Since the winter appear to be absent in my shed, it is not too cold to make some good progress. Progress the last few days has been getting to grips with Shapr3d. I Mentioned before it is one of these bits of software that will change the way casual users are going to be designing their parts. Anyway, I need something to hold my skins on the frame. For the tails end I did not mind soldering, but preparing those bits is very time consuming. I also have it in my mind that I need to make some progress to get things flying soonish. Anyway, I figured I should try to make some clips to speeds things up.
Now that I have the hang of it, it will take me 10 mins or so to ‘design’ these parts. Since this stuff is relatively small, I do need to keep the limits of the printer in mind. Still printing in 0.1 mm layers, It takes forever, but it looks nice!
Of course the Big Question is: will this survive in real life. I guess only time will tell. There are other, more stronger filaments out there, so I am not too worried at the moment.
This support is for the 6 mm carbon tube. The red tube is a 3 mm cross piece to mount it on. The complete contraption consists of 3 parts. Why so difficult? I told you, it’s all practice!
Daniel (#2 son), is doing some free-lance development work for game-figures. Once you have the design it is a small matter to see if your figure can be printed in Real Life. Since the printer is loaded up with ABS plastic, just press ”go”.
I printed this one flat, with 0.2 mm layers, and not enough thickness). I wanted to try out the effects of adding an aceton slurry to the part. I did not do anything to it, just brushed on abs-slurry. (put some scrap abs in a container with aceton, shake and stir. Add more plastic to make the slurry thicker.)
The result: promising. This is more or less the same idea as the vapor treatment, where you hang the part in a closed container with aceton vapor. Using a brush seems to produce similar effects.
With the skins ready it is time to do another trial fit. And this is where I discovered a booboo.. The bolt that locks the elevator pushrod in place interferes with the skins.
Ok, don’t panic. Think. The 3mm bolt is not really 3 mm, it’s 2.9 mm. That introduces unwanted play, so it is no good anyway. The hole in the link ball is 3.0 mm. Sooo… a bit of 3 mm tubing locked in place should do. And so it was done. Actually this is a much simpler and secure solution. (for now anyway)
Last bit for now is the creation of better fitting hinge pins.
AcrodusterComments Off on And a happy new year to you and yours!
With all the good times behind us, it’s time to start work again. Santa was kind enough to bring me a handful of drills in all sizes from 1-2 mm. So it’s time to start drilling and tapping holes again. Officially I should drill a 1.6 mm hole for a 2 mm tap, but I find that in stainless steel that is too small. Drilling 1.7 mm works just great. And since there is not really a heavy load on the bolts, it all should work.
Adding the little tabs is a lot of work, if I prepare a whole row it is easier to solder, but takes a lot of time to prepare. Making them individual takes less time to make, but is more difficult to solder. Ah well, it’s all part of the fun. I think this part of the build is the most challenging so far.
3D printComments Off on Christmas is near, so we slow down a bit.
This time of year other things need my attention, so I’m a bit slow at the moment. I’m still working on the tail side plating near the stabilizer of the SA750.
However, something as mundane as ‘a bit of plain 2mm iron strip’ proves hard to come by at the moment. Everywhere I look I can get stainless steel, but I need the lowest, softest iron I can get. I need it to make those small pesky tags to attaching the plating. This means drilling the holes at the right size for a 2 mm tap, without braking everything. As these things go, the first side went without a hitch, repeating the other side has wipes out my stash of properly sized drills. I am now waiting for Santa to deliver more.
So, in the meantime, I got a request for some multi cylinder gadgets. No problem, he says optimistically, after all the printer prints nice and smooth, at a reasonable high speed, what could go wrong?
Nothing, just that my standard slicer (the one I cursed before) did not want to know. So again back to Cura. At least we are on talking terms, it’s just a matter of dialing in all these variables.
And so you discover that PLA does shrink. Most parts I have printed never had any issues, but this one was challenging. No matter what I tried, it kept warping and popping loose from the bed. At 140 mm diameter, a 1 % shrinkage is 1.4mm. And it does shrink more then that.
Anyway, he who wastes a lot of plastic, will succeed. One of the ”secrets” I discovered was a special magic substance for coating my super duper sticky bed. (as in, I never got to stick large parts to it). There are stories around about using pva based hairspray and such. Then one dark night the lightbulb went on: I’ve got loads of PVA, it’s called wood-glue. Squirted a bit in a container, added a bit of water, mix and apply. (I’ve seen suggestions for a 10-15% ratio water/glue.) And to my astonishment, my very unwilling parts stick. No more warping, no more popping loose.
If that was all there is to the story, I would have been finished long ago. But Murphy had a good time!
My extruder stopped at random times, mostly when I was not watching.
The feed tube at the top of the filament heater popped out at midnight.
The filament escaped from the extruder
Of course a blocked nozzle to make it more fun.
My printer can print quite speedily, but that proves its (my) downfall.
Printed parts started cracking after a day.
The extruder problem was caused by a broke wire at the connector motor. Why now? Why not now? It took a bit of searching to locate that problem.
Feed tube is held by an Festo connector. It just got tired from being moved around continuously. Fixed that.
Filament guide had to be remade, including better alignment of feed rollers and tubes.
Blocking nozzle, obvious some cr@p in there.
Printing too fast: oops, actually, that is fine for small parts, where shrinkage is nu issue. Bigger parts, contrary to gut feeling, need to be printed much slower, so that the hot plastic does not cover more than 2-3cm in length.
So after all this was overcome, I have now printed multiple parts where the print-times are in excess of 18 hours. As always, the end result is much experience gained, a much better printer, and plans for a much larger volume version are being hatched!
The result is a nicely printed 9 cylinder dummy engine, printed at 0.1mm layer (with variable layer thickness at the top) speed of most sections ca 60 mm/sec. Bed is 45 C, nozzle at 215 C. GCODE file is approx 75Meg.
In order to fly by the seat of his pants, a pilot needs a seat. For weight saving reasons this one used aluminum straps. I am sure that solution was fine in sunny California, but I doubt it would be comfortable over here. Never mind, scale is scale! I might at some stage add the fake rivets that secure the ends around the tubing.
I just realize I forgot to add the attachment points for the safety belt.. Soldering stainless steel (750 C) and alu (melts at 350C) don’t go together. Guess I’ll have to fake soldering them (JB weld to the rescue)
The back support of the seat is made from heavy canvas, I must have a look if I can find some old suitable trousers!
I suppose it would also be a Good Idea to make sure you can reach the servo from the bottom of the fuselage. I can feel a non-scale access hatch coming up!
Not visible anymore is the connecting rod between stick and servo. I replaced the first solid version by one that can telescope. Just to make sure we don’t get any unwanted inputs from ye driver! It works like a servo-saver with 2 springs on either side of a solid point. I have approx 15 mm travel each way. I might do a drawing for that, lest I forget how clever I was.
Long ago I had a Yak that I had to retire because of a wing-tube that approx 3 degrees dehidral (too many snaps I guess). Anyway, I usually keep all the good parts of a retired air-frame. So I had the actual bracket for the wheel. I had a single nice looking wheel, and a bit of carbon. An old wheel axle provided the new bearing for the part.
The result looks good enough for now. The wheel axle needs changing to something steel (brass won’t last long) but that is a later job. The hideous bolt on top will also need hiding at some stage.
And yes, I want to add the weight now, so that later-on I will not have any CG surprises!
Funny enough, Probuild still caries these tail-wheels! (I got mine sometime 2002 I think, when I used to live in Trowbridge/ UK.)
The panels for the access to the rear end are made from 0.3 mm stainless steel. The main challenge was working out a method to fit the panels with screws as per full size. After the inevitable ”not fit for use” parts, I think I worked out a method that I can use at the front as well, without adding too much weight. I am using 2 mm steel strip, partly drilled and cut at the locations I want to keep. I use the panel for alignment, and when the first 2 point are soldered, I remove the panel and solder the remainder. Afterwards I cut of the bits no longer needed. Once the lugs are prepared, they are tapped with 2 mm. At present I am still working on the cutout for elevator, but already it looks great.
In hindsight I should not have followed the plans for locating the tabs. It would have been better to place one or 2 at different locations, i.e. I now need to add 2 extra to hold the front part of the cover and an additional one to hold a filler plate above the hole for the stab. Hey, it’s a Homebuilt!
It is always a good thing when the magic red lines end up where they should..
Making the bottom bracing means you have to get everything lined up properly. You don’t want to start pulling this out of whack. Since I went through all the trouble making the clevises, I might as well use them. Officially the stab side is made by drilling a hole in the flattened streamline tubing. Guess no one will know except me (and you). It is also easier at the moment to make them that way, so that I can slip the streamlined ABS tubing over the 3mm rod.
In order to give the plastic some time to cool down and to provide some stability, I print a ‘cloverleaf’. The ends are barely touching, it comes apart very easy. First trial looks good. The texture looks quite rough here, but a small amount of sanding smooths things out in no time at all. I still want to add a layer of glass, and tidy the ends to make it all look very much like ”scale”.
Also made a slightly different version, this one has a tapered front section. It looks nice too. I only flattened one side, where the screw goes, that leaves a bit more flesh for the thread on the other side. In the picture above I drilled it for a 3 mm bolt, reduced the bolt-head to 3.9mm, so it sinks into the top bit. Anyway, 3mm is too big for a 6mm rod, but the idea is good. (Since I now have the lathe setup better, the results are better too. Not good, not machinist good, but hobby good enough for the job. I drilled the 3mm screw with a 1.5 mm hole, in order to put a locking pin through. Yes, too much work. I agree (for now)
Just so I remember the sequence of work next time around.
Make sure you have the proper radius tool to make the nose radius. I had to make my own, which was not as hard as it sounds. Just take you time with the dremel. This was an old tool that I (ab)used for this purpose.
Drill a square piece of alu/brass or whatever with a 6 mm hole so that you can securely put the brass rod in the tool holder. Since I don’t have a 4 way chuck, mine was drilled off-center but that does not matter. Tap a few holes for M4 bolts to hold the brass rod. The are other methods to do this, I simply show what I did, not because it is the best method.
Cut a piece of 6 mm brass approx 20 cm, that way you can make ca 10-12 pieces at the time.
Drill the 6mm rod with a 2.5 mm drill, at least 20 mm deep. This will be tapped to M3 later. (If you have a 2.4mm drill, you should use it, 2.5 is slightly oversize if I remember correct)
Round the nose with the specially radius-ed tool. You need to do this before cutting the slots. Believe me, this will work better.
Next transfer the rod to the aluminum holder. I want to cut ca 10 mm on both sides, so make sure it sticks out ca 12 mm.
Now comes the trick: make sure the outside of the blade lines up exactly with the outside of the brass piece. You only want to cut a saw’s width off the sides. Run lathe at a fairly high speed, and feed slowly. You really want the blade to cut. Repeat on the other side. Next eyeball the blade in the middle and make a 6-7 mm deep cut.
Insert the rod in the chuck again, and reduce the backend to ca 4.5mm.
Use a bit of fine sandpaper to rub off and smooth any bits that don’t look good. When done and happy, part at a total length of 17mm.
I tapped the holes with M2, and will install proper steel bolts when all is done.
These few bits took you all day? Yeah, but I did disassemble and clean up the lathe as well, There was some play in the cross support that was hard to get rid off. It’s all good now 😉 (look at mini-lathe.com for guidance)