Speeds, Feeds, and Strategies for Bench Top Mills

[ChrisAttebery]

Bad bearing! BADDDD bearing!!!! Impressive. I haven't had any go bad in that manner. Usually mine have just started getting noisy.

[CL_MotoTech]

I have flat spotted rollers, just out right overheated them, filled them with swarf, but this is the first cage failure I have seen. We saw this all the time in our racing motors, so I am not new to this type of failure, but it was a surprise in my G0704. Being on the topside bearing, that's especially rare. I have a bearing above this too, so it's not like it's carrying the full load of the belt drive, in fact the belt drive is in double shear across the two bearings. The lower bearing looks great. At some point it was over heated, there is some blueing of the race, but despite that it shows little sign of wear. The rollers look great and the cage is fine. I changed out all bearings this time. I am not super happy with the tune of the spindle right now. I will continue to run it and tweak the lubrication and setup. Once i actually start to cut the true performance will be obvious... I have been very lucky with spindle performance lately, I hope to return to that.

[CL_MotoTech]

New bearings are in and running, albeit a spot hot. 10 hours of run time down, they haven't fried yet... At full hog the machine is insanely quiet. It blows my mind.

I was struggling a bit with surface finish before, tool chatter too. The new bearings have fixed all of those issues. That top bearing was letting go for quite a while it seems. I feel like an idiot.

[CL_MotoTech]

Cruising. The machine has been on since 3pm and will run through the night. In the morning I will setup two more billets for a final side Side A run. Once they are done, I will get the table setup for the side B cuts. Side B takes less than 10 minutes per gear.

I'm not crazy about my current spindle tune, but I think it will be fine if I do a slight adjustment on it. I just need a spot less preload. These things are so sensitive it's crazy.

[CL_MotoTech]

I started the final round of Side A's. The spindle is a little hot at around 140F. I am not going to play with it until after this run.

I am still running at 54 ipm with a 3 flute at 6k rpm for roughing. The machine is quiet as can be. This is probably the best surface finish I have ever achieved with this machine. I'll grab some more pics as I finish off these parts.

[ChrisAttebery]

What brand of bearings did you go with?

Here's a post from Forrest Addy on spindle bearing temps. They're talking about lathes in this thread but it all applies. I've learned more about machining by reading his posts than any other source.
https://www.cnczone.com/v...earings-81612/

I measure the temperature with a Raytech IR temp gun right where the lower bearing sits in the quill. I put a piece of masking tape there because the IR guns don't read well off of shiny surfaces.

[CL_MotoTech]

I think they are just the VXB house bearings. They were in plastic bags, no box.

I checked out that thread. I use an IR gun generally on the side of the head, but only do so after long runs, it takes a while to heat soak all that material. I was seeing right around 135F, too hot IMO. That aligns with the information in your thread. This is with a coolant ring, which definitely pulls the spindle temps down, so I am certain preload is too high. At one point I even smelled a bit of oil smoke, so clearly the internal temps are pretty high.

These are a spot tighter on the spindle than previous bearings and that makes adjustment just that more precarious. I use the old fashion calibrated elbow method for setup and frankly it's a crap method. I wish I could set them and move on, but I don't have any good ideas on how to do that yet.

This in mind, the new bearings seem to be okay for now.

[ChrisAttebery]

I like measuring the temp as close as physically possible to the bearing.

If you're having trouble setting the bearings try setting it like you normally do then tapping both ends of the spindle with a nylon faced hammer. Give it a couple good whacks and then check the drag again.

The Timkens I tried were tighter on the spindle than the NSK are. I had to heat up the lower Timken to get it in place. The NSKs just need hand pressure.

[CL_MotoTech]

The issue is that the last little bit of preload is so touchy. Tiny fractions of a turn makes all the difference. 1/30th of a turn can change the spindle temp 50 degrees. So no matter how hard I try, it almost always ends up being three of four tries before I get it right. Removing the drawbar, coolant ring, spindle pulley, it's not a hard process, but it takes time to pull it apart and then get it back together right. The drawbar can be especially touchy. If it doesn't get setup right then things get ugly real fast.

[ChrisAttebery]

Yeah that sounds like a lot of work. I can pull mine in about a minute now.

[steelcogs]

Honestly glad (in a way) to hear that I'm not the only one who thought the preload nut was super touchy. I've spent soo much time reassembling the spindle trying to get the perfect balance.

[CL_MotoTech]

It's not just you. My spindle is apart, again. I am going to revise the oiling setup. I also had my father weld up the PDB adapted spindle #1 (currently using #2), I am going to recut that on the lathe and hopefully get it perfect. 3rd time is a charm...

I have made a bunch of stuff over the law few weeks. Plenty of great results in there, but I decided to pull the table and carriage and clean the ballscrews and connect up oil. I never oiled these, I would just hit them with the grease gun annually. That seems silly considering I have an entire oiling setup already in place. The flushing has already begun. They are surprisingly smooth, I don't think contamination was much of an issue.

I am also redoing the table surrounds. I occasionally trigger the X and Y limit switches with chips. That problem needs to go away, so I am going to fix it with a much larger table surround. UCCNC luckily has no issues dealing with random limit triggers, I can clear the chips and hit cycle start and the parts come out fine. It's just annoying when it happens.

Also, when taking the table off I tested the amount of preload on the gibs. It was pretty tight, the table was unmovable by hand. They were too tight. I need to set them offline and then just leave it alone going forward. Snug is good, tight isn't. That said, the oil must be working well, because machining results were great, despite the overly tight ways. I am not very good at setting the gibs with oil, with grease they always had to be very tight because the grease would slowly distribute and they gibs would lossen. With oil, it's much more direct.

[steelcogs]

I also struggled a bunch with getting the gibs just right. I had real bad and unexplainable chatter issues when cutting steel in certain directions and the first thing it led me to was the gib adjustment. It's been a long time since I've messed with them but if I remember correctly the table was too tight on the ends (the gibs that tighten the table to the saddle) and probably not as tight as I'd like towards the middle. Normally this would make sense to me since that's a typical wear spot but my machine has not much time on it. But I'd gradually tighten the gibs and run the table back and forth until my clearpath servo stalled then back off. I haven't really been able to test steel again since then since I've been dealing with motor issues and I'm making a new control cabinet but I'm hoping I can get it all figured out in time. Gibs really seem to be one of the finicky things with these machines. Everyone seems to have their own different story on struggles with them lol.

[CL_MotoTech]

I wish I had gone with servos for this build, I imagine they are much easier to deal with in the long than steppers. There's nothing more annoying than losing a part to lost steps. I don't even care if servos are faster, I am however tired of randomly losing steps.

I actually replaced my table because the old one was so tight on the ends/loose in the middle. This one is much straighter even after a year of heavy use, presumably because of the oil system wear has remained pretty low. It would be cool to have the ways hardened on a table, though who knows if the type of cast iron the table is made of would even lend itself to the process. I guess the alternative is to lop the ways off and install linear rails, that's probably the best option assuming one has access to machine tools to facilitate the process. I of course, do not have that access.

[cncuser1]

CL: Scraping the ways can remove uneven tightness in the travel.

[CL_MotoTech]

I don't really have the desire to learn scraping. I guess that's where I draw the line on this project? I'd much rather pay somebody to do the machining to install linear rails on the machine. That would solve most of the issues I have with my G0704 rather swiftly. Anybody here up for doing the work?

[CS900]

I don't really have the desire to learn scraping. I guess that's where I draw the line on this project? I'd much rather pay somebody to do the machining to install linear rails on the machine. That would solve most of the issues I have with my G0704 rather swiftly. Anybody here up for doing the work?

how big is the table itself? If it fits on my PM45 I could probably help out.

[CL_MotoTech]

26" by 6". The column could be longer. Getting it all square would be the trick to it all, especially considering it's seen a good bit of use.

I got oil to the ballnuts, cleaned everything up, reset the preload on the AC bearings. I can move the table by turning the ball screw with my fingers. The ways are reasonably tight too.

The new table surrounds is fabbed up. Tomorrow I'll clean it and paint it. It's a beast, but I think it's going to work awesome. I will add some supports from the table to help hold it up, hopefully I can slide vises around on it without damaging it. I added a new Y axis chip guard on the proximity sensor too.

[CL_MotoTech]

I've got a little more playing with this surround but it's effectively figured out. I don't anticipate any major changes to it. I didn't quite get the one support bracket built out exactly perfect. I did it all by hand, not a bad way of doing it, but I didn't have a mill to do the work... Otherwise it's really nice and solid. There won't be any issues sliding around vises on it. I used truck bed liner paint on it. I wish I could fit it in my powder coat oven, I probably would have coated it silver. Alas, I ended up with the primer gray. I tested the truck bed liner on a piece of steel in a bucket of coolant for a few days and it held up fine. A lot of paints I have used tend to soften with coolant I have noticed, lesson learned. The entire thing bolts down with 11 buttons heads. To disassemble it takes just a minute or two. The button heads on the leading edge fit in the cavity of my vise, but they are above the table slightly. I can pull a bolt if I need to position my vise or accommodate another fixture, so it shouldn't be an issue really. Otherwise the entire surround sits slightly below the top of the table.

Right now, i'd say it's a job well done. The ways stand a pretty good chance of staying cleaner than my old rag tag system, and I don't see much chance of triggering the proximities with chips after this. Of course, I will have to make some serious chips to see if it works.

[CL_MotoTech]

I had a little breakthrough on these VXB spindle bearings. The inside race is too tight on the spindle. So after pulling off preload, the bearing doesn't actually move. I had to stick it in the press and move it to reduce preload. It's down to 8 degrees of climb in 10 minutes. Peak temp got to just under 90 degrees in 70 degree ambient. This is likely why my cheap bearings were so easy to adjust, the upper bearing was rather loose on the spindle. Assembly was easy. These new bearings took a lot more force. Anyways, on to machining!