Engineering notes For hobbyists

Theaded holes

Threaded holes are considered to be called out to minimum depth. If a threaded hole needs to be held to a +/- tolerance, then a measureing method must be agreed upon by both parties. Two different thread gages may give a different amount of turns and off-the-shelf hardware will give a different number as well. The same goes for broach depth.

Unless specified on the print, threaded holes may be thread milled. made with a cutting tap, or formed. 

Please note that a form tap may not be used on sanitary parts. The reason is that a form tap will typically leave tiny "bacteria birdhouses" at the crest of internal threads. (see photo to the right)

Surface finish

Fine surface finishes require special processes, more time, and of course,  extra work. If you absolutely need/want a finish finer than 125 RA, we are happy to provide it with an appropriate increase in price.

Tight tolerances

Tight tolerances are no problem. They can equal a significant increase in price per part though so only call them out if you need them. Our title block tolerances are pretty typical at +/- .010" for three place decimals, +/- .030" for 2 place decimals and fractions, (please avoid fractions except for stock callouts) and +/- 3 degrees for angles.

Holes

Holes are probably the most common machining feature. Be aware that any time a hole is required to be deeper than 3X its diameter, some problems can crop up with roundness, parallelism, runout, perpendicularity, bell-mouthing, etc. Special processes and tooling much be used to create precise holes beyond this 3X diameter threshold with a subsequent increase in price.