Y Axis losing steps

[justgary]

All -

I had a curious thing happen this weekend and wanted to share it with you.

I'm still trying to figure out speeds and feeds for different materials, and have had to be more conservative at it than I wanted. I'm impatient, and why should I wait two hours if I can only wait one for a program? Anyway, after breaking a few drills and hogging an endmill into a block of aluminum, I have learned to wait. Someone else has already reported the slipping collet business; I now clean and degrease the tool holders and tighten the drawbar better.

Anyway, here's the story. Sorry if it's kind of long.

After much play with aluminum, I grabbed a bronze bar from the scrap box, and proceeded to turn it into little chips (that's ultimately what the machine is for). I noted very quickly that bronze is not aluminum, so I slowed the feed down. When I finished the roughing pass (with an end mill), I switched to a ball-end mill. I got some squealing, so I slowed the feed even more. I still got squealing, so I slowed the RPM, and everything settled down. Until...

I noticed that I heard extra bumping noises. And it got worse. I wanted to wait until I had proof, so I didn't stop the program. In this particular case, I had intentionally used slightly undersized stock, so the program was cutting air for a while (mostly in circles around a vertical rod). The next thing I knew, it cut a groove across the face of my part, almost 1/4 inch off! Proof enough. E-Stop.

It didn't take much to figure out that X and Z were fine, but the Y axis had a distinct problem, primarily in the minus direction. Very evident "bump" noises as the table moved. Another shot from the oiler didn't help (I try to give it a shot every few hours). The noise seemed to get better as I kept moving Y back and forth, but it didn't clear up entirely.

And the machine is only three weeks old. I re-read the manual about trouble shooting, and decided to swap the X and Y controls. Definitely in the Y axis stepper or ballscrew or something.

After a little more hand wringing over what to do, I decided to visually check the Y ball screw. I pulled the way cover screws and pulled the cover back and got a flashlight, only to discover that the screw was coated in incredibly fine bronze powder. Huh, and I thought that's what the cover was made to keep from happening...

I ran the table all the way out and cleaned the screw with compressed air, oiled it, and ran the table back and forth a few times. No more bumping!

Apparently, the rear way cover lives directly under the back edge of the vise, and coolant pours onto it (literally) by the gallon. My tiny steps had created very fine bronze chips that were able to slip between the table and the cover, even though the gap looks too small for even water to pass. I have run a bead of sealant across the top of the way cover frame at the table edge, and don't expect to have any more problems.

The front way cover has a sheet metal umbrella over it, so I didn't seal it. On thinking it over now, I probably will tonight. The gap on the rear side was tiny, too. Even though no coolant really runs to the front, who knows what might get through the front cover gap?

If you develop a Y-axis stepping problem, pull the cover and check the ballscrew. The tolerance is tight enough that very tiny particles will jam it and make the motor stall. Better still, pull the cover and clean the screw now, and seal the cover at the table before you have problems.

Regards,

- Just Gary

[keen]

Thanks for that Just Gary.

The screws and nuts obviously need to be perfectly clean and lubed well for the machine to be accurate and last well.

Any chips on there would be a disaster! Luckily for you the bronze may have not been hard enough to do too much direct damage. But the jamming sounds mean possible ball to screw or nut race scuffing or impact damage.

I have made a rear gaurd which redirects coolant and swarf back into the table - but still some splashes etc end up on the Y bellow covers. So I removed the rear one to check the issue today. I traversed the Y with a clean tissue in contact and inspected it under a glass - Luckily it was only oily and fairly clean. A faint grey colour probably caused by slight metal wear - but no larger particles.

Still I 'sealed' the end face back up with some Omega sticky wheel bearing grease - to discourage any stray coollant etc from heading in that direction.

Thanks for the warning! This is a really good example of how helpful the Zone and members can be.

[jalessi]

What about something like this to protect the ballscrew?

http://tinyurl.com/8md56z

[philbur]

Do you guys have the original or the new improved y-axis way covers.

Phil

[philbur]

The compressed length is 8". I think you will give up an awful lot of axis travel.

Phil

Originally Posted by jalessi What about something like this to protect the ballscrew? http://tinyurl.com/8md56z

[justgary]

Phil -

My machine is only four weeks old today. I presume it has the new way covers (they seem to have hard ribs).

Anyway, it's not the cover so much as the butt connection of the cover to the Y saddle. Even though the gap is very small, coolant and tiny chips do leak through. The Y screw is always directly under the spindle, so any coolant that leaks through the gap will fall on the screw.

I haven't noticed the problem since then, but it has been cold in my shop this week and I haven't really been out as much. I was out last night, though, and everything seemed fine (as long as I had the kerosene heater right next to my stool). I'm still nervous as I listen to it running.

The manual suggests that referencing the machine every time you turn it on is a good time to give the oiler a shot. I generally do that, and then again every few hours of operation. Still, the oil on the screw can "grab" the coolant and particles that fall down. The best way to stop it is to run a line of caulk along the way cover at the table edge.

Regards,

- Just Gary

P.S. I know it's cold where most of you guys are. It was 43F last night at 9PM when I went out, and was probably in the mid-thirties when I came in around 11 PM. Dang, those metal parts are cold.

Probably nothing to you, but it's a cold snap to me. I actually had to wear a jacket over my shorts, tee shirt, and flip-flops!

[jalessi]

Gary,

Just to let you know its minus -14 below zero here in Lake Villa Illinois right this minute.

If you count the wind chill at minus -27 below zero you would not be out in shorts and a tee shirt for very long.

SUCK IT UP DUDE.

Jeff...

[justgary]

Jeff -

At 14 below, I'd have to break out my special pair of thermal flip-flops!

Living south of I-10 has its distinct advantages... I played soccer at lunchtime yesterday in shorts and a tee shirt and actually sweated.

Of course, it's usually 100F and 99% humidity in August, and gets into the mid 80s at night. Everything sweats then, including the ways on machinery. Keeping rust away is a full-time job.

- Just Gary

[jalessi]

Gary,

The 10 stretches from Florida to California where are you located?

Jeff...

[justgary]

I'm on the Paradise end of I-10. I'm around the corner from Eglin AFB in the panhandle of Florida, about halfway between Pensacola and Panama City.

I tried the other end of I-10 (in LA) for a few years a long time ago, and although weekends were fun, the day-to-day life just stunk. Actually, it took 6 hours to get anywhere fun on the weekends, and when you got there only 50,000 people had decided to go have fun with you. So, I guess the weekends stunk too. People who were raised in it love it. Everyone from somewhere else hated it.

To be honest, I lived about 15 miles north of I-10 out there, so that must have been it, huh?

- Just Gary

[jalessi]

The beach in Panama City is very nice, I wouldn't mind being there right now as a matter of fact.

We lived in Studio City and Van Nuys for a while, I would not want to live in L.A. again.

I hate the winters here in Chicagoland, spring through fall is awesome though.

Jeff...