Out of roundness and cattering noise during thro pass c'less grinding 1

[ahloma]

Shaft dia8.15/8.20mm material EN8m ground to 7.987-007mm dia with a roundness tol of .002mm in Giringhilli centerless grinding machine . Off late facing variation in roundness to .006mm and taper on the length of 205mm and also chattering noise during grinding .To avoid rejection doing grinding in two passes unable to continue 'cause of lose of productivity.Need advise to resort to single pass grinding without chattering noise and achiving the dimss and tol.

 

[statorwinder]

check out your MACHINERY"S HANDBOOK on centerless grinding
they have some good starting points under the heading CENTERLESS GRINDING TROUBLES

 

[steveh]

Roundness problems are usually caused by running the part too low on the workblade and possibly by running the reg wheel so fast that the part is not given enough time to round up well. It can also be caused by improper wheel selection and other things.
On the other hand, the chatter suggests that you are too high on the blade. I'm sure you know the center height of the wheels - rule of thumb is that the part is no more than 1/2 the diameter above C/L.
If you have recently changed the grinding wheel, you may have selected a wheel that is a little too hard for the application. It is also possible that your reg wheel speed is too fast. Another potential culprit is that your coolant concentration is too low. Also try changing your dressing wheel and/or reg wheel diamonds. Dull diamonds do a poor job of resurfacing the wheels.
Also, be sure to check that the part is in the groove on the blade. If it is not in the groove (worn by many parts over time) you will have all sorts of problems. Check this by high-spotting a slug and, resting it against the reg wheel, see if it is in the center of the groove.
If you have recently changed the blade, check that it is parallel to the fixture on both entry and exit sides. A blade that is not level with respect to the fixture gives a wide number of problems. A bent blade is another possiblity. If the grinding wheel ever touches the blade, you will have to change blades as it will either bow or chip off the carbide.
Taper problems can also be caused by poor setting of the guides on the reg wheel side. A guide angled toward or away from the wheel will cause taper on one end.
Be sure the reg wheel is properly dressed. Everything else can be OK but a poorly dressed reg wheel will cause geometry problems.

Simplest machine in the world but there are many variables that must be correct in order to get good parts.

Steve

 

[RamingtonStall]

Steve,

Great summary of recommendations for "ahloma".
I look forward to reading the responses after he investigates the points you mentioned.

He also mentioned Taper on his 8mm diameter x 205mm length part, so that I would also check the guide allignment on the regulating wheel side of the machine.

Based on the poor roundness on the 8mm diameter part and the taper problems, I would tear the set-up down and re-set up the machine from scratch, checking the diamonds as you suggested, the Actual Workpiece height above center, the specific wheel grade, and the specific information on trueing conditions (including diamond type and size, wheel grit type/size, and bond hardness, Trueing rate? Any special "procedures" being employed during trueing to improve surface finish? etc.)

RamS


SAT SuperAbrasive Techniques, Inc.

http://www.IndustrialDiamondCBN.com

 

[grinderguy]

The only thing not previously mentioned is: is the wheel wide enough for this amount of stock removal? I hardly ever solve a problem like this one without doing the whole set up over.

Robert Setree

http://www.advanced-grinding.com