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Author Topic: Spindle Encoder Feedback, Motor or Cutter Spindle?  (Read 2495 times)

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Offline Katoh

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Spindle Encoder Feedback, Motor or Cutter Spindle?
« on: December 08, 2016, 01:08:01 AM »
G'Day Friends

I am working on the Bridgeport conversion still :-[, but getting closer by the day which has come to a point of getting spindle feedback back to Mach.
Reading lots of threads and examining different options has pointed me to the conclusion if I can get cutter spindle feedback not motor spindle is what I need or desire, but on a Series 2 J head mill thats a little harder than done. Others have used larger motors and a 1:1 timing belt and run the encoder from the motor, which is fine but it tends rendser the back-gearing useless  for feedback will be false.

I have now 90% completed a unit where I can run a 1000line encoder AB&Z +/- off the top of my draw-bar with no issues at all giving me direct Spindle feedback (hooray)

After a little more reading and conversing with others, most likely I upgrade to Mach4 over 3 on the mill, reading through the Mach4 instructions there is a provision for feedback on (pulleys and different gearing) with ratios on the spindle tab, or am I reading this wrong?

Motor is VFD controlled, it drives the cutter spindle with a toothed belt at 1:1, no problems there. But what happens when the back gearing is engaged for slow hard work and or rigid tapping?
If these parameters can be set in Mach will it do the for me with encoder driver directly from motor or am I still better of having the cutter spindle encoded.

Thanks
When I get this one sorted Ill Ask about the lathe, where I am replacing the Spindle motor with an AC servo, will have a slight mechanical advantage to spindle driven by toothed belt ratio 1:0.8
this will have not only have encoder feedback from the servo but also pulse timing from spindle, Configuring might be a headache!
Cheers
Katoh
Re: Spindle Encoder Feedback, Motor or Cutter Spindle?
« Reply #1 on: December 09, 2016, 05:10:38 PM »
Mach 3 will handle the feedback from the motor as long as you setup and select the proper gear ratios and gears. If you have a v-belt then slippage might be a problem but if it is a timing belt then you are good to go. IIRC


Mike
We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.

Offline Katoh

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Re: Spindle Encoder Feedback, Motor or Cutter Spindle?
« Reply #2 on: December 09, 2016, 06:24:48 PM »
Hi Mike.

That was basically what I was thinking, but when I was looking into a controller for the mill (CS-Lab's) unit, they said no, spindle feedback must be cutter spindle, that’s fine if the motor and cutter are timing belt connected at ratio 1:1 which it is, but as soon as you engage your back-gearing on the Bridgeport  ratio is now 8.3:1.
I have read elsewhere also that you need to have the encoder on the cutter spindle regardless of what you do with Mach for rigid tapping to be achievable.

Food for thought, if the encoder is on the spindle cutter and the back-gearing is engaged, how does Mach then handle what the motor does, will it ramp up the motor automatically till it reaches its required RPM and position o the cutter spindle even though it needs to spin 8x times the amount?

Thanks Again.
Cheers
Katoh
Re: Spindle Encoder Feedback, Motor or Cutter Spindle?
« Reply #3 on: December 10, 2016, 07:59:53 AM »
If you setup the spindle pulleys in mach and then tell it when you change gears the rpm it should follow what you put in for an "S" value. I am not sure how it would handle the encoder bing on the spindle though. I don't have an encoder on my machines yet so maybe someone else will chime in.
We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.

Offline Hood

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Re: Spindle Encoder Feedback, Motor or Cutter Spindle?
« Reply #4 on: December 10, 2016, 03:34:19 PM »
You need the encoder 1:1 with the spindle when using the CSMIO for lathe threading or rigid tapping. So if using back gear then it means you have to have the encoder on the spindle rather than the motor. Should be relatively straightforward as you could attach a pulley to the spindle and drive an encoder out to the side via a belt.

Regarding the back gear or step pulleys then as long as you have that set up in the Spindle Pulleys with the correct ratio entered then the CSMIO will control the spindle correctly for whichever gear you are in.

Offline Katoh

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Re: Spindle Encoder Feedback, Motor or Cutter Spindle?
« Reply #5 on: December 10, 2016, 06:54:55 PM »
Hi Hood

I was thinking the same sort of thing, Haven’t decided on which system to go for as yet between the Csmio or the DSPMC both are excellent. But both say you need feedback of the spindle cutter not the motor unless its 1:1.
Reading about setup of Mach4 and the motor settings I just couldn't work out why you couldn't use the ratios in there and run the encoder of the motor. Would make things some much easier.

Quote
Should be relatively straightforward as you could attach a pulley to the spindle and drive an encoder out to the side via a belt.

On the Bridgeport J head series 2, Its the biggest pain in the proverbial trying to access the spindle from anywhere. What I’m making is a device that sits on top of the draw-bar that I’m going to tap into, then I will a sliding encoder on guides driven by the draw-bar, I call it the "bird cage" Almost complete, but still would be so much easier from the motor. I will complete it now and Ill post picks when done as I know that its always being a problem to get spindle feedback on these machines, unless you go 1:1 drive from the motor and disregard using your back-gearing.

Hood why I have your attention as I know you are the MAN! With the lathe I am going to replace the spindle motor with an AC Servo 3x size of original motor, Am going to tooth belt drive it directly to spindle with a slight Mechanical advantage just to give me a little more grunt at lower speeds, still I will have spindle speed from 0-2000rpm. 1:0.8 ratio Motor to Spindle. I planning to upgrade it to Mach4 and it uses ESS.
My thinking is I can run feedback from the encoder as the spindle motor feedback, I can still use the timing pulse on the spindle it uses now also . Will these work together? Or will I need to go again to a 1:1 ratio motor to spindle and just use the encoder from the motor?
I also want to set-up the spindle as an A axis (swap-axis sort of thing)  but I need to sort this out first.

Many Thanks Again
Cheers
Katoh

Offline Hood

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Re: Spindle Encoder Feedback, Motor or Cutter Spindle?
« Reply #6 on: December 10, 2016, 07:19:09 PM »
I think the reason it needs to be 1:1 with the CSMIO is because it uses the full encoder and syncs the Z axis very tightly to the encoder. It is done internally in the CSMIO/Enc module where as if it did it via Mach then there would likely be a slight delay which would mean axis sync would not be as tight.

Regarding the ESS and your lathe, it just uses the single pulse and it is done via Mach and there is no sync between encoder pulses and axis motion so it may well be OK to have it via a ratio in pulley setup. Having said that you may be able to set a ratio in your servo drive for your encoder output, that should do the same thing if it allows you to set the correct ratio.

Offline Katoh

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Re: Spindle Encoder Feedback, Motor or Cutter Spindle?
« Reply #7 on: December 10, 2016, 07:31:55 PM »
Hood thanks again, that cleared it up.

Ill Play around with lathe, I don’t see that one being a huge issue, HAHA (famous last words again)
I will also post some picks of the "bird cage" when fitted, could help others with the same issue.
Cheers
Katoh

Offline Davek0974

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Re: Spindle Encoder Feedback, Motor or Cutter Spindle?
« Reply #8 on: December 11, 2016, 03:20:21 AM »
On the Bridgeport I just converted, i was going to mount the encoder where the vari-speed pulley dial used to sit. I have a 30mm wide toothed belt at 1:1 and there is enough shaft in there for another small pulley maybe 10mm wide and bored out to fit. With a bit of fiddling, most of the encoder would sit inside the opening at the front.

In the end i fitted a big motor and it does rigid tapping in high gear at 400rpm very nicely, I have not used back-gear since converting but as the encoder is only used for tapping and speed display (not closed loop) it will be ok if i did use BG.

I found Mach's closed loop pretty poor and the sensorless-vector drives' version much better.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

Offline Katoh

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Re: Spindle Encoder Feedback, Motor or Cutter Spindle?
« Reply #9 on: December 11, 2016, 08:03:16 AM »
Hi Dave

I remember talking to you about your setup in a previous thread, you mentioned then about the bigger motor replacement and running the encoder of the motor. well funny thing thing is I’ve ended up doing nearly 90% of what you did, I bought a 3hp motor scrapped the original but am still going to run the encoder from the draw-bar as I have designed,  as soon as its on the mill Ill post some pics. By the way Thanks for the good ideas!
As far as Controllers go I am swaying towards the DSPMC over the Csmio, only reason the DSPMC will give me closed loop using differential step/dir with encoder feedback where the other won't, plus the ability to mix and match both analogue and digital motors simultaneously. The only thing I can say is I need to bite the bullet and get it all up and running to have any sort of comment on the performance of it.

I spent the whole day stripping the head and rebuilding it, its just was a plain mess, bearings had collapsed and a mixture of mud and grease was strewn throughout it, I removed all the power quill feed parts as they are useless to me, another day or so I hope to have it all back in one piece, then start on the quill ballscrew mechanism.

Cheers
Katoh