Hope everyone is enjoying the holidays. I've been busy with other things lately. So not much progress, but wanted to catch up.
Jrbe said:
The small end of the draft of the riser tubes should ideally be at the top / away from the part. This should allow the pieces to slide apart. You can flip it so the small end is closest to the part if you think you can snap them all off when separating the mold by twisting or separating. Still need to figure out how to get the hardened resin out of the risers if you go this route.
For this reason I moved the small end of the risers to the outside edge of the mold.
Jrbe said:
You could also swap over to just straight riser holes and push / force some silicone tubes into them. This way the worst that happens should be a tube pops out but doesn't get stuck. Extra resin can flow up the inside of the tube. It will be important to cut the inside end of the silicone hose straight where it touches the stator, the end shape will end up in the stator. Silicone tubes might get pushed out by the clamping pressure though. Some ribs or teeth inside the risers could help hold the silicone tubes in place. Could do the same for the fill tube in a larger diameter. Having this fill tube could allow a funnel to be swapped for an air syringe to push resin in. The ends of the silicone tubes could distort and leave odd bumps in the stator if they move.
Looking at your mold I'm not sure how you're filling it.
Ill see if I have issues with the drafted risers. If I do, I will try this method instead. Currently I am filling the mold by pouring the epoxy directly into it, the placing the top on an compressing it.
Jrbe said:
Consider waxing the outside of the mold too. Should help it stay clean and maybe not stuck together when it gets messy.
I did buy some wax too I will definitely use this in conjunction with the mold release.
Thanks for all the information on the resin stuff. It sounds like this could be an adventure. I am going to attempt making some nylon stators using pour and press method that I have done so far. This should allow me to at least test the mold dimensions and the mold release stuff, along with other things, like the using clay to plug holes so I can pop it out with a dowel after.
I will in the mean time convince my wife to let me spend even more money on this project, and Ill see if I can get a vacuum chamber and make a resin trap.
I will start with the gravity method, and if this causes issues, I will attempt to make the vacuum infusion work, but I have concerns with putting it in the bag then putting that in the press. I worry that the shape will be somewhat compromised, but who knows, this might work well.
I'm trying to iterate on the complexity as the original idea here was simplicity. And its getting away from that a bit by involving a vacuum chamber/ vacuum infusion stuff, but that's not going to stop the project.
APL said:
I've used some cling wrap for some things, resin doesn't stick to it, but it might wrinkle slightly. Clear packing tape doesn't stick either. Fiberglass polyester resin is cheap for simple test's if your epoxy is costly.
Thanks for the suggestions, that could be an easy way to make the mold non stick, as there are no really complex geometries in the mold itself. I bought some cheap table top epoxy on amazon. Its got a really long cure time, and is not something I will ultimately use on the real stator, but it was cheap for a good amount. Ill look at the fiberglass polyester stuff next though.
APL said:
Came across this photo of the Marand motor the other day,.. looks like they use a thin fiberglass board in the center, and just catch the edge of the end windings. Might be something to try, add strength, and could drill the holes after the cure? Outer edge looks like pure resin.
Thanks for sharing that one. I'm not sure I saw that from Marand before, but since I moved away from the 3d printed core, my motor is very similar to theirs.
Unfortunately, since mine is an out runner, I cant/don't want to do anything on the outer diameter, but that same concept could be applied to the inner, currently I am planning on making a puck basically, and use some machine screws to fasten the stator to the hub. I'm sure there is room for optimization here, that might come with future generations, where I could make a disk with mounting points on the inner diameter that are smaller, and would result in needing less epoxy.
Also I redid the calculations on the weight savings of the back iron reliefs. I just don't see the point. At least not for my case. Theirs is a much larger diameter, so it might be a more significant weight savings, but it would only save ~20g in my case, which is less than 5% of the total weight. Obviously Marand's goals outweigh the complexity of machining/design, but mine does not unfortunately.
going back to the second silicone mold I had made. I tried to make a stator with it. and it sort of worked. but I dont like how inconsistently the silicone would compress. Its adding too much variation to the back face. I might revisit using this in the inner/outer diameter, but for now I am going for a purely 3D printed mold.
Here's some pics
and here's the new mold