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Author Topic: Spindle speed sensing on a Bridgport  (Read 4368 times)

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Spindle speed sensing on a Bridgport
« on: July 25, 2012, 01:48:17 AM »
Hi guys,

I'm finally making progress with my NC conversion of my Bridgeport Series 1 clone - guess I'll be around a lot from now on!  I've got the head all in bits removing the quill self act and stuff, and it's in need of a new drive system anyway, and while I'm in deep I was looking at fitting the spindle speed setup, so I don't have to take it all apart again. 

As I see it, the only sensible place to put it is below the back gear on the splined end of the spindle.  That is always going to be true spindle speed then, instead of having to work it out from the top pulley or some other bit of the drive system.  I reckon a proximity switch would work well, its what we use at working for counting rope lengths, and they are very acurate and trouble free.

I've been doing some research and found that Mach3 looks for one input per rev to work with the C3 card to generate a spindle speed readout.  Can the system cope with more inpulses?  I was oriignally thinking about bolting a block of stainless onto the side of the splines to trigger the proximity switch, then hit on the idea of setting it up to see the high points of the splines, which would mean 6 impulses per rev - is that possible?

Offline Hood

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Re: Spindle speed sensing on a Bridgport
« Reply #1 on: July 25, 2012, 06:20:56 AM »
You could set up a ratio  in Spindle Pulleys to take account of the 6 ppr but whether it is a good idea will depend if the pulse is long enough on each trigger, that is especially true if you are using the parallel port.
Using the top pulley is not a problem as you can just set two pulleys up in Mach, one for the normal gear and one for the back. This has the advantage that if you are controlling the spindle from Mach then you can select the reversed option for back gear pulley and when you command a M3 it will still rotate in the correct direction.
Hood
Re: Spindle speed sensing on a Bridgport
« Reply #2 on: July 25, 2012, 08:22:19 AM »
Hmm..you've got me thinking.  Maybe a bit of background would be a good idea, maybe I'm trying to overcomplicate things.

I bought the machine from work.  The original motor (for vari-speed pulleys) had killed its bearings, fretted the shaft, and chewed up the windings.  We were quoted £750+VAT to have it repaired, at which point they decided to scrap it instead.  Not being able to afford the £750 myself, but not going to pass on an otherwise good machine, I've opted to replace the vari-speed with an equivliant of an earlier stepped pulley version of the bridgeport, and drive it with a 3-phase variable speed motor and drive.

To that end, I've worked out that in order to use a good frequenzy and speed range on the motor, and still have power and torque at the tool, I should fit a 3-step pulley drive using 1:1 and 2.8:1 and 1:2.8 drives.  I originally calculated a 5mm pitch x 15mm timing belt would handle the power, but being unable to source pulleys that I wanted, I've swapped to A section v belt instead.  This came with its own problems in that the motor spindle isn't long enough for 3 pulleys with taperlock bushes, but I've overcome that with a plan to machine my own pulleys.  Being a CNC turner by trade that will present no problems.

From what you say, I'd be better off just mounting the proximity switch on one of the pulleys up top, where its easy to get at too, and setting up 3 pulleys in Mach for Hi range and 3 for Lo range?

Offline Hood

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Re: Spindle speed sensing on a Bridgport
« Reply #3 on: July 25, 2012, 08:30:26 AM »
You would just need two pulleys set up, one for Normal gear and the other for back gear if all you are wanting is spindle speed. The position of the belt on the three pulleys will make no difference as all three pulleys on the front shaft will turn at the same speed no matter what.
If you are planning to control the speed via Mach then you will likely have to set up 6 pulleys.


Hood
Re: Spindle speed sensing on a Bridgport
« Reply #4 on: July 25, 2012, 08:32:24 AM »
I am planning to use Mach to control the spindle speed yes.  I have no problem with having to drop into the Mach settings to tell it what pulley its on when I have to change the belt.

Would I be right in thinking that if it was in the wrong range Mach would tell me?

Offline Hood

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Re: Spindle speed sensing on a Bridgport
« Reply #5 on: July 25, 2012, 08:48:42 AM »
What would happen, or should, if you called a spindle speed that was out with the pulley range (Min/Max) then Mach should tell you but it would just continue I think at the min/max speed you could get in that range.
It would be better to alter the spindle speed macro so that it popped up a warning and halted proceedings until you changed.

Hood
Re: Spindle speed sensing on a Bridgport
« Reply #6 on: July 25, 2012, 09:11:14 AM »
I think then, setting a proxy switch on the top of the pulley and having 6 pulley setting - 3 automatically reversed for back gear - is probably the way to go then.  I can also consider cheaper alternatives to the proxy switchs we use at work, maybe going for one of those things that go each side of a disk instead.

Thanks for your help Hood!

Offline Hood

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Re: Spindle speed sensing on a Bridgport
« Reply #7 on: July 25, 2012, 09:17:22 AM »
When I had the old step pulley Bridgeport I just cut a slot in the top pulley as I never used that ratio with the VFD. I then used an opto, Optek OPB917b.
If you are going to be making the pulleys then it should be fairly easy just to leave a bit extra meat on the top then shove in a grooving tool deep enough for the opto to fit in and then just slot out a bit about 10mm wide on the mill to trigger the opto.
Hood
Re: Spindle speed sensing on a Bridgport
« Reply #8 on: July 25, 2012, 09:33:02 AM »
You can also do it quite simply by using a reflective optical pickup on the timing belt.  Just paint a section of the belt white.

Regards,
Ray L.
Regards,
Ray L.

Offline BR549

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Re: Spindle speed sensing on a Bridgport
« Reply #9 on: July 25, 2012, 10:16:14 AM »
I inserted a small disc into the top shaft and used an OPTI to read it.  It has QC30 spindle so it never uses a through bolt to hold the tool holder.

You really do not have to change out the vari drive unless you just want to. You can use a cheaper commercial flange mount 3phase and add a shaft adaptor to the motor shaft to replicate the original BP motorshaft. Works fine here. AND much cheaper.

You can also go single phase if needed.

(;-) TP