Frame question

[Ttownbucket]

Please give me your thoughts on using 3" x 2" x 1/4" rectangle tubing to build my frame out of, with a 3" schedule 40 round tube for the front cross member. Is this overkill? Will the corner radius be too much? I really like the idea of being able to drill and tap holes to mount various components (non-suspension). I think it will only add about 40-50 pounds to the frame over 3/16" which will give me a good excuse to spring for aluminum heads to make up for the added weight. Let's hear what you guys think. Thanks.

Jason

 

[smokeyco75]

Mine is 2x3x3/16 and it will handle a big block no problem.

 

[hulkamania]

We use 2x3 3/16 for our T frames.

 

[Golly]

3x2 x 3/16 is minimum requirement down here. It's really only fuel and brake line clamps you need to drill & tap the frame for? Other stuff, like proportioning valve and fuel pump mounts , I just weld a small plate on the frame the same size as the mount, and tap that. Looks pretty smart I think.

 

[bobs66440]

I think 1/4" would be good. It's convenient to drill/tap for things like shock mounts, headlight/tail light mounts, etc. I don't believe you would notice the added weight...who cares on an overpowered 2000 lb car anyway?

 

[iroct]

Thats what I used for my coupe. I also wanted the choice of drilling and tapping. Worked out well for me. I would use it again Dwight

 

[choppedtop]

I use nut certs for anything 1/4"thread and up.
Lee

 

[RPM]

The silver car in my avatar had a 1/4" frame in it. I only did because of the drag race 4 link in the rear, and no roll cage to stiffen the frame. Probably overkill. All of the frames we build for customers are 2x3x3/16"

 

[Screaming Metal]

Mine is also 2x3x3/16s. Hot Ford 460, FMX Trans, man. valve body w/shortened tail shaft, narrowed Ford 9" w/3.5 gears....

 

[Screaming Metal]

Overkill is good...to a point. 2x3x1/4 will handle a Blown BB with no problems. On my 3/16s frame wall, need to tap the frame, I use weld nuts to attach things, on my rear kickup, I use cheekplates on the frame for re-enforcement .... but thats just me....and my 2 pecos

 

[Ttownbucket]

Does anyone see any downside to using 1/4" other than weight? Mine will be a fairly mild small block Ford. Hoping around 300HP, so I'm not really worried about twisting the frame with engine torque. Thanks for all of the responses.

 

[fluidfloyd]

Jason,

I don't think you really need 1/4" wall tube. If you're looking for torsional stiffness then I would prefer to see either cross members or X members. I also prefer weld bungs or plugs over all other choices for threaded holes. Any hole drilled into a structural member that will take bending loads (as in weight, bouncing or twisting) will be a stress riser and is always subject to the starting point for a crack. By welding in a small diameter threaded bung you have effectively eliminated that issue. One other point that may or may not matter to you is the outside corner radius. I don't have a material book with me but a 1/4" wall will be bigger then a 3/16" corner. This will be a purely personal choice. I know that sometime I might sound anal about somethings but it comes from years of making mistakes and experience in the racing world. I know you will powder coat your frame and that is the one thing I dislike in true high performance type racing cars. Powder coat does tend to hide small cracks until it's into failure. I don't think you can even paint T/F or funny car chassis's anymore. Even though a heavy wall mild steel frame isn't a race car it will get far more real world road mileage so the possibility of problems are always there. It's just two easy to eliminate the possible problems and not worry about it. Then you can coat away. Hope this will be of some value to you. Good Luck.

George

 

[Golly]

I agree with fluidfloyd. The strength is more in the design than just frame thickness. A couple of welded in crossmembers will make it a lot more rigid.

 

[bobs66440]

Does anyone see any downside to using 1/4" other than weight? Mine will be a fairly mild small block Ford. Hoping around 300HP, so I'm not really worried about twisting the frame with engine torque. Thanks for all of the responses.

To answer your question, no, there's no downside other than the corner radius mentioned.

 

[Ttownbucket]

Thanks everyone for the input. I agree with pretty much everything everyone said here, and certainly got some good info. If someone has a picture of a welded in threaded bung I would like to see it. For some reason I can't picture what it should look like in my head. I'm not necessarily considering the heavier tube for frame rigidity. I will certainly have at least two crossmembers and maybe a crossmember and a K member when my frame is done. It's more for the ease of mounting things like headlights, radiator supports, tail lights, tank mounts, brake lines and so on. Again, thanks for all of the input and feel free to continue to add to this thread.

Jason

 

[fluidfloyd]

Thanks everyone for the input. I agree with pretty much everything everyone said here, and certainly got some good info. If someone has a picture of a welded in threaded bung I would like to see it. For some reason I can't picture what it should look like in my head. I'm not necessarily considering the heavier tube for frame rigidity. I will certainly have at least two crossmembers and maybe a crossmember and a K member when my frame is done. It's more for the ease of mounting things like headlights, radiator supports, tail lights, tank mounts, brake lines and so on. Again, thanks for all of the input and feel free to continue to add to this thread.

Jason

Jason,

I don't have any pictures but I will explain it. Just say you wanted to put a 3/8-24 thread in the side of your frame tube. You would drill a 5/8 diameter hole where you wanted the you threads to be. Then you would machine a 3/4 or 7/8 diameter solid rod down to 5/8 diameter leaving a larger diameter flange (3/4 or 7/8) at one end. Turn your part around and re chuck in a lathe and drill and tap to 3/8-24. Press this into your drilled hole in the frame and TIG fuse the larger flange diameter to the frame. Now you have a threaded hole with as much thread length as you want and no stress riser problems. You can do this in both flat sides or in round tubes. The round tubes will be limited if flange diameter versus tube diameters. With smaller thread size you just reduce the bung/flange diameters to your required needs. Any questions just ask. Hope this will help you. Good luck.

George

 

[old round fart]

I don't have a lathe so I have drilled a hole big enough to put a net in the hole and weld it in. Smallest I have done was 3/8".

 

[TriodeLuvr]

McMaster Carr sells weld nuts for this purpose. They're not available in fine thread, but they're inexpensive. A 50-pack of 3/8 x 16 is less than $8.

Jack

 

[fluidfloyd]

McMaster Carr sells weld nuts for this purpose. They're not available in fine thread, but they're inexpensive. A 50-pack of 3/8 x 16 is less than $8.

Jack

Jack...Those just swell up in the frame hole and lock themselves in place. That still doesn't eliminate the drilled hole in the frame from being a stress riser. By machining a like part as you have shown you can weld or fuse the flange to the frame rail and have no stress points for a possible crack to start. But like they say, "You pays your money and you takes your choice!"

George

 

[EX JUNK]

Jason, here is a picture of the K member in my frame that may help you.



This is the best shot that I have of the welded bungs. They go through the frame and are welded on both sides.



Jim