Cheap mill abuse...don't choke

[Shotgun]

My mill table was shaped like a bowl. I think it was shipped that way from the factory. It's a round column mill, and the pattern is what you would get from letting a block get too hot will grinding. The center swells from the heat more than the sides, the grinder cuts it flat in that condition, and then the middle sinks like a souffle after it cools back down. The sides were .006 higher than the middle, with several swells and dips. Well, I don't have the money to keep buying accessories AND send the table out to be reground, sooo.....

Got an 8" grinding wheel made for an angle grinder. It has a 7/8"-11 arbor, so I cut a 2" piece of a bolt off my homemade steadyrest, and turned one end to fit in my ER32 collet. Lowered the head all the way down, and mounted the disk. It didn't tram, so I had to knock off the top of one side of the disk's arbor. The nut in the disk registers against the bottom of the collet, and removing a little material from the nut forces it to cock in the correct direction.

Cranked the speed up to the highest it will go, brought the disk down to make sparks on the high spot, and slowly start moving the table around. When it stops making sparks, I lower it about half a thousandth. So far I have a mirror finish, with just a few small places that are still making sparks. You can also tell a spot is high by listening for the wheel contacting the table. Go over the louder portions a few times, even with no sparks, and they will quiet down.

So far, I have a mirror finish on the table top, and grinding dust everywhere else. The next step will be to disassemble the table and power wash it.

 

[Aukai]

Resourceful

 

[Lo-Fi]

Looks pretty dark good to me! Like it.

 

[Shotgun]

Surface plates, bluing and scrapers would have cost hundreds. This thing cost me less than six bucks. I go out in the morning and run it across the table several times, then come back in the evening and do it again. Give the table time to cool and settle. I've been at it since Sunday morning, and I think I'll be done this evening (Tuesday).

 

[graham-xrf]

No choking, nor spluttering at all - it was all just logical, and well done!

In this case, you were not trying to work directly on the ways. Instead, you just used their primary property to re-work the table surface, as if it was a workpiece. Surface plates, bluing and scraping were surely never necessary!

I guess you could hang an indicator over it and move the table underneath, in sections, and discover how it tracks over the ways, if you feel the need to. You could also use a sensitive level moved in increments to plot it, again only if you feel the need to. If the level reads the same while being advanced half it's length in stages along the bed, you can plot the ups and and downs. It helps to be exactly level to start with, but not mathematically necessary. Most folk level up the mill when they first set it down.

Definitely a low cost fix, but surely so obvious that others must have done some variants of this before.
If there are downsides, I am sure the folk here will let us know.

 

[Ulma Doctor]

folks often grind their surface grinder chucks.
the principle of using the tool to grind itself is not new, but it sure works nice!

 

[Shotgun]

I guess you could hang an indicator over it and move the table underneath, in sections, and discover how it tracks over the ways, if you feel the need to.

That's how I uncovered the problem in the first place. I'd been trying for two weeks to square an aluminum block a couple inches per side. The closest I could get was .016 runout across every face. My best friend, a machinist, came over to help me out. He first had me clean up the ways with a diamond honing stone, and then the table and the vise. Still couldn't get the vice square. The bottom of the vice was off by sever thousandths.

So, I stuck the indicator I use for tramming on and ran the table back and forth, marking the measurement right on the table every few inches with a sharpy. It only took a few minutes, and the numbers showed a clear pattern of "wavyness". Steadily increasing then decreasing, but mostly dipping in the center. I'm going to do the same thing when I think I'm done to prove it out.

 

[markba633csi]

That's the nice thing about beater machines, you get to experiment, and not a lot to lose.
-m

 

[addertooth]

If the ends are high, there may have been a non-grinding answer for that problem. If the Gibs are loose, AND the table is cranked far (left/right), the weight of the table hanging out with no base support can "lift" the end under the head. At first glance, it would look like the table was ground low in the middle, and high on the ends. If you tighten your gibs, and the center becomes the "new high spot", then loose gibs were your *original* problem.

 

[martik777]

I used a similar wheel to make parallels from hardened stock or for DIY surface grinding