Boring a bearing journal vrs reaming

[RSG]

There's enough past posts on the PM forums to believe even the cutting fluid used can sometimes show a size change depending on what's being used.

Thanks Pete! This statement is true as I have experienced it. When I switched from one coolant to another I noticed right away that the final hole was slightly larger so I learned to compensate by speeding up my feed rate. Problem is I'm not consistent with it. I'm trying to visualise that tailstock slide apparatus you mentioned and will have a look on youtube for it. As for bed wear in the tailstock ways, I'd say there's virtually none. I've hardly moved the tailstock back and forth and when I have it's always had lots of way oil.


Harold - to answer your question I only leave .005" to .007" but can leave less if you feel it will produce a better hole. The reamer I use was factory ground and I feel confident in it but can get my friend in Ohio to grind one for me at .625" to be sure that all the cutting edges are the same. Both you and Glenn have mentioned gripping the reamer with only very small amount so I will try that as well. Currently I do all the testing on 2" dia pieces of aluminium to try to simulate the effects but I have found it still reacts differently when I work with the actual parts at 5" dia.

Mr Ron - I might try what you mention but my question to you is what dia reamer did you do this with?

Glenn - A while back I did some extensive work aligning my tailstock with a long bar and made cuts at both ends and tweaked the tailstock till I got them very close (a few tenths). I was happy with the results but if you have another method I'm all ears.

Once again, thanks for the help fellas! I appreciate it a lot.

[Harold_V]

You would be well served to better understand how a chucking reamer cuts. Unlike hand reamers, they are circular ground, so the body diameter generally dictates size. The flutes are backed off, so only a narrow margin of the circular grind remains, done to lower friction of the reamer in the generated hole. They also taper grind the body diameter a few tenths for the same reason. With proper alignment, such reamers cut ONLY at the end, the chamfer of the flutes that you likely have noticed. That's where you should concentrate your attention. If the junction of the chamfer with the body diameter of the reamer isn't exactly the same on each of the flutes, the reamer most likely will not cut a reliable sized hole. The greater the amount of material left to be reamed, the greater will be the error.

One of the things you can do to alter the way chucking reamers behave is to hand stone each of the flutes at that juncture, with the express idea being to blend the cutting edge with the body diameter so there is no sharp corner. Be mindful to not introduce negative relief, and to stone the flutes equally. The small radius that you create can serve to smooth out the resulting bore, assuming you aren't fighting alignment and have not created a high flute, on which the reamer will often wing.

I make mention of the reduced amount for reaming only as a suggestion. It may or may not make a difference, but it is one of the little tricks you can investigate to see if there is an improvement in the results achieved.

There should be no change in the results when you move from a rigid piece, such as the stock of which you made mention as compared to an actual part. If there is, alignment becomes the chief suspect. That's assuming that you are using the same type of material. If, for example, you do your experimenting with 2024-T351 or T4, then apply that to 6061-T6, you can expect different results. They do NOT share the same machining qualities.

H

[RSG]

Thanks Harold!

I'll have to do some research on hand reamers vrs chucking reamers. I appreciate the info here and it has given me cause to think. In an answer your query regarding the test material, yes it is the same material - 6061-T6 aluminium