3D printing?

I have been using Autodesk 123D with some success, it is the first package I have found that is simple enough for me - and the price is right! I have a Sumpod (don't laugh) mdf printer that works well enough now and am mainly printing masters for "lost plastic" casting in brass and gunmetal. 2" scale nameplates, 5" gauge cylinders and some spare hand pump castings for a Sweet Pea most recently.

Andy

I built a RepRap Prusa from a kit, works OK. For design I use DesignSpark M echanical from RS. It is a cut down version of SpaceClaim which I think is a professional 3D design package. It does not seem to be talked about much but I find it good and its free..

DSM can save as STL format which you feed to a slicer which converts it to gcode. I use Slic3r. Finally you need something to feed the gcode to the pr inter, I use Pronterface (Printrun).

Roger Woollett

Greetings Andy, Have you considered using wax as the printing medium? I used to do lost wax casting years ago and am considering making a wax extruder for lost wax casting. Somewhere I have a wax extruder for making wax wires and the like and I am thinking about pairing it with a stepper motor. Cheers, Eric

I had wondered about 3D printing as a means of doing lost wax but instead was wondering about the burn out properties of PLA as that is a common building material and I think I have seen mention of it used for lost wax type processes.

I have no practical experience, but I'd expect PLA would burn out well, almost certainly better than nylon or ABS.

Melting point of PLA is higher than wax, at about 140C, so adjust temperature profile accordingly - maybe try about 190C for the melt-out phase.

-- Peter Fairbrother

Greetings chaps, Eric, I hadn't considered printing wax - pla is difficult enough to get right and it would seem to be fixing a problem that I don't have, pla burns out very well with a minor change to my usual burn out schedule which as Peter suggested was to raise the melt out phase in my case from 120 degC to

200. The 10 hour process then goes up to 680 deg so just about anything is history and a nice toasty workshop in the morning as well! I want to experiment printing a master that is not 100% fill and injecting the voids in it with wax, the temperatures should be fine since I usually inject at around 70 deg C but if the pla has softened at that temp I will have to try ABS which means a heated bed and a whole new set of printing issues. I am hoping this will reduce the time to print the larger masters since it could easily be 5 to 6 hours at the moment. Cheers Andy

Would you need to inject/fill the voids at all? I don't think the investment cares much whether the master is filled or not.

Vacuum debubbling might be a problem with a hollow master, but you can vacuum the raw investment then vibrate-debubble the investment in the flask while it hardens and still get a fairly good result.

Or perhaps sprue the hollow for vaccuum?

I have seen a homemade printer with two pairs of nozzles (one material, one support), one of each pair much larger than the other for fast filling, the other small for detail surface finishing.

-- Peter Fairbrother

Greetings Andy, Thanks for the reply. I hadn't considered PLA. In the past I have burned out many plastic items and always hated the fumes that came out. Even though exhausted outside the stink has always bothered me because I wonder what kind of crap I'm putting in the air. Does most of the PLA melt out then/ Cheers, Eric

Greetings David, It seems like everybody is either thinking about or actually using PLA. Thanks for the suggestion. Eric

Ive been using the beta release of 123D for a couple of years. It worked fine except the stl export was 10x to small... I built a reprap Huxley, and print PLA and ABS. Ive recently got a new PC, so Ive installed the latest 123d from the internet. Also seems fine, though not tried to print anything new yet.

Dave

I seriously doubt my printer's ability to print an airtight model but see what you mean. I have always vacuumed twice and don't like changing a routine that works. I haven't grasped "sprue the hollow for vacuum" I am afraid. Two nozzles sounds an excellent idea - more distractions from the main objective though.

Andy

Hi Eric, I cast 2 or three times a week, mainly lost wax, and honestly find the fumes from the pla less unpleasant than the wax, I steam de-wax before burning out waxes but any residue has to be burnt out because the melt-out phase of the cycle completes at about 3am and I am snoring long before then. I suspect if your oven is arranged to collect melt out from the flask you could remove the melted plastic after an hour at 200 degrees or so. I find I get complete burnout of the pla with no ash residue I can detect.

Cheers Andy

OK, thanks. I'm assembline an Ormerod 2, but no progress for a few days whilst I clean out and diagnose the dishwasher (for which I now have 10 slicing wounds because the framework is little more than tinplate)

For component design FreeCAD is worth a try:

Success!

I wasn't clear - what I meant was make the sprues hollow tubes, and connect the hollows to the voids in the master, so air can get into and out of the voids via the hollow sprues.

You are printing the sprues, I expect?

That way when you vacuum the flask the air in the voids exits through the hollow sprue (and it re-enters via the sprue when the vacuum is removed).

So the pressure in the void is pretty much the same as the pressure in the vacuum chamber, and the master won't implode or explode (hopefully).

I think it is fairly common on advanced machines, but a bit rare on home-made ones.

-- Peter Fairbrother

Neat idea, I hadn't thought of that. I sprue using wax rod I make myself onto a wax tree that screws onto the flask base. My usual hot pen attaches the wax to the pla well enough to survive investment and vacuuming.

Generally no, some models I have printed a stub to facilitate attaching the sprue, printing is still the part of the process most likely to go mammaries uppermost so I keep it to the minimum necessary.

I can see that working but still suspect it would need a pretty watertight master which I doubt my ability to print reliably.

Andy

Ok, well it shouldn't be hard to make hollow sprues, just make them a little thicker. Attach as normal, then get a long drill and cut through the blocked end and the master shell into the void.

I don't understand - why should the master need to be any more watertight when it's hollow? As long as particles of investment don't get in, it shouldn't matter if a little water does.

Once the investment is set, the only thing that counts is the shape it is set in :)

-- Peter Fairbrother