drilling for 8mm pots

[stormbringer]

Hey all,

I have a bunch of Alpha pots with 8mm bushings. The mounting hole is supposed to be 0.323" (8.2 mm).
I see that there are metric unibits with an 8-mm step; I guess that could be reamed out a bit using a de-burring tool?

What are the best options for drilling the pass-through hole on the front panel? How do you do it?

[Enzo]

Drill your 8mm hole with your bit. Just because the data sheet wants an extra 0.2mm doesn't mean you need it.


And if you do, then a few strokes with a rat tail file will open the hole a little.

[bluto]

A tapered reamer works well too, I often drill slightly smaller than I need and then enlarge the hole with it....makes a rounder hole than a drill and gets rid of burrs too. Many hardware stores carry them for $15 or so...

[stormbringer]

Thanks Gents!

[nashvillebill]

A drill bit letter size "P" is exactly 0.323 inches...or, use a common 5/16" which will be .3125 and chances are it'll fit, if not use the tapered reamer as shown.

[Mick Bailey]

8.2mm is the clearance dimension to give an easy fit for a nominal 8mm thread. The pot has a +/- tolerance on the thread and the size given means that even at the maximum tolerance size the pot will still easily fit in the hole. I find that many bits cut slightly over due to being ground marginally off-centre and an 8mm hole works fine.

Reminds me of an ex-ICL (International Computers Ltd) draughtsman I once employed. He said that when they were drawing up the sheet-metal cabinets they'd spec an 8mm hole for a 6mm bolt and put a large washer each side "To guarantee everything would fit together when it came to final assembly"