Front crossmember questions
- Thread starter Zandoz
- Start date
donsrods
Member
I've always used round tubing because I just think it looks cleaner on the front of something like a T bucket. However, on my current rpu project I am using 2 x 3 x 3/16 wall box tubing because I wanted that look to this car and didn't want it to look like a T bucket.
It's really 6 of one, half dozen of another as far as advantages, disadvantages. The box is a little easier to fit in as all you have to do is miter cut the parts that match up and then weld it. With a round tube you have to do some holesaw work and then wrap the frame rails around the tube to finish it off. Strengthwise, I can't see either one being a problem.
You ask about size and thickness. On a round tube I use some 2 and 3/4 diameter tubing x 3/16 wall, and on the box tubing I use 2 x 3 x 3/16 wall. For the frame on my rpu I went to 2 x 4 x 3/16 and tapered it down to 3 inches at the front to look less bulky. But on a typical T bucket frame I use 2 x 3 x 3/16. I just like the rounded corners of the 2 inch vs the 1 and 1/2 wide, which tends to be more square.
Here is my current one with the square crossmember.
Don
It's really 6 of one, half dozen of another as far as advantages, disadvantages. The box is a little easier to fit in as all you have to do is miter cut the parts that match up and then weld it. With a round tube you have to do some holesaw work and then wrap the frame rails around the tube to finish it off. Strengthwise, I can't see either one being a problem.
You ask about size and thickness. On a round tube I use some 2 and 3/4 diameter tubing x 3/16 wall, and on the box tubing I use 2 x 3 x 3/16 wall. For the frame on my rpu I went to 2 x 4 x 3/16 and tapered it down to 3 inches at the front to look less bulky. But on a typical T bucket frame I use 2 x 3 x 3/16. I just like the rounded corners of the 2 inch vs the 1 and 1/2 wide, which tends to be more square.
Here is my current one with the square crossmember.
Don
Actually, I'd usually prefer the round tube also, but in this case, I'm planning on a whole heap of unconventional. Angled frame rails with a R&P steering setup, mounted on top of the crossmember...the steering shaft passing alongside the radiator...all hidden inside a track/sprint style nose. The square tube crossmember should make mounting the rack, and mating with the angled frame rails, a lot simpler.
I had been thinking along the lines of a 3x3 1/4" wall square tube, but it's sounding like that may be a bit of overkill.
I had been thinking along the lines of a 3x3 1/4" wall square tube, but it's sounding like that may be a bit of overkill.
meangreen
Active Member
Yes, 1/4" wall is more "beef" than you really need. The front crossmember is fairly short and therefore very rigid, so it's not prone to flexing. Some on this site insist on 3/16" wall tubing, others are satisfied with 1/8" wall thickness. If you are planning on using a heavy, torque-monster engine like a Hemi or a blown big-block, the 3/16 wall would be advisable. Otherwise, it's a matter of preference. Over the last 40+ years I have built over 20 complete frames including several T-buckets, some C-cab deliveries, an Anglia, at least a half-dozen Model-As, a '37 Chevy, and the Deuce replica under my coupe. All but one of the C-cabs were built from 1/8" wall material.
In this case, no torque monster...just the opposite. It's going to be a GM 60 degree V6...please don't hurt yourself laughing. This is going to be a casual cruiser, not a ground shaker.
I had planned on 3/16 wall for the frame rails, just as a matter of playing it safe...now I'm starting to think maybe 1/8" may be the way to go, especially considering I'm planning on a shorter than typical 96" wheelbase. Based on the weight of a 20' section of 3x2, it would save 34 lbs. Hmmmm.
donsrods
Member
Jim is right, 1/8 is really more than sufficient. I only use 3/16 because we tend to overbuild everything, and the 3/16 wall also gives a little more thicknes so you can tap threads into it for non structural things like line clamps, etc. 1/4 would be way overkill IMO, but the car sure would sit nice and low. 
Don
Don
Don
Don
1/8" would be fine for that little V-6, but when you win the lottery and get that blown 454 to drop in there, then what. There is not much difference in the cost of a length of steel.
They use 1/8" wall in drag cars, but they have a full cage with lots of triangles to help support all of it.
No blown big blocks likely for this little car, even given a lottery win...short wheelbase with a 27' body wouldn't leave room...LOL. I think if I hit the lottery, I'd build something around a V12 Jag engine. I've always loved em.
Now back to reality...I'll probably stick to the 3/16 wall. As Dino said, better safe than sorry.
Jim is right, 1/8 is really more than sufficient. I only use 3/16 because we tend to overbuild everything, and the 3/16 wall also gives a little more thicknes so you can tap threads into it for non structural things like line clamps, etc. 1/4 would be way overkill IMO, but the car sure would sit nice and low.
Don
Don
If this thing gets any lower, I'd have to plan on a trencher mounted off that front crossmember...LOL
Ted Brown
Member
Lots of good answers here... The two main differences between the 1 1/2X3"x 1/8" (= .120) wall over the 3/16 wall 2"x3" is the fact that the smaller size id 'Decorative' tubing, and it has tight corners,,, the 2"x3" x 3/16" is a Structural size, and the corners are larger and a bit more rounded... I used to like the tighter corners better, but age has mellowed me out, and like the fact that with the heavier material, brackets welded onto the frame, may not need to be a large, like the area that welds to the frame, with the .120 wall, the bracket needs to go from top edge, corner, to the bottom... To keep the bracket from working itself out of the thinner material, you have to grab the corners for more strength... especially with mounts that hold suspension parts, like shocks and springs and radius rods... the longer the bracket, the more leverage is working against it, and it needs more material at the frame end, to keep it from working out of the frame, a FLAG on the brackets (up through the whole frame, welded to the topside as well as the bottom) will give you much peace of mind ESPECIALLY with a clutch chassis... As stick shifts are a lot stressful on those type of connection points... JMHO and BTDT
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