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Signing UpStep 1: Planning / Materials
The solution that we arrived at was to use a Harbor-Freight Pneumatic 1/8" Micro Die Grinder, and attach it in-plane with a precision linear slide rail. The Micro Die Grinder runs at 56,000 RPM and has the 1/8" collet that I needed for the PCB drill-bits.
The keep the die-grinder in-plane with the rail, we decided to mount the linear rail to a self-centering drill-press jig.
The parts list:
1.5" Square Steel Tubing - Scrap from Around the Shop
56K RPM Micro Die-Grinder Drill - Harbor Freight - $10.00
- http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=47869
Self Centering Drill Press Jig - Harbor Freight - $6.00
- http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92046
THK Linear Slide Rail - $10.00
- Ebay, Search for "THK Slide" or "Linear Slide"
MDF for deck - Scrap from Around the Shop
MISC. Screws - Scrap from Around the Shop
Springs - Home Depot / Lowes - $5.00





































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However, I agree with your findings of the prices. This instructables must have been written 20 years ago when thing where cheaper.
If I had welding equipment & some scrap iron, I'd probably weld the frame like in the instructable (which is a great one, I should have mentioned that in my first post). But I don't have welding equipment & I'm not good at searching out that kind of help, so 80-20 is the path of least resistance for me. I got addicted to the 80-20 T-slot stuff (not the HT) at my previous employer, and since then I've never looked back.
I work really close to an OSH, I should shoot over there & see what they have. Tomorrow I'll be in the vicinity of a Harbor Freight so I figured I'd pop in & spend some money. I haven't had the best luck with their stuff holding up but it's so inexpensive, I know that going in... :-\
Anyway, I'm an EE and not an ME, so all those courses that taught things like load shear and tensile strength & static & dynamic loading are long forgotten ( :-( ), but I know that the 80-20 materials are incredibly strong and used in a LOT of industrial applications. The reason I mention shearing etc... is that (as an avid mtn biker myself) I know that the dynamic environment of a loaded bike rack going over bumps, potholes, rutted dirt roads, etc. is different than a static load of say 1 ton on a cart.
My only concern would be the joining points during heavy transient loads/bumps. The extruded aluminum material is extremely strong & rigid, the question would be if the connectors are strong enough & can be tightened enough to ensure nothing would come apart during travel. Funny enough, I have a Bones 3-bike rack that I bought about 10 years ago, before I became aware of 80-20. Were I to need a new rack today, I might consider a similar project.
Anyway, I want to mention that the support folks at 80-20 are EXTREMELY knowledgeable & helpful & don't turn their noses up at you if you aren't BigCo. They (in my experience) treat all (potential and current) customers well. So my point is that if I were in your shoes, I'd call them up & mention what you want to do, and see what they can do to help you. I've never done a CAD design, all of my needs have been simple and I order simples pieces that come together at right angles.
The nice thing about the extruded aluminum, in addition to the light weight & cool aesthetic (IMHO), is that is doesn't rust.... kinda nice for an application like a bike rack.
Anyway, here a couple of links that *might* be of additional assistance:
The 802- Deflection
Calculator]
and
The 80-20 Design Resource Center
Sorry, I kinda feel like I punted on this, if I was a stronger designer I'd take a shot at your bike rack myself.
One other thing (then I'll stop the rambling) is there are a couple other places, at least, that offer strong lightweight aluminum construction pieces. I don't have firsthand experience with these 2, but they may have reference designs or assistance that get you going:
Faztek T-slotted aluminum solutions and TSLOTS extruded aluminum materials
I have a feeling that it's only a matter of time before some industrious Instructable fan will make the bike rack!
80-20