Acceptable runout?

[Michael Arruda]

Hello all,

Another thread in my quest to accuracy. I bought a PC 890 router. It had a bad lower bearing. Took it back, got another one. I also received my collets from Precisebits.com the same day. Tried it out on router #2- .0005 runout at the spindle nose, .002 on a 1/4" Garr tool endmill. .001 on the 1/8" indexing pin that Precisebits incudes with their collets.

Took back router #2 and got router #3. Now reading .001 on both 1/4" and 1/8" bits. Ran a test cut through a piece of corian scrap. 1/4" bit measured .245, cut was .247. 1/8" bit measured .124, cut measured .126. So, I'm getting .002 runout in actual operation.

Would I do better with a Bosch router? Ron at precisebits said to try a Hitachi router- do you guys think any of this is going to make a hill of beans difference? Am I expecting too much out of a router? I was having .003 runout with my Makita router, which is what started this whole thing.

I don't do too much small inlay work now, but would like to do more- the smallest bits I have to use are .0197. with .002 runout, my tool wobble will be about 10% of the tool diameter, which I believe is into the chatter and breaking range.

Thanks,
Michael

[Scott Shepherd]

I'd think you are pretty lucky to get .001" runout with a router like that.

[Prashun Patel]

Only you can answer that question. I've never measured the runout on my reconditioned (twice) Bosch router, and it's produced the tightest butterfly inlays I could ever want.

If it were me, I'd make some test pieces and only consider switching if your results are not satisfactory.

[Angus Hines]

I guess the real question would be are you manufacturing heart valves ???? If not Im guessing your as close as you'll ever get !!!:D

[Mick A Martin]

I agree with Angus do you really need that precision, wood shrinks and expands more than your runout. :)

[Michael Arruda]

I know that I'm splitting hairs as far as the plausible accuracy of wood goes- my concern is the actual cutting. I'm concerned about breaking tiny bits. I guess my only real option is to chuck up that .0197 and cut something to see if it snaps it or works fine. I've scoured the internets and have yet to come up with a solid answer of "acceptable" accuracy. I guess that's so that people who are just cutting parts to 1/64" don't spend this much time obsessing over their CNC to get pin point accuracy.

Numbers are all well and good, but it's time to let the tires meet the road and go do some more cutting, huh?

Thanks everyone!

-Michael

[Scott Shepherd]

Michael, runout can be critical with carbide, not so much with high speed steel. In the earlier days of carbide, it was not micrograined carbide. It would fracture easily. What made it fracture was inconsistent load, or thermal shock. For instance, if you used coolant on it and the nozzle didn't hit it just right as it moved around the work piece, that would cause thermal shock and would break it.

You also had to ease into the work. You couldn't start running at 100 ipm and just fly into the work. You had to get the cutter engaged into the work before you put the load on it.

Runout would cause one flute to hit light and the other flute to hit hard, which is bad, in theory, because carbide doesn't like to be shocked.

Carbide wasn't widely available to most shop floor guys because it took very rigid machines because it took a lot of pressure and the tools were expensive.

However, with the invention of micograin carbides, a lot of that changed to some degree. Overall, carbide still doesn't like to be shocked, load or thermal, but with the finer grain carbide, it's not AS critical as it used to be.