I don’t currently have a mill but I know people who do. That and a small injection press are both things I’d like to get in the workshop if productivity justifies it. I was more musing for the time being but good to know that short run molds can be made cheaply and easily.
Back to the rubber, the gasket rubber you said about, this stuff?
The RTV is usually premixed, I have seen some that require stirring.
The moldeling clay is pretty generic. whatever you can find locally will probably work. PLastecine is a brand name, but that stuff will work fine. To use it, you either warm it manually by kneeding it, or place a small amount if it in a microwave for a few seconds until soft, then press it into place.
I’ve got some stuff coming tomorrow hopefully to try making a mold. I’ve got two ideas in mind for making it which I’ve drawn up quickly on paint to see if either way is right.
The green line is the gate to inject the resin through, the red line is the air vent and the blue line is the parting line. You see on the shorter back end of the needle I have drawn a rectangle which represents a counterweight on the otherwise flat bottom side of the needle, I think this unfortunately prevents me from making a simpler 1 piece mold? My feeling is the B example is the right way about it.
Aside from the mold, the 3D printed part printed with the smaller .3mm nozzle and 0.04mm layer height was infintiely stronger, and looks absolutely brilliant. At that resolution you’d expect a nice surface but it’s head and shoulders better than anything I’ve ever printed before. The heat concerns still stand though and as opening the cluster up and getting the needle out isn’t exactly a doddle (far from it) the final product will be casted to hopefully ensure longevity.
What I thought would be a simple half hour job has turned into a bit of a challenge and a learning curve. I’m still not sure if the needle is weighted and balanced properly, I guess we’ll find that out when it comes to fitting and using it, as I’ve no idea how you go about balancing a speedo needle and there’s no information I can find on it anywhere online either.
Either of those options would work, I would be tempted to cast it face down, with the parting line along the thin edge and the fill spout off the back of the counterweight and vents off the back surface, since any damage there would be hidden when the needle is in the car.
To balance something small like a speedometer needle, you can basically use something with a very fine point to balance a fixture holding the needle in place in the center of gravity. The taller the fixture is, the more precise the balance will be. For this particular application I would use a pin fixed in a base of some sort (or a small nail) and then print a roughly cone shaped hollow piece with a flared base that the speedo needle would sit on. First set the cone shaped thingy on the pin and make sure it is level and sits right. then set the needle on the cone and see which way it tilts. If it is counterweight heavy, you trim some weight off. if it is tip heavy, you add some weight to the counterweight. Tape works temporarily for this.
To balance overall weight if it matters, you take a known weight needle, and then make a helicopter style balance arm (like this one http://www.hobbypartz.com/blbamawicafi.html) and then just make sure the new one weighs the same as the old one.
Good point about the orientation in the mold, that was actually my initial idea but I thought it would be difficult to get out of the mold with only the counterweight to pull on.
Regarding balancing, the problem is knowing the ratio. I don’t have a complete needle to compare with but I’m pretty sure it’s point heavy. I’ve had an idea of printing the point and gluing it onto the original base, as the part will be casted it matters not if the materials at each end are different as if I do it right it will be properly balanced when all made of the same stuff.
I know there’s lots of different types of epoxy, the one I had is a very low viscosity, ultra clear, 2 parts resin to 1 part hardener if that’s any help.
I don’t want to cast these things from epoxy if its going to turn to goo and droop in the heat locked in a dashboard.
Ok cheers. Made my mold tried injecting my first casting, didn’t go well the pressure pushed the mold halves aside and everything spewed out the edge
I opened it up and cleaned it all off leaving a very thin coating on one mold half hoping it would help seal then poured into the cavity instead. I’m worried about the epoxy reaching the thin tip of the mold by pouring as the cavity is horizontal with the pour hole leading from the top to the back of the counterweight as you suggested to help hide any ugliness. I put the mold straight onto my TAZ bed at 80•C hoping the heat would help lower the viscosity a bit initially helping the epoxy reach all parts of the mold before speeding up the curing process as such small volume in such thin areas is likely to take awhile to cure fully.
As an aside will painting a coat of epoxy over the 3D printed version not help stiffen it up and prevent it flopping in a bit of heat? I hadn’t thought of that initially.
I usually make two small wooden plates and have them on either side of the mold, with a couple of screw C clamp holding them in place at the edges, just tight enough to keep them from expanding, but not enough to squish the mold (you don’t want a spring clamp for that. If your vent is right on the tip of the needle, the plastic will flow to the tip with no problem. should be pretty easy to trim there as well.
You can epoxy coat things to add strength. Something small like that is going to be difficult. I’d probably add a single carbon fiber thread if I was going to do that to add lateral stiffness. I don’t know that it would help all that much though. If you are printing ABS it should be fine. You can also use acetone vapor with ABS to get a stronger, more solid part.
Good idea that. Was going to do the same with a small vice clamp but as I was going to stick it on my TAZ bed I didn’t want all that weight on it and also heat wouldn’t have transferred into the mold.
The vent is right on the tip but as the tip is so small, I couldn’t balance anything on top to pour the mold so just punched a pin through after it had set. I think it’s a bit to small as when I injected with a syringe first attempt nothing oozed out of it.
I’ve given it a go painting the 3d printed part. I’d already done light sanding, acetone smoothing and clear coat on it, but it’s still to thin and flexible. We’ll see how that turns out.
This molding business is something I should have started learning long ago. The more I think about it there’s a ton of stuff in the pipeline I could really use molding for over the printer. Have you used the proper casting plastics before such as smooth cast/crystal clear etc? What are their properties like for functional parts? As I can’t really find much info about them, everyone just seems to use them for models.
Mold making is certanly fun, and you can do an endless variety of things with it!
In the situation wher eyou have an air vent that is too small, you can use a hobby knife to cut away more of the mold ( a V profile cut works well). The silicone carves pretty easily with a little practice. Just run the knife outside the too small air vent on either side, should be plenty big then.
I’ve played with a fairly large variety of plastics, some metals (pewter, Tin, etc) as well as various clear plastics. The tricky part with the clear plastics is getting all the bubbles out of the plastic. The strength, if you use the right hardner and don’t get one of the “gummy gel plastics” is generally quite strong. Most of them are Acrylic or Epoxy based so they harden well. You almost are required to vaccume pot them though or you will never get the bubbles out. If you do that, they are generally quite strong with decent impact and sheer strength. Some of the clear resins are actually stronger than some of the opaque ones.
The conditions you do a casting in have a huge impact on final part strength. Too cold or too hot a day can make for soupy or brittle parts, adding powders or dyes to a resin can change the look dramaitcally, but can lead to a weaker part. Vacuum potting usually makes for a much stronger part.
I’m probably way off the direction this topic has come to, but, trying to answer to the original subject let me say this:
I have worked with BluPrint from Taulman3D and I must say that is quite stiff and brittle, much like PLA, very clear and most importantly comes with a Tg of 110C. So, it’ll be safe even in a car left at Sahara!
It is a bit difficult to print due to the high extrusion temps (nozzle@260, bed@110) and the glue stick for the PEI, but I really think you can do what you want.
I recieved a complete original needle today to use as a comparison. There is actually a lot of flex in it, about as much as I’m getting with the ABS used on a .3mm nozzle. Strength wise im now satisfied a 3D printed part will suffice. I now just need to test temperature, locked in a car I figure the max they’re ever going to see anywhere in the world is 80•C (more likely to be between 50-60 at the very most). I’m not sure how I’m going to test their performance in a heated environment yet.
I’ve asked for a load of samples of clear filament for the clear one. Bluprint, T-Lyne, HD Glass, Polycarbonate, XT-Copolysester, some others too. I think I already know it’s going to be one of two but I like trying out new filaments and they all hve their unique properties so I thought I’d give them all a go.
Is there a properly stiff solid white (or other colour) filament? Aside from PLA.
Some people line that Tauman N-vent filament, I haven’t tried it myself since I generally have really good luck with ABS. It’s supposedly higher temperature and stronger than PLA.
Just having a go with the bluprint sample. This first attempt printing with my .5mm nozzle at 0.04 layer height, 10mm/s (all speeds), 100% fill at 270•C isn’t quite clear enough, lots of white looking lines between each thread of plastic. Maybe some advance in speed or possibly temp will help clear it up?
But wow, is this stuff easy to print with! Quite happy to go straight on to the PEI at 90•C at such low layer height with a .5mm nozzle. No stringing, no horrible blobs. I think I’ve fallen in love
