# Cheap mill abuse...don't choke



## Shotgun (Nov 10, 2020)

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 (Nov 10, 2020)

Resourceful


----------



## Lo-Fi (Nov 10, 2020)

Looks pretty dark good to me! Like it.


----------



## Shotgun (Nov 10, 2020)

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 (Nov 10, 2020)

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 (Nov 10, 2020)

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 (Nov 10, 2020)

graham-xrf said:


> 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 (Nov 10, 2020)

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


----------



## addertooth (Nov 10, 2020)

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 (Nov 10, 2020)

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


----------



## Cooter Brown (Nov 10, 2020)

Is that step at the end of the table showing how much you had to grind off? It looks like almost .150"


----------



## C-Bag (Nov 10, 2020)

Shotgun said:


> 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.
> 
> ...


I look forward to seeing what you find at the end of the process.


----------



## f350ca (Nov 10, 2020)

If the wheel will cover the whole surface in one setup it should work. As said no different than surfacing a mag chuck on the surface grinder. I also surfaced the table on the shaper, using the shaper.

Greg


----------



## graham-xrf (Nov 11, 2020)

f350ca said:


> If the wheel will cover the whole surface in one setup it should work. As said no different than surfacing a mag chuck on the surface grinder. I also surfaced the table on the shaper, using the shaper.


Greg - I get it that a wheel that covers the whole surface in one go is best, like when the top of an engine block is reground, but what is the likely result of using a smaller wheel in two passes?

You should see the two pattern marks, but would there really be a significant "step" where the second pass overlaps the first?


----------



## f350ca (Nov 11, 2020)

I meant doing the whole table end to end without swinging the head to reach the ends. Don't think my Bridgeport clone has enough table travel to do it. 
When I did my shaper table I had to use a carbide cutter to avoid wear going across, but could stroke front to back without resetting the ram position.

Greg


----------



## Shotgun (Nov 12, 2020)

f350ca said:


> I meant doing the whole table end to end without swinging the head to reach the ends. Don't think my Bridgeport clone has enough table travel to do it.
> When I did my shaper table I had to use a carbide cutter to avoid wear going across, but could stroke front to back without resetting the ram position.
> 
> Greg



The big issue with using one large wheel to cover the whole table is getting the tram right.  First of all, that ain't easy on a round column mill to begin with.  And then, at least initially, what are you tramming TO?  Which part of the bowl  If that big wheel is cocked sideways, I'm going to be grinding another bowl into the table.

What I've done so far is to take it down so that I have -.001 in one or two small spots, .002 across most of the table, and .003 on one high spot at the front of the table. All measurements are relative. That is much better than it was, so I trammed the mill again, taking the height differences into account.  I took and recorded measurements at four corners ( right front, left front, right rear, left rear), with a circle that approximates the bolt circle holding the colum.  Then I left the indicator, and moved the table under it to each spot.  That gave me the relative level that each tramming position was indicating off of.  A little math, and I had the number that each bolt position on the column base had to move up or down.  Since the position of my measurements matches the position of the bolts, the calculated values are direct readings.  I use a feeler gauge set for shim.  If the position had a .022" shim in there, and I need to go up .002", I swap it out for a .024".  I use a pickup magnet to pull the previous shim out.  That way, I don't have to leave the shim sticking out.  Each leaf of the gauge set is enough for three shims.

With the newly trammed head, I'm running the grinder again.


----------



## Shotgun (Nov 12, 2020)

How I mapped out the table. Running it around under an indicator.  The fractional parts of the numbers are somewhat of a guess.  "It wasn't on a mark, but closer to one than the other" sort of guess.


----------



## Shotgun (Nov 12, 2020)

addertooth said:


> 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.


The gibs are tight, but I'm going to crank them down till it is difficult to move the table and then run a test.
The thing that would argue against it would be the "waves".  Mapping out the whole table, there were high spots in the middle, and it was not symmetric from side to side.
Really, the table was a basket case.


----------



## Shotgun (Nov 12, 2020)

Cooter Brown said:


> Is that step at the end of the table showing how much you had to grind off? It looks like almost .150"
> View attachment 343711




I think that is an artifact of the lighting.  There is definitely a step, but not that much.


----------



## Shotgun (Nov 12, 2020)

graham-xrf said:


> Greg - I get it that a wheel that covers the whole surface in one go is best, like when the top of an engine block is reground, but what is the likely result of using a smaller wheel in two passes?
> 
> You should see the two pattern marks, but would there really be a significant "step" where the second pass overlaps the first?



You'll be able to see the two passes if the angle of the light is just right, but you won't be able to feel or even measure it.  The final passes are made slowly, with just enough pressure to barely hear the wheel touching.  If you're one of the lucky who still have some, you can comb your hair in the finish.


----------



## MrWhoopee (Nov 12, 2020)

I'm fascinated and impressed with what you've been able to accomplish so far. This is a lot of top speed operation, has there been any noticeable heating in the motor or spindle?


----------



## Shotgun (Nov 12, 2020)

MrWhoopee said:


> I'm fascinated and impressed with what you've been able to accomplish so far. This is a lot of top speed operation, has there been any noticeable heating in the motor or spindle?



Haha!  Yeah the motor started warming up last night.  I got greedy yesterday morning, and fed the disk down too far.  It was making good sparks, but it ended up tripping the breaker. For the most part, I've been taking it in short runs so as not to heat the table.  Now I'm at the point where I'm making extremely light passes.  Just enough to hear the disk scraping on what I suspect to be the low spots, and just an occasional spark on what I think are the high.  So, there isn't a lot of load on the motor except for the system drag.

I haven't even thought about checking the spindle, though.  Of course, I had just taken it apart, cleaned and greased it last week.  I would have waited if I had thought I would be doing this.  I'll be repeating that process once I'm done here.


----------



## pontiac428 (Nov 12, 2020)

Steady as she goes.  I see this process as looking a lot like using a tool post grinder, where a relatively flimsy setup holds a wobbly, vibrating grinding disk and work is done slowly- to good result, because the grinding disk ultimately does make contact in plane.  I'm also interested in seeing what you can achieve with this method!


----------



## Shotgun (Nov 13, 2020)

It should be noted that I'm learning on the job here. The lesson for last night was how large a role temperatures play on this game.  The attached picture shows the layout of measurements right after grinding (black), and after sitting for over an hour (blue).

The other thing I'm learning is that I need to switch over to the indicator to map out the table more often.  I'm thinking I may have already done more grinding than necessary if I had been more methodical about measuring before cutting.


----------



## MrWhoopee (Nov 13, 2020)

Shotgun said:


> It should be noted that I'm learning on the job here. The lesson for last night was how large a role temperatures play on this game.  The attached picture shows the layout of measurements right after grinding (black), and after sitting for over an hour (blue).
> 
> The other thing I'm learning is that I need to switch over to the indicator to map out the table more often.  I'm thinking I may have already done more grinding than necessary if I had been more methodical about measuring before cutting.



I think you are doing an outstanding job given the tools available, regardless of your level of experience. 

This is a great lesson/example of how higher degrees of precision multiply the difficulty. Without higher precision equipment, hitting .0001 is not just 10x harder than hitting .001.


----------



## Cooter Brown (Nov 13, 2020)

Are you using any kind of coolant while grinding the table?


----------



## Shotgun (Nov 13, 2020)

MrWhoopee said:


> This is a great lesson/example of how higher degrees of precision multiply the difficulty. Without higher precision equipment, hitting .0001 is not just 10x harder than hitting .001.



I'm thinking this might have gone better if I had used a conical grinding wheel.  I think there is some flex in this wheel.

Cooter, I was using some water based cutting oil initially, but it mixed with the grinding dust to form a paste that clogged up the disk.  In fact, another lesson learned last night was to clean the disk with some degreaser periodically.  When it clogs, it just pushes around, rubbing the top, leaving a mess of grind marks.  5 minutes of scrubbing the face with deagreaser and a tooth brush, and it cuts to a mirror finish.


----------



## MrWhoopee (Nov 13, 2020)

Shotgun said:


> I'm thinking this might have gone better if I had used a conical grinding wheel.  I think there is some flex in this wheel.
> 
> Cooter, I was using some water based cutting oil initially, but it mixed with the grinding dust to form a paste that clogged up the disk.  In fact, another lesson learned last night was to clean the disk with some degreaser periodically.  When it clogs, it just pushes around, rubbing the top, leaving a mess of grind marks.  5 minutes of scrubbing the face with deagreaser and a tooth brush, and it cuts to a mirror finish.



Yes, ideally a cup wheel would be the choice.

Perhaps plugging the drains and filling the t-slots with water would help to absorb the heat from the metal without actually wetting the grinding disc.


----------



## Lo-Fi (Nov 13, 2020)

Think I might try this with my Bridgeport table. It's had a few "hot suppers" and been left to rust at odd points in its life. Loving the surface finish you've achieved!


----------



## Shotgun (Nov 13, 2020)

MrWhoopee said:


> Perhaps plugging the drains and filling the t-slots with water would help to absorb the heat from the metal without actually wetting the grinding disc.



That picture I posted of the measurement differences between warm and cold. . .well, the warm was "slightly warm to the touch".  I don't know that water would do anything other than make a mess.  Maybe it might catch some of the grit?

Anyway, I don't have drains.  I'd have to sponge it out afterwards.

I did a few passes at lunch, but first I ran a diamond dresser across the face.  Put the dresser in a vice, set it on the table, then ran the table across the bottom of the disk.  It cut much cleaner, scalping the section I had measured to be high spots, and leaving the sharpy on the place I measured to be low.


----------



## Shotgun (Nov 24, 2020)

Lessons Learned:

Maybe I should have named this thread "I had to destroy my mill to save it"?

Warning:  Don't try this unless you have time for your mill to be down a week.  This is a SLOW process.  But, maybe this will speed things up for others that might attempt it.

First of all, do NOT use the grinding device that I showed previously.  This device is meant for a hand angle grinder, and is thin.  The one pictured is 1/4".  It flexes.  Imperceptibly so, but if you use one and then switch to a cup type grinder, you'll see that the "pad" will leave crowns on the table.  With enough pressure for it to remove material, it will flex down into the slots, and then back up.  We're looking for tenths accuracy across the table, to the thousandths that it is flexing is a big deal.

That said, my table started out with a wave pattern that had crests on both ends and the middle, and from front to back.  The max differences were about .0006.  I now have it down to .001 across the table (except for one bad spot where I screwed up.)  I'm taking one more pass today, because I think I can get closer.  Follow this process to get it done ASAP (which is still a really long time).

1) Mount a dial or drop indicator to the quill.  The indicator should have a resolution of at least .0005.
2) Run the indicator across the table, using a sharpy to mark the reading every few inches or every time it centers on a mark.
3) Connect matching readings.  You'll end up with a rudimentary topological map.  Color in the high areas with the sharpy.  I just filled it in with slashes.  Fill the next highest areas with a different color sharpy.
4) With the cup grinder in the quill, bring it down to the cup just makes the barest of a scraping sound as you move the high spot under it.  Do not bring the grinder down a stationary table.  Do not get greedy and try to cut more at once.  Listen very carefully, and stop dialing the quil down as soon as you hear the first scrape.
5) Now very slowly move the entire table under the grinder.  If you did step 4 correctly, you will see that it skims off the markings on the high area, and makes the next highest fade a bit.  With the flexible pad I started with, everything would get erased.  With the cup, you can see where the high spots are scalped off.  The meaurements in the low spots won't be touched.
6) Take a break.  I mean, go to bed.  Leave it alone.  Don't touch it.  Go talk to your significant other for a change.
7) Wake up, have a cup of coffee, then repeat steps 1-6.  You're remeasuring again, because while the cup is an order of magnitude stiffer than the pad, it still flexes.  You'll see that the high spots are reduced, but they're not completely flat.  You're taking a break, a LONG break, because that table heats up as you're grinding, completely changing the measurements.  I've noted up to .001 difference between measurements taken immediately after grinding, vs the next morning.  What's worse, it expands at different places depending on how much grinding work that spot got.  The high spots will read higher than they would if the table temperature has a chance to equalize.
    This localized heating can work to your advantage in the initial stages. The table will rise up at the high spots to meet the grinder, because the grinder is heating.  But, it is a feedback loop.  If it rises up too fast, the grinder really goes to work on it, forcing it to rise up faster, causing the grinder to work harder, then it starts throwing sparks all over the place, followed by you panicinc to switch the machine off, and when you get up the next morning you have a new low spot, and the world has new curse words that you just invented.  I now know a lot about low spots, run-on sentences, and curse word creation.
       Anyway, you might safely be more aggressive in the beginning, but as you start approaching truly flat, you'll want to be barely skimming the surface and giving the table longer breaks to cool.  Five tenths will be a deep cut.  Also, as it gets flat, pay particular attention to the feel of the cranks as your turning.  I noticed that the force necessary to turn the crank was noticeably different in the high areas.  It wasn't "difficult", but I could definitely tell that it took move force.  I let that help guide me to places where I'd make multiple passes.  The force doesn't seem to drop during those multiple passes, possibly because the warming table is coming up to meet the grinder.  Use the turning force as as a hint, but don't try to grind everything to an equal force in one session.  The cup sound is also informative.  You can definitely hear when it is working, up to it making almost a bongo drum like sound when it is really digging in.  Reduce the DOC if you hear that.


I will post a picture of the final table results later today or maybe tomorrow.  I'm waiting for the table to cool.


----------



## pontiac428 (Nov 24, 2020)

Just curious, because I totally understand the DIY approach, but did you call around to local shops and get a cost estimate for a blanchard grind or even a surface grind on the table?  Considering what it costs to do multiple precision processes on an engine block, I can't imagine it would be more than a couple hundos to get surfaced once you find a shop with the capacity to do it.  Your table is about the same size as the deck on an inline 6 commercial diesel, so there should be a shop in every industrial area in the country with the capability.


----------



## Shotgun (Nov 24, 2020)

pontiac428 said:


> Considering what it costs to do multiple precision processes on an engine block, I can't imagine it would be more than a couple hundos to get surfaced once you find a shop with the capacity to do it.




My budget for this job was $10.  I blew it out and spent over 20.   She who keep the wallet (among other things, apparently) would not be happy with a couple hundred. Though, that certainly is a good idea.


----------

