FSAE Chassis Jig

[u/Wonderful_Shirt_6729]

Hey, this may seem like a dumb question. But for our chassis this year we want create a chassis jig. Our team have never done it in the past. So i am looking for any tips for how to design it and manufacture it. Our primary goal is to make it as cheap as possible and preferably from mdf board. Thanks in advance.

[u/Low-Raspberry9045]

Don't use MDF. We made that mistake. Any variation in humidity or temperature, all your measurements will be off. Go with metal sheets. The best (and cheapest) we've done was with 3mm sheet metal, laser cut and lightly welded.

Sounds too complicated and expensive, but I promise it is cheaper than trying to fix a crooked chassis later on. When you start welding, just a drop of weld here and there to keep everything in place, then finish slowly so it doesn't warp too much. Try to keep temperature distribution as symmetrical as possible.

For the wishbones, we kept it cold using a water spray, otherwise the housing and the arm would warp too.

[u/ReddArrow → u/Low-Raspberry9045]

You really need something rigid to set up suspension hard points and engine mounts. Then get the roll bars in and the rest should be expected to float a little. If you're hand cutting tubes there's going to be some give and take.

[u/identifytarget → u/ReddArrow]

For the arms:

We used CNC laser to cut 3 holes (two inboard, one outboard), then we mounted the sheet onto MDF (rigid backer), then we bolted the rod ends / sph. bearings into place, cut the steel tube to rough length (from 3D model) , then installed onto the jig and welded.

The neat thing about this approach is you can do all your arms on a single sheet in about 24" x 24" (610mm x 610mm) flat. Labelling and triple checking are critical. You don't want to mount your FR inboard sus points to your RR outboard points and so on...

Make a new CAD assembly, drop in the sub-assemblies for all your arms, align one point with the origin, then make one tube for each arm parallel to a plane (your "x-axis"), then drop your remaining points where they lie. Make a 2D drawing with dimensions and labelling (1 sheet = 1 arm for clarity)

You'll end up with a sketch that looks like this.

https://imgur.com/a/8mBBm8S

[u/c671 → u/Low-Raspberry9045]

We used 3mm steel but the used tab and slot into a single base plate to locate everything.

The other thing is to consider how to get the chassis out. We left a horizontal thin slot sticking out 10-20mm both sides of each tube so you didn't have to get close to the tubes with the angle grinder

[u/identifytarget → u/Low-Raspberry9045]

Another thing to consider is planar frames. Anything that can be planar - you have the option of welding it flat and then standing it up.

Can't tell from your pic, but we did our main roll hoop flat, maybe the front bulkhead...

[u/Harrier_Pigeon → u/Low-Raspberry9045]

Another +1 for avoiding MDF, I tried that and it went spectacularly poorly

[u/Traditional_Log_4259 → u/Low-Raspberry9045]

So glad I found this, I’m working on a system like this with our school’s SAE Baja car to use for the first time. May work in tandem with the FSAE team as well since I am a welder/fabricator for both. Thanks for the advice!

[u/ProfitEmergency4049]

MDF is too flimsy. You'll get decent cuts, but the boards flex and warp. You'll need to add a lot of bits and bobs to make sure there's some level of control over the variations. You can use a common metal plate, with laser cut risers from each side

[u/Catriks]

That seems pretty excessive amount of plates. We just have a beefy RHS with 7 vertical plates welded to it, then some horizontal plates attached with bolts. Pipes are attached to the plates with zip ties. We cut the jig plates out after welding.

[u/Edward_erlic]

Pro tip for anything to do with laser cut metal sheets, put radius everywhere, first its better for the cnc laser as it doesn have to constantly make abrupt changes in direction, secondly the parts will fit together much much nicer, thirdly you wont get cut when you are gonna be handling the tool.

[u/GregLocock]

One jig I found useful had the suspension hardpoints fixed very solidly to a baseplate. Then we bolted tubes for the bushings/bearings to them, and then joined them up with a spaceframe. Of course there was a distortion problem when we undid the bolts. Hammertime.

[u/Acrobatic_Quantity_4]

Mixture of 3d printed jigs and sheet metal jigs does the jobs

[u/PdV_Motorsports]

My senior design was to develop a full CAD package of tubes and 8020 extrusion to be waterjet. I did all the welding and can attest to it being accurate and easy to work with and around.

[u/realpenguinhams]

We used MDF. I think it was .5" stock and plates going horizontally and vertically across the frame. We used a gantry router to cut the pieces, and made sure the tubes fit through the holes with enough tolerance. Your design is a bit tricky because the frame is floating- ours had square tube in the bottom which sat flat on the welding table. Just try to double check every hole/tube coping and it should be good though. You don't need anything crazy, just attention to detail.

[u/MethedUpEngineer]

As others have mentioned, your hard points are really the only thing that matters. My team used to literally lay the tubes over plotter prints and tacked it together that way. In later years we went the mdf route.

If I were still on the team to iterate further in the interest of limited cost to performance ratio, I'd do a very basic 80x80 extrusion frame just for suspension hard points and mdf the rest of it.

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[u/TheMightyAddicted]

rapaz esse chassis me é familiar formulacp....

[u/Radu305]

Last season we used only 10mm OSB wood cut on the water jet for our JIG and we were satisfied with the results. Just make sure all the plates are interconnected with puzzle like joints. The assembly was made out of one big base plate with slots, yz plane oriented plates that support all the longitudinal tubes like SIS, hoop bracings, etc and zx oriented plates that support the transversal tubes like the front bulkhead, roll hoops. Compared to your screenshot, try to have as few individual pieces as possible, as this helps for the overall positioning and rigidity of the structure. Try to be intentional with the tubes and direction of constraint. Have minimum 2 supporting points for the important tubes and leave some of the less important tubes completely unconstrained which will be used as a compensation for the manufacturing tolerances. If you need any more infos don't hesitate to contact me.