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Aluminum angle vs steel angle

WizardOfBoz

Diamond
Joined
Sep 30, 2006
Location
SE PA, Philly
Hi all. I purchased, at a steep discount, a woodworking dust collection system. It's one of those with a blower leading to a ring with a bag below for sawdust, and a bag above to filter anthing that doesn't drop into the bag. Interestingly, it has a 2HP blower, which is more HP than my poor old Craftsman Contractor saw has driving the blade. In any case, I got the discount 'cause it was missing the stanchions that hold the ring (attached to the two bags) up. I fabricated stands and had a pretty superior design, except for the attachment points. Each stanchion has a 3/8 threaded rod sticking up. The ring to be supported has two threaded 1/4-20 holes about 1-1/4 apart. So I need some sort of angle iron that is about 1 x 3 I guess. I had some 2x2 lying around so I attepted to use that. Cut an inch long piece. Trim one leg to 1 inch. Drill one hole in the 1" arm, and 2 holes in the 2" arm.

As most of you know I'm an engineer, not a machinist, and the experience in this simple project left me a bit humbled. I mean, I got it done, but not very well and not very elegantly. Seriously, I salute the guys here who can nail mechanical specs.

In any case, the 2 inch side limit forced me to put a hole too close ot the 90° angle. The hex bolt head is interfered with by the fillet on the steel angle. It works, kind of, and I could just leave it. Alternately, I could replace the hex head bolts with SHCS and it the interference would not be as obvious (will probably go this route). I could then say "Yes, that's how I designed it...." 😁 A third possibilty would be to redo the thing, but with 1x3. This would give me all the clearance needed and would be more maintainable.

But the question regards the relative profiles of Al and steel angle. It seems to me that the steel angle has a fillet (which is what is interfering with my bolt). When I look at aluminum angle extrusion, I see little or no fillet. Is this correct? This affects whether I buy a drop of 1x3 angle, or if I can use 1x2 aluminum. Thanks.
 
That's a long story...but in any case yes, steel angle generally has an inside radius/fillet that makes it tricky to install a bolt. Some steel is sold without this feature but it's not that easy to find. If I were you, and you did the things the way I do, I'd spotface the area where each bolt needs to be to provide a flat surface for the head to seat on. Or, if aluminum is strong enough for what you need, use aluminum without the fillet.
 
Standard end mills have a slightly concave end profile, and leave a convex bottom surface when plunged to make a hole, as I discovered by using an end mill as a counterbore.

Edit: concave/convex might be the wrong terms; I don't know that the profile is spherical. On some end mills I inspected it seemed more like a V-shape.
 
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That's a long story...but in any case yes, steel angle generally has an inside radius/fillet that makes it tricky to install a bolt. Some steel is sold without this feature but it's not that easy to find. If I were you, and you did the things the way I do, I'd spotface the area where each bolt needs to be to provide a flat surface for the head to seat on. Or, if aluminum is strong enough for what you need, use aluminum without the fillet.
I don't have a mill but I can get a piloted drill on my DP to spotface the existing angle. I'll probably then change to button head socketed cap screws. So it looks like my design was actually what I intended!

Thanks, all.
 








 
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