Wednesday, April 23, 2014

What I did on Marathon Monday

For this post I'd like to share the process I went though to make a prototype base plate for a teaching kit I'm working on. It turned out a bit like a guide, but I'm not necessarily saying this is how to do things. It's just what I did and it seemed like a natural way to write it.

Here's the short version of why I did this:
My UROP advisor teaches 6.131 Power Electronics Laboratory. After seeing what I did to his 6.115 kits he asked me to come up with something for this class as well. I'll get a post going for that project, but it's taking me a bit longer to write up because it's a doozy. There will also be a real update on what I've actually done to the 6.131 kit once it gets a bit more finalized and all my time isn't taken up by classes.

Fire up your favorite CAD program and get your part drawn out.

I use SolidWorks which has some pretty nice sheet metal tools which let you fold and unfold your part. Other programs probably have it too, but SW is what I know. This flattened view is what you make your process drawings from.

Here's an assembly view for a bit of context. The upper bent metal part is from the old version of the kits, but will be reused in this new version. Previously, the legs of the kit were 2" by 0.25" aluminum standoffs that would come loose and were a bit too wobbly to carry over into this design.

Low shot of the assembly.

Print your drawings. One with dimensions, one at full scale.

Trim your drawings and stick them to some stock

Measure critical dimensions to ensure you aren't about to waste a few hours.

Cut part profile using a bandsaw / shear / grinder / sander / files.

Check critical dimensions again.

Center punch bolt holes and drill to appropriate size.
Note the hole close to the bend line ended up being distorted by the bend. Ideally, the base plate would have used this position for mounting, but just in case they did distort, I also added the larger holes that bolt though the ventilation slots.

Bike over to the shop where you have access to a bending brake.

After modifying your design on the fly so it is physically possible to bend on your brake, bend-o flex-o into shape.
I had to cut the front side flange down about half an inch so it didn't contact the bed of the brake. In the below picture, the front flange is already bent and is behind the clamps. This is also why I'm working at the very end of the brake rather than the middle.

Check straightness and critical dimensions. Height was good to within 0.003". Length wasn't great, but worked as a prototype (about 0.1" too long after bending)

Assemble using whatever hardware you can get your hands on. Make note of what hardware you probably should have ordered a few days ago. In this case I'll be using 1/4-20 truss bolts on the top and nylock nuts on the bottom.

Be sure to take multiple angle shots that sort of match your CAD screenshots.

Finally, decide what alterations should be made to the part. If they're major, make a new one. If they're minor, adapt what you've got and adapt the drawings.

The plan is to send drawings of this part to be manufactured in quantity by some company with tools fancier than ours once I really nail down the design.

Until next time.


The bent up feet have arrived from a fab shop. They're all spot on and fit the existing kits without issue.