Introduction: BAJA SAE Subframe
Here is the step-by-step guide on designing and fabricating an aluminum subframe that will hold the crucial drivetrain components for your Baja SAE kart such as the engine and CVT pulleys.
Step 1: Design Your Subframe to Your Liking
Free Briggs & Stratton Model 19 10-hp engine and Dana-Spicer H12 FNR Gearbox designs can be found on GrabCAD and be used in your SolidWorks assembly. The subframe was designed with 1/4" thick 6061-T6 aluminum and would incorporate the mounting bolts from the gearbox to hold the gearbox to the subframe. This step also allows you to determine what belt length you will need for your CVT pulleys.
Step 2: Build a Scale Model of Your Design
I had used 1/4" thick wood to create a scale model of my design. This step allows you to finalize your rear chassis design on your Baja kart.
Step 3: Test Fitting Subframe With the Rear Chassis
Step 4: Order Your Material, CVT Pulleys, and Gearbox
Order correct CVT bore diameters for your engine and gearbox. Order extra shaft keys just in case. When ordering belts, add an extra inch (for deflection) to the Center Distance between pulleys.
Step 5: Test Fit the Good Stuff
Step 6: Begin Milling Your Aluminum Plates
Step 7: Drill Mounting Holes Using Driveshaft Bearings
Step 8: Finish Milling Any Features
Step 9: Check It Out!
Step 10: Find Yourself an Aluminum Welder
I used the Klutch 140si MIG Welder for the job since it was available for use. Plus it was FREE! A TIG welder would have been preferred as well as produce prettier welds.
Step 11: Appreciate Your Work
Paint will hide those brutal welds inside the box that were hard to reach with the welding gun.
Step 12: Throw on the Good Stuff!
The next step is to drill the mounting holes for the engine and on the bottom subframe plate to attach it to the kart's chassis.
Step 13: Bolt Everything Down and DONE
Finger guards will be fabricated to encase the CVT pulleys and will attach to the left side of the subframe. A forward and reverse selecter cable will mount to the right side of the subframe to connect to the gearbox shifter shaft.