Drilling Steel For Sheet Metal Screws

When using regular sheet metal screws, as opposed to the self tapping kind, you have to pre-drill the correct size hole. For the #14 sheet metal screws I'm using to hold the new subframe elements in place on the unibody until I bolt or weld, that turned out to be a 3/16" bit. The hole needs to be just big enough to fit the shaft of the screw, or else you'll break the head off when it gets to the point where the hole is too small. That's what happened here:



When you're sliding a new piece of metal up inside an existing subframe rail, and you don't have any way to clamp it or force it against the surface it will be contacting, you need to pre-drill the hole before you put the piece in the unibody. Otherwise, the drill would just push it back from the hole:

Run Time = 23 seconds



I found this nice little chart for the smaller sheet metal screw size pilot holes after the fact. This other site heavily quotes the I.F.I Fastener Book. While there, I learned that there's a "right" side to a stamped flat washer, something I never knew. The side with the chamfered edges (smooth rounding) faces out to the bolt head or nut. Interesting.

Buying Steel Tube For Car Frame Repair (Unibody)

Bought steel for the first time in my life this morning. I went to the local steel supply company (they do retail as well as commercial) to get some steel tubing to try to replace unibody elements with my own frame, and I also intended to buy some 18 gauge cold rolled steel sheet for the floor repair. It turned out they didn't have any 18 gauge scrap, wthat means I'll have to buy a 4'x 8' sheet if I get it from them, which costs about $68, and weighs 2 lb per square foot, or 64 pounds a sheet. I didn't want kill somebody having it fly off my roof rack and I didn't want to fold it in half, so I'll have to come back with a pickup truck if I buy the sheet steel from them.

They did have some light wall steel tube in stock, so I bought two 6' lengths of 2"x3" rectangular tube, with a 0.083" wall thickness, or 1/12". The weight on the tube is 2.73 lb per linear foot, the next thickness up being 1/8" (0.125") which weighs 3.85 lb per foot. I'd set out intending to buy 16 gauge, which happens to work out to a 1/16" (that's happenstance, not a U.S. steel gauge translation), but they didn't have tubing that thin. I'd done a little Internet research which suggested that 16 gauge was common for unibody frame elements, but I'm happy with the steel tube I bought.



Doing the research, I noticed that new car manufacturers have switched to metric for sheet steel measurements, and I saw number ranging from 1.0 mm to 2.0 mm in discussions about frame construction. 1.0 mm is a little under 0.04 or 1/25", meaning 2.0 mm is right around the 1/12" that I ended up buying. While steel is priced by weight, the United States Steel Gauge is given in fractions of inches (or translated to mm). I'll just give the ones that work out nicely to inch fractions:

1/8" = 11 gauge = 3.18 mm
1/16" = 16 gauge = 1.59 mm
1/20" = 18 gauge = 0.953 mm

All I need now is one of these steel cutting machines:-)

Run Time 2:17



The problem with buying steel tubing rather than steel channel is that I'll gave to do more cutting, and all I have to do it with is a 4-1/2" grinder with cutting wheels. I don't know how accurate I'll be, but I have enough extra stock to practice a little. My goal is to leave the tube whole (four walls) wherever possible, but to cut and peel back the ends for flaps to attach to the existing body steel where possible. Should be interesting when I get out to my garage/studio tomorrow and start measuring.