Another Mitsui grinder thread - spindle chatter?

Hi guys,

We've got a MSG200 6x12 grinder in the shop that came out of a toolroom. My problem is I get horrible finishes with it. I've never worked on grinders before. I have tried several wheels and get the same results, bad chatter even with.0005 cuts. Hard or mild steel. Wheels have been trued on the machine with a diamond as usual practice. Chatter gets worse as the wheel is used. Ive tried norton pink 80 and 100 git wheels and i think it has a 60 grit camel wheel on it now.


Where should I start?

Thanks in advance!

Chris

Chris,

If you have a 46 grit wheel, start with that. It will be a lot more forgiving for you to learn with.

As far as the chatter, make absolutely sure your wheel is tight and fully dressed. Hjt the wheel with a piece of graphite and then dress it. When you think it is dressed, shut it off and make sure all the graphite is gone from the diameter.

I have seen a beginner mount a wheel not tight enough, and fail to dress it fully. You might think its dressed but in reality you still have to take a lot more before it is true.

So make sure your wheel is tight on the hub, and make sure it is dressed true all of the way. Lightly feel it with your finger too, youll feel if it is running true.

If you do all of that right, then investigate the spindle. Put an indicator on the spindle and check it for runout and radial play. My mitsui has almost .0003 of runout and i can get a decent finish, fyi.

The next thing to check would be related to the table.

Alex

Alex,
Is the runout because of bearings, or bent spindle?
If bent, could you lightly dress the spindle insitu ?

Dan

maybe bad bearings

Agree to try a 46 wheel as the 80 and 100 are very fine. Still they should give a smooth finish going across .0002 with a fresh new facet diamond dress for a few passes..
If a ball way machine balls or ball ways may be dirty or shot.
Agree listen to, and indicate for loose at spindle bearings for up and down and in and out..( you will get some with moving the whole spindle head so don't consider that)Spindle can feel tight and still be bad... finding reasonable would clean balls and ball racks.

I read the grizzly surface ginder rebuild thread late last night and picked up a few tips as well. I ordered a 46I wheel and a new diamond. The shop has one of those adjustable Hi-Lo diamond mounts, is that acceptable or should I make a 15deg rigid block?

Should I be dressing on the 7 O'clock position with the diamond facing into the wheel rotation, or at the 5 O'clock with the diamond going with the wheel rotation? I know it's basic, but I'm pretty much self taught and it's a good way to pick up bad habits!

What about the wheel flange, I've not pulled it from the machine, could that cause a problem? I guess if it's dressed it should take any eccentricity out correct?

How do I check the bearings? Am I looking for end play or radial play (or both) I have a tenths indicator and a good mag base. I've never had this problem with a grinder before. Last shop I worked at had a 8x18 chevalier that would grind a mirror...I figured a Mitsui would make that look bad!

Thanks!

Chris

50BMG DUDE said:

Should I be dressing on the 7 O'clock position with the diamond facing into the wheel rotation, or at the 5 O'clock with the diamond going with the wheel rotation?

Click to expand...

The tip of the diamond dresser should tilt with the wheel rotation. 10 or 15 degrees off radial/perpendicular is typical. It doesn't matter so much what o'clock position you use. This is a safety precaution, not a dressing performance issue. If you accidentally cram too much of the wheel into the dresser, it will tend to deflect away, rather than plunge deeper into the wheel and tear out chunks.

If you're using a dresser mounted on the chuck, lock the table X axis.

Regarding the chatter, make sure you've snugged the wheel securely to the wheelmount hub. If the wheel can move around, it may become unbalanced after dressing, or even be impossible to dress properly in the first place. Also inspect the hub internal and spindle exterior tapers to make sure there's no burr or dirt interfering with a proper hub installation.

[adjustable Hi-Lo diamond mounts] Make sure it is dead flat on the bottom. Yes make a flat bar dresser with the hole at 10 or 15* about angle, perhaps 1 1/5 wide 4” long so you might slide it on a bar off a angle plate for angle dressing on the table. Set diamond a little past 6:00 on the go side. As sfriedburg said wheel should fit hub close to the mount so less out off balance. With wheel hub off the spindle should feel smooth running,, then with mount on should still feel smooth.
*How does the table movement feel with hand on chuck just using long travel (*with spindle off)?
What does the grind look like with locking the long travel so it can not go more to the left and then taking a grind with just using the cross feed for a .0002 per pass with a fresh dress wheel?

If you have room you can mount the hi-lo on the mounting pad.. then get right down close to chuck height. Hi-los can be a little tippy so take care how you use it.

Chris,

Chatter is a monster of a subject as there are just so many different causes of chatter, some of which are:

An out-of-balance wheel
An out-of-true wheel
A bad belt
A bad bearing
“self-excited” chatter from too-large of a normal force
“self-excited” chatter from having a resonant frequency connected with your wheel RPM
A wheel that wears unevenly
An unstiff dresser
Vibration in the dresser itself
Etc. etc.

A common culprit is an out-of-balance or out-of-true wheel. Here’s a quick calculation. Count the number of chatter marks around the workpiece. Then, take the wheel RPM and divide it by the workpiece RPM. If these two numbers are close to each other, you probably have an out-of-balance or out-of-true wheel. If the first number if much, much larger, you probably have “self-excited chatter” from a dull wheel, perhaps from dressing dull.

To complicate matters, if this second number from above is close to an integer, you’ll have trouble. If it’s “irrational”, you can get away with some imbalance. For example, Wheel-RPM/Workpiece-RPM = 8.000000 is terrible, 8.00024 is bad, 8.03 is kind of bad, 8.175343 is good, 7.91934 is good, 7.0002 is bad.

A frequently cause of “self-excited chatter” is using a grit mesh size that’s too large and then dressing the wheel dull to get the surface finish you need. This dull wheel increases the risk for chatter drastically.

This is stuff I teach in my courses and which is given in The Book of Grinding. Check out my webpage for more info.

I hope this helps.

Jeff

Dr. Jeffrey Badger
The Grinding Doc
Welcome! - Metal Grinding Expert Classes and Clinics - TheGrindingDoc
Take your grinding to the next level:
High Intensity Grinding Course – Feb. 29 - March 2 in New York City
High Intensity Grinding Course – April 25-27 in Toledo, Ohio

Like I said before, make sure your wheel is tight and that it is dressed true on the entire diameter. Chances are one or both of those possibilities are causing your problems.

BuffDan, i believe my spindle is bent. Not sure how to true it up in situ, advice?

Alex

Alex,
My spindle is out about the same.
I was just curious if it was possible to "dust" the spindle while in place.. Probably dumb question.

Dan

[Probably dumb question.] not dumb..a good question.

Yes the spindle nose can be dusted (if bearings are tight and true) but with much care to get the angle spot on and not take off any extra stock (just take some blue from low) if you intend to set another grinder on the chuck. In a pinch I have hand honed the high side to about 2/3s round under a tenths indicator then fired up and held a flat hone to the nose to smooth out flats and then to a blue in to a new mount..

I have thought about setting a stone or cut from a diamond wheel (perhaps 100 grit) in a chuck held fixture to dress the running nose but have never tried this method..

I commonly check the mount face and with a carbide bit take a skim to true up. Spindle end should have a line up mark and the mount put back with its line up mark to match.

Yes dressing the wheel takes out the hub error but with diamond wheels and wheels often taken on and off with the mount a true mount is best.
Good to also have a mount up mark on a wheel so the clearance to the hub goes the same way each time the wheel is re mounted.

So I put a tenths indicator at 3 O'clock position on the spindle and with just a light touch I get .001 movement on the dial, If I push hard from the 9 O'clock side I get a couple thou. If I put the indicator on the wheel flange (no wheel) and push in on the spidle nut with my thumb I get .0003 deflection, and if I pull out on the flange I get about the same. I'm thinking the bearings are toast yes? Any good links to rebuilding a Mitsui spindle? The boss is a tight ass and won't spring for having it done because we only use it once in a while. He said he'd rather sell it and find another machine.

Thanks

Here's a link to someone who rebuilt the spindle on their DoAll..
He describes dusting the spindle nose also.
Benchtest.Com - Workshop - DoAll D624-8 Surface Grinder

Dan

50BMG DUDE said:

So I put a tenths indicator at 3 O'clock position on the spindle and with just a light touch I get .001 movement on the dial, If I push hard from the 9 O'clock side I get a couple thou. If I put the indicator on the wheel flange (no wheel) and push in on the spidle nut with my thumb I get .0003 deflection, and if I pull out on the flange I get about the same. I'm thinking the bearings are toast yes? Any good links to rebuilding a Mitsui spindle? The boss is a tight ass and won't spring for having it done because we only use it once in a while. He said he'd rather sell it and find another machine.

Thanks

Click to expand...

The spindle should checked warm but a light touch getting .001 if it is the shaft moving in the tube that is too much. [push hard from the 9 O'clock side I get a couple thou].. be sure it is not the whole tube moving. Might take off the end cap.. or just tighten them a bit depending on how they preload... and add some load to the bearings. *Some times a spindle can get knocked enough too seat a bearing tighter so getting looser with not killing the bearing. That easy try should be made before you invest in a rebuild or other machine. IMHO.

Tightening the end caps sets the preload In the DoAll.. don't know how your spindle gets preload.. perhaps the same or someone can post...