BP CNC Retrofit---for my school lab

[2Springers]

Hi all,
I am a new member here, and relatively new to CNC. I am coaching a robotics team at the high School I teach at, and we are realizing we will need a larger CNC mill to accomplish our tasks. We have a small benchtop toy mill that utilizes Inventor and Edgecam. I have a 1954 Series 1 BP vert. mill with a J head. The mill has been well taken care of, and I have just finished a maintenance overhaul on it. I would like to convert this to a full 3 axis CNC mill. I have seen many kits, independant parts, and retailers, but I dont know much about the retrofit kits or the suppliers to be able to tell which one is best, or even specifically what I need.
I know many threads exist here, and I have looked, but I fear im a little out of my league trying to make heads or tails from them.
I have about $10K to work with for this project, but I do not want to spend it all on this.. I was hoping to grab a small cnc lathe with the leftover $$.

So--- I was looking at the CNCMasters Kit. http://www.cncmasters.com/CNC%20Supr...ofit%20Kit.htm
is that any good? I hate the way the Yaxis motor sticks way out, and also how you need to replace the original handwheels with the motors that have handwheels on them.... to me, that seems dinky.. I wouldnt want to do manual machining using these handwheels... seems like undue stress on the motor shafts...

SO... I welcome any and all help the CNC pros here can offer.

Thanx!!

[HimyKabibble]

Handwheels on a CNC machine are, at best, a totally unnecessary safety hazard. I can't understand why people insist on putting them on.

The maximum speed of 50"/minute is painfully slow for a machine that size - that's almost a full minute to run the X axis end-to-end. I would consider 100 IPM an absolute minumum, 150 much more desirable.

If you have the time, it's not *too* difficult to do your own conversion. I did mine using servos, and it works very well - 350IPM rapids, and more than enough "thrust" when cutting. The basic X/Y conversion took perhaps 3 weeks, about a year ago, with all the parts made on the machine - one set of "crude but effective" hand-made parts, then a nice set of CNC'd parts. The knee another few days, using the same basic drive design, and going through the bevel gears and leadscrew. I just finished the quill drive a few days ago, after using the machine with the knee as the Z axis for the last year. The knee will now be relegated to providing tool length compensation only.

My motors do stick out, but with longer belts, you could tuck them out of the way. I really have not found it to be a problem.

Though, if I had it to do over again, I'd buy a used VMC....

Regards,
Ray L.

[fatoldman7]

Hi Ray, very nice retrofit, I do have a few questions for you, It looks like you built all your mounts, is this correct? What motors, driver boards , and software did you use? Did you document any of your work to this forum, or can you share any links that might be of help for those doing a similar project. I to am looking to retrofit BP mill in the near future, any any information would be useful. I have been doing searches, but it seems there is good information, but it is spread out amongst many posts, is there a FAQ for BP conversions in these forums? Thanks for any information you can provide.

[HimyKabibble]

Originally Posted by fatoldman7 Hi Ray, very nice retrofit, I do have a few questions for you, It looks like you built all your mounts, is this correct? What motors, driver boards , and software did you use? Did you document any of your work to this forum, or can you share any links that might be of help for those doing a similar project. I to am looking to retrofit BP mill in the near future, any any information would be useful. I have been doing searches, but it seems there is good information, but it is spread out amongst many posts, is there a FAQ for BP conversions in these forums? Thanks for any information you can provide.

The motors are 850 oz-in peak DC servos from www.homeshopcnc.com, with 500 line US Digital encoders. The drivers are Gecko G320s from www.geckodrive.com. Ballscrews are 1" Nook XPR (0.001"/foot max. lead error), with home-made double-nuts (If I were doing it over, I'd just buy pre-made double-nuts, or anti-backlash nuts). Power supply I built using a 1500W, 45V transformer from www.antekinc.com, and two PMDX PMDX-135 power modules from www.pmdx.com. Breakout boards are a pair of Homann MB-02s, from www.homanndesigns.com. Spindle is controlled by a Teco FM-50 VFD, using a Homann DC-03 controller. I'm using Mach3 from www.machsupport.com, with a SmoothStepper motion controller from www.warp9td.com. The PC is just a generic 3GHz machine. All the electronics are mounted in a single 24" x 24" x 12" Hoffman NEMA4 enclosure.

As I said, I made all the parts on the machine. First set was very crude - made from flat plate, manually milled and drilled. (See picture below). Once those were mounted, I had 2-axis CNC, which allowed me to make the "nice" pieces. Once those were mounted, I made the knee axis drive, so I had 3-axis using the knee as the Z axis. I used it like that for the last year, and just a week ago made the quill drive.

X and Y have 4-pitch ballscrews, driven through 2.5:1 GT2 belt reducers, giving 20,000 steps/inch. The quill has a 5mm pitch, 20mm dia. ballscrew with single anti-backlash nut, driven through a 2:1 GT2 belt reducer, giving 20,320 steps/inch. The knee retains the stock 5-pitch leadscrew, and 2:1 bevel gear, driven through a 4.8:1 XL belt reducer, giving 96,000 steps/inch. X, Y and the quill are all actually good for 400 IPM, though I normally run only 200. The knee will do 75 IPM, but I normally run it at 50.

I do have DXFs for the belt reducers (X, Y and the knee are all the same basic design, only the mounting holes differ between the three), but they're a little confusing, since they were setup for my own use, for CNC machining only, so they don't really represent what a normal person would consider a full set of design drawings. I could probably be persuaded to make you a set, if you were interested. It is my intent to sell the quill drives as a product, as I can sell them for considerably less than the commercial units available (and I'm unemployed for 18 months now, so any income is good!). The quill drive will be tested on a real Bridgeport in the next week or two. The X/Y/knee drives have, so far, only been mounted on a Chiwanese BP clone, but the way they're designed, only the intermediate adaptor plates would require modification to suit the mounting bolt locations on the BP. The drive housings themselves will work fine as-is.

Regards,
Ray L.

[2Springers]

Thanx for the pics and insight. I think I can do this mod myself, however, I really dont know anything about the electronics that would drive the system. The motors and mounting seems straight forward enough to do. My only issue, is how do I acquire/manufacture the mounting brackets without a CNC (yet).

I am very glad you told me how slow 50ipm is. I will certainly look for faster motors.

I appreciate the help already. I will be back with more questions no doubt.
My first new question is why does it take so long to do this conversion for most people? Is it because you had to machine parts to make it happen first? Or is it because you run into problems, or necessary repairs? Or maybe just because most people only work on this in their spare time?

[HimyKabibble]

Originally Posted by 2Springers Thanx for the pics and insight. I think I can do this mod myself, however, I really dont know anything about the electronics that would drive the system. The motors and mounting seems straight forward enough to do. My only issue, is how do I acquire/manufacture the mounting brackets without a CNC (yet). I am very glad you told me how slow 50ipm is. I will certainly look for faster motors. I appreciate the help already. I will be back with more questions no doubt. My first new question is why does it take so long to do this conversion for most people? Is it because you had to machine parts to make it happen first? Or is it because you run into problems, or necessary repairs? Or maybe just because most people only work on this in their spare time?

"My only issue, is how do I acquire/manufacture the mounting brackets without a CNC " - Look at the first picture in my last post. My first parts were made entirely manually - flat plates with drilled and bored holes. Not pretty, but perfectly functional, and took just a few of days to make. Then, I had two-axis CNC, which is enough to do all the rest nicely, and very quickly.

"why does it take so long to do this conversion for most people?" - Many reasons. For many, it is a part-time thing. Also, they have no machining skill at the outset, so there's a learning curve. Many people try to do everything at once (enclosures, coolant, etc, etc), rather than doing the minimum and growing from there as needed. I've seen people spend *years* building up elaborate systems, before making the very first chip. For them, the build is the goal. For me, I wanted to make parts ON the machine, not make parts FOR the machine. If you put enough thought into it up-front, it's really not that hard to do.

The electronics, if you do it right, will take as long as the mechanicals. It did for me. But, it pays off. You'll see many people who have all kinds of electronic problems - flaky operation caused by noise. My electronics have been rock-solid from day one. Take the time to do it right, and follow good design practices - proper grounding and shielding is critical to reliable operation.

Regards,
Ray L.

[CNCfun&games]

2Springers:
Enclosed is some info. which may help in your retrofit.
I'll check and see if i still have an extra set of X & Y mounting plates I can donate to the cause. PM me if you are interested.

[Garland]

Hmm... I have access to a BP knee mill at father/law's that sits most of the time as he does small tasks for his Wood work cabinet business.

I also use it as a machinist but Im looking for a personal CNC...I think a retrofit on this machine would be Ideal IF I could keep its manual goodness in tact for father/law.

what ballpark figure $$ would I have into this project if I pieced together the parts needed for retrofit compared to ordering a complete kit?

I would like to pay as I go instead swallowing the whole kit cost up front. Only if its not a nightmare service/install wise.

thoughts? I think Im in the same boat as the original poster looking for guidance.

[Garland]

Hmm... I have access to a BP knee mill at father/law's that sits most of the time as he does small tasks for his Wood work cabinet business.

I also use it as a machinist but Im looking for a personal CNC...I think a retrofit on this machine would be Ideal IF I could keep its manual goodness in tact for father/law.

what ballpark figure $$ would I have into this project if I pieced together the parts needed for retrofit compared to ordering a complete kit?

I would like to pay as I go instead swallowing the whole kit cost up front. Only if its not a nightmare service/install wise.

thoughts? I think Im in the same boat as the original poster looking for guidance.