Tube Socket Holes

[defaced]

Any tapping or light machine oil will work. A small container of it will cost like 5 bucks at a hardware store and last you years. You can also use light engine oil like 5w-30.

In high school shop, the cutting fluid for our automatic hack saw was Elmer's glue mixed with water.

The other thing to note is to use a pilot hole, otherwise you risk your bit walking while you're trying to start the hole. I typically use an 1/8" pilot.

[GregS]

Thanks a lot for all the replies. That's very helpful.

Greg

[GregS]

I finally got this done and it was a success - thanks to the help and suggestions I received here in this thread.

I used the step drill bit method. When testing hole sizes on scrap metal I found that the 1 1/8" size had a bit of a loose fit for my sockets and 1" was too small of course. When drilling the 1 1/8" size, rather than drilling right through, I stopped the drill numerous times and tested fit with the socket until it had a nice snug fit. The edges of the holes aren't quite as neat as a result but I think it's a worthwhile compromise.

The tip about attaching wood blocks to the workbench to stop the chassis from rotating if the bit grabs really saved the day here as it did grab big time on the last two holes. I think the last two holes were more of a problem because I started from the corner of the chassis where it's more rigid and worked towards the middle. Had I started with the middle holes the grabbing might have been less of a problem as the chassis would have been more rigid before the other holes had been drilled. Maybe this experience might benefit someone else doing it the same way.

Anyway, I just wanted to say I was able to get this right the first time because of the help and suggestions I got here.

Thanks again,

Greg

[GregS]

Sorry, double post.

Greg

[stingray_65]

Congrats!

most any aspect of any construction project becomes simple and do-able for anyone once they posses the knowledge and tools.

with that knowledge and then the experince of having done the task at hand you gain skill.

so very glad you didn't have to gain the skill of dodging a rapidly spinning workpiece LOL but you will if you make enough holes enough times in sheetmetal with a drill

hope to see some pics of your handy work soon

[GregS]

Ok. The edges of the holes aren't perfectly clean but, like I said, I tried to drill a size in between steps to give the socket a tighter fit. I have found that the hole centre tends to drift slightly as I drill successive steps even if I started it in exactly the right place. The drift was consistent for each hole though so they are perfectly aligned anyway. I guess a drill press is a must if accuracy is really important.

I'm trying to upload a picture. Hope it works.

Greg

[defaced]

Bits will still walk, grab, and not work perfectly even on a drill press because of the slop in most drill presses movements and the nuisances of how a drill bit cuts. It looks like you did a hell of a good job.

[stingray_65]

SWEET!

[james23]

Tube sockets were typically mounted in holes on a sheet metal chassis and wires or other components were hand soldered to lugs on the underside of the socket. In the past, printed circuit boards were introduced and tube sockets were developed whose contacts could be soldered directly to the printed wiring tracks.

[J M Fahey]

..

[isaac]

My dad (in extension me too. ;-)) has an old excello milling machine (non CNC all manual but still great) and that thing is wonderful for doing tube socket holes. I mean you could just use a drill press but the mill is so much easier, plus you can do so much more with it too. :-) Just use a big drill bit, like the kind of bit you'd use for cutting holes in the electrical panel in your house.

[Steve A.]

For real chassis punches, you can get used Greenlee Radio Punches for less than $10 a piece. Unlike modern Greenlee punches which are sized for conduits and such, the radio punches are the (considered obsolete) tube socket sizes like 1-3/16" and even square-shaped transformer punches.

I have a set of Greenlee knockout punches for electrical conduit and I've used them to make holes for octal and 9 pin tubes. They are pricey so you might want to look for them at flea markets.

The unibits work great- they make a rounder hole than a regular drill bit which can sometimes make a rounded triangular shape (don't ask me why!) I have had better luck with the old unibits I bought that I bought in the 90's for ~$20 than the cheap ones you find at Harbor Freight. Helpful hint: use blue masking tape to mark out how deep you want to drill.

Steve Ahola

P.S. This thread is an oldie but a goodie.

[defaced]

The unibits work great- they make a rounder hole than a regular drill bit which can sometimes make a rounded triangular shape (don't ask me why!)

Because sheet metal is so thin it cannot support the bit during cutting. So as you cut, the bit grabs, cuts, grabs, cuts, grabs, cuts, until you make the hole. The grabbing in combination with any deflection/bending in the bit forms what is basically a two piece planetary gear (I'm sure there's a proper term, but gear design isn't my forte). You can avoid this by using backup material to help support the point of the drill bit as it drills through the work. This movement has been exploited to allow one to drill a square hole:

Animation:
How to Drill a Square Hole - YouTube
Demo Video:
Drilling Square Holes - YouTube

[J M Fahey]

FWIW these socket holes were made on aluminum with Starrett hole saws.
Low RPM in a steady drill press, lubricated with kerosene.

Sill flat sheet:


Last check "everything fits" before final bending:


After bending:




Finished chassis:


Mounted in 4x10" cabinet:

[Steve A.]

Because sheet metal is so thin it cannot support the bit during cutting. So as you cut, the bit grabs, cuts, grabs, cuts, grabs, cuts, until you make the hole. The grabbing in combination with any deflection/bending in the bit forms what is basically a two piece planetary gear (I'm sure there's a proper term, but gear design isn't my forte). You can avoid this by using backup material to help support the point of the drill bit as it drills through the work.

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.

FWIW these socket holes were made on aluminum with Starrett hole saws.
Low RPM in a steady drill press, lubricated with kerosene.

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"