Fabrication step by step with box tubing.

#1
I will try to lay out the steps we use to fabricate the half scale NASCAR chassis that we build in the Motorsport program at Greenville Tech.

This is a basic description of the steps involved with box tubing. I will do a complete round tubing thread after this one.

One rule of thumb that I have lived by for as long as I have been welding is " The better the fit, the better the finish". Keep this in mind as you cut and fit parts and you will get better joint fit up and better welds too. Look closly at the pics of the rear frame rail and you will see a prime example of this very thing. You can see the actual fit of the joints after they are clamped and tacked in the jig. Then you can see the finished weld. Look at the difference in the weld appearance with a tight fit and a gap in the joint.

I cant stress enough how much you need to have a plan of parts fit up and welding order. Somethings are covered by another part and once you have welded the second part on you cant go back and weld the previous part.

1 - We have patterns for 4 things on the frame. The front frame rail, the rear frame rail, the front cross member and the truck arm cross member.

2 - Lay out your patterns or your sketch of what you are planning. I find that if I sit down and draw it out as close to scale as I can it flows a lot better.

3 - Decide what stock you need and then cut your stock to length. For the main frame rails we used 2'' x 3'' box tubing. For the front and rear frame rails we used 2'' x 2'' box tubing.

4 - Now is the time to do any miter cuts or offset cuts that are needed. Both front and rear frame rails required multiple miter and step cuts to complete the proper fit. Once you have all the pieces fitted to one another then you are ready to tack all the pieces together.

5 - When tacking the pieces together use a quick but solid tack on all the corners of the joints. This way you start welding at a tack and end at a tack. A good weld will burn through the tack and leave a solid weld bead.

6 - If you can weld the parts in a jig fixture then do so but leave them clamped in place until they are fully cooled. Metal fixtures are best but a good wood fixture will hold a part in place just as well.

7 - If you have a master jig then you are now ready to fit the parts in the master jig. Our chassis uses a master jig so our front and rear frame rails were added after our main frame rails were fitted. We now have a complete frame rail front to rear and it is all clamped in the master jig until the final welding is done on everything that will be attached to the rails.

Jigs and patterns.









Parts cut, fitted and tacked in the jig.





Parts welded and waiting to cool.





Frame rails assembled and welded in the master jig.





More coming tomorrow.

Doug
 
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#4
Thanks guys for following. I went back to school and looked at this project and realized that there really isn't much to add. I covered the jig fixtures and the patterns and the fit up. I honestly don't know what else to add to this short of answering questions.....

I thought that I would have more to add but there is not anything left for this project once the frame rails went in the master jig and were welded in place. We have been building the sides of the roll cage and started on the sheet metal as well.

If you can add to this with fabrication techniques for box tubing please do. If you have a question please ask.

I will be adding to this as we do other projects in class.

Doug
 
#5
Doug, maybe add a bit about cleanliness too. Clean your metal before welding, yeah I know a given, but for those that don't, most metal has an oily finish to "prevent" rusting while in storage. Oil and welds don't mix well.

And tidiness helps too. I'm anal when doing just about anything, nothing drives me nuts more then walking into a shop where things are strewn all over the place. Stumbling over stuff, can't find things cause they are somewhere other than where they belong, equipment that doesn't work right because it wasn't maintained, has me crawling up the wall.

All of these, like said, are givens, but sometimes they need to be reinforced. So says the guy who's son is the polar opposite when it comes to things like this. KIDS!!!
 
#6
And tidiness helps too. I'm anal when doing just about anything, nothing drives me nuts more then walking into a shop where things are strewn all over the place. Stumbling over stuff, can't find things cause they are somewhere other than where they belong
LOL.... Don't come to my shop........ I haven't had time to clean in years. And it drives me nuts too.....
 
#7
Doug, maybe add a bit about cleanliness too. Clean your metal before welding, yeah I know a given, but for those that don't, most metal has an oily finish to "prevent" rusting while in storage. Oil and welds don't mix well.
EVOL brings up a good point. You should prep your metal before welding. Grind all the mill scale off of the areas to be welded. Especially with a MIG machine. They don't like dirty metal be it rust or mill scale or paint or just greasy oily surfaces. The cleaner the weld area the better a MIG will weld.

Doug
 
#9
Here is the result of our efforts. So far we have built a complete chassis and then this roughly 2/3 complete chassis and the other 3 chassis are still not finished....

You can see when it comes out of the master jig that it is only an outer section from the front and rear rails to the outside. We did not build the inner bars or sheet metal as we just want to hang each side on the wall flat. I built the right side again and Bruce built the left side. The one change that I made was to add a battery box to the right side. If it was a road race chassis it would have a battery on the right side. I wanted the extra detail so I added it.

Cage started,



More cage work,



Right side door bars from the inside,



Fresh out of the master jig,





Cutting her in 2.....





There will be a couple more pics after Monday when we get the upper bars cut to length and get it ready to bring home.

Doug
 
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#10
Got the upper bars cut to length and it will now mount flat to the wall. We are planning to cut a piece of plywood in the shape of a ghost body to mount the chassis to. Haven't decided how detailed the ghost body will be. Just have to wait and see how it looks...

Here is the half chassis loaded up and ready to head home.

 
#11
Got the upper bars cut to length and it will now mount flat to the wall. We are planning to cut a piece of plywood in the shape of a ghost body to mount the chassis to. Haven't decided how detailed the ghost body will be. Just have to wait and see how it looks...
I suggest a simple matte black silhouette; focus would be on the frame and not distracted by a detailed body. Clear-coat the frame.
 
#12
I suggest a simple matte black silhouette; focus would be on the frame and not distracted by a detailed body. Clear-coat the frame.
I have considered the matte finish in a light color for the board. But at the same time I want to paint the frame light gray like they typically do on the race cars. If I do then I am afraid that it will loose all the detail. Bruce is going to do the same thing and he is going to clear coat his frame. I have considered it but I am not fully committed to either yet... The display chassis at school is clear coted so we know exactly how they will look clear coated but not painted.

The other option is to paint the full chassis that we built in clear and the half chassis in grey. After it is on display at a student showcase for the Motorsport's program it will be coming home with me. I am going to hang it from one of the I-beams in my shop. I have 16 foot walls so I just have to decide how I want to hang it. I have thought abought just hanging it buy the rear cross member on one of the uprights. Or put the bottom against the wall with it parallel to the floor. I guess I will have to just try it and see what it looks like.

I will post a pic of it when I hang it. Maybe someone has a better Idea..... Sometimes my ideas are duds..... :shrug:

Doug
 
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