Looking for pipe fabrication tips

[Chuck Bunnell]

I'm in the process of attempting to fabricate an expansion chamber for my shifter. I'm going to be using the cut cone method and would like to hear a lessons learned kind of thing from those of you that have made these before. I already have a shear, slip roller, assorted grinders and cutters, and a mig welder that I'm not entirely confident in. What are the tricks of the trade here? Thanks!

[John Scott]

quote:

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Originally posted by Chuck Bunnell:
I'm in the process of attempting to fabricate an expansion chamber for my shifter. I'm going to be using the cut cone method and would like to hear a lessons learned kind of thing from those of you that have made these before. I already have a shear, slip roller, assorted grinders and cutters, and a mig welder that I'm not entirely confident in. What are the tricks of the trade here? Thanks!

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Chuck
You are off on a real adventure. I recommend you visit TSR web site http://www.tsrsoftware.com/tech.htm
for some basic info and access to Tom Turner's software. We used his software to develop several shifter pipes and it works well. Tom also has a lot of info on how to build a pipe, which is probably what you need.

As to the equipment you have, it is a good start. TSR pipe software includes apps to layout cones that you can cut, role and bend.

We used TIG welding but found that the TIG welds were very brittle. I broke several pipes at the welds in the curve at port exit. A shifter vibrates a lot and this area is quite stressed. One solution is to just get an RCE/RLV pipe (maybe that someone altered during a driving incident), cut off and use the curved part. Also, the connection to the stinger and the exhaust manifold are hard to make and recycling them is quick.

You will also need a lot of detail on your engine to effectivly use Tom's software.

We found that the development state of the RLV/Banke and RCE pipes is quite high and you need to be working a total package with a good engine builder to advance very much. However, we were able to make small, specialized gains and I learned more about engines than I ever expected. Plus people come and look and wonder at what you are up to...

[Mark Watkins]

Boy you certainly learn a lot about the value of excellent metal fitment. I tig'ed mine and it came out fine. However, you learn very quickly that RLV and RCE kinda know their way around the block. Based on my experience, they both offer a great value. Being off 1/2 inch in tuned length can make a potentially good pipe into an excellent garage decoration.

Mark

[Chuck Bunnell]

To provide a little more background on this adventure I've chosen, I'll type a few syllables. My shifter is a laydown, enduro, road racer, whatever you want to call it. I started building much longer ago than I really like to admit which mostly means the motor is fairly out of date. It's an 86 CR125 which is a cylinder fed configuration. I had the clever idea to reverse the cylinder to put the carb in the front and the exhaust out the back like a "normal" kart. My background is clutch karts. This makes packaging the shifter stuff much easier, especially since my enduro is narrower and lower than a typical sprint shifter. But mostly it means that a custom pipe fabrication is required to get anything that will actually fit. I posed the pipe question to the forum at http://www.macdizzy.com and got some good responses. About that time I also purchased a copy of MOTA 5.0, a two cycle engine simulator. So I have spent a fair amount of time collecting the data to properly model the engine in MOTA. Another user there spent some time with my model and came up with a pipe design that works really well with it. I'd really like to test it in the real world to see if the model was accurate or not. I wouldn't consider a cut cone method if I had to do one of them twisty shifter pipes that curl around the engine. All I really need are two bend points in my pipe and then a "U" shaped stinger pipe to fit the kart. It really makes me more impressed with those that knock these pipes out for a living. Also makes me think there are some tricks or steps along the way with mystery fixtures to help out. On the bright side sheet metal is fairly cheap as far as learning goes. Thanks for the replies so far.

[Andy Szyszkowski]

quote:

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Originally posted by Chuck Bunnell:
I'm in the process of attempting to fabricate an expansion chamber for my shifter. I'm going to be using the cut cone method and would like to hear a lessons learned kind of thing from those of you that have made these before. I already have a shear, slip roller, assorted grinders and cutters, and a mig welder that I'm not entirely confident in. What are the tricks of the trade here? Thanks!

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Chuck,

As a start, I found it much easier to simply buy the cones (including head pipe) pre-made to your spec's from Aircone in Henderson, NV. I weld the seams in the cones myself, though they can do it for you. I've personally never had success welding sheetmetal this thin with a MIG (maybe I need more practice!). For pipes, I actually prefer an oxy/acetylene torch over a TIG for speed and versatility. You'll need a real small tip. I use .025" MIG wire for filler when needed.

You'll need some bucks to hammer the welds (if needed), and to blend any abrupt inside surfaces. These also help to "bring back-to-round" the cones from deformation after welding.

Make sure to use multiple tack welds, which will reveal itself if you make some practice runs (much suggested if you've never welded sheetmetal before).

I first weld the headpipe to the flange and start my cuts for the appropriate routing. I like to use 7.5 degree cuts (we're talking shifter pipes), which yeild a relatively smooth 15 degrees when you twist the sections 180 degrees. I like to use the axial weld seams for referencing. Again tacking in several places around the perifery, I tack as many sections together as feasible before the final perifery welds in case I need to make some adjustments.

Don't forget to compensate for the amount of material lost with the saw cuts. Fourteen cuts (for a shifter pipe) @ .050" cut width = .700". For a clutch kart pipe with three cuts at a more severe angle (say 15 degree cuts each yielding 30 degrees to total of 90), it's less a problem.

I've built lots of shifter pipes, many following the TSR software parameters. With your out the back configuration however, it certainly helps to minimize the complexity by a whole bunch. I've built four CR125 enduro laydowns, so drop me a line if I can be of any assistance.

Andy

[Chuck Bunnell]

Thanks for the reply Andy. I learned sheetmetal MIGing when I worked at the body shop doing rust repair back when I was in school. Not really that much different than any other MIG weld. Just got to match your wire diameter, heat and wire speed to the material. I think I'm using .030 thick sheet or so. Just about the max that my shear and roller can handle. Been a while since I bought it. The butt welds have been easier than I thought they'd be.

Restoring or making the tubes and cones round is definitely a challenge. All I have set up now for beating and banging is a one inch diameter bar of 4140 mounted in cradles on an I beam bolted to the bench. That way I can have an unsupported end sticking out if need be. Kind of curious what some of the other shapes used could be and where/how to get them.

Cutting the cones to make the bend is definitely a challenge. Do you just hold it by hand in the bandsaw or do you have some magic fixtures to hold it? This appears to be the hardest part of making a pipe. Also, when you cut the cone losing that little bit of material, do you need to do anything to get the ends to line up properly?

I've also learned from the fabricating I did over the weekend that I'll need to start at the header and slowly work my way back cone by cone in order to make this thing fit my kart. The packaging is kind of tight.

Thanks for the advice.

[Andy Szyszkowski]

quote:

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Originally posted by Chuck Bunnell:
Thanks for the reply Andy. I learned sheetmetal MIGing when I worked at the body shop doing rust repair back when I was in school. Not really that much different than any other MIG weld. Just got to match your wire diameter, heat and wire speed to the material. I think I'm using .030 thick sheet or so. Just about the max that my shear and roller can handle. Been a while since I bought it. The butt welds have been easier than I thought they'd be.

Restoring or making the tubes and cones round is definitely a challenge. All I have set up now for beating and banging is a one inch diameter bar of 4140 mounted in cradles on an I beam bolted to the bench. That way I can have an unsupported end sticking out if need be. Kind of curious what some of the other shapes used could be and where/how to get them.

Cutting the cones to make the bend is definitely a challenge. Do you just hold it by hand in the bandsaw or do you have some magic fixtures to hold it? This appears to be the hardest part of making a pipe. Also, when you cut the cone losing that little bit of material, do you need to do anything to get the ends to line up properly?

I've also learned from the fabricating I did over the weekend that I'll need to start at the header and slowly work my way back cone by cone in order to make this thing fit my kart. The packaging is kind of tight.

Thanks for the advice.

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Chuck,

For beating and banging on the cones, I too have a one inch bar, but with a spherical end for small diameter blending. The pipe guys also use tapered segments of larger diameters to beat on. Another cheap back yard approach is to buy various sizes of trailer balls and mount them to a bar for hammering the welds and blending. You can as well, machine the ball to a short tapered segment.

For cutting the cones, I tilt the bandsaw table to half the cone's included angle. I made an adjustable guide for the 7.5 degree cut(or whatever angle of cut you choose). It took some experimentation to find just the right saw blade configuration and speed for a good clean and consistant cut. Use gloves when cutting!!

As for losing material, if you make a lot of cuts, then it is definately a concern. If not, don't worry too much. I add to cone length after mapping the pipe, but keep the starting and ending diameters (which only slightly affects the finished angle). To get the match "back" and some of that lost angle, you can hammer the cut end to slightly expand it's diameter. The whole trick is to estimate beforehand the number of cuts. Ignoring the loss in length has always yielded a pipe that I found was slightly too short (in the case of shifter pipes, but not clutch kart pipes), though you can fudge a little here and there.

So, these are just some of my own experiences. In the end, I've found it is far more cost effective to simply have someone else build the pipe, as it takes far more effort than most believe. The first few pipes were fun. Good luck with your project.

Andy

[Jack Burroughs]

Did a lot of pipe fab. back when the silencer cans went on the old 200 yam. pipes. Use tig with argon at least 75% and 1/16 tungsten, not over 60 amps, 680 or 308 s.s. 1/16" wire, good fit-up=good welds. Also made header pipes from 308 s.s. tube and plate, knock-on-wood, never had any breakage. takes a lot of practice to weld sheet metal, these things will help a lot.