Dr. Who - Key to Time - Clear resin cast

[Dalex]

Figured it was time for an update...

One of the first things I needed to do was determine the size of the Key To Time. The consensus seemed to be that it was a 6" cube, although there was some opinions that it could be larger.

So I made two cardboard boxes, one 6" and one 7", and took photographs of myself to compare to screen captures:

Seems pretty clear to me that the cube size is 6".

A quick paper mock-up of one of the segments just to be sure:

Looks right to me! Now, on to the actual molding...

I spent some time thinking about how to do this in plaster. One of my concerns was how to accurately cut and sand the inner sides of a segment. For example, in the image above you can see the top of the segment has an acute angle, which is going to be difficult to cut and even more difficult to sand and polish.

I realized that all the Key to Time segments could be further subdivided into pieces with no acute angles. In other words, each of these sub-pieces would be a geometric shape in which each side could be polished against a large flat surface without fear of damaging the adjacent sides. These piece could then be glued together (and adjoining sides sanded) so that they appear as one solid piece.

I took the original paper cut-out plans for Segment #1, and modified it to make the necessary sub-pieces. I also figured I'd throw in the lengths of the sides and angles while I was at it:

It may be hard to tell, but those three pieces actually fit together to form the first segment. (FYI, if anyone's interested I can provide the PDF for this.)

The next step is coming up with a mold for my plaster...

 

[Dalex]

I realized that every segment was no larger than one-half cube. So it seemed pretty clear that I should make a box capable of holding at least 6" by 6" by 3". Furthermore, most of the sub-pieces would be best carved from a brick half that size, so I added a plexiglass divider that could optionally be slid down the middle:

The box is actually larger than 6" x 6" x 3". This is so that I can roughly cut out the pieces with a coping saw, and then further refine my cuts and sanding to get exactly the right dimensions and angles.

Anyway, on to pouring the plaster...

Wait a while for it to harden, and voila, two bricks ready to go:

I knew from earlier experimentation that the bricks would still be wet inside for a while. So I had to let them sit for a few days in front of a heating duct in order to dry them completely.

Finally it was time to get my coping saw and get it work. I did a rough cut of one block:

Each of these pieces are a little larger than the final size, so I have some working room to sand things down.

And that's where I'm at now. Hopefully this week I can find some time to start refining these pieces. We'll see how that goes...!

 

[Dalex]

Here's one of the pieces sculpted and sanded:

Now on the others...

 

[Kestre]

Very nice work.

 

[Rebelscum]

Really nice. The corners look like perfection.

 

[Siebigteroth3]

Very nice, I look forward to seeing the final product.

 

[Dalex]

Thanks for the encouragement guys!

One of the nice things about working in plaster is that if I make a mistake, I can repair it with spackling. Helps to fix gouges or re-create a chipped edge, and with a bit of sanding it blends right in.

Still need to figure out how to give the final model a smooth glass-like surface when I'm done. I'm hoping I can just spray it with a few coats of an acrylic varnish or something, but I don't know if that'll work. I guess I'll have to do some experiments.

 

[Dalex]

Thought it was time to post another update.

I finished carving all three pieces that make up the first Key to Time segment:

Glued together, you can see it taking shape:

A little bit of spackling and sanding to cover up the seams, and voila:

You'll notice I didn't bother fixing the convergence of the corners in the center. It's because it won't matter as that part will be drilled out in the next step, which is to drill along where the three axes of the cube would be. If I was doing the entire Key to Time, I'd wait until I had all six segments assembled in a cube before doing this part. But since I'm just concentrating on making one segment, I figured now is the time to do it.

I don't have a drill press, but I have an idea of how to put something together that should allow me to drill in a straight line. I'll hopefully get to that later this weekend...

 

[Dalex]

Well, my improvised solution for drilling the holes -- which involved mounting a drill on a table and making a sliding tray that would glide the model in a straight line toward it -- didn't work so well. Or more precisely I wasn't as careful as I should have been while doing it.

The main hole (that runs from the front of the segment to the back) ended up being a bit more skewed than I would have liked. It's not horrible, but it's off by about a quarter inch towards the back, so I think it needs to be re-done.

I'm going to try to fix it by filling the hole in with some new plaster, letting it harden, and then trying again. I'm a bit worried that the drilling won't go smoothly since the new plaster won't be tightly bonded to the original, but we'll see what happens.....

 

[Kestre]

A shame you don't know someone with a drill press you can borrow.

I'm still waiting for my mold/cast guy to have some free time to work with the pieces. He thinks mid-April.

 

[Dalex]

A shame you don't know someone with a drill press you can borrow.

Yeah, if I decide to end up doing the entire Key to Time, there's no question I'd use a drill press. (And I'd redo this first segment properly.) But I figured that for just a single segment I could get away with approximating the holes.

Chances are though I'm just going to get in on your run.

I'm still waiting for my mold/cast guy to have some free time to work with the pieces. He thinks mid-April.

I can't wait to see it! Have you asked what he's casting in? I'm dying to know...!

 

[Cut Snake]

My thought on your hole issue.

What if you could secure it so that you know the hole will be aligned correctly, then drill a hole larger than you need. You could then refill the hole with plaster, with a rod or some such thing of the correct size in the centre to act as your new hole until it's dried.

Love the project, can't wait to see more progress.


:edited to make sense.

 

[Kestre]

I haven't asked him his casting material. All I know is he says it doesn't need to be degassed.

 

[Dalex]

What if you could secure it so that you know the hole will be aligned correctly, then drill a hole larger than you need. You could then refill the hole with plaster, with a rod or some such thing of the correct size in the centre to act as your new hole until it's dried.

Hmm, that's an interesting idea! I'd have to find a way of making sure that the plaster didn't adhere to the rod. Last thing I'd want is to have that rod permanently embedded in the middle of a solid chunk of plaster! Maybe a silicon rod would work OK, especially if it was given a coat of vaseline first.

Alas this idea will have to wait, as I've already poured the plaster in the crevice left by the misaligned hole. I'm cautiously optimistic that this will work, as when I did this yesterday there was a bit that splattered onto one of the sides, and this evening when I tried to remove it I found it had fused quite tightly to the original plaster. So maybe I'll be OK.

And if this doesn't work, I'll try the embedded rod idea!

 

[Dalex]

Hey guys,

Sorry for the delay in posting an update. But stuff was in a rough shape after I filled the misaligned hole and re-drilled a new hole. Plus a bunch of edges got chipped in the process:

It took a while, but I was able to finally get things into shape again:

This time the holes are aligned perfectly. (The hole looks a bit wide and off-center in the picture above, but it's just the camera angle making it look wide, and the position is actually correct as it is not meant to be centered over the ridge.)

I apologize for the poor lighting in the pics. I'll take some more during daytime after the next step, which is to spray it with an acrylic glaze. I'm using Krylon's Triple-Thick Crystal Clear Glaze, which promises to leave a "bright, glass-like coating". In fact I tried it on a few practice pieces of plaster and it seems to work really well (although it requires several coats), so I think along with some sanding and polishing it'll be just the thing I need to get that perfect finish for casting.

 

[Straker]

Nice! I'm totally interested if you make a run. Just watching your progress alone is wonderful though.

 

[Dalex]

Thanks for the encouragement!

So as promised, here are a few more pictures after spraying the model in acrylic and doing some polishing. I find that high grit sandpaper followed by some buffing with Novus #2 polish seems to work quite well.

I still have some tweaking to do. There are some chipped parts that need to be repaired, and the finish is not perfectly smooth in some parts. There's also some blemishes caused by dirty fingers, etc, but I'm not too worried about that as long as the surface is smooth.

The edges and corners got a little more worn than I would have liked, but since this is just a practice piece I'm not too worried. If I go ahead with doing all six segments, I'll definitely be re-doing this piece and being more careful about keeping the edges crisp.

I'll be heading over to Sculpture Supply Canada this weekend to pick up whatever I need for molding and casting. And here's where I'd like to ask for some advice...

I would love to use Smooth-On Crystal Clear, but it doesn't look like I'll be able to get access to a vacuum chamber or pressure pot. (Unless someone knows where you can rent these in Toronto??) So with that in mind, is Smooth-On Crystal Clear still my best bet? Or is there something that would work better for my particular situation? :confused

Thanks in advance for any advice...

 

[Rebelscum]

I'd suggest you block sand the flat spaces to level the high spots. It looks glossy, but not glass flat.

It's a work of art with plaster though. I'd never have guessed you could do such nice work with it.

 

[Dalex]

I'd suggest you block sand the flat spaces to level the high spots. It looks glossy, but not glass flat.

It's a work of art with plaster though. I'd never have guessed you could do such nice work with it.

Heh, thanks! And yep, I hear you! I definitely want to get all the surfaces as glass-like as possible. Right now there's still a bit of an orange-peel texture to them, plus a few uneven parts. I'll do the best I can!

So you've had a lot of experience with Smooth-On Crystal Clear. How bad would it be to not degas the silicon rubber first, and to not use a pressure pot for casting? Keeping in mind that this is just a test piece -- I'd like it to look good, but it doesn't have to be flawless.

Ultimately I still want to see what Kestre comes up with before deciding whether to do all six pieces.

 

[Rebelscum]

Heh, thanks! And yep, I hear you! I definitely want to get all the surfaces as glass-like as possible. Right now there's still a bit of an orange-peel texture to them, plus a few uneven parts. I'll do the best I can!

So you've had a lot of experience with Smooth-On Crystal Clear. How bad would it be to not degas the silicon rubber first, and to not use a pressure pot for casting? Keeping in mind that this is just a test piece -- I'd like it to look good, but it doesn't have to be flawless.

Ultimately I still want to see what Kestre comes up with before deciding whether to do all six pieces.

When you mix the clear it will have bubbles in it so I don't think there's any chance of them all disappearing without pressure and when you pressure, you'll have pimples on the casting from the mold if the rubber wasn't degassed.

While I'm not sure how feasible it would be, the plastic can be polished just like acrylic with micromesh, then buffing wheels.