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DoAll 612 randomly decides to cut an extra .002 deep on just one pass.

Labrat

Aluminum
Joined
Apr 20, 2012
Location
Virginia
I have a new-to-me DoAll 612 surface grinder. It works real well except every now and then it decides to cut about .002 deeper for just one pass then return to normal, leaving a nice low spot on my chuck right in the middle of me taking off that last .0001.

It only happens when I traverse from left to right. It only happens when I travel right up to the left stop (but not bumping into the stop).

As a workaround, every time I see it starting to do that, I get back off the chuck, move the Y until I can move left and right cutting air behind the chuck, then come back to where I was and continue where I left off.

The only thing I can think of is a piece of grit is getting into the ways and lifting the table. Do I need to tear this thing down and give it a good cleaning? Or can I just keep the oil flowing and hope all the dirt works its way out? Or is this something altogether different?

FWIW, this machine is showing multiple signs of a retarded prior owner, including a chuck that was .009 out of parallel with its travel, a bone dry reservoir in the oil pump, a 120 grit wheel that had never been balanced... I'm a total newb to grinding, but come on.
 
I have a new-to-me DoAll 612 surface grinder.

It works real well except every now and then

this machine is showing multiple signs of a retarded prior owner

Do I need to tear this thing down and give it a good cleaning?

QED

about that hop - is this hydraulic auto feed, auto increment? Or is it a manual grinder?

smt

non sequitor: my D1030 came out of VA, really WVA since it is the spur that includes Bergton. Kid brother who lived there bought it for me.
 

Yeh, I see I practically answered my own question there.

It is a manual grinder.
About the hop, I've screwed up numerous times and caused wheel hop. I've done a lot of reading, watched some youtube videos; I'm getting past that. (I bought this machine a month ago and have never operated a surface grinder prior to that.) I'm reasonably sure this isn't hop. It only happens after I move back onto the chuck moving left to right after having made a full pass from right to left. Since I know that is where it happens, I move darn slow so I can detect it on the first .100 of travel instead of going a couple inches causing real hop which digs in another .005 or so. The few times this happened, I went ahead with the pass anyway - just going slow enough that it doesn't hop, it cut just like one of the roughing passes except that it tapers back to the plane that all of the other passes were at - usually by the time I get about half way across. Then its cuts normal again.

More non-sequitor: Small world. I grew up near Corning. I heard Hardinge is moving operations back to Elmira - is that true?
 
Could be a little sticky in the vertical column Just a quick guess.
A little too much clearance in the vertical slide.
A change when you change the cross direction to come back on the part can be a tad of end play in the bearing pre-load.
I have seen that with a ball was rack not tight (very rare).

Oh, and with changing wheel cross feed direction the wheel load changes from more loaded to less loaded.

*I make a practice of returning to the start position with the cross and only cross travel on the part in one direction.

If needing to mid start, I mid start there with going the same direction as the beginning start.

What are you calling hop?
 
What are you calling hop?

I'm becoming less sure that I know what hop is, but if I take too heavy of a cut, the machine seems not rigid enough to handle it, makes sounds that make me pucker, the wheel seems to bounce as it goes across making divots in places and not getting the full depth of cut in others, and doesn't cut right again until I dress the wheel.
 
That could be the hardness or grit size of the wheel. Could also be the speed of long travel across the part or the cross amount.

The wheel is like a mill cutter so if you push it too hard/fast it will chatter.

Wet grinding there is little way to tell, dry grinding you see space between the sparks or sparks being
almost solid.

Almost solid trail of sparks gets near that maximum the wheel can grind.
 
My guess is the wheel head is moving up and down by itself. Test the down feed with an indicator--grinder and wheel stopped, indicator attached to the wheel head and indicator tip touching the chuck, feed down and see if wheel head moves down the full amount, repeat. after a few repeats see if you can push the wheel head down enough for it to stay down.

It may be sticking on the ways or on the down feed screw and you are getting a stick-jump. cleaning and lube may help.

I believe the weight of the wheel head is mostly responsible for the downward force.

Lost
 
Long ago a buddy had manual G&L that would do this... grinding along just fine and all of a sudden would just dive into the work. Replacing the spindle bearings solved the problem.
Dennis
 
I heard Hardinge is moving operations back to Elmira - is that true?

Seems to be. Would be a nice fantasy to have (perceived?) "banksters" start bringing manufacturing back to the US.
Hardinge sold all their production facility at the auction a few years before the buy-out, except for some niches like spindles still being made here. But the machining cells, tooling, large inspection tooling, and various way grinders were gone. So making machine frames here with ways, suggests some investment.

I have a B & S mechanical auto surface grinder that before i scraped it would sometimes have the effect you mention. The Z ways (table in/out) were so bad the location was not positive, and the saddle could shift to be a little higher or lower depending where it was on the banana ways. I cured that by re-scraping the whole machine.

After that, after a while, it started doing it rarely, mostly on auto table traverse. It was riding up on the shifter ramp at the left end. I lowered the axle, and then made a new axle and lowered the pinion shaft as well, with new bushings. It was slopping around enough to sometimes push up on the rack. I had lowered (raised) the rack after scraping, but probably not enough. That grinder had a lot of wear.

Try shaking things around on the column to rule out what the other guys mention.
However, with the amount of wear you describe, and the way the issue manifests, i'm more apt to suspect something in the table ways/rack/pinion interface. Possibly even just long neglected mounded up swarf/dirt.

Consider also that on a well worn grinder, the the table saddle ways wear to be crowned, and the bottom of the table ways themselves become hollow in the middle. So going back & forth, the ends of the table rise at the end of the travel each direction. At this point, the table usually becomes somewhat unstable on the variable geometry ways, and can shift, slide & wiggle a bit. (whether you see it visibly or not without an indicator) Combine that with the Z ways banana wear the other direction, & there is easily enough slop at the extremes for a thousandth or couple of unpredictable height vagary "depending".

smt
 
i should take off the table and see if it rides on the ways or maybe on something else (from wear).
 
This same thing happened to me using the same grinder. It the time I thought the wheel had slipped and was no longer concentric with spindle. I'm rethinking that.

One test you could do is lay a 12" long parallel on the table and sweep it with an indicator. On my grinder the middle 50% of travel is with in .0002", One end is out by .002 vertical and horizontally. The other end was out by .0015". I guess it does not always ride up the same way each time.

Vince
 








 
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