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Surface finish question

daryl bane

Titanium
Joined
Mar 12, 2002
Location
East Texas
I am doing some cylindrical grinding on a K. O. Lee Univ. tool and cutter grinder. I am grinding a 1" dia 4140 steel round. The wheel is a new Norton 6" 32A 60grit K, freshly dressed front and sides . The part is in a motorized spin fixture between spring loaded dead centers running reverse to the direction of wheel rotation and am using coolant. After spark out, the finish to the naked eye looks great, but under a loupe, it has a tiny longitudinal flutes like slats on a barrel. Bad bearings, wrong wheel?
I am a complete novice at grinding and any help appreciated.
 
I guess I'm ignorant. You will have to explain how to do this because I thought the dressing took care of that, especially in a small wheel, 6" dia. Forgot to mention that on the 1st post.
 
Check to see if your center holes are circular and not fluted. You can bore them truly circular in the lathe, however, if you over bore them you run the risk of your grinding centers bottoming out in the holes and the part will be supported only on the very points of them. Not a good thang.

T in D

on edit..............What condition is the spin fixture you're using in? Best results use the centers provided with the machine and drive the part with a smooth belt.
 
Daryl, my mistake, I originally thought you were using a diamond wheel, upon re-reading your post I see I was mistaken. In that case what you describe is more than likely bearings. -Mike
 
Holescreek, whew, you had me going there. :) The part rotates between two dead centers, the center is part of the fixture and the motor powers a pulley around it. You need a drive dog attached to the part to spin it. The center holes look smooth under a loupe and the wear pattern suggest correct contact. Tim, you out shootin' fireworks with the grandkids Sat.?
 
A tool and cutter grinder is a light duty machine. You are not going to get a perfect finish like on a dedicated cylindrical grinder.
I used to do a repeat grinding job on a cylindrical grinder. Some of the parts were an inch longer and would not fit on the cylindrical grinder so I had to do them on a K O Lee t&c grinder, which did not work nearly as well.
 
Dressed?

I have found that a faster dress can sometimes help.
Might try an I.
Might also try narrowing the wheel.
Only change one thing at a time and keep good notes.
 
My first guess would also be the centers. They will look good if they are spinning on a dead center, that doesn't mean they are perfectly round. Any out of round condition in the center can be magnified in the larger o.d. of the part. That's why a lot of grind shops use center laps after centering in the lathe, to ensure perfectly round centers.
 
Daryl,

In my experience that surface appearance is always caused by vibration of some kind. The comment about using a long flat belt to drive the work piece is correct. Looseness at the drive dog or in the grinding wheel attachment to the grinder spindle can cause it. Roughness in the connection between the grinding spindle and its drive motor can be a source of the motion. That kind of surface finish is generated by the cutting tool(in this case the abrasive grain) moving in and out of the cut. If you have the dead centers pushing hard on the part and well greased I doubt that is the source of the problem. Check all the bolts holding the set up. I some times get some benefit from laying on a bag of No.9 lead shot to damp out a set up.
 
Many thanks for the replies. I never really cured it, by changing belts styles, wheels, dressing, etc. I found that changing wheels(narrower,finer grit) masked the finish, and it looked great but alittle lapping to the surface and a very uniform artifact, almost like new machine way "flaking" would appear. I do believe it is a vibration issue, but I hope not inherent with the machine design. I just happen to have a bag of Shot just for this type of thing but didn't think about it :(
 
Only one side is spring loaded, but the spring loaded center is locked down when you are ready to work. Good thought though,thanks.
 
Only one side is spring loaded, but the spring loaded center is locked down when you are ready to work. Good thought though,thanks.

Daryl

You shouldn't lock down the spring loaded center. If you do this the part will expand during grinding, pushing the centers apart, then when the part cools down there will be play between the part and the centers. There should always be tension but not too much. The land in the centers of the workpiece should be on the small, rather than the large side. The smaller the better. Even just a hole (no land at all) will work on a small part. A large land will often cause trouble if the centers in the fixture are not exactly aligned.

Gene
 
abrasive techniques

Redress wheel .002 or .003 b4 finish size. Do this with each part. Try this and let me know how it goes. It worked for me.
 








 
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