Two steps forward, one step back…
The repair of the first Rudder Hub print continues successfully. And I machined the center piece of the manufactured servo horn that’s going on the rudder stock. Those were the good things. My 4th and last attempt to print a new Rudder Hub failed miserably with almost a complete delamination of the base layers. I never had this problem before with this printer and I did print the repair sleeve and the top assembly for the rudder stock in between these failures.
Let’s see the good stuff first.
My sizing on the repair sleeve was dead on. It slide nicely onto the 1/2" brass rudder stock and fit loosely in the rudder hub, but good enough in the printed part.
Here it is after epoxying the sleeve into position. I used the rudder stock to hold the part in alignment while the epoxy set. With this being the actual part I’m going to use, it will need some more cleanup.
For the Servo Arm, I had some 1" round brass stock. First I had to hacksaw a chunk that would fit onn my tiny lathe. If I had a “real” lathe with a reasonably-sized hole through the arbor, I would have just chuck the piece in and got to work. I had to first get my hacksaw at my daughter’s house. My son in law borrowed it and forget to give it back. I rarely use this, but when you need it, there is no substitute.
I turned the lug end to just fit into the hole I cut in the brass arm. It didn’t have to be a tight fit. The whole deal is going to be soldered together.
I turned the part around and turned the o.d. of the body so it coincided with the edges of the arm. I couldn’t cut it all the way back to the smaller diameter, and didn’t trust the relatively light 3-jaw chuck. I also have a very robust 4-jaw independent chuck and put that to use to ensure that the piece is concetric and true. I use a Starrett Last Word dial indicator to get the runout to about 001".
After turning the o.d. I needed to chop off a whole lot and again used the hacksaw to do this. I have cutoff tools, but the lathe isn’t powerful enough to do very deep cutoff operations.
After cutting the excess I faced that end, center-drilled a starting point and drilled through with a smallish diamter pilot drill. I followed this up with the largest drill my machine can handle—1/4"—and then used a small boring bar to open the hole to a clearance fit of the rudder stock.
I turned it around again and shortened the narrow end. I only need a lip on that end for the soldering. I need all the stock on the fat end to handle the set screw, which I will do tormorrow.
Here it is cleaned, but not yet soldered.
I also got reasonably successful prints of the upper rudder support, but there was a drawing error in it. I could still make it work and my upper bearing just about fits. Need to relieve the hole slightly. I have modified the drawings and will attempt to reprint.
Now to the horrow show.
This is what a severe delamination looks like.
Notice that the initial part of the raft is firmly attached to the build plate, but the transition layers are not. I did a Google search to find out causes for this and made modifications to the printing parameters concerning the raft. Those changes made things worse, not better. I’m at a loss since the first print, while incorrect, did actually print. Everyone I attempted after that had some degree of delamination, from mild to wild. The first five layers cure for 8 to 12 times the working layers exposure time. I was curring my rafts at 35 seconds, but after reading about the problem reduced it to 26 seconds. My exposure time is 2.1 seconds. Then for the next five or six layers, the exposure time is reduced by a linear progression until it reaches the working time of 2.1. This is where the trouble is and I don’t yet how to fix it.
It’s why that reject part is so important.
Because of the misshapen supports, there’s a good chance that there is some resin stuck to the barrier film. If there’s even a very tiny bump on the film, the auto-leveling will report an error. This means, removing and emptying the vat through a fine mesh filter to catch anything floating in the resin, removing any bumps on the film and replacing and refilling the vat. It’s a messy part of the process that I don’t relish.
