RPM pickup without Encoder?

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Roadstercycle
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RPM pickup without Encoder?

Post by Roadstercycle »

Hi everyone, I'm new here and just ordered my Acorn. In the meantime I am getting a Win 10 computer setup for it and thinking about different issues that are popping up by converting. The most troubling is not being able to run an encoder on my CNC mill spindle as I can not mount it due to the air servo tool changer cylinder. So my question is: Can I run the magnetic pickup I'm using now in Mach 3 to give Acorn the needed RPM signal to do rigid tapping? Or do I put an encoder on the motor and only use 1 gear ratio to do rigid tapping? Is there a way to tell Acorn that motor RPM is 1000 and spindle is say 400. Hopefully I worded this correctly and explained it well enough. Thanks in advance.
DocsMachine
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Re: RPM pickup without Encoder?

Post by DocsMachine »

As I understand it, no, you need a proper 2000-line encoder (8K pulses per rev) in order to supply the proper data the board needs for rigid tapping.

And no, you can't mount it to the motor, unless the motor is geared 1:1 with the spindle.

Doc.
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Re: RPM pickup without Encoder?

Post by 762x51 »

Merry Christmas !!

If you would let the forum know what mill you have and maybe a photo of the spindle then maybe someone that has a similar setup can recommend how an encoder could be mounted.
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Re: RPM pickup without Encoder?

Post by tblough »

As Doc stated, it needs to be 1:1 with the spindle because the Acorn uses the encoders index pulse to start the tapping cycle and the encoders feedback to sync the Z feedrate to the actual spindle feed throughout the tapping cycle. No more broken taps because of pitch mismatches.

If done right, you can rigid tap 2-56 threads AND you can re-tap the SAME hole! A lot of people use a small timing belt (Stock Drive Products) to add a spindle encoder to a machine with a power drawbar. IIRC, Dwane Elrod at Elrod Machine makes a spindle encoder kit for Bridgeports and clones with PDBs.
Cheers,

Tom
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Re: RPM pickup without Encoder?

Post by frijoli »

Roadstercycle wrote: Mon Dec 25, 2017 1:33 am Hi everyone, I'm new here and just ordered my Acorn. In the meantime I am getting a Win 10 computer setup for it and thinking about different issues that are popping up by converting. The most troubling is not being able to run an encoder on my CNC mill spindle as I can not mount it due to the air servo tool changer cylinder. So my question is: Can I run the magnetic pickup I'm using now in Mach 3 to give Acorn the needed RPM signal to do rigid tapping? Or do I put an encoder on the motor and only use 1 gear ratio to do rigid tapping? Is there a way to tell Acorn that motor RPM is 1000 and spindle is say 400. Hopefully I worded this correctly and explained it well enough. Thanks in advance.
No, you can't do it like Mach 3.
It's not about RPM, it's about position. Mach never really did tapping and threading "accurately". I don't mean to say it didn't work it just wasn't the same as knowing the true spindle location in relation to ball-screws.

Acorn actually uses the encoder to "lock" the screw and spindle together when threading and tapping as if it were mechanically connected.
The encoder gives position of the spindle throughout the entire rotation. The reason is if the spindle slows down the threading tool/tap immediately follows. (or as fast as the electrons get there) :)

Clay
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unofficial ACORN fb group https://www.facebook.com/groups/897054597120437/
martyscncgarage
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Re: RPM pickup without Encoder?

Post by martyscncgarage »

tblough wrote: Mon Dec 25, 2017 10:09 am

A lot of people use a small timing belt (Stock Drive Products) to add a spindle encoder to a machine with a power drawbar. IIRC, Dwane Elrod at Elrod Machine makes a spindle encoder kit for Bridgeports and clones with PDBs.
Anyone ever price Elrod's spindle Encoder?
It is a challenge to fit an encoder to a Bridgeport style spindle head with power drawbar.
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Roadstercycle
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Re: RPM pickup without Encoder?

Post by Roadstercycle »

So it looks like the only way to do it would be make a timing belt setup with a removable belt in my situation. The issue is the spindle moves up and down too in manual mode. So I would have to lock the quill (spindle) in alignment with the encoder drive and attach the belt when needing to do rigid tapping. It's no big deal really, just time to make it. It will be a fun project.
martyscncgarage
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Re: RPM pickup without Encoder?

Post by martyscncgarage »

Roadstercycle wrote: Mon Dec 25, 2017 4:55 pm So it looks like the only way to do it would be make a timing belt setup with a removable belt in my situation. The issue is the spindle moves up and down too in manual mode. So I would have to lock the quill (spindle) in alignment with the encoder drive and attach the belt when needing to do rigid tapping. It's no big deal really, just time to make it. It will be a fun project.
Welcome to the world of industrial control. Effort is worth it.
Do take pictures and show how you accomplish the task for others.
Marty
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
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