Creating expansion chamber template from existing exhaust

[neevo]

I am keen to bite off a big project, mainly so I can improve my fab skills but also because my expansion chamber on my KTM is a little beaten up. I want to have a go at creating a segmented expansion chamber and wondering how I could potentially use the existing one on the bike a as a template?

Thought about cutting up small pieces of tracing paper and wrapping them around until I got rough shape... thoughts?

The other solution is to put all the details of the pipe into a exhaust program, build a pipe from scratch, then chop it up to create the shape around the frame.

Here is the original KTM pipe shape (although not the original KTM pipe):

This is what I am trying to achieve:

I realise some will be sceptical about a novices ability to do this, but I'm keen to give it a go at least. Only thing I will waste is argon, stainless sheet and my time. Worth a crack eh?

 

[stroker crazy]

Worth a crack eh?

At the very least you are going to learn many things!

I'm about to head out for the evening so I don't have the time for a lengthy post right now, but I will put one together tomorrow.

Crazy

 

[neevo]

Thanks crazy! I don't expect to end up with anything useable, but it's having a go that counts and I think I have enough ability with the TIG now to weld it and can use my dolleys and hammers well enough to finesse metal.

Sure a slip roller and some cones to hammer against and I would get something that resembles an exhaust even if it doesn't work

I plan on buying a mandrel bend for the first part and tube for the end, all the rest I am keen to create out of segments.

 

[2_DONE_THE_TON]

i have no experience on exhaust design,but with my architectural design background i would go this way.

measure and template the old exhaust

build in rhinoceros 3 d software

section cut

"unroll" surface

-->what you get are 2 dimensional templates of the sections to cut roll and weld.

nearly every freeformed surface is possible.

 

[teazer]

Try to draw a line down the centerline of the pipe. As it changes direction, it may be easier to stop one line and start another further round the pipe. Then mark it every 20mm and measure the diameter. Then draw those out as a flat straight pipe. You should see a classic chamber shape emerge once it's straight.

The next trick is to work out where to bend it. Then use the appropriate software (there are a couple out there) to work out teh angle cuts and print out the sections and stick it together as a test piece and tweak the angles in the software until you get exactly the shape you want. Then print out a clean copy and start cutting and welding. Check out the Jim Lomas web site for a video of how to make a pipe.

 

[Maritime]

I can't help at all but I want to watch. You will learn a ton I am sure and the first pipe may suck but the 5th will be better and the 10th you could probably start selling. And no matter what your welding and fab skills will get better.

 

[irk miller]

I've never done an exhaust, but when I make templates out of complex forms I cover them with several layers of painter's tape. Then cut the tape off in ways that will allow it to be flat.

 

[Walms]

Try to draw a line down the centerline of the pipe. As it changes direction, it may be easier to stop one line and start another further round the pipe. Then mark it every 20mm and measure the diameter. Then draw those out as a flat straight pipe. You should see a classic chamber shape emerge once it's straight.

The next trick is to work out where to bend it. Then use the appropriate software (there are a couple out there) to work out teh angle cuts and print out the sections and stick it together as a test piece and tweak the angles in the software until you get exactly the shape you want. Then print out a clean copy and start cutting and welding. Check out the Jim Lomas web site for a video of how to make a pipe.

+1
Following the outside will net a slightly longer tuned length overall but if you are copying a motocross pipe for the street, that's probably a good thing!
Good luck with it, you'll have something to be proud of when you're done.

 

[ncologerojr]

I have some experience working with pie cuts. I actually practice with them pretty often because I have some pie cut plans for future projects. IMO copying that exhaust isn't too complicated.

If you break it down, it's just two pie cut cones joined at the large ends along with a couple straight bends. If you just measure the large and small diameters of the tapered area you can order the appropriate sized cones. Coneeng.com is a good source for the cones. Then figure your center-line radius and how many cuts you want to use for the bends. This app works well: http://www.motokarts.com/resources/pie_cut_calculator.xls. The rest is pretty self explanatory.

Here are a few tips I've learned.

-Use a piece of angle iron to draw a straight line up the cone/tubing, then measure and draw another line up the other side. This helps with making your cuts, as you have to flip the cone/tube 90 degrees between each cut. It also helps when lining things up.

-A horizontal band saw works best for the cuts. Also take the time to clean up the cuts and taper the weld area, it will pay off in the end.

-Remember that you can only cleanly join like cuts. Meaning 7.5 degree to 7.5 degree for example. When you cut tube at an angle the diameter changes and dissimilar cuts won't line up and weld as clean. Its easy to forget as your working, ask me how I know lol.

-A lot of pro's start by making a bucket of equal sized/same cut pieces and rotate them as needed to give everything a uniform look.

-Lastly join Instagram and check out guys like 60andpregnant, Charlieturbos and toxic fab for inspiration and tips.

Good luck! Give it your best and you'll be happy.

 

[neevo]

Thanks all. Some reading there. I like the idea of the tape but not sure how you would cut it to get the right shapes.

Bit more research and I will see what a suitable plan of action would be.

I have a load of 1.5mm zinc covered steel here that I will use to do a practice run on, then we step it up to stainless once I have the process worked out.

 

[irk miller]

Thanks all. Some reading there. I like the idea of the tape but not sure how you would cut it to get the right shapes.

Bit more research and I will see what a suitable plan of action would be.

I have a load of 1.5mm zinc covered steel here that I will use to do a practice run on, then we step it up to stainless once I have the process worked out.

Have you welded zinc coated steel before? The stuff is pretty toxic and fumes like hell since the zinc has such a low melting point.

 

[teazer]

Deviant is right. Zinc coated steel will kill you. Try plain steel. 20 - 22 gauge works. It's really thin but strong enough for a pipe.

For angle cuts on cones, you need something a little more advanced that that pipe curve software. I want to say that it's Pipe cone generator or something similar that's out there. Check the free MOTA app for chamber design. I 'm sure there's a cone generator in that or at least in the pay version. As Ian Williams (IWT) in SA.

 

[neevo]

I usually grind off the zinc before welding but head the warnings. Will grab some straight cold rolled instead to use.

 

[neevo]

Looking into it a bit more I've come up with 2 options:

1. Start from the beginning and input the required data into some software and come up with a basic straight pipe. From here I assume I cut the larger sections up (matching the angles of each joining part) and use this to worm the exhaust around the frame

2. Try my damnedest to copy the existing pipe. My concerns with this is that I won't be able to accurately copy the sections and so when it comes to welding them up I may have gaps etc

I can find software to create the pipe dimensions and lengths. Does anyone know of any software that let's you manipulate the pipe and create new angles and cutouts to factor in weaving it around the frame? I suppose CAD style software?

 

[neevo]

Thinking this might help to build the pipe from scratch:

http://www.buildandclick.com/html/tuned_pipe.html

Obviously it helps to create a pipe based on specific inputs and this could be used to create the base. The thing I'm not clear on is how can I twist this template around the frame into the original design?

 

[teazer]

That software is not worth the 20 bucks it costs.

Take the option behind door #1. Just draw the line and measure it every inch or so and when you draw that out on paper you will be able to see the cones and parallel section. Then you use something like http://www.conelayout.com/ to design the individual pie cuts.

You need the basic straight pipe design first and then you decide how many sections and let the software work out a template for each section (pie cut). But you need the overall pipe dimensions first.

 

[neevo]

I'm cool with that teazer. How do I then turn a straight pipe into a bendy one?

I assume I can just cut up the sections but that will make it much shorter won't it?

Was trying to find software where I could take straight pipe and manipulate it into the shapes on the first post.

 

[teazer]

The trick is to start with a straight design - not an actual steel pipe.

Step 2: decide where to make the bends in a cone and how many to get a smooth transition.

Step 3: plug that into the Cone Generator and it will spit out templates for each set of dimensions/curves you input.

Step 4: Cut a set of templates out of stiff card, roll them and construct a cardboard pipe

Step 5: Fine tune that paper design as necessary by changing the angle through which a section is to curve.

Step 6: take that fine tuned design and print out templates, cut the steel, one section at a time and weld up one steel section at a time.

I find the hardest part of that process is deciding on how much of a curve I need and that comes down to angles and number of sections. That's what takes me a couple of attempts and a few sheets of card to get it right. The trick I hear, is to use a length of welding wire to mark out the shape along the centerline of the pipe and use that as a guide

 

[stroker crazy]

… use a length of welding wire to mark out the shape along the centerline of the pipe and use that as a guide

Discs of stiff card glued to welding wire the right distances apart are a big help in visualising the shape.

Crazy

 

[neevo]

My brain hurts!

So I'm pretty happy measuring up the pipe. Will draw a line down the centre and measure diameters at set intervals.

Looks like cone layout software (of the same name) is good to pint out the cones, had anyone used this software and can you create complex shapes at all or is it a program for single cones only?