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Offline Davek0974

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Bridgeport Knee Mill Conversion?
« on: May 10, 2016, 10:13:32 AM »
Anyone here converted a manual Bridgeport mill to CNC?

After building my plasma table and my mini-mill, both of which are working lovely, I WANT MORE CNC  ;D ;D

The old Bridgeport is looking for some love but is it worth it?

It would need a ball-screw conversion kit, these are available, plus I am guessing servo drives on X, Y and Z so I have encoder display, the knee doesn't seem to get driven on the few vids i have watched so far.

On the plus side, its already driven via a VFD  ;) and i could likely recoup some cash by selling the working power feeds and new DRO i fitted last year.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives
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« Reply #1 on: May 10, 2016, 11:46:46 AM »
Ive thought about the same for home/hobby use.

While talking with acouple of the mechanicals which are hired at work to fix the cnc machines, they all said the same thing. If you put ball screws in and do it right, you should beable to move the table by hand (grabbing the table itself with your hands and movinging it around) with no serveo/steppers motors hooked up. And with that said, i could not image bringing able to use the machine manually after the conversion, the cutter would be moving the table/part where ever it wanted to.

But then again, ive read online a number of people doing this, so who knows.

What ive thought about doing is making a smaller cnc x/y table which would bolt on my mills table and just convert the Z.

Just some food for thought incase it hasnt crossed you mind.

-
~ What was once an Opinion, became a Fact, to be later proven Wrong ~

Offline Hood

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Re: Bridgeport Knee Mill Conversion?
« Reply #2 on: May 10, 2016, 01:40:03 PM »
Did a clapped out BP as my first retro and it made a crap machine quite good.
I bought second hand ballscrews off ebay and adapted the dog bone so they fitted.
I converted the quill for the Z.

It was just steppers I used and if I recall I got about 2500mm/min max rapids.

Regarding being able to push it about by hand, doesn't happen. Maybe if you put very course pitch screws on it then it would but 5mm pitch it was more or less the same as it was with the original screws, maybe a wee bit freer.
I went to a fair bit of work to adapt things so I could keep the handwheels, two weeks later I was cutting them off as I never used them, much easier just MDIing and I knew nothing of G Code at the time.

You tend to get good money for manual BP's don't know why as they are not the best knee mills in the world but suppose the name sells them. Used to be able to pick up series 1 and 2 CNC Bridgeports for cheap if they had dead controls, so it was usually better to sell the manual and buy a series 1 or 2 and retrofit Mach to it.

Now however the CNC ones seem to be going for almost as silly money as the manuals so may not be worth trying to do that.



Hood

Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #3 on: May 10, 2016, 01:58:22 PM »
Thanks guys, results from various forums seem to concur - some say its ok, some say waste of money buy a donor CNC and fix.

It was just a thought really, I will be watching the listings for old cnc stuff and carrying on dreaming in the meantime ;)

In its defence, the Bridgeport is my favourite machine, the things I've done on it have been amazing but have also been bitten by its flexibility as well.

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

Offline Hood

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Re: Bridgeport Knee Mill Conversion?
« Reply #4 on: May 10, 2016, 02:10:50 PM »
I wasn't saying not to do it, I meant that a while back the best option was to sell the manual and buy a CNC as it was easier and cheaper to do and often you would end up with more money left over as the manuals sold for good money.
Now however the CNC ones are getting good money so probably not as good an option as previously.

Personally I would look for a bedmill and retro that, sadly they do not come up very often.

My original retrofit was the best thing I did to that BP, as said it was clapped out so it wasn't the most accurate retrofit but it hugely improved it over being a manual.

Hood

Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #5 on: May 10, 2016, 02:24:04 PM »
Seems the way it goes, when i got the BP i paid £500, a year later and they were up to over £1000, now they are way more, for a decent item. Getting a donor would be useful as it means i can keep the BP running while fixing/converting the donor, no idea where to put it though :)

Will keep an eye on the 'bay ;)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives
Re: Bridgeport Knee Mill Conversion?
« Reply #6 on: May 10, 2016, 06:48:09 PM »
When you get all done it is still a knee mill, with a really short Z axis. A short Z axis just plain sucks. You wind up spending time and money trying to find a combination of tools all about the same length. I worked on a CNC knee mill for four years. We now have a bed mill with a 21.5" travel Z and we use all kinds of tools without a second thought.
Re: Bridgeport Knee Mill Conversion?
« Reply #7 on: May 11, 2016, 01:06:18 AM »
$.02 more...

i ran my 10 x 50 Acra knee mill, knee driven, pc controlled and built by CNC Automation here in NH USA, for 11 years, with NO problems related to the knee driven part.  in fact having the spindle free was the best part.  position over a hole, and mdi hand tap holes small as #2-56 with the tap held in a drill chuck.  or lift the spindle and watch the program run with cutter above part.  also enables you to use a quick change tooling like ultron snapchange, or a power drawbar and TTS type tooling.  no its not a bed mill, but with high positive insert cutters, moderate cut depths and fairly high feed & speed, you can move metal, including steel, at a pretty impressive rate.  if i was doing a lot of tiny short move work, or engraving, id like the quill driven.  otherwise, no.  my acra has 15"+ of cnc Z

it has ballscrews, fat ones at that.  so i dont have to deal with a cnc with old acme screws.  but having said that, i worked with a company for years that only employed big clunky worn out machines.  one of these they retro'ed with an old clunky cnc system.  despite the large amounts of backlash and way slop, this machine never sat empty.  they found ways to program so the looseness wouldnt crash the machine.  of course it could not machine a 30" dia +/- .001 hole, but folks lined up to have that hole put in at +/- .015 tolerance.

and im lucky to have dc brush servo motors already mounted.  but i think 50 ipm of stepper bridgeport would be great, when hand cranking is the alternative.

i did say my acra has 15"+ of Z.  well no it doesnt.  it is electronically brain dead. old like me heh. but im working on it now with the help of a forum member, in a year or less i hope to see it uccnc guided, and using Mach too, and a better machine than when i bought it.  i did a lot of great stuff on her, hope to have her ready when i retire from working for the man which ive been doing for 6 yrs or so, the man has been kind enough, but working for me i like the boss a lot better.

then, after all this fun, theres the lathe in the corner.........
 









Offline Davek0974

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Re: Bridgeport Knee Mill Conversion?
« Reply #8 on: May 11, 2016, 03:28:05 AM »
I guess a CNC bridgeport is better than nothing but i really like the idea of having a donor to fix up at my own pace - taking the BP down for any length of time would usually bring in a flurry of jobs needing it, sods law.

My issue would be where to put it while fixing and finding one to buy without dropping loads of cash, don't forget this is still a hobby business not a job-shop. I plonk it in the garden under a gazebo maybe :)

I'll keep looking but it's probably a pipe-dream at present.

It's surprising how little i use the lathe now so wouldn't be my third choice for cnc ;)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives
Re: Bridgeport Knee Mill Conversion?
« Reply #9 on: May 11, 2016, 10:26:14 PM »
$.02 more...

i ran my 10 x 50 Acra knee mill, knee driven, pc controlled and built by CNC Automation here in NH USA, for 11 years, with NO problems related to the knee driven part.  in fact having the spindle free was the best part.  position over a hole, and mdi hand tap holes small as #2-56 with the tap held in a drill chuck.  or lift the spindle and watch the program run with cutter above part.  also enables you to use a quick change tooling like ultron snapchange, or a power drawbar and TTS type tooling.  no its not a bed mill, but with high positive insert cutters, moderate cut depths and fairly high feed & speed, you can move metal, including steel, at a pretty impressive rate.  if i was doing a lot of tiny short move work, or engraving, id like the quill driven.  otherwise, no.  my acra has 15"+ of cnc Z

it has ballscrews, fat ones at that.  so i dont have to deal with a cnc with old acme screws.  but having said that, i worked with a company for years that only employed big clunky worn out machines.  one of these they retro'ed with an old clunky cnc system.  despite the large amounts of backlash and way slop, this machine never sat empty.  they found ways to program so the looseness wouldnt crash the machine.  of course it could not machine a 30" dia +/- .001 hole, but folks lined up to have that hole put in at +/- .015 tolerance.

and im lucky to have dc brush servo motors already mounted.  but i think 50 ipm of stepper bridgeport would be great, when hand cranking is the alternative.

i did say my acra has 15"+ of Z.  well no it doesnt.  it is electronically brain dead. old like me heh. but im working on it now with the help of a forum member, in a year or less i hope to see it uccnc guided, and using Mach too, and a better machine than when i bought it.  i did a lot of great stuff on her, hope to have her ready when i retire from working for the man which ive been doing for 6 yrs or so, the man has been kind enough, but working for me i like the boss a lot better.

then, after all this fun, theres the lathe in the corner.........
 

You are right about the loose quill being very nice. Which is why I said bed mill as they typically have a quill. Since you are only moving the head, with a counterweight up and down instead of the entire knee, table and part you do things like peck drilling a lot better.  I peck drill all the time.  Can't see the point of CNC if you have to stand there watching for chips to wrap around the drill all the time and possibly causing a crash.