Making machine screw threads vibration proof in copper-to-brass connection

Would using something like an M4 Taptite screw work. It would have the benefit of saving you tapping the holes in the bus bar as well as them being resistant to coming loose due to vibration. HTH. rob

Through-holes?

Peen the end of the screw.

Loctite works very nicely.

Steve

LowEnergyParticle wrote:

Tri-lobular self-tapping (actually, tap-forming) screws are widely used to assemble disk drives, as they don't loosen and they don't generate metal dust. Lubricant may be useful in copper.

Joe Gwinn

Hi Joe - I'm sure these may also be called Taptite screws (well at least one brand of them!) regards

1) use 'binding head' screws.

2) toothed lockwasher

3) blue locktite

4) red locktite

Jim

It looks as if brass screws are used for electrical conductivity. That lets out special steel or plated screws and chemicals like locktite. It does leave room for safety-wiring the screws, or special washers. Star washers may be all you need. You could possibly drill a small hole next to the screw for the tabs on a tablock, essentially a piece of sheet metal bent to set a tab in the holer and another shoved into the screw slot. Drilling thru the base and using locknuts is probably easiest, if the part allows.

Hmm. Could be.

Joe Gwinn

Thanks a million for all the great ideas!

I especially liked the trilobular screw threads idea. I looked them up on the Taptite site:

they are remarkable little critters indeed! The binding head screws are also a good fit for this project; I'm going to see if anyone makes a trilobular thread on a binding head screw. Several of you mentioned star washers, and that is also a good solution although it's either/or with the binding head screws.

Loctite is your friend, but in this case I need electrical continuity and multiple releases & reinserts, so I'd better pass on a liquid thread locker. Also, I've got no access to the rear of the busses, so peening the screw tips once inserted wouldn't work. I really liked the safety wire idea and the tablock, but the customer is low-tech and I'm unconvinced they would reliably restore the safety wire or tablock after maintenance work.

Thank you all for the help! Dave

The copper buss bars I had in my prototype 3 phase 50 amp/phase machine was for a ground buss - and the 10-32's and 1/4" studs were staked in or pressed into holes. The head/shaft of the screw was grooved such when pressed, it cut in tight and won't turn. The bar was done in the prototype shop - so I don't know the source of the screws. But I suspect they are easy to get.

You could take the heads - say a countersink on the back side - and braze it to the bar. But copper tends to sink heat like everything!

Martin

Mart> I need to build a set of copper buss bars, each drilled and tapped for

The screw does not contribute to conducitivity here. All the current travels from the lug directly into the bussbar.

At any rate, check a locktited screw with a simpson meter. You'll find it has the same resistance as one that has not been threadlocked.

Jim

That doesn't seem like a definitive test; I think you'd need a milliohmmeter with Kelvin connections to test with, rather than an ordinary ohmmeter. (I'm not saying the resistance is different, merely that you can't tell with an ordinary meter.)

-jiw

All of the screws in my old (now in my 3 phase box) buss bar were plated steel or Nickel for the big one. Jim was right - the washers and lugs carry the current. Deal with strength not conductivity. Torque the bolts down...ability.

Mine was 1/2" x 2" x 12" IIRC. Full of screws - I thought to many for this new project of mine, but turned out just fine.

Martin

Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member

jim rozen wrote:

Simpson did make some low-ohms meters....

Jim