Re: KMB1 Conversion - CHATTER
The KMB1 is starting to develop some chatter when profile cutting in the Y direction. It doesn't matter which direction, and it doesn't matter if its conventional or climb milling. My first thought is something is bad in the X axis lead screw assembly. Either the ball nut or the bearings.
Then I wondered. Hoped more likely that maybe I just need to adjust the gibs. I have never adjusted them, and to be honest I never considered whether or not the previous owner ever did since I bought the machine from a third party on behalf of his widow.
Now how to adjust the gibs. Hmmm... The X axis seems pretty straight forward. There is a visible screw at each end of the gib. Not sure how to get the feel for it though. On my little machines I can disconnect the lead screw and push the table around by hand, but the table on this thing is significantly heavier than that. Then there is the Y axis. It looks like the gib and adjustment screws must be hidden under the wipers.
Re: KMB1 Conversion - CHATTER
Adjusted loose (I loosened it to make sure) the Y-axis drew almost 3 amps. Across the range of travel with less variance from ends to middle. Both of those were expected since the Y likely sees less travel than the X its likely to wear less. Since its heavier its loose gib current should be higher. I adjusted it to bracket 4 amps as well, although due to the heavier weight it might have needed to be a little higher. Its 4 amps median current across the range of travel its got less than a 1/4 amp of variation.
I don't know if this really is the correct way to adjust the gibs on a CNC Mill, but it sure makes sense. Obviously a lighter machine would require less current and a much heavier machine would require much more, but the principle makes sense.
Now to see if the chatter has improved. Well, after I make a new rear Y-Axis way cover. I still think its likely a problem in the X -axis lead screw assembly, but I have my fingers crossed. Especially since I have a few more 4140HT parts to machine for the current job.
One thing seems odd. I see less dither on the servos. I think the looser gibbs might have been causing it to over shoot from the mass of the table and saddle. Dither was never really bad (even on the scope it seemed acceptable), but sometimes I'd hear it for a for tiny fraction of a second on a stop with the spindle off. During testing right now I didn't hear it even once.
Thinking About Scrapping It Out: KMB1 Conversion
I retrofit it, and I rebuilt it, and I repaired it many times. It still functions, but its in desperate need of repairs again. Both the X & Y have excessive backlash. The Y is just old and worn out, but the X probably needs a whole new ball screw assembly. In the middle of a job it went from about .001 backlash to about .035 backlash. I'm sure could sell the servo motors and the quill easily enough. The rest, who knows.
I had been still using it for roughing blanks for use on the smaller machines. Basically entering code one line at a time to do functional manual milling using conventional only to take up backlash and measuring the parts. Its usable that way. I'd been using it that way for quite a while. Here is the thing though. I can slightly more easily do that same job on the new (last year) South Bend knee mill and it will make cuts the Hurco will balk at, choke, chip weld, and break an end mill trying. The South Bend has a modern 3 phase 5hp motor being powered with a 7.5HP VFD proper power and current program for the motor. It gives me pretty darn close to a real usable 5HP based on some of the crazy cuts I've made with it. Trust me when I say I do more work with the manual knee mill than with the CNC knee mill now... because its just faster.
Basically every time I fix its more than a minor little thing, and it works great for a couple months until something else craps out, and I just don't use it. I've got two smallish lathes I could put there and get more use of the space and take up less space. I do use the lathes, although the smaller one may also be on its way out if I don't decide to CNC it. On top of that I am working on a bridge mill that will do more of the type of work I do on a daily basis, and at the moment I do not have a place to put it. Of course power in my shop is an issue as well. When I built the shop it was just supposed to be a warehouse. I figured the 100 amp sub panel I put on it was way overkill. Well, now I am constantly bearing in mind that electrical capacity budget in my head while running machines. What the peak "could" be and what the real load "probably" is. If I eliminate the Hurco I can use its electrical budget allocation for the new bridge mill I am building.
I don't know. Just thinking. Just another one of the thoughts that probably kept me out of the good schools.