CNC Conversion?

[muleworks]

Hey fellas,
I was wondering if one type of bridgeport (or other brand names) or year was better for converting to cnc over another. I have heard that a bridgeport boss that has been put out of use b/c of out of date control systems are good and cheap. I just can't understand the difference between the boss and a manual mill. How much slack can a mill have in it and still be accurate for a cnc conversion? The largest stepper motors I can find are 1200 oz and I was thinking about using gear reduction 3:1. Will this provide for a fast mill with lots of power or just kind of a getrdone thing. I not expecting a machining center but would like for things to run pretty smooth. Thanks for your help. Oh yeagh do you power the z axis from the quill or from the knee feed?

Thanks
Chris

[ViperTX]

The problem with the Bridgeport Boss..is the cost to replace / repair the controller....so people chuck them. If you're looking for total CNC....then you need to control both the quill and da knee.

Steppers in the 1200 oz-in range should suffice.

The biggest benefit of picking a Boss over a manual mill...is that the Boss already has ballscrews.....it's CNC enabled. Other stuff has been done to the Boss to reduce friction....

[muleworks]

Hey Viper,
I know ballscrews will have less backlash but will the standard feed screws work for a cnc mill, or would I be compromising accuracy? Is it pretty straight forward to replace the standard feed screws with ball screws? I dont understand why you need to have a quill feed and a knee feed. There both just moving the z axis, can you give some detail on this. I am going to do a complete retrofit on the mill (power supply, driver, steppers, ect) so the boss and all its drive components will be taken off. How big are the boss series compared to the standard bridgeports, they looked huge in the pictures. Thanks again for the help!

[Karl_T]

I guess you could use standard acme screws for CNC but it would be a HUGE compromise. Way more backlash, and its not constant- more in the middle- and you'd need bigger seteppers because of more friction. (My bridgy has 40 thou backlash in the middle and less than 5 on the ends)

Normally you'd CNC the quill, not the knee because it takes a huge stepper/servo to move the knee. Again, a boss is all set up for CNC on the quill.

There's no reason you can't replace the standard acme screws with ball screws but it might be expensive.


Boss series 1 is basically like a 2J manual bridgeport with a beefier table. SeriesII and III get to be pretty big machines. I just seen a series 1 go for $250 a couple weeks ago - dead control of course.

Karl

[ViperTX]

$250....I'd take one for that price....tack on another $1200 for shipping it....sounds like a bargain.

[muleworks]

Hey Again,

Thanks Karl and Viper for the info! I never have touched and will never have the money to buy a new bridgeport; do they come from the factory with backlash or is it just from years of wear. Can a boss still be used as a manual mill or is it totally cnc only? If I found a boss 1 for a good price and it was pretty old, would it still be usable? Another words is it likely that it would be woreout from years of cnc use or do they usually stay pretty tight? Thanks again fellas, your help is very appreciated. I am from alabama and machine shops are becoming scarce, I have been to 4 auctions around here local in the past 6 months. Most of the "machinist" left are what I call handle turners. They sit at the same machine every day doing the same job and are not very skilled at thinking outside the box. I am a welder and trying to pick up a few skills here and there. I would like to find me some old timer and sit him down in my shop for about a month and let him talk my ears off. Does anyone have one for sale or loan?
Chris

[jdelaney44]

Chris, the cheapest way to go is to get a series 2 Boss and replace the controls. Keep the steppers.The screws are likely to be in pretty good shape.

Each machine is going to be very different with respect to wear. I think my machine was originally and Army machine that got surplussed out. The original paint is O.D. It was doing a lot of drilling only by the looks of the chips stuck in the knee. So, the ways are pretty good. The head is a little screwed up.

I've not done the Boss thing. But from what I've seen over the past few years, that is what I would do next.

I'm in the middle of a Series I 2J conversion now. It has been a lot of work. If I had just done the Series 2 Boss I'd be done. Shop around. Great deals are out there. You'll be surprised over the next few months how many machines you'll find within driving distance of you. Maybe a long drive. Atlanta too far? Rent a truck and a car trailer.

But.....if cash flow is the issue, like it was for me, chipping away at a Series I conversion might be the way to go. OBTW, I am using servo motors.

I have some old but never been used Reliance Micro 100 series motors. Nema 34. E-Bay find. I just got the quill under power at only 33V and it can over come the quill lock with ease. My final voltage will be 56V. It's rated at 100V. So I was worried about the torque at a lower voltage but, no problem. Lesson being there are a wide range of motors that will work.

If you haven't heard of them, check out www.geckodrive.com or www.rutex.com

Both are good makers of stepper and servo drives.

With a PC and some of their drives you have a pretty easy replacement for the stock controls on any of the Boss machines.



-jd

[muleworks]

Hey JD,
Thanks for the info! I am pretty comfortable with the drives, pc, and steppers. I have been running a torchmate 3 for a little while and getting ready to build a 4 x8 plasma table. I was unclear on which machine best suited overhauling weather a manual mill or a previous cnc mill and almost everone says a previous cnc mill. I will start hunting one down, I have seen a few on ebay go for less than 500 dollars that was within a few hours of driving. The transporting wouldnt be a problem we have tractor trailer rigs but I figure a flat bed gooseneck would be fine. I figure a old cnc mill would weight around 5000 at the best? I noticed you said a series 2 over a series 1. Is it a reason for that? Thanks a million yall!
Chris

[zcases]

I recently got two Boss 5's that were "supposed" to be ready to run. Well they didn't and I will be retrofitting one with (most likely) gecko's and Mach 2. I would consider selling the other machine or control parts from the one I gut. The problem appears to only be bad drive transistors........but after seeing and researching Mach 2 and geckos, I am more excited about going that route anyway.

[machintek]

The transistors are the most comon things to go. Anyone that has one of these machines keeps a box on 2N6547 transistors. BUT, having worked on these for 23 years, there are ways to make these drives a LOT more reliable. I have people that now have run for years without blowing one.

George

[chineguy]

Hey guys check out Excitron drives. I have not bought them yet; but they have some real torque monsters though. Rated in Inch pounds not Oz. inch. I would recommend trying the knee for a Z axis. It is much more rigid and has less slop than the average worn quill. Rig a counter balance by using an air or nitrogen cylinder under the knee and you should reduce the power to drive to a resonable level. I have not tried it yet but it is what I plan to do on an old Hardinge horizontal knee mill we have at work. The air would obviously be cheaper and you could easily adjust the pressure with a regulator to what worked best. Just enough to equal out the load so the screw turns the same torque each way. Most go down real easy.

[machintek]

A BPT series 2 standard already has the air cylinder. The old Series 2 NC has the air cylinder and a knee ball screw and drive. Plus X and Y ball screws and drives. This was mentioned in a prior post. It would save a lot of time and work for you.

George