Bridgeport Manual to CNC conversion...

[Davek0974]

Am I right in my belief that if i want real-time display of position in Mach3, I need to use servo's and encoders?

[komatias]

Am I right in my belief that if i want real-time display of position in Mach3, I need to use servo's and encoders?

No, you can use optical encoders too. There is a screen out there that allows you to have 2 DRO's. However, you cannot use these as positional feedback in Mach3

[Davek0974]

Hmm, just had a thought...

Instead of dropping around £2k on building a mini-mill/router, what I should have done is use that cash to convert the Bridgeport and fit an adaptor mount that enables me to hold the 24k water-cooled spindle - best of both worlds??

I could even mount a complete Z-axis on the rear of the ram where the slotting head should fit!

The BP has a lovely 48" bed, ok maybe it only has 9" of Y axis but thats still not too shabby I think, certainly I've done a hell of a lot of big jobs on the old girl.

So, what would the drawbacks be here?

The new spindle has the speed I need, I think a BP conversion can reach 4-5000 mm/min rapids which is where the mini-mill is set so thats no issue, ballscrews would provide the same accuracy as the mini-mill has presumably.

Hmmm......

[komatias]

You lose Z travel when you convert the bridgeport's quill and another bit more when you add the adapter to hold the high speed spindle. Apart from that, I cannot see any issues except the speed at which your motors are able to move the bed. Good lubrication is key here. 4-5000 is way to quick for stepper conversions but possible with good servos. I have restriced mine to 3000mm/min actually.

[Davek0974]

Ok, but by building a custom Z-axis and mounting it on the rear of the ram I would retain whatever travel I build into the new axis, it means swivelling the ram round to change from heavy to light milling but thats about it, plus would need two z-axis drives - heavy and light.

The Z on the heavy side is a pain, a couple that i have seen today - one replaced the quill lever with a toothed pulley and drove that via a planetary gearbox reduction - seemed ok, another replaced the fine-feed hand wheel and drove that, the ones that mount to the front of the quill I am not too impressed with, have read a few tales of quills being trashed by the single bolt pulling out.

As for speed, so far most of my mini-mill work ranges from 600mm/min to 150mm/min - hardly blistering, I'm sure the old girl can match that ;)

I think this may be an interesting project.

[komatias]

Yes, that would do it. I have gone with direct drive on the quill and do not over drive it. The fine feed goes through a clutch while the backlash on the lever is too much for CNC.

[Davek0974]

Good points, thanks.

By direct, I gather you have the screw nut coupled to the front where the depth-stop used to sit?

[Davek0974]

Something that rarely gets mentioned...Power required...

I have a 3ph 2.2kW spindle motor on a vfd, 700w X servo, 700w Y servo, 400w Z servo, maybe 100w for pc and controller on this machine.

How do i calculate the supply capacity allowing for diversity - it will not be running 100% flat out all the time :)

I know i need to uprate the MCB's and supply cables as the build was originally for the small 1.5hp spindle motor.

Adding up the maximum ratings for all drives gives a figure way more than i can supply :)