Advice on Bridgeport converted to CNC for sale

[Charlieman22]

Now you've introduced a lot of moving parts and more factors in the equation

Indeed - and I appreciate ya'll not throwing in the towel!
I'm on a steep learning curve - but every post/response has advanced my understanding of the feature sets, and refined my own view of what I want.

Power Down Feed (PDF) is a great feature. Yes, it's a big player in a well-bored hole, but it comes in handy in straight drilling and a little of everything else.

One of those insights I note...

If you can report back on the Brigeport you're negotiating over... like model and/or control, we might be able to figure out what it'd take to make it really useable in manual mode.

Great. Posting (some re-posting) of pics of the BP. Manual will be significant portion of my work - so this is not an insignificant point. Don't want to be wrestling with the (stepper?) motor's trying to move the table around.

There's a clean Enco clone for $2k in Santa Clarita.

Ha - trust me - I am watching... I spoke to the guy today in Santa Clarita. Below is a pic of the ways (saddle?) I got him to send. Seems kinda well used compared to the Bridgeport ?

Last two pics are the Enco in Santa Clarita. You can see the Enco's ways are not in as good a condition as the BP. BP has a spare controller on the shelf. Not sure the story there. Would come with it.

 

[Papa Charlie]

After reviewing this thread, I would like to offer this:

1) You can buy a brand new PM machine for $6.5k as you say, but you still have to buy all of the tooling that is needed and that can add up very quickly.
2) This machine may not be perfect but it does run, seems as though you would be able to do all of the tasks you currently have in mind and depending on the tooling, you may or may not have to buy anything more than the expendables for a while.
3) CNC is great if you are going to do production work, creating the same part over and over. If you are doing that, then you may want to consider a higher end unit with current controls and drivers. But in truth, from your description above, it doesn't sound as though that is your plan. At least for the present. Again, if it becomes your plan down the road. then consider something that will be working as apposed to you working on it.

Without knowing what the tooling is and I mean a detailed list, it is hard to say what the value is. His comment was he has $3000 worth of tooling. What, how old, what condition, etc. It is real easy to spend as much money on the tooling and accessories as you will on the machine.

Frankly, if it were me, once you have a clear understanding what else he is offering you, make an offer of $3000. You can always go up and he could come down.

The final option is to wait and continue the search. While nice units do come up and sometimes for some pretty good prices, it is more rare for them to have all the tooling in good condition to go along with them.

 

[spumco]

Great. Posting (some re-posting) of pics of the BP. Manual will be significant portion of my work - so this is not an insignificant point. Don't want to be wrestling with the (stepper?) motor's trying to move the table around.

Quick research on the CNC4 controller indicates its a close-loop stepper driven thing. Dumb steppers, but encoders of some sort feedback to the control. DOS-based 286 PC interface. There's a long thread on the LinuxCNC forum about retrofitting something with that control:

https://forum.linuxcnc.org/38-general-linuxcnc-questions/10613-centroid-cnc4?start=0

If it were me, I'd go in to that deal planning (i.e. mentally budgeting) on retrofitting the system. Even if it works, it can't do helical interpolation and you'll probably spend quite a bit of time just figiuring out how to run the ancient thing.

The steppers are belt-drive, so it should be easy to pull the covers off, drop the belts, and fit a handle on the Z and Y axis. Use it El Manual for now, maybe leave the steppers as power feeds.

The good part is that all the mechanical hardware is there for an easy retrofit with a PC-based control system. Three steppers & drives, motion controller, and a cheap PC. Bamma-jamma, modern control.

 

[jwmelvin]

Three steppers & drives, motion controller, and a cheap PC. Bamma-jamma, modern control.

Don’t steppers make a machine kind of terrible for manual use, because of the torque cogging when de-energized?

 

[extropic]

Walk away from the BP. Let it go to someone ready to appreciate it.

Buy a shiny new Chicom or Taiwan machine. You will learn quite a lot.

 

[spumco]

Don’t steppers make a machine kind of terrible for manual use, because of the torque cogging when de-energized?

Yep. That would be miserable, but...

Back-driven brushless servos will generate electricity that the drives may not like very much, especially if they're driven by a 2 or 3:1 belt ratio to get the RPM in the right range for a servo.

And my guess - just a guess - is that the steppers on it are a NEMA frame and it's a little hard to find true NEMA servos. Not impossible, but not cheap-cheap. DMM charges extra for NEMA frame/shaft over the metric version, and Teknic isn't giving away the Clearpaths. Beyond that and you're in to Parkers and Allen-Bradley motors if you want real NEMA frame/shaft compatibility.

But a decoupling connection is a pin-pull away, and steppers are cheap. Want manual? Pull a pin and the leadscrew freewheels while the motor & belt just sit there. There are obviously much more clever ways to decouple a drive system from a shaft, but I was spitballing something quick and dirty.

 

[spumco]

Walk away from the BP. Let it go to someone ready to appreciate it.

Buy a shiny new Chicom or Taiwan machine. You will learn quite a lot.

Always sound advice if the budget permits.

 

[JimDawson]

Back-driven brushless servos will generate electricity that the drives may not like very much

All permanent magnet motors can just as easily be a generator if driven. Steppers are even worse when back driven, they just virtually lock up. The only motors that seem to work well for manual driving are brushed DC servos. I like your drive pin idea

The brushed DC servos on that BP are really quite robust and easy to control with the correct hardware, I wouldn't change them, but that antique control needs replacement with a more modern system.

 

[Charlieman22]

Ok - there is drinking water from a fire hydrant - and then there is accidentally getting plowed in the face and washed across the street.
Having picked myself up - and still feeling the weight of my soaked clothing - I am here:
- Not good to operate manually when motors engaged. Miserable to turn knobs and bad for electronics even if I could
- Old system isn't going to do the fancy helical cutting. Bonus - I now have a name for that cool action I have seen before
- Slip belts off - or come up with a quick release is an option - tho perhaps the steppers would just be boxes in my way.
- Add new control that allowed me to move stuff with button pushes rather than physical handle turns? Jim is that what you were suggesting?
- Buy new - looks like $6000 - $7500 from where I sit for comparable size knee mill - best case. PM835S with X axis power and DRO = $6K
- Buy used.

On that last point: the machines I am seeing at 2K-3K all have heavy wear on the scrapings and their own set of issues.
Add a DRO and or an axis drive that has failed and they are all in the $3500-$4K range for my baseline manual operation desires.
Might as well strip off the CNC from this BP - and put the original screws back on and be in just as good a shape with a BP rather than used clone?

 

[JimDawson]

- Add new control that allowed me to move stuff with button pushes rather than physical handle turns? Jim is that what you were suggesting?

Not at all. Here is a picture of my machine, handwheels and servo motors. This machine can be operated as full manual, 2, 3, or 4 axis CNC with a flip of a switch and a mouse click. Also of course it will jog with a button push.