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Author Topic: Bridgeport Knee Mill Conversion?  (Read 162527 times)

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Offline Hood

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Re: Bridgeport Knee Mill Conversion?
« Reply #130 on: May 22, 2016, 05:23:56 AM »
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This is where my brain fogs-over again - does the lower power matter when cutting or does it just mean less electricity is used to do the work?

If my calculator says i need 4Nm to do a task at 100rpm and the motor is rated 6Nm at 3000rpm - it will do the task easily yes?

I may make things worse by trying to explain but....

Ok you need the torque to do the job but you also require the horsepower to do it in the required time.
The tapping calc I linked to can maybe make you think it is all surface speed but you also have to take into account the feed per rev, a tap has a fixed feed per rev due to the pitch, a M10 has to move at 1.5mm per rev.

So you need the torque to drive the tap round but you also need the horsepower to feed it at 1.5mm per rev.


So you may have enough torque to twist the tap in the material but you may not have the required horsepower to feed it at the required rate.

See, told you I would probably make things worse :D

Regarding your  bushes, I may have a kit, bought it for my series 1 boss but never used it, not sure if it is the same size as the 2J head or not?
I could measure the bushes if you want.


Regarding the power, you will probably find you have plenty, my Computurn lathe has a 12Kw servo for the spindle, 2x 3Kw motors for axes, a 0.5Kw servo   for the turret and various other motors such as oil pump (0.75Kw) Coolant etc etc. The Chiron has 3x 2Kw axes motors , 8Kw spindle, and coolant pumps as well as other electrical stuff ( on both machines) such as lights, and all the components in the cabinet. Both machines are  via a 32 amp breaker (C Type) and I often run both machines at the same time with no issues.

Hood

Offline Hood

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Re: Bridgeport Knee Mill Conversion?
« Reply #131 on: May 22, 2016, 05:52:48 AM »
Ok here is maybe an analogy that helps explain it better, or maybe not ::)
You have a shaft with a rope round it and a drop with a weight attached to the rope.
You turn the shaft with your hands and say it requires 1Nm to turn the shaft to lift the weight, so no probs you can easily apply 1Nm. so you will be able to lift that weight.
Where the power comes in is the time it takes to lift that weight a given distance, so say the max power you can apply lifts the weight a given distance  in 1 minute.

 Because that is the max power you have then it can not be done any faster but you need to do it in half the time.  (drill or tap or cutter needs a certain feed per rev)  so you get your twin brother to give you a hand, you now have double the available torque but you don't need any more torque so that doesnt make a difference.
 You however also have double the HP so you can raise that weight the same distance in half the time.

Hood

Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #132 on: May 22, 2016, 06:01:59 AM »
Thanks Hood, the analogies do actually help ;)

One thing I had omitted in my last post was that I still have the back-gear for low-speed high-torque as before so maybe I really don't need such a large servo, just one that will cover down to say 500rpm and then drop into back-gear for the heavy stuff.

Or is it better to just stop polishing the turd and use the vari-speed head as a step-pulley with the additional range variation by VFD??

This is a tougher decision than fitting the damn ball-screws!

I guess the servo spindle is always a future-fit option if i leave room in the cabinet etc.

Or i could fit a roof extension to the shop and get a proper machine which probably would cost less ;)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Bridgeport Knee Mill Conversion?
« Reply #133 on: May 22, 2016, 06:21:23 AM »
What may also help is the actual definition of 1 HP.
It is the amount of power required to lift 33,000lbs a distance of  1 foot in 1 minute. So if you have 2HP you can lift that same weight (mass)   1 foot in 30 seconds or 2 feet in one minute.
Pushing a drill into material will be the equivalent of the weight/distance/time, it is the force needed to push that drill the required distance  at the required feed rate.


Using backgear would  allow you to use a smaller motor, as said I have a 3.5Kw on the Beaver mill and have never needed to use the back gear, if you went for a 1.5Kw then used the back gear when required you will probably be ok.
I cant recall the ratio of the back gear on the BP's but think the Beaver is 10:1.


Hood

Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #134 on: May 22, 2016, 08:08:35 AM »
Thanks, that helped a lot ;)

Had another play before I started tearing her down for a full strip/repaint/rebuild ;)

If I kept the existing power setup, there is a possible working option where I can set the head at two positions - 700 and 1500 and then using the existing VFD I at a reasonable 25Hz to 75Hz range I can get full speed variation from 40rpm in back-gear to 3000rpm in high - having the vari-speed in there to multiply the torque where needed allows for power lost in running at lower Hz it seems it would all work.

HOWEVER, it's not as much fun as having just one high range and one low range with the luxury of full G-Code control - the main question is - is it worth the £400 approx. that it will cost to do the conversion???

The input shaft on the head is a nice 1.375" so no issue getting a taper-lock pulley on there, the motors seem to be 19mm so again no issue, 1:1 poly-v pulleys and belt would do it along with a new motor mount plate.

As it is it's going to need new bushes for the sheaves and a new main belt at least, not finished stripping yet.

SO, what would you guys do - rip it out and splash the cash on luxury OR repair and refit??
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Tweakie.CNC

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Re: Bridgeport Knee Mill Conversion?
« Reply #135 on: May 22, 2016, 08:39:11 AM »
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SO, what would you guys do - rip it out and splash the cash on luxury OR repair and refit??

As it's all your money Dave - 'splash the cash'.  ;D

(you asked for opinion).

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Hood

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Re: Bridgeport Knee Mill Conversion?
« Reply #136 on: May 22, 2016, 08:42:49 AM »
Ideal world is Servo big enough not to need to worry about back gear.
Ideal isn't always practical though :D

Ok so I have this bushing set you can have if it fits, see pic.

How much would a new belt cost though?

Regarding driving with servos, on my machines I have fitted timing belts, if going 1:1 and using the motors encoder for feedback then it is best that it can't slip. If you have an encoder on the spindle itself then doesnt matter if it slips.


Hood

Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #137 on: May 22, 2016, 10:17:25 AM »
Thanks for the parts offer Hood, appreciated, they do look like the right bits.

I will price it up correctly tomorrow with timing pulleys, what size belt - 25mm x 5 or 8 pitch?

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

Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #138 on: May 23, 2016, 04:09:45 PM »
Ok, I'm holding the alterations to the spindle drive for the moment, will keep the vari-speed and modify later - better things to focus the cash on.

Drives and motors...

These are the drives... http://www.aliexpress.com/store/product/New-Servo-motor-and-driver-set-2-4N-M-0-75KW-3000RPM-90ST-AC-Servo-Motor/314742_760999511.html

I have one on the bench for testing with the CSMIO and an old Mach3 setup.

Do servo drives need any setting up ? I have set the motor model in the drive but the rest of the million settings? Never used a servo before ;)

Anyone know these specific drives?
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Bridgeport Knee Mill Conversion?
« Reply #139 on: May 23, 2016, 04:36:21 PM »
There will be lots to set up, such as I/O, command input type etc and also you will need to tune the motor/drive and then once that is done you need to tune the IP-A, assuming of course it is the IP-A you got.

Do you have a link to the manual?
Does it have set-up software or is it all via the front panel?

If you want that bushing kit for the vari pulleys just send me your address via PM.
Hood