Tube Socket Holes

[J M Fahey]

Thanks for the explanation! BTW if you draw lines through the center of the rounded triangular hole I think that you will find that they are all of equal length from one side to the other. Just think if prehistoric man had invented the rounded triangle instead of the circle- it sure would be a bumpy ride home!

My good Unibits don't do that with a 12 or 14 GA sheet metal chassis*** because they are more like a stepped hole saw than a stepped drill bit.


So what kind of brake do you use to bend the sheet metal? It used to be fun when I was HVAC service manager at a sheet metal shop because of all of the equipment there!

Steve

*** The plural form of "chassis" is "chassis"

I bought this one practically as scrap metal at a failed factory liquidation.
Originally had a 400mm set of blades (hence the "400" engraved in it) and I had a special 600mm set milled, to be able to make "Twin type" 2 x 12" combos.



You'll also see some punching dies (for other machines) in all odd sizes, including narrow slits for graphic EQ or mixer controls, rounded rectangles for rack mounting "ears" and so on.

[Mick Bailey]

The triangular hole is trochoidal - same as a Wankel rotor if they were perfectly formed. The sides are all equidistant, as Steve A mentioned.

When drilling holes with step drills, tapered reamers or whatever, centrepunch the hole and mark a number of concentric circles (doesn't matter about the spacing). The last one should be slightly smaller than your finished size, so that the last bit of cutting takes it out. Now, if the hole wanders, take a round or half-round file and correct the hole partway through, using the circles as a guide. It doesn't need to be precise. Then continue cutting with your bit, checking as you go.

Even with the work clamped down these bits will move off-centre slightly. Their self-centering action is imperfect and they'll drift unless your setup is super-rigid.

[mac dillard]

If you want to go the punch route these are the best for the $ I have been able to find. Just watch your thickness

Metal Working

[Mick Bailey]

I can compose my 'lonely hearts' ad after seeing this pic;

"Lonely middle-aged man, lives with his mum and cries himself to sleep every night. Interests include metal fabrication, amp building, electrical and electronic theory. WLTM female of any age, looks or description who owns a PM400 press. Please send picture of press and tooling"