The Big Think

May 5, 2015

JAG 04 and a Milestone!

Filed under: The R2 Project — jasony @ 6:17 pm

Big day today! But first:

Last night I cut the final part of the main body on the Waterjet. It was by far the longest cut I’ve had to do (though not the most complex). Gratefully, the WJ performed perfectly with no garnet clogs or pressure drops. I did two 22:00 cuts for a total of 44 minutes of cutting. I cut two identical parts.

Here’s the FlowCut software with my part all laid out and pathed, ready to cut:

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The solid lines are cutlines, the dashes are traverses (where the cutting tube moves but shuts off the water so it’s not making a cut). The colors denote what percentage of speed the machine uses. In short, if you tell the machine you’re using .5″ 6061 aluminum (which I was), it calculates the fastest possible cut speed to get through the material. You won’t get a neat or clean cut (you’ll have pretty jagged edges), but it will go all the way through the material. In order to get a neater/smoother cut you tell the machine ahead of time that you want it to go at only 80% of optimal speed, or 60%, or whatever. Then as it’s cutting you can dynamically speed up or slow down the cutter as it cuts out critical surfaces. You can see in the above photo that the top and bottom edges are dark blue (the 40% speed). This is because those surfaces will be drilled and tapped and a flat and neat cut is critical. The light blue lines are less critical and the purple lines are only there to cut out chunks of aluminum for weight reduction. Make sense?

Anyway, once I was happy with how the layout looked I did a dry run and the machine ran the 22 minute cycle with the pump off (so basically free since you only get charged for cut time). After that I clamped down the part and did the cut.

But first! The previous day I’d gotten to this part and realized that the narrow piece of aluminum I’d purchased was only just barely wide enough for the part with very little room left over to lay down the weights that I normally use to secure the aluminum blank. If I’d have executed the cut I’d have risked running the cutting tube into a weight, breaking it, and have to pay TechShop $250 for a replacement. So what to do? Why, spend 6 hours on the manual mill machining up a set of custom clamps, of course! Four pairs of brackets (5052 aluminum) with a threaded rod connecting them. The bottom bracket has threaded holes that the rod screws into while the top bracket has oversized holes so they can slide up and down the threaded rod and be captured and tightened down by nuts and washers. Today I cut a nice little lasered box for the whole system. I’m even going to powdercoat the metal pieces red for visibility (well, really just because I can). It’s a good system. Here’s the narrow piece clamped down on the water jet table:

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The aluminum brackets hold the piece very securely and the blast skirt that surrounds the mixing tube (where the water comes out) easily clears them. The tube would probably still break off if it hit the brackets but this gives me a lot more room to maneuver.

So once this was all done I started the pump, hit play, and watched the machine do its thing.

For the first few seconds after the stream starts (eight or so) you can tell that the water/garnet mix is cutting its way through the .5″ of aluminum. All of that water has to go somewhere so it bounces back off the part, gets turned to (very warm) steam, and sprays everywhere. This is not a neat machine to operate. Wear grubbies. My arms got a light sandblasting from the overspray from each of the pierces. Once the stream is through the material, though, it’s smooth going. All the water exits out the bottom of the part and gets absorbed by the water in the tank.

Now that the critical JAG04 parts (shoulder plates) were done, I hit my milestone: all basic frame parts are now done! Today I went in to TechShop and precariously balanced/clamped the parts together into the frame to check fit. Looks like everything fit fine though I won’t know for sure until the holes are tapped and bolts/screws installed.

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There are some curved pieces on the front that you can’t see since they’re held up by holes and screws that aren’t there yet. Speaking of holes and screws:

NEXT STEP: Now that the basic frame parts are done I’m entering once again into uncharted territory. I have to drill out (enlarge) the holes that the waterjet cut by just a little bit. I’ll clamp each piece onto the mill, locate the exact center of the hole with a “wiggler” tool I just bought, and then swap out the wiggler for the correct tapping bit. I’ll then enlarge the hole and swap out the drill bit for a spring loaded tap guide which I’ll use to keep the tap handle perfectly straight. Then I’ll tap and clean the hole so that it has nice neat threads. Lather, rinse, repeat.

One hundred and fifty one times.

Yep, most of those holes you can see on the frame need to be slightly enlarged and have threads cut into them. I also need to drill and thread the ends of each of the vertical 3/4″ aluminum rods (I’ll do that on the lathe with basically the same procedure as described above). One hundred and fifty one holes. I’ve tapped exactly five holes in my entire life. I’m pretty nervous about this. I figure I’ll be doing this at a rate of ten or so holes per day. I’ll doubtless start slow as I figure out how to find the centers of the current holes and get a feel for tapping (the last thing I want to do is break off a tap in my beautiful frame pieces) as well as get into a groove on procedures and muscle memory. I figure it’ll take me three or four weeks of work to finish this step. Boooring but important.

You know, it is possible to actually buy a frame online for about the same amount of money as I’m spending do to this myself, but it’s really rewarding and fun to learn so many new skills. I really feel like I’m stretching what I can do and adding some skills to my skill set.

By the way, I discovered something: if you assemble an R2D2 frame at TechShop don’t expect to get any work done. Little R2 was the star of the work area (called the “Hub” at TechShop) this afternoon. I probably had a dozen people come up and ask me what it was and then start offering all sorts of suggestions of what I should do. So for the record:

1. No, there won’t be a holoprojector (yes, you’re very clever for saying this… you’re the hundredth person to do so)
2. No, there won’t be a short guy inside (ditto)
3. No, it won’t be completely autonomous (though I’ll try and make it at least as smart as a Roomba) (and ditto again)

Onward!

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