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Author Topic: Spindle Speed measurement question  (Read 5105 times)

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Offline mckoz

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Spindle Speed measurement question
« on: November 23, 2008, 03:38:58 PM »
Hi all, I'm in the process of converting an Industrial Hobbies manual mill to a CNC (Mach3 of course), partially using their kit, and partially my own experience with Automation and Control systems. 

Anyway, I'm going to use cnc4pc's step and direction board to talk to a vfd, and will probably use one of my old plc's as a modbus slave for certain aspects of control of the system.  As I'm sure most folks don't have an unlimited budget and must balance performance against cost (as do I), I would like to get a recommendation on a spindle speed detection component to provide a closed loop speed control system.  I'm currently planning on taking the speed reference off the top of the spindle shaft, since I've got about 5 inches exposed on the top of the gearbox head.

Thoughts and recommendations?

David

Offline Hood

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Re: Spindle Speed measurement question
« Reply #1 on: November 23, 2008, 03:59:08 PM »
OPB 917B is what I use for spindle index.
Hood

Offline mckoz

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Re: Spindle Speed measurement question
« Reply #2 on: November 23, 2008, 05:44:52 PM »
Thanks for your reply!  I looked it up, looks like a hall effect switch?  I assume that is one pulse for every revolution, does that provide enough resolution for threading?  Also, where did you purchase it?

David

Offline RICH

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Re: Spindle Speed measurement question
« Reply #3 on: November 23, 2008, 07:08:31 PM »
Dave,
Mine came out of the junk box. I use a single index and with the latest Mach update threading seems to work
well. Pic attached for one on a lathe for what it's worth.
RICH

Offline Hood

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Re: Spindle Speed measurement question
« Reply #4 on: November 23, 2008, 07:08:57 PM »
I am in the UK so I got it from RS Components http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=opb-917b&x=0&y=0
Yes one pulse per rev is all that is need for threading on the lathe but you said you have a mill so afraid if you are thinking of doing rigid tapping then Mach doesnt support that yet. The SmoothStepper may change that but only time will tell.
 Some guys have done rigid tapping on a mill by using the swap axis feature and saying that their spindle is the A Axis and coding suitably for it however you will have to make sure your motor tuning is spot on as any bogging down will screw things up fast.
 Also I would think this is only possible with stepper or servo spndle motors and dont think a VFD and induction motor would have the same control but could be worth a try.
 Your other option of course is a floating holder for your tap and that should work if you code carefully.
Hood

Offline mckoz

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Re: Spindle Speed measurement question
« Reply #5 on: December 02, 2008, 02:18:20 PM »
Thanks Hood and Rich.  I've just mounted the 3-Phase AC drive, and I'm using the cnc4pc step/direction board to drive a tverter chinese knockoff VFD.  I have a fairly large Moog bushless servo motor that is resolver based, and based on Hood's comments I've begun to look for a drive that will handle the Moog.  I've found a resolver to encoder board out on the web, but I haven't found a drive yet, NOR have I decided whether to just ignore the resolver output and install an encoder.  Any advice on either of those options will be appreciated!

I'm going to continue the build out with the 3-Phase VFD motor and try some of the threading while I'm looking for a servo drive, I'm very interested in the results that Rich is getting.

David

Offline Hood

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Re: Spindle Speed measurement question
« Reply #6 on: December 02, 2008, 02:55:40 PM »
What size is the moog motor? ie Continuous current, peak current and voltage?
Hood

Offline mckoz

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Re: Spindle Speed measurement question
« Reply #7 on: December 02, 2008, 03:44:18 PM »
I'm waiting on a spec sheet request from Moog, once I get the info back I will post it - currently I only have the nameplate of the motor.

David

Offline Hood

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Re: Spindle Speed measurement question
« Reply #8 on: December 02, 2008, 03:55:35 PM »
What info is on the nameplate?
Hood

Offline mckoz

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Re: Spindle Speed measurement question
« Reply #9 on: December 02, 2008, 04:12:32 PM »
It's  out at the shop, I'll be out there later today and will get the nameplate info...

David