Re: Warco VMc /Chester 626 knee mill CNC conversion
« Reply #28 on: July 24, 2008, 11:57:23 PM »
Thanks. I'm begining to think that maybe my steppers aren't quite big enough. Still it's only a gear change and slowing down the travers so I'll get it going one way or tuther then upgrade in future if need be. Your bridgeport look a bigger beast than mine so maybe it would take 3 times the torque to get it performing properly. I'd be v happy with a performance half of yours ie 1250 mm/m.

Offline Hood

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Re: Warco VMc /Chester 626 knee mill CNC conversion
« Reply #29 on: July 25, 2008, 01:49:55 AM »
perfo
 think your steppers should be fine, your mill is quite a bit smaller than the Bridgeport. Another thing  is the Bridgeport has plenty power with the 916 oz/in steppers, I was at one point thinking of reducing the gearing to ge better rapids. Have a new mill I am working on now with AC Servos so not going to bother doing anything to the Bridgeport.
Hood