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Quick question for machinists

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Dr. Steve Brule:
I usually leave .2mm or so on smaller holes (under 8mm) and .3mm or .4mm on most things larger. Depends on the job though, sometimes you can need a bit more clearance, sometimes get away with minimal. I generally like to have as little as possible.

G:
It depends on what you are asking it to do.

THere is a standard "clearance" hole size which will be given on charts as explained above, but sometimes you want it a closer fit so that a reciprocating load is less likely to wallow it out, or with a softer material you might want it looser to allow for a bit of deformation.

The reason that the 3d printed part came out with undersize holes is because of "stringing" on the curves, it works much better to print holes as "polyholes" rather than round holes. Google "polyholes" and "hydroraptor" for a fuller explanation.

Is this a Yeti?

:)
G. 

tecnic1:
I'll preface this by clarifying that I'm not a machinist, but they do occasionally let me put down specs long enough to design machined parts.  I also work in an industry where we often don't give a fuck about money.

But for a critical pinned joint like this, where even small amounts of play would not be acceptable, we would drill the hole intentionally undersize, and finish hone it until the actual bolt being used just fits.  In face we sometime specify the allowable force to insert the bolt to make sure someone doesn't get crazy with a hammer because they are ready to go home.

Doing so allows us to get the fit we want regardless of the tolerance stack-up.

Brooklynrider:
I was told beforehand that the 3D model would have some distortion and it wasn't a totally accurate model of what I am making. I was just seeing if all the angles were correct and if the holes were spaced correctly. It's an older Morewood btw. Thanks for everyone's help.

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