[harrysin]

Well if the hole (collett) is .250 than the shank has to be smaller (.249) otherwise it ain't gonna fit.

I just checked these three bits picked at random and the accurate one happens to be one of two that I bought off E Bay some years ago and they cut just fine. 1/4" = 6.35mm

 

[harrysin]

Things they never told us in 'shop'...
https://www.engineersedge.com/manufacturing/drill-mechanical-tolerances.htm
I did not know that.
That would bring up the obvious question, what if you actually want a hole .250"
Everything manufactured has upper and lower acceptable tolerances (ie .2493 to .2489 for example...no idea what the actual parameters are).

I'm guessing you need to place a custom order. I know that my machinist neighbour worked to incredibly exacting specs in the aero-space sector.

Very interesting Dan, it reinforces what I have said on this forum many times when members talk about attempting to get to 0.001" in wood!! Such members seem to forget that, unlike metal, it moves with the weather, even if 0.0005" is achieved on the day, tomorrow the sun may not be shining and it's raining, how accurate is it then?

 

[harrysin]

That's what reamers are for.

Metal!

 

[harrysin]

And then there are the tolerances when two parts have to fit together or only look the same. I see posts where someone thinks that two parts have to be alike and spend a lot of time and effort doing that when they really only have to look alike and it takes very little time or effort to do that.

Getting back on track, Pat Warner once said what he thought was the maximum allowance in shaft size. Does anyone remember what it was? I'm sure it was less that 2 thou but it seems to me that it wasn't much under that.

Another thing that I've said several times on this forum is "if it looks right it is right" who is going to take a magnifying glass to the project.

 

[harrysin]

Collets by design should allow for a slight variation of sizes. They are probably designed exactly to the specified size, but can accommodate undersize bits.

I have a bunch of Porter Cable routers, and I think their collets are slightly undersize, as bits won't usually slide out even when they are loose.

The MUSCLECHUCK is so accurate that a bit will slowly lower itself into the collet. At least one other member has confirmed that.

 

[harrysin]

This true,Harry, I have found bits though that are undersized by.005",that will not tighten up in the musclechuck, but will tighten up in a regular router collet chuck.
Herb

I haven't found that with the chuck itself but I have a couple of 1/4" bits that won't lock in the reducer sleeve supplied by Derosa engineering, makers of the MUSCLECHUCK.
Realistically, a precision tool like the Musclechuck does deserve precision bits.

 

[harrysin]

I have found that when I buy dowels the nominal size is close to what it is supposed to be,but can vary enough that it is too loose or way too tight.
Many times I have used the metal reamers which are very accurate to enlarge the hole for the dowel. I have found that wood working bradpoint and forstner bits vary in dia. from actual size too.
Herb

Years ago when dowels were smooth with a slot down the length I often found them over or under size but with the advent of the splined ones they are usually a gentle hammer fit without danger of splitting the wood and still have room for the adhesive.

 

[harrysin]

Now THAT is precision. Fortunately not required on wood.