Ballscrews and knee lift for Chevailer FM3VK?

[Splint]

Hi,

I have a Chevalier FM3VK manual mill which I would like to convert to CNC. I will need ballscrews for the table and knee and a load supporting device (presumably a pnumatic ram) for the knee. I think I'll leave the top end as is. I know there are a few places that sell ready to go kits for Bridgeport mills but I dont know for sure if the parts for Bridgeports are perfectly compatible with Chevalier mills.

I have emailed Chevalier asking for dimensions of the existing leadscrews so I can compare with what's readily available, but getting replies from companies with requests like that is very much a long shot. I could if need be take it all appart and measure it up but I would prefer not to.

One feature that is an absolute must is that the machine will still be usable as a manual mill when done.

Where can I get a load supporting device for the knee, and who would be a good supplier of ballscrew kits?

Thanks
Splint

[Al_The_Man]

Does this mean you are CNC'ing the Knee as Z?
You could use a Ball Screw Jack such as Nook make, even if there is slight backlash, the pressure will always be downward to take it up.
The motor is mounted on the Jack input worm drive shaft, right angles to the B.S.
If fitting pneumatic counterbalance, you will need a cylinder either side of the knee and a compensating valve set up to maintain pressure in the up and down stroke.
Al.

[HimyKabibble]

Originally Posted by Splint Hi, I have a Chevalier FM3VK manual mill which I would like to convert to CNC. I will need ballscrews for the table and knee and a load supporting device (presumably a pnumatic ram) for the knee. I think I'll leave the top end as is. I know there are a few places that sell ready to go kits for Bridgeport mills but I dont know for sure if the parts for Bridgeports are perfectly compatible with Chevalier mills. I have emailed Chevalier asking for dimensions of the existing leadscrews so I can compare with what's readily available, but getting replies from companies with requests like that is very much a long shot. I could if need be take it all appart and measure it up but I would prefer not to. One feature that is an absolute must is that the machine will still be usable as a manual mill when done. Where can I get a load supporting device for the knee, and who would be a good supplier of ballscrew kits? Thanks Splint

Once you convert to ballscrews, it's really not particularly usable as a manual mill. First, the handwheel calibrations will be way off, and much faster. A machine that size will require at least 1" ballscrews for the X and Y, and probably 1.25" for Z, and all will be 4-pitch at best. So, a turn of the handwheel that was 0.001" will now be 0.0125" (assuming your leadcsrews are 5-pitch). Second, ballscrews will back-drive, so unless you lock an axis, cutting forces will cause it to move - a lot. Besides, once you have CNC, why would you want to run it manually? Anything you can do manually, you can do faster, and better, using jogging and MDI.

For ballscrews, I highly recommend Nook XPR screws, purchased directly from Nook. Their service and pricing are excellent, and the XPR screws are nearly as accurate (0.001"/foot), and smooth, as ground screws, but at the price of rolled screws. FAR better than Roton and the other common makes.

Regards,
Ray L.

[Splint]

Thanks for the responses guys,

yes, I want the knee to be the z axis. Al, would a ballscrew jack eliminate the need for a counter weight/load bearing system?

The reason for a manual and cnc mill all in one is because my father will also be doing a lot of work in with the manual side of things because he's never had much exposure to using computers, he just grew up in the wrong generation and trying to teach him now would be too difficult, let alone time and inclination.

I have seen a Bridgeport with a lever which enguages and disenguages the belts which run between the steppers and the ballscrews. Getting appropriate gears on the stepper and ballscrew should allow the manual and cnc opperations to work at relevent ratios.

How many mm or inches per rotation of the leadscrew do cnc bridgeports typically move?

Cheers
Splint

[Al_The_Man]

Typically the X,Y & Z quill would be .2" pitch.
If you read many of the previous posts on CNC'ing the knee it is not that practical, with the weight of the knee and XY table and any appreciable part weight, the resulting inertia to do fast moves requires a very large motor, especially when doing functions like peck drilling etc.
I have a counterbalanced knee on an Excello with Nook style B.S. Jack, but it is just for initial positioning. The quill is the true Z.
Al.

[Splint]

Originally Posted by Al_The_Man I have a counterbalanced knee on an Excello with Nook style B.S. Jack, but it is just for initial positioning. The quill is the true Z. Al.

Is the both knee and the quill controlled by the nc code or do you manually position the knee at the start of the machinng cycle? I've never heard of a Bridgeport stye machine where both the knee and the quill are cnc controlled at the same time. Is the knee controlled by a MPG?

[HimyKabibble]

Originally Posted by Splint Is the both knee and the quill controlled by the nc code or do you manually position the knee at the start of the machinng cycle? I've never heard of a Bridgeport stye machine where both the knee and the quill are cnc controlled at the same time. Is the knee controlled by a MPG?

I'm about to set mine up that way. The knee will be used strictly for tool length compensation. I've modified the Mach3 M6 toolchange macros to accomplish this.

Regards,
Ray L.

[DareBee]

For running manual I suggest putting on 2 electronic handwheels that run the XY at your set jog rate.
My lathe does that it set rates of .0001/.001/.01 per click of handwheel.

[Splint]

Originally Posted by HimyKabibble I'm about to set mine up that way. The knee will be used strictly for tool length compensation. I've modified the Mach3 M6 toolchange macros to accomplish this.

That sounds interesting Ray. I hope you do a build log so we get to see it.

Splint

[Al_The_Man]

Originally Posted by Splint Is the both knee and the quill controlled by the nc code or do you manually position the knee at the start of the machinng cycle? I've never heard of a Bridgeport stye machine where both the knee and the quill are cnc controlled at the same time. Is the knee controlled by a MPG?

Just the quill is CNC, the knee is just with a jog switch and a BLDC motor for this, but I had no need for precise positioning, I could have made it an extra axis to allow a PWG to position it.
Al.

[cncsnw]

Ballscrews are readily available with 0.200" and 5mm leads, if you want to keep manual hand dials.

In the States, Elrod Machine supplies Bridgeport retrofit kits that include such screws plus motor mounts and manual handwheels.

See http://www.elrodmachine.com, look for "CNC XY Ballscrews" and "CNC XY Brackets".

[Jason3]

Did you consider retaining the existing screws? I have a Chevalier FM3, the X and Y screws have double adjustable nuts and there's very, very little backlash in mine (about .03 mm). You may get good results just using Mach3's backlash compensation. I'm intending to retrofit mine too, but thought I'd give it a try with the exisitng screws before I spring for ball screws.

I'm pretty sure the standard size is a 32 mm dia. screw. I understand Hiwin do rolled and ground kits for a range of machines, and the prices are apparently not bad at all. I've requested a quote for a kit for my machine, having bought a number of Hiwin ball screws in the past and been very pleased with them.

Will you post a build thread for your retrofit? I'd be very interested, seeing as I'll be heading down the same path at some point...

Regards,

Jason