Creating 3D QR codes

[jsc]

Also, I'm still curious, what were we supposed to have noticed about the Permastone box?

[Toby]

Toby, looks like there might be an issue with TobyCad that's causing some strangeness to occur with the retaining walls. Are you sure they're fully joined up? They get sliced like this, which is not ideal:

That's just laziness on my part. I didn't model it as one piece because the arced part was easier to model as a sweep and the ends as lofts. It'll print ok- not perfect I know, but it's just a tool to make something else. I've never had a problem with a part like that as long as it's tall enough that the join has plenty of opportunity to stick. It doesn't have to be super strong, and even if breaks it doesn't matter because the frame surrounds the whole thing and holds everything in place while the plaster sets. (EDIT: I was careful with the frame and modeled it as one piece.)

Did you print and try to cast with it yet?

Also, I'm still curious, what were we supposed to have noticed about the Permastone box?

Here's a hint: (My next post will reveal the source of the image on the right).

permastone.1.JPG (77.75 KiB) Viewed 12648 times

[Toby]

That's from Will Newton's thread on this forum:

viewtopic.php?f=8&t=9&p=1015#p1015

I like how much the surface finish of Will's print came out like the original plaster cast.

[jsc]

I redrew your molds in DesignSpark Mechanical, for practice at mold making.

Do you design in clearance for the fits? I didn't, and everything is super tight, and I had to take some passes with a file. It's setting up now. I also forgot to use a mold release, I'm hoping the take-apart mold saves me. I didn't get Johnson's sealing wax yet, I was going to use mineral oil (until I forgot about it). How do you apply the release?

[Toby]

No, I don't put in clearances. More often than not it fits together right off the bed- that's how it was for this mold. But sometimes you need to file, especially on corners where you get that "deceleration blob" effect we talked about once.

Did you remodel and print the tops part too? I would expect for that the plaster casts might need a bit of sanding in order to slide into the lower portion.

I forgot the mold release the first time I cast this one also. My advice: give it a good long time to set, like 2 hours at least. I only waited about an hour or less, and there was no chance. It still will be difficult to get out- the sides will fall away easily, but the bottom will cling pretty tightly in this case. Don't be surprised if it doesn't work the first time.

Oh.... I just realized.. this is hard to describe in words, but did you re-model the bottom portion of the mold so that the walls that drop down from the central portion are perfectly vertical? If so.... well, no chance of getting that one out I'm afraid. They need to be ever-so-slightly angled so the plaster is naturally inclined to push out from the mold.

I've tried dish soap, vaseline, varnish, talc, and probably a couple of other things- but I can't specifically recall mineral oil, though I'm sure I did something like it. Paste wax is the best so far. You rub it on with a paper towel like you're rubbing it into wood. Let it dry, and put another coat on for good measure. When that dries polish it a bit with a tissue and then it's rady. It seems to fill in some of the nooks and crannies as well as be something plaster doesn't readily stick to.

The better way to do these things is to print in flexible material-- that would allow you to peel the mold off and not worry about damaging the plaster.I have some flex filament, but so far I can only print it at such slow rates that I haven't much felt like doing a project with it.

Also I should mention, you can always print the object you desire and then make a silicone mold from it. If I had to make my living doing this, that would be the way to go. But silicone is expensive and it's another step to the process, so I like fooling around with the direct method.

[jsc]

I added a small fillet there, but it doesn't go all the way to the top. May be insufficient, we'll see.

[Toby]

Here's what I mean by the angle in the mold. This is a picture of the profile used to sweep out the bottom portion. The arrows show the angled walls.

mold_angle.JPG (12.06 KiB) Viewed 12644 times

[Toby]

Ah, that fillet might work. It won't hurt that's for sure.

[jimc]

Thats what they call draft angle toby. I dont know if there is a tool for it in yours and jins cad software but in rhino there is a draft analysis tool which will tell you area that will give you trouble removing a part from a mold. Maybe dig around in your software. There might be something similar

[Toby]

Ah, that's right jim. Now I remember reading about that recently. No chance of a feature like that in TobyCad unfortunately. But maybe Jin has it in DesignSpark.

I made a mistake- that picture was for the top mold. By now everyone gets it I'm sure, but here's the bottom mold profile anyway:

mold_angle.JPG (9.67 KiB) Viewed 12638 times

Trying to model molds directly is kinda confusing to tell the truth. Especially when it has to be a take-apart kind in rigid plastic. Anyone who knows about mold-making would probably consider it loopy.