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Spindle RPM
« on: February 01, 2008, 08:05:57 PM »
I have set up my spindle on my mill to run from 300rpm to 3500rpm with ratio set to 1 as my rpm sensor is reading from the spindle. I have set the Campbell board to give 0.to 5v (as required by my spindle control board) over this range and it seems quite linear as 1750 rpm gives a reading of 2.5 volts. the RPM as read by the index pulse is exactly the same  as shown my tacho. I am using Mach 3 v2.64
The problem is that I can not get the measured speed to match the requested speed. I have use spindle feedback in sync mode checked in spindle setup. I have also tried spindle calibration.
Can anyone advise where I may have gone wrong.

regards
Arthur

Offline jimpinder

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Re: Spindle RPM
« Reply #1 on: February 02, 2008, 03:21:45 PM »
Arthur - I seem to have this problem.  I take it you have done the spindle calibration on the automatic mode. This on my lathe then set the spindle moving at an increasing rate. It then came up satisfactory - save data  (or something similar) which I did. But the spindle speed still seemed to be about 10% up in my case. This I reckoned to be because my feed to my Omron Inverter scaled 0 - 12v instead of the asked for 0 - 10.

That seemed to be the case all the last session with the lathe, and although I was using G96, Constant surface speed mode, the actual speed seemed to be up on the asked for speed.  Today, when turning some little thing up, I set the speed using the speed DRO on the screen. I had reset the lathe with a G97 - The recorded speed was exact (within 2 rpm either way ) of the asked for speed of 800.

I don't know if the programming gang can comment on the apparent problem ???
Not me driving the engine - I'm better looking.

Offline Perfo

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Re: Spindle RPM
« Reply #2 on: July 17, 2008, 04:27:18 AM »

Have you gents made your own once per rev probe ? If so could you point me towards any posts that discribe what designs work ? I have searched for the data but not much luck so far. Thanks.

Offline Hood

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Re: Spindle RPM
« Reply #3 on: July 17, 2008, 04:48:17 AM »
Perfo
 I use an Optec 917b slotted optical switch, can be had from RS in the UK.
You will also need a 220 Ohm resistor to limit the current to the LED in the switch.
 You will then need to fit a disc to the spindle which has a slot in it, I use a 10mm wide slot on both the mill and lathe and they work well, disc Dia is 80-mm on the lathe and 100mm on the mill. Heres a pic of the one on the mill.
Hood

Offline Perfo

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Re: Spindle RPM
« Reply #4 on: July 19, 2008, 04:16:12 AM »
Thanks for that Hood. It looks a simple enough addition and should give a pretty good clean output. Did you need any interfacing electronics? Are you coupling this directly to a breakout board or smoothstepper or what have you ? It looks like it's only £5 from RS so no point trying to build something myself

Offline Perfo

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Re: Spindle RPM
« Reply #5 on: July 19, 2008, 04:24:41 AM »
I suppose I'm still on topic with the this question. Now I've got my OPR probe sorted what do folks find works for controlling the spindle speeds? At present my 626 mill has only got the swap the ratios of the pulleys type speed control. I could rig up a thyristor fired motor speed controller but this would only give me a wider range per ratio or is there enough torque if the ratios are left on the fastest setting and just control the motor speed. How do you fellows do it ?
Thanks

Offline Hood

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Re: Spindle RPM
« Reply #6 on: July 19, 2008, 05:51:44 AM »
Thanks for that Hood. It looks a simple enough addition and should give a pretty good clean output. Did you need any interfacing electronics? Are you coupling this directly to a breakout board or smoothstepper or what have you ? It looks like it's only £5 from RS so no point trying to build something myself

I just connect through the breakout, although on my first mill I connected directly into a second parallel port. Only thing you need is the optical switch and resistor and a 5v supply.

 
I suppose I'm still on topic with the this question. Now I've got my OPR probe sorted what do folks find works for controlling the spindle speeds? At present my 626 mill has only got the swap the ratios of the pulleys type speed control. I could rig up a thyristor fired motor speed controller but this would only give me a wider range per ratio or is there enough torque if the ratios are left on the fastest setting and just control the motor speed. How do you fellows do it ?
Thanks

What type of motor do you have? AC? Single or 3Phase? DC?.........

For AC 3 Phase you can use a VFD but you will not get good spread of torque so ranges still need to be used.  Slow spindle speeds are used for large cutters/drills etc so you need torque, a VFD wont provide that unless you drop the gearing also.  That is my experience and opinion at least, others have disageed and I suppose it all boils down to what you are doing and how capable your machine is.
Hood

Offline budman68

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Re: Spindle RPM
« Reply #7 on: July 19, 2008, 08:27:12 AM »
Quote
I just connect through the breakout, although on my first mill I connected directly into a second parallel port. Only thing you need is the optical switch and resistor and a 5v supply.


Hood, I can not seem to find the data sheet on that switch, any chance you have one? I'd like to give this a try in the future but can't find that particular switch in the USA so I thought I'd try to cross reference it with something else.

Thanks,
Dave
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Offline Perfo

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Re: Spindle RPM
« Reply #8 on: July 19, 2008, 09:43:21 AM »
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=4550919
This is the switch in the UK you can view the datasheets on line.

http://www.alliedelec.com/Search/SearchResults.aspx?N=0&Ntt=slotted+optical+switch+917b&Ntk=Primary&sid=11B3A79D9029&i=0
This is the closest I could see on the US site.

The switch doesn't do anything particularly clever it's a light source (often infrared LED) and a photodetector often a photo transistor either mounted in an IR transparent package or has small lenses to stop cross talk etc. As long as it will run on the voltage you need and will provide a sink for the data pin (usual to put a pull up resistor on the output) you may also need to put a current limiter resistor on the feed to the LED depending on what one you get. Oh and ensure it will run at the max frequency you intend but this is unlikely to be a problem.
The thing I worried about is would the parallel port read it quick enough to get an accurate reading or would there need to be some electronic scaling but Hood has answered this one and fortunately it'll bolt straight on. I'll be trying to connect mine to the smoothstepper board (on order) which has a dedicated input for spindle speed (I think).

Offline Perfo

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Re: Spindle RPM
« Reply #9 on: July 19, 2008, 09:54:29 AM »
It's a 1.5HP single phase. I suspected the low speed torque would be a problem if left on the high gearing. Still it's not a problem to change belt pulleys before a job and thus will give me a band of speeds available with some sort of variable frequency motor control. As I'm trying to do as least invention as possible to get it up and running have you any experience of a variable frequency controller that will work on Mach 3 for 1.5 hp single phase ?  I've also got a lathe that I may be converting (if this one goes well) and hopefully building a large 8' X 4 ' router in the future and the good thing is all the drivers, speed controller and most of the CNC kit except for the steppers will be able to be used on all of them and thus will cut the cost of the conversion somewhat. Thanks again.