bolting square aluminum without crushing walls

[greencactus3]

we're gonna use .125in wall square 1x1in aluminum for some things this year. and were wondering about if you wanted to say.. bolt a pillow block to one face of the aluminum. so, drill a hole through the whole thing. as in 2 opposing walls. and then bolt goes through the pillow and then the whole alumiunm.. through 2 walls with space between. gets a nut on the other side of the aluminum.
if we crank down on the bolt, the walls of the alumiunm get crushed. how do we do this without crushing? not cranking as hard might not be a good idea as we dont want axles wobbling around.
and drilling a massive hole on one side of the alumiunm so we can fit a nut through that is an option but will take away structure from the square, as 1in sides means a lot of surface area taken away.
anytips from the veteran teams? btw our pillows are steel or zinc or sumthing. not aluminum so welding that on would be complicated. if possible,. i dunno

[EricH]

Try a washer between the nut and the square tube. The washer should be close to tube size, if possible.

[Chriszuma]

what we do is drill a hole the diameter of the bolt through the piece, and find a piece of round aluminum tube that fits the bolt inside it. Then on the side that will have the part attached, drill the hole large enough to accomodate your tube. Cut a piece of the tube so it is flush with the outer edge when you sink it into the hole. Then sink your new spacer into the hole and bolt your stuff on, putting the bolt through the tube. It's definitely the most effective method, because you can put insane amount of torque on it and it won't deform the squareness at all.

[greencactus3]

Originally Posted by Chriszuma

what we do is drill a hole the diameter of the bolt through the piece, and find a piece of round aluminum tube that fits the bolt inside it. Then on the side that will have the part attached, drill the hole large enough to accomodate your tube. Cut a piece of the tube so it is flush with the outer edge when you sink it into the hole. Then sink your new spacer into the hole and bolt your stuff on, putting the bolt through the tube. It's definitely the most effective method, because you can put insane amount of torque on it and it won't deform the squareness at all.

good idea. but what if both ends of the square aluminum are already covered with another piece of aluminum?

[Travis Hoffman]

Originally Posted by greencactus3

we're gonna use .125in wall square 1x1in aluminum for some things this year. and were wondering about if you wanted to say.. bolt a pillow block to one face of the aluminum. so, drill a hole through the whole thing. as in 2 opposing walls. and then bolt goes through the pillow and then the whole alumiunm.. through 2 walls with space between. gets a nut on the other side of the aluminum.
if we crank down on the bolt, the walls of the alumiunm get crushed. how do we do this without crushing? not cranking as hard might not be a good idea as we dont want axles wobbling around.
and drilling a massive hole on one side of the alumiunm so we can fit a nut through that is an option but will take away structure from the square, as 1in sides means a lot of surface area taken away.
anytips from the veteran teams? btw our pillows are steel or zinc or sumthing. not aluminum so welding that on would be complicated. if possible,. i dunno

The magic of wood - wherever you need more support for mounting things to your frame, cut square blocks of wood, sand them down to size, and use a mallet to tap them into the aluminum for a nice press fit. Then drill and fasten away. Doesn't add much weight, either.

[Not2B]

Since you can't get into the ends of the tube (DOH - hunk of metal or wood IN the tube is a great idea.) then try the washer idea. OR - put a plate of metal on either side of the channel to act as a long washer. The point is, spread out the area the force is acting upon. Pressure = Force X Area.

Farmington Hills, eh... I mentor in Plymouth, but I live in Farmington Hills. And one of the other mentors on our team grew up in Farmington Hills. Small world...

Good Luck!

[gren737]

we've been using that style of frame for years and i have cranked down on the bearing journals VERY hard, i don't think we've ever crushed a bar from over tighteneing the screws. and i'll add we always use semi-thick hardened washers on 1/4 bolts for the drivetrain stuff. so i guess my advice would have to be get some good washers and you should be allset.

good luck!

[greencactus3]

Originally Posted by Not2B

Since you can't get into the ends of the tube (DOH - hunk of metal or wood IN the tube is a great idea.) then try the washer idea. OR - put a plate of metal on either side of the channel to act as a long washer. The point is, spread out the area the force is acting upon. Pressure = Force X Area.

Farmington Hills, eh... I mentor in Plymouth, but I live in Farmington Hills. And one of the other mentors on our team grew up in Farmington Hills. Small world...

Good Luck!

cool. too late for shoving things in now tho. and i just remmebred that the aluminum tube we crushed last year was thinner walled stuff. i beliee we wont crush these. ill try on a scrap tomorrow just in case tho.
yea, and i live and go to school in farmington hills. but we get our welding and not too easy to machine stuff done in plymouth. really small world lol

[Peter Matteson]

Bolting through box is poor engineering practice. I'll spare the explaination today. A better answer would be to rivnut (rivet nut) the aluminum.

http://www.bollhoff.com/web/usa/en/w.../index_us.html

You can get them and the tools from McMaster-Carr.

Pete

[Max Lobovsky]

Originally Posted by Dzdconfusd

Bolting through box is poor engineering practice. I'll spare the explaination today.

Please, don't spare the explanation. I'm interested. I assumed if you sufficiently supported the tube or used washers, bolting through would be fine.

[Peter Matteson]

Originally Posted by Max Lobovsky

Please, don't spare the explanation. I'm interested. I assumed if you sufficiently supported the tube or used washers, bolting through would be fine.

Short version:
If properly supported no it is not a problem. The issue is the compressive stress on the box makes it a weak point and the probable location of a structural failure. This combined with overtorqued fasteners, because even if you calculate the proper bolting torque for the necessary pre-load people rarely use a torque wrench to assemble this type of setup. Also the grade 8 bolts we usually use on the robots are stronger than the box aluminum. In theory you want the bolt to fail before the box deforms so that you don't do any structural dammage to the frame. I hope that helps.

[Chriszuma]

Originally Posted by greencactus3

good idea. but what if both ends of the square aluminum are already covered with another piece of aluminum?

I don't think you quite understood what i was trying to say. You sink your piece of tubing in from the side of the square. the bolt then goes through the small hole on the other side, through the tube, and through the other part, then is nutted. It doesn't require any premeditation really.