Metal tubing question...welders' wisdom wanted!

[Fat Hack]

When welding steel tubing together at a 90 degree joint, with the idea that something (in this case, exhaust gasses!) will be flowing THROUGH said tubing, is it best to pop the appropriate diameter hole into the larger tube, then to insert the smaller tube into the hole a ways...or should the smaller tube be contoured on the end to fit the circumfrence of the larger tube?

Flow restriction won't be an issue with a bit of the non-contoured small tube sticking inside of the larger tube...I was mainly concerned with strength, and what most welders would prefer to have brought to them for welding!

(Once I get all of my pipes and pieces cut, I will have to seek out someone to weld the parts together)

Trying to iron out the exhaust system on the Chevy...functional portholes in the fenders are my goal!

[Hot Rod To Hell]

If you "fismouth" the smaller tube (like a tubing notcher cut)and weld it to the larger pipe, you will have a larger surface area of weld, so I would guess that to be stronger. http://www.jalopyjournal.com/ubbthreads/images/graemlins/crazy.gif

[Paul]

dito, fish-mouth the small tube and use it to mark the hole in the large tube.

butt weld with no projections inside

butt you knew that http://www.jalopyjournal.com/ubbthreads/images/graemlins/wink.gif

Paul

[Unkl Ian]

[ QUOTE ]
Is there an easier way to "fishmouth" the tubing...

[/ QUOTE ]
Power tools.

[Paul]

you can buy a jig that holds the tube and uses a hole saw in your drill press

I've seen them at welding shops.. Dale Wilch used to sell a version.

you see them used more in roll cages then headers.

Paul

[burndup]

$35 Harbor freight drill press... or cheaper at a garage sale.
$40 HF Tube notcher jig for drill press
$7 Milwaukee bi-metal hole saw

[Junkyard Dog 32]

I mad a simple set of jigs to fish-mouth tubing with my plasma cutter.
They're just a piece of angle iron, that you clamp, lenghtwise, to the tubing. There's a stop that hits the end of the tube, and a raised peg, to which I welded a washer (used to bolt my different sized half-moon patterns that I run the plasma torch against).
I make the cut, then rotate the pipe and switch to the second jig. It's the same as the first, but the stop is located about a 1/4" further out, to center in the first half-moon cut.
Works good...

You can do 'em freehand, too. It just takes a good eye. Besides, if you're good with a wire-drive, who minds a little gap?
The trouble spot is always getting the "points" thin enough to straddle the other pipe. Know what I do? I grind them points right down. Then do a little fancy fill work with the welder. Saves a ton of time working on the fit.

JOEhttp://www.jalopyjournal.com/ubbthreads/images/graemlins/cool.gif

[tommy]

If you aren't going to build a lot of roll cages, take your time and cut 1 fishmouth with a pair of snips. When you get a good fit make a wrap-a-round out of poster board tracing the fishmouth. Use it to mark the rest of the tubes and you'll save lots of time and money.
http://fototime.com/{31A93FEF-7915-4C06-B6C4-E6FA3901B706}/picture.JPG
This is one for a square cut. I could give you directions to lay out the end cut and the hole pattern, but you would have the job done by the time you layed it all out. For our apprenticeship we had to make patterns for a small pipe stabbed into a larger pipe on a 45 deg. angle including the hole pattern.

Give me a torch and I'll have it done before you can get the paper ready. You can hold the small against the trunk and lay the torch on it's side on the trunk. Cut away the part that makes contact until it fits all the way around. Mark around the end and cut the hole just inside the line.

[DrJ]

If your freehanding the cut, seems to me if you hold the tube another is needing to be fishmouthed up tothe side of the other and shown a high intensity flashlight thru the one tube it will cast a shadow at least close to the shape you need on the fishmouthed piece.

[Cadillacin Marcus]

w

[stolenmojo]

i'll chime in that the best thing you can do with the fishmouthing jig in the drillpress is throw it away first. you'll do it in the end anyway, save the hassle. on thick tubes the holesaw chunks teeth or goes out of round, on thin stuff it looks like a beaver attacked your tubing. i like the reverse of tommy's suggestion. wrap cardboard (like a file folder thickness) around the tube to be fished out. tape it together to make a tube. trim that with scissors until it fits right, transfer to tube. death wheel and tootsie roll and your done. that exhaust idea looks sweet.

brandon

[choprods]

Cut a V knotch in the END of each small tube about half the amount of that small tubings DIAMETER.........then slightly "round the "fishmouth" shape a little with a grinder....its an exhaust pipe-right?[Not a roll cage]...... http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gifOH AN' MAKE THE 3 EXIT PIPES HUGE...to scare us at the starting line...... http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[draggin'GTO]

Screw fishmouthing the three tubes. Just cut three holes in the larger tube and insert them into the holes, just make sure it's a snug fit and then weld 'em up.

Should be a cool-looking set-up, gonna be a bit of exhaust soot build-up on the fender around the ports after a while though.

[autocol]

hack: you got a friction cutter? it's a drop saw with a gigantic angle-grinder blade in it...

i could cut you a fit that was good enough to weld with a TIG in about 3 minutes a tube. worksheet looks thus:

1. mark roughly with pen.
2. go apeshit with friction cutter.
3. test fit.
4. repeat step 2, with slightly less apeshit-ness...
5. see step 3.
6. repeat step 4, scaled down in agro again.
7. etc
somewhere between 8 and 15. weld.

unk was right. powertools are the go.


if it's worth anything, the go karts i make at work are EXACTLY what you're doing, OVER and OVER and OVER. once we have a design, we "fishmouth" as you guys call it, the tubes in custom jigs with a milling machine, but you know how we do the prototypes?

see above!

[laverda]

Hey Hack,
For some reason I could link to the thread ... but ... try this program

Miter Program (http://www.ihpva.org./tools/tubemiter.exe)


and this is my comment.
"Furter to tubemiter progam .. an excerpt from the author.

SNIP

Tubemiter.exe

A tube mitering program for Windows to print on any printer.
The other one is a Hypercard application for Macintosh,
and once I dug up a Mac and a PostScript printer, it was very
useful. However, it doesn't take wall thickness into account,
which is important when doing small angles or equal sized
tubes. My program also deals in metric units.

File/Settings... puts up a dialog box. You input:

* Diameter (in mm) of tube being mitered
* The wall thickness of this tube
* The second tube diameter (the one it abuts up to)
* The included angle in degrees.

It paints the picture on the window, and File/Print... prints it
on any connected printer.

There are two curves - the dotted one is the template you
would cut if the wall thickness were zero (similar to the
HyperCard program's output) and the solid curve is the template
corresponding to the requested wall thickness.

If the mitered tube diameter is greater than the second diameter,
then the second tube passes through two holes in the mitered tube.
This situation is handled by continuing the template on the
other side. Small gaps may appear in the curves; this is a known
"feature" of the way the program works.

Giles Puckett
giles@research.canon.com.au

SNIP

The Chopper Builders Handbook suggested that some 'fudging' may have to occur as the program works best for thin walled tubing (bicycle dimensions) ."

I found it with a search parameter of 'miter' on the HAMB. I wonder what the search actually does, I could not find this thread searching by my name, but rather had to try a number of words till 'miter' worked. Odd.

Later,
papa al

[Deuce Rails]

[ QUOTE ]
Is there an easier way to "fishmouth" the tubing...

...one that DOESN'T involve about a million hours and a hand file??? http://www.jalopyjournal.com/ubbthreads/images/graemlins/crazy.gif



[/ QUOTE ]

Use a pair of snips like Tommy suggested. How thick is your tubing? It should cut easily, and you can sneak up on the right shape. No need for a million hours with a hand file.

--Matt

[4t64rd]

Street Rod Builder (the one with the green and black Deuce on the cover) has a article about fishmouthing tubing, you do a little math and make a paper template. Listed to methods, hacksaw and angle grinder and milling machine.

I don't have time to scan it (packing for Vegas) anybody else?

[Hot Rod To Hell]

Hey HACK.... if you only need to make a few cuts I'll let ya borrow my tubing notcher, but if ya break it, I'll break you. http://www.jalopyjournal.com/ubbthreads/images/graemlins/blush.gif http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[LUKESTER]

rough cut a V in the tubes, buy a 1 1/2" sanding drum ( $5 ace hardware) put it in your die grinder and go to town..... simple as that.... LUKESTER