Overtightened screws warped a passive radiator

jimbo1421

Hello,

While cleaning off the old Armacell from the PR on a SRS 3.1TL, I saw signs that the screws had been over tightened. The metal around the screw holes had dimpled a bit. Setting the PR rubber side down on a flat desktop I can see waviness where the basket has bent slightly, as much as 0.012" measured with a feeler gauge. A straight edge set across the screw hole definitely rocks across it. I don't know if I did this or the previous owner. I have filed down the bumps on the inside, but that doesn't deal with the waves.

Can I count on the Armacell to fill the gaps and make the coupling between the PR and soundboard? Would Mortite be a better choice here? It seems risky to try to flatten the PR, but maybe some one here has a good technique.

Jim

pkquat

If the entire ring is warped, when you tighten it down it should be fine. If it is warped so much that it is not straight, then the basket and ring may need straightening. If it is only a dimple in the ring where the screw is then you can try flattening that area with a small punch on an anvil of a vice or some hard surface, or maybe even small pliers or vice grip clamps that will fit over the lip could squeeze it flatter.

A picture would help.

westmassguy

Once it's torqued down, using Larry's rings, or Hurricane nuts, it will straighten out.
The Armacell should take care of any gaps. I would not recommend Mortite.

jimbo1421

Thanks, wmg. But the tight spots (the valley of the wave) would be directly under the screws, leaving the crest in between with the 0.012" gap filled with less compressed gasket. I don't see how it would straighten itself out, even with my new rings. Or is the gap not enough to fret about.

Jim

jimbo1421

Thanks nb. I tried this, using Larry's template under the PR to keep its rim from pressing into the MDF. It does snug down flat, but springs back when released. I feared to tighten more since that would cant the mating surface.

Jim

ken brydson

Not in my wheelhouse but can you double up the gasket?

Schurkey

That's why I advocated for reinforcing rings on the front side of the basket. The baskets are flimsy, torquing the fasteners distorts the basket. Ten thousand auto mechanics have had to straighten stamped sheetmetal valve covers for exactly the same reason.

OTOH, nobody else seemed to think it was a problem.

http://forum.polkaudio.com/discussion/141640/rings-of-power-or-what-evil-weed-have-i-been-tolkien

jimbo1421

ken brydson wrote: »

Not in my wheelhouse but can you double up the gasket?

In this other thread I was advised not to.

http://forum.polkaudio.com/discussion/172649/replace-old-armacell-or-leave-it-be#latest

Jim

jimbo1421

Schurkey wrote: »

That's why I advocated for reinforcing rings on the front side of the basket. The baskets are flimsy, torquing the fasteners distorts the basket. Ten thousand auto mechanics have had to straighten stamped sheetmetal valve covers for exactly the same reason.

OTOH, nobody else seemed to think it was a problem.

http://forum.polkaudio.com/discussion/141640/rings-of-power-or-what-evil-weed-have-i-been-tolkien

That sounds right to me.

Jim

ken brydson

jimbo1421 wrote: »

ken brydson wrote: »

Not in my wheelhouse but can you double up the gasket?

In this other thread I was advised not to.

http://forum.polkaudio.com/discussion/172649/replace-old-armacell-or-leave-it-be#latest

Jim

Again not my specialty but I don't see where that addresses a warped flange. Rings might pull it flat again but short of them a double gasket might seal the gap. I could be totally wrong, rum might be talking...

motorhead43026

How ridiculously tight would you have to tighten it too warp it. The torque method used by most goes like this. "Tighten nut or bolt till it turns freely, and then turn one half an additional turn".....lol.

jimbo1421

There are both dimples at the screw holes and upward warps between them. If I set the PR face down on a flat surface and press down so that the rim is touching the table, I can slip as much as a 0.012" feeler gauge under the rim at each screw hole. Also, if I put a straight edge across the back side of the screw holes, it rocks quite a bit. I filed down the bumps that the dimples made on the back side. It's the waves between the holes that I ask about, and how to flatten them without totally messing up. Or should I just leave it be and let the Armacell do what it can to damp out the basket.

I doubt if I torqued the screws enough to create the dimples. It must have been the previous owner, who repaired a tear in the cone.

Jim