HREW rectangular tube question

[Ronin8002]

Got a question for the engineer/fabricator folks out there.

I'm working with some 2" x 3" OD HREW .25" wall structural steel tubing. The piece I am using is going to be about 3" long. It is for an upper coilover shock mount.

My current design requires that I drill two 19/32" holes through two walls of the tube (the two 3" sides). A 1/2" Grade 8 bolt will be going through these holes and will be used to attach the shock, so it is a double shear setup.

Now, one of those holes is going to be going right through the seam on one of the sides of the tube. I know the seam is normally talked about as the weakest point in this type of tubing, but with the way the seam will be stressed (right on its axis, compression and tensile) will this be an issue? Corner sprung weight is 1150 lbs but since this is a suspension mount the stress will be dynamic.

 

[Turdle]

Can you sleeve the hole?

 

[Ronin8002]

Can you sleeve the hole?

Yes. I guess I could just drill it out larger and weld some kind of 1/2" ID bung or sleeve in it. Main thing is that the ID of the rectangular tube needs to remain 1.5" on the short side.

 

[RockRanger]

So you are planning is something like the sketch I did?

What about just making it out of 4 pieces and welding the corners together. That way you don't have to worry about the seam. This is how I would do it.

If you want a bung to weld in I am pretty sure ruffstuff makes what you need.

If you get me the dimensions today I can try to cut it on my Plasma table tomorrow and then mail them to you.

 

[Brian1]

How much material around the hole, will it be centered in that 3" piece or towards one edge? If centered it would be fine but if it is out to the edge it could rip out and a weld washer or teardrop reinforcement would be better. That would only need to be about 1/8" thick and welded to the tube.

 

[Ronin8002]

Thanks for the replies!

The 4 pieces thing is an option but if a sleeve or bung would be strong and safe then I would rather do that...simpler.

It basically will look like your diagram but the two bottom corners will be bevel cut on a 35" angle to allow the top of the shock to have some room to swivel as the suspension cycles towards max bump and max droop.

Also the holes won't be halfway up the tube. The centers of the holes will be 5/8" from the bottom edge of the tube so there will be a minimum of 3/8" of material from the edge of the hole to the bottom edge of the tube. Basically like this:

Again, it is 1/4" wall tube, and if I am thinking correctly, most of the stress will be on the upper part of the hole (it's an upper shock mount, so the bolt that holds the shock will be pushing UP most of the time under the weight of the vehicle). The only stress I can see being on the lower part of the hole will come from the coil spring on the shock when the suspension gets unloaded. Maybe in light of all of that it'll be fine? What do you guys think?

 

[Ronin8002]

How much material around the hole, will it be centered in that 3" piece or towards one edge? If centered it would be fine but if it is out to the edge it could rip out and a weld washer or teardrop reinforcement would be better. That would only need to be about 1/8" thick and welded to the tube.

Weld washers, like these?

http://www.ruffstuffspecialties.com/catalog/FIXIT.html

 

[Brian1]

Weld washers, like these?

http://www.ruffstuffspecialties.com/catalog/FIXIT.html

Yes that would be your best bet to distribute the load around the seam. You could also simply use a holesaw to cut out a round plug of some 1/8" steel, weld it on and then drill through both the 1/8" and 1/4" to get your finished size hole.

 

[4x4junkie]

Could just weld a piece of 1/8" flat steel maybe 2"x2" over the side that has the seam on it, then drill your hole through both the 1/8" and 1/4" pieces of steel (total 3/8" thick). Might not be the prettiest way to do it, but certainly is simple and would work for that.

FWIW, I've yet to ever have an HREW tube (round or rect.) split along the seam (and I've mangled a few pieces up pretty good too).

 

[Ronin8002]

Could just weld a piece of 1/8" flat steel maybe 2"x2" over the side that has the seam on it, then drill your hole through both the 1/8" and 1/4" pieces of steel (total 3/8" thick). Might not be the prettiest way to do it, but certainly is simple and would work for that.

FWIW, I've yet to ever have an HREW tube (round or rect.) split along the seam (and I've mangled a few pieces up pretty good too).

Good idea on the plating over the seam. I think I could make it look decent. On the other hand those weld washers look good and they would keep the hole from "ovaling out" over time too.

 

[snoranger]

FWIW, I've yet to ever have an HREW tube (round or rect.) split along the seam (and I've mangled a few pieces up pretty good too).

I have. Just bending it in a tube bender at about a 20 degree bend. It split right down the seam and colapsed. Ive never trusted HREW since.

 

[IZwack]

The design sounds fine - especially with 1/4" wall tube.
My only question is why use 19/32" holes when the bolt going through them is only 1/2"? That is 3/32 of slack - too much in my opinion - 19/32" is only 1/32" away from 20/32" which is 5/8".

My current design requires that I drill two 19/32" holes through two walls of the tube (the two 3" sides). A 1/2" Grade 8 bolt will be going through these holes and will be used to attach the shock, so it is a double shear setup.

 

[Ronin8002]

The design sounds fine - especially with 1/4" wall tube.
My only question is why use 19/32" holes when the bolt going through them is only 1/2"? That is 3/32 of slack - too much in my opinion - 19/32" is only 1/32" away from 20/32" which is 5/8".

Thanks for the reply Typo...meant 17/32". Probably could just drill a 1/2" hole and that would work too. Figure a tighter tolerance is better for something like this.

I went ahead and ordered the weld washers last night too. That'll change the hole size, so I'm going to adjust the design a bit so I've got more metal between the edge of the hole and the edge of the bracket.