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Author Topic: Bridgeport Knee Mill Conversion?  (Read 159091 times)

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Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #510 on: September 25, 2016, 07:27:49 AM »
Job done :)

100 holes spotted, drilled, countersunk, blind-tapped M6 :)

Picture below is the finished sub-table and here's a short clip of my peck-drilling...
https://youtu.be/7pixPYu1UFA

The surface parallelism measures 0 to +0.03mm in X and 0 to +0.02mm in Y so I'm not even going to bother doing a facing cut.

The tapping cycle was almost perfect, the modified post processor had a +10% retract rate - this was wrong as you could hear the tap pulling on the last thread as it came out, I've modified the post so that it's 1:1 all the way now.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #511 on: September 26, 2016, 10:21:18 AM »
Back to a possible motor upgrade....

SO, we fit a decent motor, 3Hp seems to fit the figures, a new sensorless vector VFD and throw an encoder on top which is connected to the CSMIO via the ENC module.

Am I right in believing the spindle speed would then show up in Mach3 as the correct reading from the the encoder?

Would the speed be a closed-loop in that if I ask for 500rpm, it will give me 500 not 490 or 510?

Just figuring whether or not to keep this idea on the burner or shelve it for a while ;)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Bridgeport Knee Mill Conversion?
« Reply #512 on: September 27, 2016, 04:45:57 AM »
As far as I know the CSMIO requires the Index pulse and it is definitely required for peck tapping.

As far as the speed control, there are two methods, open and closed loop, how well either will work will depend on how good the VFD can control the spindle I would think.
I have never used a VFD with the CSMIO, don't like them all that much. I have however used the CSMIO/IP-S and the 0-10v output with a servo spindle and it was spot on, reason I did that was it was before the CSMIO/IP-S had the option to use Step/Dir for a spindle.

Hood

Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #513 on: September 27, 2016, 04:54:20 AM »
Thanks

the cost between a new 3Hp motor/vfd/encoder and a servo is about the same

BUT

I cannot get the servo to match both speed AND power it seems - this means running a far bigger slower servo and gearing up.

The 3Hp AC motor has plenty of torque down to silly speeds according to the specs - something like 15Nm at 146rpm all the way up to 8Nm at 2900rpm

The servo seems only affordable at 1.8kW /6Nm & 18Nm peak 3000rpm. Any bigger and cost goes silly.

It does seem the CSMIO is geared towards servos.

Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #514 on: September 27, 2016, 05:11:55 AM »
Is it possible for some kind soul ;) to say one way or the other if a 1.8kW AC servo is just too weedy to replace the 1.5Hp7Nm AC motor i have already??

My views are restricted by knowledge and muddied by confusion :)

The original motor has about 7Nm - with the mechanical vari-speed probably about 15Nm at bottom speed 450Rpm but only about 2.5Nm at top speed 3000rpm

The servo has 6Nm continuous and 18Nm peak - now I have no idea what "peak" is or how long it can maintain it before going Chernobyl on me ;)

This is where my knowledge runs out.

Simple question, forget cost, will the servo work or will it stall out at low speed ?

Bearing in mind this is a Bridgeport and not a metal hogging monster so heavy cuts are intermittent.

Knowing this would simplify my choices by narrowing things down a bit .

Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Bridgeport Knee Mill Conversion?
« Reply #515 on: September 27, 2016, 06:43:39 AM »
Remember our previous chats on the subject Dave?
Torque may well be fairly constant, HP/KW will not be, whether that is with Servo or Induction motor via VFD.
You are trying to compare a variable geared motor which is ALWAYS running at full HP/KW and a servo or VFD controlled motor which is only running at the rated power when at rated speed, torques may well be close but will the servo/VFD have the power to do the work in the required time? That is the reason when servos or VFDs are used  they are always bigger than you would get away with when using a variable geared motor.
Gearing is the best of both worlds in this instance, where it falls down seamless, accurate  variable speed adjustment on the fly.

Hood
« Last Edit: September 27, 2016, 06:47:29 AM by Hood »

Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #516 on: September 27, 2016, 06:58:31 AM »
Yes, i do recall, but still confused :)

And to muddy the waters a bit more, I do have the motor on a VFD at present, to get my speed range semi-adjustable from MAch3  I am running the mechanical controller only in one of two positions - 700rpm and 2200rpm, the rest of the variation in speeds from 450 to 3000 is covered by the VFD running from 25Hz to 75Hz.

It sort of works reasonably well, Mach gets its knickers in a twist at times but mostly all good so far.

Now, I have no idea as to what this is doing to the power from the AC motor but I guess its not all good, thats why i limited the range from 25 to 75Hz only, its an old motor and not made for inverters so did not sound too sweet at 100Hz and was useless below 25Hz

Also throw in the serious power losses from the vari speed drive - i did read a paper somewhere that listed 75% efficient so thats a pretty big loss.

Any of that help me - i doubt it ;)
« Last Edit: September 27, 2016, 07:01:29 AM by Davek0974 »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #517 on: September 27, 2016, 07:25:22 AM »
Trying to get the lightbulb to come on....

If i have a tool that takes 20Nm to rotate it and a motor that can provide 20Nm torque but zero Hp - would that mean the tool just stands still?

Then if i want to propel that tool forwards into something (my head probably) at say 100mm/min I need to increase Hp above zero to some positive figure that i have no doubt can be calculated?

So my theoretical tool might need 20Nm and 5Hp to make it move at 100mm/min ???

Probably still in cloud cuckoo land.... ;)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Bridgeport Knee Mill Conversion?
« Reply #518 on: September 27, 2016, 08:06:03 AM »
That is basically it Dave, HP is the power required to move a mass a given distance in a given time. If you look up the charts on manufacturers sites you should find info on the HP required to drive a tool at the optimum feed, this info is readily available for drills and taps certainly, milling cutters not so much but in most cases they would be less anyway unless really chewing metal.

Regarding your servo in the example above, at 450rpm it would only be about 0.3KW.

Hood

Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #519 on: September 27, 2016, 08:18:28 AM »
Nice,

Been messing with my speed/feed calculator, looking at all the figures i usually ignore ;)

Mild steel,
50mm facemill with 5 tips, full-width cut, 1.6mm deep = 420rpm, 201mm/min, 0.4kW 9.24Nm
20mm endmill 4 flute, 35mm DOC, 5.4mm engagement = 650rpm, 204mm.min, 0.81kW 12.12Nm
15mm drill = 650rpm, 111mm/min, 0.37kW 5.5Nm

So using your quote of 0.3kw at 450rpm the answer is NO it will probably stall on a 15mm drill and a 20mm endmill but be ok with the facemill.

Yes, I *could* enter the actual power curve into the calculator and it WILL give me a solution BUT I think going lower power than a 1.5hp Bridgeport is a little pointless.

That clears that up then I think, forget the servo, if anything IS to be done it will be a 3Hp AC motor, sensorless-vector drive, braking resistor and encoder I think.

Thanks all for the patience ;)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives