help settle this debate

we are having somewhat of a debate between our engineering manager and our grinding department. side "A" says that centerless grinding is the only way to get things round and to size and side "B" says that centerless grinding gets things straight and to size but frequently leaves them lobed (not round) and that grinding between centers will leave them round (according to the quality of the centers) and to size but may leave them tapered and/or barrel or hour glass shaped. i wont say which side said what yet but which side is right? A or B?

They are both right and yet neither is right.

Done properly both methods can produce satisfactory results, but the arguments are probably based on the results of poor control of the processes. Which is the more error prone? That is probably the most important factor.

Regards,

Mike.

I have had to deal with a vendor's lobed centerless grinder work. Seldom can tell anything with an ordinary OD mike, but check it with a vee anvil mic. The opposite of round.

John Oder

Centreless grinding does have a reputation for producing lobed work but I think this is more down to setup and operator than a deficiency in the process itself.

BTW Air Gauging will tell you an awful lot about the accuracy of ground parts.

Regards,

Mike.

Either process is capable of producing round and straight parts. Centerlessed parts do no need to be lobed and cylindrical ground parts don't have to be hourglass shaped or tapered. It's all controlled by the craftsman at the controls.
Give him what he needs and get out of the way.

Gene

Have to agree. Both process will make good parts. This is just a matter of the man behind the machine.

I have made lobed parts on a centerless. I like them better; they only have three high/low spots. When you do it on an OD grinder you can have lots of high and low spots. Much more work to get them out.

It is easy to barrel or waist parts on either machine. Each machine has its own needs to make a part correctly.

Alex is 100% correct; it is the person running the machine that makes the difference. (I am getting better )

The real question is "How round" do you need. If it is that critical, you best lap them.

Sounds like the three problems you have are more of an operator issue than the machine not running true. Don't try going to size until you have the parts round and true. You may have to take more than one cycle if the parts have alot of stock on them or they are hard to grind due to the wheel make-up or type of steel. Don't take this as a slam just need to refine you procedure.

I agree, either process can produce good or bad parts as described. Most of the time the construction of the part dictates which process is required so you don't really have a choice as to which process you have to use. Both are extremely accurate in the right hands with the correct machine. RJT www.progtool.net

the gist of the discussion is that side "A", in this case our engineering manager, says that centerless grinding is the ONLY way to get things round and to size. side "B", our grind department personell, says this is not true. and by way of explanation they say while centerless grinding can leave things round and to size it is not the ONLY way, in fact a tendency of centerless grinding is that things are FREQUENTLY lobed. this lobing can be reduced or eliminated to a certain extent by good grinder practice and workmanship. and if you dont have good accurate centers in a part ground between centers it will be hard to make those parts round as well, and parts ground between centers MAY be tapered and/or barrel or hour glass shaped, these have to be dealt with with good practice and workmanship and these conditions with the exception of taper are less likely with centerless grinding. once again the main point of the discussion is wether or not centerless grinding is the ONLY way to get things round and to size or not and i think the responses above indicate that that is not the case.

When in doubt, I've found it best to trust the guy that's actually doing the work, not the paper shuffler than doles it out.