Legs 7: Getting Close

I set up the table saw yesterday to make a very shallow cut around the body of the legs. There's a detail there on R2D2 that needed to be added. I've tried to get a good picture of it several times, but no luck. My camera doesn't do extreme closeups very well. I set the saw blade to run .06" high (yes, that is possible), and then after carefully measuring the location, I ran the legs through so that there was a groove that runs all the way around:

The tape helps prevent blowout with the outer layer of the plywood.


I also finished gluing the curved pieces to the center legs:



Then I cleaned the excess glue up off of those, and used the orbital sander to bring down the edges of the MDF pieces where they overlapped. I got the MDF pieces all sanded flush and incorporated. I also put a 1/2" axle hole in them. Be sure to clamp a scrap to the back side when you drill to prevent blowout. The center legs are almost finished. I'll go over them once more for any gaps or dings that need to be filled, fill them, finish sand, and then I'll put a coat of primer on them to see to what extent any seems or joints are showing through. You can also see the modification on the tip of the leg here. This extra wing will rest down flush into the foot shell groove and provide a stable joint between leg and foot. And since this is on the back of the leg, it would still be possible to straighten this leg up for an upright posture:



I also finished gluing and nailing the four ankle panels to the bottom of each leg. And today I cleaned up the glue and then sanded the sides on the belt sander to get a good clean joint.



Once that was done, I could finally lay out the lines for the leg tip:




I roughed those cuts in on the band saw.



And then finished them down close on the belt sander with the belt tipped up to 90 degrees. The end results are starting to look familiar:



So what remains is to mount those curved pieces on the right onto the ankles, cut the round hole into the shoulders for the shoulder detail, and then do some finish filling and sanding.

One problem I've been having is blowout on the the outer finish layer of the plywood. I don't know if I got a sheet that had too little glue in the final layer or if the final layer is just too thin, but some spots are really fragile and friable. The worst example is when I made this cut through with the band saw:



It all blew off of there so suddenly an severely that I have to think that they messed up on the glue here. But I'm not sure. This sucks as it produces a lot more work for me and it lowers my confidence about the rest of the pieces enduring use over the long term. I have a couple of options to fix it (the other spots are much less bad than this). I can try to fill the region in with glue, body putty, or fiberglass/resin Bondo and then sand it in to blend. I think the last option will make the best looking and most durable results. I'll work on that this week. I also think that once I get some primer on there to seal these up, and then their new owners get several more coats of primer and several finish coats of paint, that paint will cure and form a consolidated skin that will be more durable. The wood won't do this once it's painted right. But I have to be extra careful until then.

MDF Horseshoes

I recently completed a batch of R2D2 horseshoes. These go on the outsides of his shoulders. I've gone through several designs and techniques. What I've settled on here is a single piece of 1" thick MDF. I've routed out the detail pockets in the front, then I rough out the shape on the tablesaw and bandsaw. Then I round the curve and finish the sides with the belt sander. Finally, I use the router with a 1/8" x 1/8" groove router bit to cut the shim on the back and then the grooves along the inside. The process is elaborate and it all has to be done in just the right order with jigs and so on. I've tried PVC layers, MDF layers, and several designs, but this is definitely giving the best results. I've got several pairs of these for sale for interested builders. These are perhaps the most complicated pieces on the droid besides the feet and they will consume a lot of time and resources, so I think this is a bargain at $85 a pair.

Here's the back showing the shim:


And the front with the pockets:



A closeup of the inside grooves:



The shim from the outside:



Another shot of the grooves and pockets:



The club officially authorizes periodic runs of aluminum parts, including these horseshoes. In order to make it worthwhile, there needs to be enough buyers to do a large group of them. Aluminum horseshoes are much more expensive--usually around $225 or more. If you want aluminum, I encourage you to go that direction and help make the machine shop runs possible. I've built these horseshoes for builders who do not have the budget for aluminum and who are not able to do the sort of construction I can pull off with my shop.

R2 Goes to Sam's School

On Wednesday, just before Thanksgiving, I took R2 over to Sam's preschool to see all the kids. They were very excited. There seems to be a short or something going wrong with the sound system. When I would press the button for one of the sounds, I'd get an amperage spike and the sound would cut off short. I turned the sounds off for the visit until I can investigate the problem:





The motors are still running weak. I think that on one of my very first tests, I pushed the left motor too hard and damaged it. Every since, its response has been sluggish. I am eager to get more reliable, responsive, and higher torque motors in there. The answer is a set of the NPC 2212 motors from NPC robotics. And I think I am going to build a Senna style drive train (the files are in the files section of the Yahoo group). I've been searching around for some cheaper parts alternatives. The Surplus Center has all the gears, axles, chains, and extra links that are in Senna's plans. Mike got his from McMaster Carr, but the Surplus Center options are much cheaper. And since they have keyway slots already cut in them, there's no need to buy the keyway broach cutter for the project. So I think I can save about $150 on the project, which is substantial. The keyways are little slots that have been cut into the axles and into the gears. When you slide the gear onto the axle you then put a small strip of metal into the slot and it locks the gear to the axle for the power system to turn it. That will be the next project after these two sets of legs are done.

Legs 6

I got the rest of the main bodies on the legs glued up today and sanded the curves on the top. Next up, I went to work on the curved ankle details. You will remember the big 1.5" thick blank that I made a few posts ago for this purpose. I've got 4 pieces to cut for the two center legs and 4 pieces for the 4 outer legs. Check the plans. The dimensions are slightly different.

First, after marking the curves on the ends, I used the bandsaw to rough in the curve cut all the way down the blank. This will save me a lot of sanding later.



These cuts take some tricky set up and dangerous maneuvering on the bandsaw:



Then some sanding on the belt sander got me to here:


I'm applying soft, even pressure along the full length of the piece and rolling it constantly back and forth on the belt until I get close to the profile of the curve I'm after.

I moved over to the table saw and cut four of these to 4" and four of them to 4.1" as per the plans, giving me 8 semi circle plugs. Next a diagonal slice needs to be trimmed off of them at 35%. I set the table on my bandsaw to 35%, adjust the fence and play around with the fit a bit, then I can run these through and slice it off:



Once that's set up, it's easy to do all 8:



The pieces that go on the outer ankles have a little recessed rectangular pocket in them. I have a trick for making those. The pocket is .25" tall, and .06" deep. I set up the router table with a .25" groove bit and the router fence 1.3" inches away (per plans):




Then I run all four of the outer pieces across the router to make a groove in them:






Then I cut a little strip of MDF to fit tightly into this slot, but a bit thicker. Next I cut some strips, and glue them back into the sides of the groove leaving the rectangular pocket at the correct dimensions.



I used a paint brush to put just the right amount of glue in there. I want the glue to ooze out just a bit and fill up any gaps between the base and the strip.
Once these dry, I can put them onto the belt sander and bring them down flush with the base piece. They may take a tiny bit of filler, but they'll be ready for paint and I have perfect rectangular pockets now exactly to the blueprints.




Now that all of these are shaped, I can start mounting them onto the legs. First, the center legs:



I use enough glue to ooze out of the sides a bit and fill in any gaps, and I purposely made the curved piece a tiny bit wide. Once these are dry, I can return to the belt sander and bring them down flush with the base. Once I get the ankle pieces glued onto the legs, I'll put the slotted curved pieces on them too.

Legs 5: Under Shoulder Pockets

Now the basic shapes of the legs are all cut and part of the layers are glued:


But before they can be permanently joined, the pockets under the shoulders need to be routed out. The way to do that is to use the Senna style template I made yesterday and rout out the pockets. I'll take the legs apart into two halves and route both sides, then put them together to box in the pocket:





I'm using a 1/4" slot cutting bit on the router and a bronze collar that rides along the template:



So when the two halves are joined, they form this recessed pocket:



These are just held together with a screw for now. I'll clean up the edges, do some sanding and get these ready for paint. Eventually, the little under shoulder hydraulic greeblie will fit in here:



Since the under shoulder detail takes up most of the pocket, there's no need to do too much finishing work on it. I may add a piece of styrene across the back of the pocket at the bottom where it shows to give it a clean look. The router method is definitely the best thing I've tried here. This pocket can be very hard to cut and very hard to finish. Repeat this for the rest of the legs and we'll be ready to glue and move on tomorrow:



One part that's coming up is the compound curved piece that mounts on the outside of the ankles for all three legs:



Some builders bend styrene to form these, or use preformed tubes. I'm going to build up a blank from MDF and then make the two cuts. I'll glue the plies today so it will be ready soon for that step:



This stack is 5 1/8" by 1 1/2", which is big enough for both the outer ankles and the center ankle pieces. 48" long, I think. After this cures, I'll cut two blanks--one for the outer ankles and one for the center ankles because they are different widths. Then I'll rough in the curve with the table saw and bandsaw. I'll cut the wedges and finish on the sander. There is a small recessed slot in these too. I have some trickery planned for that.

Outer Legs, stage 4

I'm going through some complicated ordering of cuts and gluing stages in order to accomplish a couple of things. I want to be able to finish sand all inside cut edges with the belt sander or maybe the orbital sander before assembly. I also want to glue multiple pieces together where possible when they are all going to be cut to the same dimension. If they are glued first, the cutting second insures that they are all aligned. But both of those goals can't be met with every part of this. There are three big pieces that are glued together that make up the outer legs. The outer most one is cut down to a point and goes down into the slot on the foot shells. The inner two are cut off higher so they clear the tops of the foot shells. Here I've glued the two inboard pieces and then cut them off at their shorter length.



Then I sand that edge clean. Next I glue the longer outer piece onto those. This piece closes up the passage inside for the wiring. Next, I set up the table saw to make most of the cuts down the blank. You can start to see the shape of the leg come out here (no, the saw isn't running here).


Cutting them this way helps me get a straight, consistent cut. Since all of my blanks are the same size, I can set the saw up once and then do all of them quickly. Just flip the piece over to do the other side. Before making these cuts, I scraped the excess glue off of the sides from yesterday's glue ups. Otherwise, the glue will push the piece out from the fence and mess up the cut. I slide a chisel down the glue drips when they were about 2 hours old. They were dry enough then to come off, but soft enough to be pliable. Then I hit the side with the belt sander a bit before this cut. I also marked the point where the leading edge of the saw blade underneath would come to and made sure not to cut too far into this piece. Very important. I'll finish this cut--since the table saw leaves a curved cut in there--on the bandsaw.

Next I cut the angles under the shoulders with the bandsaw. I've got a wide blade with a pretty high tooth count on there right now, so cuts like this are straight and pretty clean. The edges that are left will need some filing, and then some cleaning up with an orbital sander.



Next I've roughed out the curve across the top of the shoulders on the bandsaw, and then I take it to the belt sander again for cleaning up. Starting too look more like a leg.




Next up, it's time to deal with those frustrating under shoulder pockets. On my first set of legs I did not find a really efficient way to do these. Victor Franco, with Mike Senna's help, has worked out a trick by routing out these pockets oversized and then lining them with thin MDF. His results are nice once all the joints and cuts are filled and sanded. I'm not going to go that far. 90% of the pocket cuts will be covered by the little greeblies that fit in here. But I do think I'll copy part of their method to rout them out. So I've made a template on 1/8" MDF for cutting. If you haven't done it, take your R2 plans to kinkos on a jump drive and get them printed up full size. I had an extra full size leg blueprint for this:



I sprayed some spray on adhesive to the MDF and to the back of the paper and then just smoothed it on. Then I cut it out on the bandsaw. I've cut the pocket profile slightly large--about 1/16" over--so that I can use the template collar on my router for this. The next stage will be tricky. I think what I am going to do is this. I've got the two big inboard pieces of the legs glued together for the both sets of legs. I think I'll screw the third outboard piece onto those and then cut them all into the shape like the one above. Then I'll take the outboard piece off and cut these pockets with the router. Then I'll put the outboard piece back on with glue. We'll see what sort of results I can get inside the pockets this way. I think it will be clean enough to require a minimum of additional work. But that's all for tomorrow.

Once those pockets are cut, I can glue the final two pieces on the inside and outside of the ankles and finish them out. That will be tricky too. But I'll be able to explain with pictures better when I'm there.

Center Leg

The center leg is assembled with two layers of 7/16" plywood for the central piece, sandwiched by pieces of 11/16" on either side. The center piece is the bit that sticks down into the slot in the foot shell. That slot is 1" thick. With glue and paint the two plies of 7/16" is just right. So I cut and laminated those together. The screws will be hidden by the outer pieces:


And then I cut the outer pieces. Here I've screwed them together and put the curve line on them to be cut out. By screwing them together and cutting them at the same time I save time and I get the curve on both of them exactly the same.




I have found that for curves with a small radius like this (anything less than 9"), I get the best results by roughing in the cut with the bandsaw and then finishing it on the belt sander:






I got that belt sander from Grizzly Tools when I was building kitchen cabinets and furniture more and had a lot of sanding. It is huge--the sanding area is 6" x 48", I think. And it tilts up with this table on the side for doing right angles. It cost a bundle at the time, but it's been worth every penny. It's a 220 volt machine which required some creative wiring in the shop, but the motor doesn't bog down under any load that I've put to it. The results here are fine:




The curve cut has exposed a couple of small voids in the plies, so bit of body filler putty and another light sanding and they are ready to go:




Since these edges will be up against a larger piece, it won't be possible to sand them or finish them effectively once the center leg is put together, so I save myself a lot of hassle by getting them paint ready before they go together:




The whole stack of all four pieces will look like this:



And then screwed and glued together with another run on the belt sander to get all four edges clean and flush:




You can see the layout marks on a design modification I've made on the R2 plans here. I've sloped one side of the pivot point back at an angle so that it will all rest flush into the slot on the foot shell. The one on the right has the line for the cut that the plans call for. The pointed design on the real R2 isn't very good for several reasons. First, there's a lot of weight and torque that gets put on a relatively small area here. This front foot shells will be leading into cracks in the sidewalk and all kinds of rough terrain. Leaving more material here makes the joint stronger. Second, if you watch the discussions on the club board, everyone is having problems with their foot shells popping up and shifting around. So it's common for builders to go back and add ankle locks to keep the foot shell in position. This is a much sturdier, more effective ankle lock. And with the full length of that section resting down into the slot on the foot shell, the weight is distributed better. The alteration will be visible from the back if someone got down close to look at it and knew what the real one looks like. But the advantages here outweigh the disadvantage. And here's one more shot from the side. You can see that the lines are clean, straight and smooth. All done with power tools--no long hours scrubbing with sandpaper by hand.