Need Advice for Clone Conversion

[lerman]

I have a "Unimac" clone of a Bridgeport knee mill with a 42x9 table, 24x12 travel. I would like to convert it to CNC with the quill as the Z axis. It will be used mainly for prototype work, with some light production on aluminum a few hours a day.

Elrod seems to have what I would characterize as a top of the line quill conversion. They also sell ballscrews and XY conversions. In a recent email to me, Dwayne Elrod said, "I really encourage knee mill retrofitters to use 1350 Oz. In. motors..."

An alternative to Elrod's ballscrews are Rockford ball screws. They are described as precision rolled ballscrews. They are less expensive than the ones for Elrod, and also less precise. But they are certainly accurate enough for my work.

The questions:

1 - Do I really need 1350 Oz. In. motors? I was looking at the Reliance 0690 servos that are rated at 22 Lb. In. (352 Oz In) continuous. Elrod gears them up 2:1 and I would do the same. There seems to be a factor of 3 or more in cost.

2 -- Who besides Elrod has a Z axis quill conversion? Are they any good? What provisions are made on these conversions for limit and home switches?

3 -- The acme screws on my machine are 1.250-5tpi. The largest of Rockford's screws in 5 pitch seems to be 1.150 in diameter. Is that likely to be a problem?

4 -- Who besides Elrod has motor mounts/pulley kits for the X and Y axis?

5 -- My intention is to use EMC for the software (I'm a linux guru), and pico controllers. Does anyone have any comments on these choices?

Are there any other questions I should be asking? Do you have answers?

Thanks,

Ken

[dserratt1]

I just put the Rockford Ballscrew kit in my series 1 and there a direct bolt in, however the stated acuracy is wrong its about .004 per foot not .002 but if your going to use mach3 is has screw mapping.
Next the motors the torque is needed for accel, decel and hogging out, if you use low enough gearing you can use those motors. Here is the downside lets say you use 5to1 gearing you get 1760 inlbs of torque but at lets say 2000 rpm /5 for your gearing and /5 for your pitch gives you 80ips for your rapid travel. you will have a slow motion CNC machine. Also you will have to custome make your own motor mounts.

[Hood]

Originally Posted by lerman 1 - Do I really need 1350 Oz. In. motors? I was looking at the Reliance 0690 servos that are rated at 22 Lb. In. (352 Oz In) continuous. Elrod gears them up 2:1 and I would do the same. There seems to be a factor of 3 or more in cost.

I am using 916 oz/in steppers on X and Y and 260 oz/in on the Z. I have 2:1 gearing on X and Y and 3:1 on the Z and have not had any problems at all so far. I am almost ready to swap the motors over onto my series 1 CNC Bridgeport but I will be using a 916 for the Z on that.

2 -- Who besides Elrod has a Z axis quill conversion? Are they any good? What provisions are made on these conversions for limit and home switches?

Sorry not much help here as I made my own brackets up.

3 -- The acme screws on my machine are 1.250-5tpi. The largest of Rockford's screws in 5 pitch seems to be 1.150 in diameter. Is that likely to be a problem?

It wont be a problem as when you look at a ballscrew the ball track is not nearly so deep as the acme thread so the root of the ballscrew will still be thicker than the acme. I have 20mm on mine and again no problems.

4 -- Who besides Elrod has motor mounts/pulley kits for the X and Y axis?

As above, made my own so cant help.

5 -- My intention is to use EMC for the software (I'm a linux guru), and pico controllers. Does anyone have any comments on these choices?

No experience with that or any other controllers so will just tell you what I think of the one I use. I use Mach3 and it works really well, there is a great community on the Yahoo group and also on the suport forum. Art (Mr Mach) is a genius who is always adding functions and helping out. The Yahoo group and the forum also has a huge number of very knowledgable people and they work in conjunction with Art to make things happen. I have been using Mach for about a year now and the progress it has made in that time is unbelievable and I would say it must be one of the best CNC controllers around for the hobbiest and I think even some of the big players are starting to take an interest in it.

Hood