Aluminum T-Slot Fastener Bolts Strength

[yak]

Hello,

I have two questions.

I've spent a lot of time reading over threads on aluminum stands, such as this one: https://www.reef2reef.com/threads/show-us-your-t-slot-aluminum-stands.302935/page-3

I reached out to a well known company that does them, and admit I am confused on their answer. I asked about the strength ratings of the fasteners used (how many lbs load rating, etc) with reference to the sump, not the main display tank.

The main display tank would have the load transferred to the vertical legs, but all the pictures I see show sumps sitting only on the horizontal cross-beams..... which are only held by the anchors horizontally.

When I asked for the direct load rating of these, I was told that the extrusion bars do most of the load bearing. I responded with a photo showing sumps sitting across the middle of the bottom cross beams and clarified.

I was told again, "It would still be the extrusion bearing most of the load with the connectors just securing the pieces in place."

Am I missing something here?

1 ) How do the extrusion cross beams on the bottom of the stand do most of the load bearing, when they essentially are floating in between the length-wise bars and only connected by the anchors on each side?

I then browsed around online and found references in catalogues of example strengths for a 6" 1515 profile:

Can anyone help me understand this? Not exact extrapolation, but if 6" is 700 on average, if the cross profile for the sump was say 36" wide on the bottom, could it be 705lb/6 = 117lb. So each anchor fastener on the bottom could be capable of holding around 100lbs for a 36" long bar? And with all the anchors in each bar across the bottom, it ends up being enough?

2) My second question is I read that stainless steel and aluminum should not be used together due to galvanic corrosion (similar to a boat and sacrificial anodes). I see one company uses stainless steel anchors with aluminum profiles. Others use zinc. Is this an issue or is that only for untreated/non-anodized aluminum?

I am new to aluminum stands, so go easy

 

[ScottD]

Looking at that table a single faster is good for 950. Double that because you have one an each end and that’s what that single piece of extrusion that spans from one leg to another is good for. Think about a simple bridge with a tractor trailer truck sitting in the middle. The weight of it travels through the bridge and is spilt between each end. The cantilevered amount is describing where it’s only supported on one end, (think something like a diving board). So they are correct in saying that the bar takes the weight of the sump. It takes that weight then splits it between the fasteners at each end.

About the zinc vs stainless steel. I would use the zinc fasteners as like you said, the stainless will have a reaction. The anodizing doesn’t apply here since that is only a surface treatment. As soon as it’s milled to accept the fasteners that anodizing is gone where it’s been milled.

Let me know if you have any other questions or want me to clarify anything.

 

[yak]

Looking at that table a single faster is good for 950. Double that because you have one an each end and that’s what that single piece of extrusion that spans from one leg to another is good for. Think about a simple bridge with a tractor trailer truck sitting in the middle. The weight of it travels through the bridge and is spilt between each end. The cantilevered amount is describing where it’s only supported on one end, (think something like a diving board). So they are correct in saying that the bar takes the weight of the sump. It takes that weight then splits it between the fasteners at each end.

About the zinc vs stainless steel. I would use the zinc fasteners as like you said, the stainless will have a reaction. The anodizing doesn’t apply here since that is only a surface treatment. As soon as it’s milled to accept the fasteners that anodizing is gone where it’s been milled.

Let me know if you have any other questions or want me to clarify anything.

Thank you for the reply. The bridge analogy makes sense. I wonder why some offer stainless steel hardware then. I think 80/20 's stainless steel is 18-8. I will keep poking around to learn some more.

Would be nice if there were calculations for bolt/anchor strength at various lengths. All I can find is the 6" 1515 example.

 

[Harpo]

Hopefully your horizontal extrusions are resting on top of the vertical extrusions

 

[ScottD]

Thank you for the reply. The bridge analogy makes sense. I wonder why some offer stainless steel hardware then. I think 80/20 's stainless steel is 18-8. I will keep poking around to learn some more.

Would be nice if there were calculations for bolt/anchor strength at various lengths. All I can find is the 6" 1515 example.

I wouldn’t be surprised if the reason for the stainless hardware is customer driven. People think stainless is better. Now it’s possible to that the rate of corrosion of zinc from the environment is as much as the rate of corrosion of stainless mixed with aluminum. Or maybe a certain mix of stainless is better. I’m not sure.

As far as calculations for cantilevers greater than 6” goes, my guess is that after 6” the specific series of extrusion is going to play more a part in that than the fastener alone. The father out you go the less shear force the fastener is seeing and more the extrusion is seeing and the math gets more complicated.

 

[ScottD]

Hopefully your horizontal extrusions are resting on top of the vertical extrusions

He’s talking about on the bottom of the stand, where you can’t have the horizontals on top of the verticals.

 

[yak]

I wouldn’t be surprised if the reason for the stainless hardware is customer driven. People think stainless is better. Now it’s possible to that the rate of corrosion of zinc from the environment is as much as the rate of corrosion of stainless mixed with aluminum. Or maybe a certain mix of stainless is better. I’m not sure.

As far as calculations for cantilevers greater than 6” goes, my guess is that after 6” the specific series of extrusion is going to play more a part in that than the fastener alone. The father out you go the less shear force the fastener is seeing and more the extrusion is seeing and the math gets more complicated.

Hmmmmm - so is there a concern for corrosion and a stand collapsing after "X" years due to using zinc or stainless anchors/fasteners? I guess you could go around the stand and replace one anchor fastener at a time..... should hold up ok during replacement haha

 

[yak]

Hopefully your horizontal extrusions are resting on top of the vertical extrusions

I was referencing the bottom where the sumps sit. That's another good point though... if the entire top frame should rest on verticals. I see many that are designed with the two long beams on supports but the widths are then floating between. I guess the same analogy applies with load rating, but I'd be more inclined to have the entire top resting on top of vertical support at the corners and mid-way, similar to the well known 'rocketengineer' wooden frame build from a long time ago.

 

[yak]

Hmmmmm - so is there a concern for corrosion and a stand collapsing after "X" years due to using zinc or stainless anchors/fasteners? I guess you could go around the stand and replace one anchor fastener at a time..... should hold up ok during replacement haha

No, this wouldn't work now that I think about it - since the connectors have to be slide down the length of the t-slots before assembly. So, is there a danger of the anchors rusting out after "X" amount of time?

 

[ScottD]

No, this wouldn't work now that I think about it - since the connectors have to be slide down the length of the t-slots before assembly. So, is there a danger of the anchors rusting out after "X" amount of time?

I would be more concerned that the silicon seams of a tank give out before the fasteners corrode enough to cause a stand failure.

 

[ScottD]

I was referencing the bottom where the sumps sit. That's another good point though... if the entire top frame should rest on verticals. I see many that are designed with the two long beams on supports but the widths are then floating between. I guess the same analogy applies with load rating, but I'd be more inclined to have the entire top resting on top of vertical support at the corners and mid-way, similar to the well known 'rocketengineer' wooden frame build from a long time ago.

Here is the stand I designed and built for my 135 gallon cube I’m working on setting up. As you can see the top has two beams sitting on the vertical post as and then pieces filling in between. The anchor fasteners are plenty strong enough to hold the fill in pieces. The chart you had above said each fastener is good for 950 Lbs. I’ve got 2 on each end since I’m using 15x30 extrusion. That gives me 1900 lbs of shear strength at each end of the fill pieces. That’s about what my whole weight is going to be for the tank, stand and sump. So 2000lbs conservatively spread over 8 of this connections gives me 250lbs of the 1900lb capacity. That’s over a 7.5x safety factor.

 

[Sleeping Giant]

Hmmmmm - so is there a concern for corrosion and a stand collapsing after "X" years due to using zinc or stainless anchors/fasteners? I guess you could go around the stand and replace one anchor fastener at a time..... should hold up ok during replacement haha

if you add cross bracing in the middle of the horizontal beams (H), you'll have more than enough to hold the sump and then some.

 

[Sisterlimonpot]

if you add cross bracing in the middle of the horizontal beams (H), you'll have more than enough to hold the sump and then some.

That's exactly what I would've recommended, if fear of exceeded sheer strength.

But Scott the reefer, laid out why you shouldn't be concerned.

 

[yak]

if you add cross bracing in the middle of the horizontal beams (H), you'll have more than enough to hold the sump and then some.

Are you referring to this? I drew in a line on @scott_the_reefer 's photo

 

[Sleeping Giant]

Are you referring to this? I drew in a line on @scott_the_reefer 's photo

ya, but if you use the same thing as the picture it's basically the same idea

 

[ScottD]

Are you referring to this? I drew in a line on @scott_the_reefer 's photo

You only need them going one direction. So you’d either put them the direction you drew yours or the direction I have them. My stand is 37”x37” so in my case it doesn’t matter. What size tank/stand are you looking at having?

 

[Townes_Van_Camp]

Thank you for the reply. The bridge analogy makes sense. I wonder why some offer stainless steel hardware then. I think 80/20 's stainless steel is 18-8. I will keep poking around to learn some more.

Would be nice if there were calculations for bolt/anchor strength at various lengths. All I can find is the 6" 1515 example.

T-slot was created for manufacturing enclosures and environments. Stainless fasteners are required in some facilities in some spaces as werll as corrosion resistance. It's not always about the strength.

 

[Harpo]

Stainless steel is great with steel but as previously posted the galvanic reaction is very real especially in a wet/salty environment. Stainless also Gauls. I prefer steel fasteners with a dip spin organic finish that is good for 1000 hours of salt spray corrosion protection. Electroplated zinc fasteners might have 240 hours.

 

[SteveMM62Reef]

I’d go on Amazon and get Bostik’s Mariner’s Choice Never-Seez for those Bolts. Use a 1/2” Drive Inch/Pound Torque Wrench and tighten the fasteners o the Low End of the Torque Specifications. BTW, I wouldn’t just let the Can Set on a Shelf some place. I call Never-Seez, “I’m not getting any Younger Slave.”

 

[yak]

You only need them going one direction. So you’d either put them the direction you drew yours or the direction I have them. My stand is 37”x37” so in my case it doesn’t matter. What size tank/stand are you looking at having?

Not yet building, but planning for a future build. Probably over 500 gallon. Doing all the research long before