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Need Encoder for threading
« on: June 03, 2012, 12:00:05 PM »
I tried to do a search on "Encoder" but had no results.

Anyway, I'm doing a retrofit on a Denford CNC lathe.

Retrofit almost done

To cut threads I mounted a stepper motor to the spindle.
Stepper motor setup

 For normal turning the timing belt needs to be removed from the stepper. It works great for theading plastic but lacks the power to thead steel.
see it cut threads

Can somone recomend a source and part number for a encoder that can be used with Mach3 for threading?   I should be able to mount the encoder
where the spindle stepper motor is.    I'm using a Bob Cambell breakout board.

I have already read the Mach3 download about threading.   The download did not mention the encoder used.

Thanks   Jim Glass
« Last Edit: June 03, 2012, 12:04:53 PM by jimglass »

Offline Hood

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Re: Need Encoder for threading
« Reply #1 on: June 03, 2012, 12:17:36 PM »
I wouldnt bother with the stepper for threading, if your normal spindle motor is half decent you can use that. What you need (if using the parallel port) for an index pulse is not an encoder but rather something like an optical switch or a proximity switch. I used the parallel port I used an opto with a slotted disc, the one I used was an Optek OPB917B.
Hood
Re: Need Encoder for threading
« Reply #2 on: June 03, 2012, 06:30:50 PM »
Hi Hood;

Pleasure to communicate with you again.   The last time was 2006 when I was doing my Bridgeport CNC retrofit.    That thing has worked out very well
for me.

For the Optek OPB917B to work do I need to make a disk with holes or slots?   If so is 100 holes or slots what I need.  The Optek OPB917B is only $9 so the price is right.

Jim

Offline Hood

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Re: Need Encoder for threading
« Reply #3 on: June 03, 2012, 06:38:27 PM »
A disc with one slot is what you need. Disc size I used was approx 100mm dia with a 10mm wide slot and it worked well.
You will also need a 220 ohm resistor to limit the current to the LED of the opto.
Hood
Re: Need Encoder for threading
« Reply #4 on: June 04, 2012, 03:47:49 AM »
Will the Optek OPB917B connect easily to the Bob Cambell breakout board?   I thought I saw the Optek OPB917B ran on 35 volts.   Did I read that
right?

The Breakout board uses connector J23 for the encoder.
PIN 1  Isolated  GND
PIN 2  Isolated  GND
PIN 3  Isolated  to PIN 12 Parllel port (IN1)
PIN 4  Isolated  to PIN 13 Parllel port (IN2)
PIN 5  Isolated  to PIN 15 Parllel port  (switch)
PIN 6  Isolated  to +5V

A one slot disk should be easy enough to make.
Thanks,
Jim
« Last Edit: June 04, 2012, 03:52:58 AM by jimglass »

Offline Hood

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Re: Need Encoder for threading
« Reply #5 on: June 04, 2012, 04:33:43 AM »
The OPB 916B or 917B need a voltage from 4.5v to 16v, if I recall, so 5v is fine.
Take the 5v from Pin 6 and connect the white wire to it, also connect the resistor tothe 5v and then the red wire to the other side of the resistor. The Black and Green wires go to Pin 1 or 2 and finally use one of the inputs to connect the blue wire to and it should work fine.
In Mach go to Ports and Pins, Inputs and set the index up to the  port and pin number you connected the blue wire to. Even if you do not use Mach to control the spindle you will need to enable the spindle relays ( only needed if using the parallel port) You will find that option on  the Spindle setup page(from Ports and Pins)
 On General Config page make sure the Index Debounce is zero or near to it.
For the index to work you need to tell Mach the spindle has started so even if you dont have Mach controlling the spindle you still need to have a M3/M4 in your code or press the spindle button in Mach, that is so that Mach knows to look at the index signal.
Hood
Re: Need Encoder for threading
« Reply #6 on: June 04, 2012, 05:52:30 AM »
jim, was the original denford optical switch missing from the lathe

Offline RICH

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Re: Need Encoder for threading
« Reply #7 on: June 04, 2012, 06:45:36 AM »
Jim,
I also would not recommend a stepper motor to be used on the spindle for threading.
The single slotted disc works fine. I use Halls affect for the index. It will be more expensive than a OPB but it suited my needs better
for mounting.

RICH
Re: Need Encoder for threading
« Reply #8 on: June 04, 2012, 08:37:25 AM »
jim, was the original denford optical switch missing from the lathe

Yes, I bought the lathe on Ebay from a guy that was parting out Denford lathes.    I bought the lathe bed with ballscrews, and purchased
the original spindle motor, chuck and tailstock separately.   Right or wrong, it was what I was looking for.    I was told the Denford
is the same or similar to an EMCO 8.

I'm also working on a toolchanger for my Denford.   I built this indexer as a prototype now thinking of building another one that is  smaller.     I found a way to address the backlash issue with worms and worm gear setups.
http://www.chaski.org/homemachinist/viewtopic.php?f=9&t=93146

The guy I bought the lathe from was using a stepper motor on the spindle for cutting threads so I copied his idea.    I had a stepper motor, timing belts and pulleys on hand so it cost only some time to set up.   Plus I learned how to have a stepper move in angular steps thinking that knowledge would be used on my CNC indexer.

The stepper motor on the spindle for cutting threads was rather impressive to see work.   All my experience has been cutting threads on geared lathes.    I used delrin plastic to cut my first CNC threads.    But the stepper failed miseralbly cutting a 5/8-18 in steel.   The stepper did not have the power and lost steps.    The stepper might work well on 10-32 and smaller threads but I'm not going to bother
trying it.

Thanks,  Jim

Thanks,  Jim
Re: Need Encoder for threading
« Reply #9 on: June 04, 2012, 10:40:23 AM »
cncdoctor does an index pulse board that works well with mach, which is a break beam device.