Square hole in square tube

[bubblybill]

I have no idea what Im doing! I dont have any engineering background and I havent worked with metal as Im mostly wood orientated, So I could really use your advise/help.

Im designing a cnc wood router and I would prefer the frame to be made from steel. I need to make a bracket to align the rail but I dont know how to go about cutting a square hole in a rectangular box section of mild steel

Please forgive my attempt at drawing, but It probably better than me trying to explain in words

Any ideas, help, or humorous comments welcome.

I wouldnt use a hammer to put a screw in as I do have some technical ability but could really use some help.

Thanks in advance

[Geof]

Get the smallest fine tooth saber saw blade you can find. Drill a hole just large enough to take this blade at opposite corners of your square hole location and cut it out with a saber saw. Go slowly and use some tapping fluid as a lubricant; if the lubricant starts smoking you are running the saber saw too fast.

[Superman]

2 other methods

--mark out the square, drill out on the corners ( they need clearance anyway ), hacksaw the lines as Geof suggests

or

--mark out the square, cut across the diagonal corners, mill in a vee in both parts and then clearance drill the top, tap the bottom for bolting together

[bubblybill]

Thankyou for advice, Looks like my design will be born after all !

[Mcgyver]

there are ways to cut a square hole, but because of the challenges good designs tries to avoid them unless absolutely necessary....maybe have a round hole and an adapter that fits inside it and insidethe square tubing (brazed maybe)?

[dertsap]

if you have a drill press handy then you could easily lay out the square then drill with a 1/8 dia drill bit all along the layed out lines , then clean it up with a die grinder or file

[youngjim]

If you can leave a bit of a radius at each corner then it'll be more resistant to cracking from flexing. Either leave a bit of material at each corner (i.e. don't file it square) or drill a small hole centered on each corner if the design permits.

Jim