knee mill conversion

[mtechserv]

I'm interested in hearing from other people that have converted manual knee mills (bridgeport type) to CNC.
I want to convert my mill to a 2 axis CNC. I understand the basic components needed, but I'm not sure which components would be best. This is an older mill, so I'm not planning to dump a lot of money into it. Therefore, I figured a stepper system would be the best route. I'm mainly interested in obtaining information on the size / type of steppers and drivers.

The mill has a 9 x 36 table and a bridgeport m-head. It is used on a near-daily basis to mill aluminum, plastic and low carbon steel.

Any help would be greatly appreciated.

[BigDaddyG]

mtechserv,
Hey man, I have done several of the conversions. You mentioned steppers for a large mill like that look for some very beefie steppers. Look in the 800+ range. You will want to work the beds as well. A little elbow grease and some good compunds on the ways and beds since you have it apart. The other thing, Ball Screws! Check and see what is being used. Duplicate them in a good Ball Screw with dual nut 0-backlash set up. If it does not have a lub system, when you have it apart would be a good time to add one, they are simple to make up.

Why just 2 axis. You will just do the other axis soon anyway! I mentioned the larger motors, make sure you look for boards that handle around 10 amps or more. Also you will need a beefer power supply for the larger motors. They are out there. You can Ebay most of it. Ball Screws can be done for around 300 bucks.

Good Luck, if you need any help just let me know.
Regards,
Glen

[mtechserv]

Thanks Glen,
I figured the steppers would need to be large. I know some mills I've seen are using somewhere around 1000 oz/in steppers, but I wasn't sure if that was overkill. Apparently it's not.

Do you have any suggestions on ballscrew suppliers? I've looked at Roton and Rockford, but I haven't requested any quotes yet.

I've been thinking about the third axis. Is it better to drive the quill or the knee? I've seen conversions both ways. However, most of the commercial CNC knee mills I've seen drive the quill. Some people argue that you can have some "play" in the quill and only suggest driving the knee, but I would think you could also have rocking in the knee.

Thanks again for your help!

Brian

[HuFlungDung]

The knee is heavy, and needs a counterbalance. I'd vote for the quill drive, especially when you might be executing drill cycles. I'd "feel sorry" for the knee and knee motor doing peckdrilling of a few hundred holes. Even a quill drive Z axis servo will heat up doing that!

[BigDaddyG]

Brian,
I agree with Hu...Dung, if your not pushing the machine (which it will take) the quill is fine for most work. That is where the cleaning and working of the way's comes in. Your 1000's are not overkill at all.

As for the Ball Screws, I prefer the Thompson (you can get them thru msc) because of the nut design. Getting near 0-Backlash is cool! You can look around, some sell the balls with the center yoke all in a package, it might be worth looking into, but can be pricey!

You can always add the third axis later on but plan now. If your looking into boards, you can get some fine boards with the high amp ratings in 3 axis in some cases cheaper than two stand alone drivers.

Good luck man, where are you located? I am in Tampa Fla area?

Glen

[fyffe555]

Hey Glen, you have a PM.

[mtechserv]

Good point Hu...Dung. For the type of work I'll be doing with this particular mill, it sounds like the quill drive is the way to go.

Thanks again for the info, Glen. I'll look into the Thomson screws. Any suggestions on where I can find the 3-axis boards? If seen some kits like this, but I beleive they were for smaller steppers.

I'm located in central PA.

Brian