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shank or cutter??
 

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Discussion Starter · #7 ·
No, I made a collet for someone and they mentioned they could not easily get a .250 shank to fit. I machined it to slip fit a .249" shanked bit.

Checked all my bits and not one is .250. They are all between .249 and .2493
 

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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
 

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Paul
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Making a 'roller' for a roller stand the other day. I noticed the same issue, drilling a 1/4" hole and expecting it to turn on a 1/4" bolt. I could barely get the bolt in (without using a hammer). So I measured some bits to see if I could find an oversized one... all of them were undersize! I finally found a knurled punch that opened the hole a bit. I guess the knurling added a little width to 1/4" material it was made from???
 

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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.
 

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Paul, remember the old military saying- Don't force it, use a bigger hammer! The bolt can measure under the 0.250 at the body but when the threads are cut, they are slightly bigger than the stated diameter. Ran into this many times.
 

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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?
 

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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
 

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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?
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.
 

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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?
That reminded me of the conversation I had with the owner of an Italian coffee shop/restaurant. He was explaining to me that they grind their beans for the day based on the weather! Apparently it makes a big difference in the quality of the finished product, the cup of coffee.
(He also said that the roasters of Starbuck's beans should be in jail... ;) )
 

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