2x Studio Scale Falcon Gun Turret- Scratchbuild

[swgeek]

If you're going to cast parts in a pressure pot, you have to vacuum degas your rubber, otherwise you'll get warts on your parts. Some times you won't even be able to see the bubbles in the rubber but with the pressure, the resin will find them. Also, did you say you were running your pot at 60 psi? That's way more than you need. The most I'll do is 40 psi and 30 is probably all that you need. One more tip for making a brush up rubber mold. After you apply your first layer, use an air nozzle to spray your rubber to pop bubbles. You want to use enough pressure to get through the rubber and pop bubbles but not so much preasure that you blow the rubber off of your master, if that makes sense?

 

[Bondo Fett]

If you're going to cast parts in a pressure pot, you have to vacuum degas your rubber, otherwise you'll get warts on your parts. Some times you won't even be able to see the bubbles in the rubber but with the pressure, the resin will find them. Also, did you say you were running your pot at 60 psi? That's way more than you need. The most I'll do is 40 psi and 30 is probably all that you need. One more tip for making a brush up rubber mold. After you apply your first layer, use an air nozzle to spray your rubber to pop bubbles. You want to use enough pressure to get through the rubber and pop bubbles but not so much preasure that you blow the rubber off of your master, if that makes sense?

That is good intel, thank you. I have been making new casts at closer to 25psi, that seems to be plenty. Obviously I didn't need to be crushing the resin down so hard. Again, live and learn (also share and learn!).

 

[Bondo Fett]

So, third times the charm. I made a third rubber mold, urethane this time, and poured. Not my preferred way, because it forces me to use release for castings that are to be painted later. Its material I have on hand at my shop and it just never gives me trouble with bubbles. Polytek 74-45. I didn't take any pictures this time, just crashed through it.

Got four nice castings out of it, still using Smooth-On's Onyx. I really like that resin, it is super hard.

I washed the finished casts in Krud Cutter, then TSP substitute, then Dawn detergent. I'm pretty sure I got all the release (Mann 205) off. I wrapped some styrene sheet around the vents, it gives better sense of scale, and I didn't think I could reproduce detail that fine with a cast.

One or two little bubbles to deal with, but I'll wait for a coat of primer so I can see 'em better.

Epoxied them together using a jig. This is as square and true as I can get them:

And used another jig to drill the pivot axis:

Next its back to the drawing board to design the mounting/swivel frame and find out if this contraption will fit the rest of the turret already built.

 

[joberg]

Looking mighty good

 

[Bondo Fett]

Starting to fit together. I can't believe it I'm able to keep it all square and true. Not bonded yet, just a dry fit for now.

Now on to the mounting bracket arms, or whatever you call them. Using the drill press as a lathe again. This time trying to form my model out of urethane foam instead of balsa, its what I have to hand. Unsure if this is a good idea or not.

 

[joberg]

Looking real good; eager to see your next update

 

[Bondo Fett]

Change of plan- I ditched the foam when I realized my actual piece would be much smaller, just went with Bondo on a stick:

You can see the aluminum profile I made, I didn't even turn the drill on, I rotated it by hand until I built up the shape.

Shot of primer.

Casting this thing in halves, I found the centerline.

Quickie silicone mold.

Four urethane resin halves, slushcast so they are somewhat hollow. My plan is to bond them around the support frame armature, encapsulated in epoxy. Hoping the resulting rig will be strong enough to hold up the quad barrels.

Washed and trimmed halves. About four and a half inches long, 3/4" diameter.

 

[Bondo Fett]

Heres my build up of the gun support frame. I didn't document the construction as well as I would have wanted. Its all built around a 1/2" aluminum tube that fits perfectly inside the brass tube in the wedge shaped mounting block. The flat portion of the frame is made from a slab of sheet aluminum epoxy laminated between two sheets of .030" styrene. Not certain the thickness of the metal, but all together they add up to the same thickness as my table saw blade kerf. The thing isn't very big, but it seem pretty rigid.

I filled the tube with some epoxy to add some surface area and to keep it from chattering when I ran it partway through the saw. Got a nice center cut.

Here's the whole unit trimmed out with some brass strips for the details and for the strength. The two projecting 'horns' will be the center ribs inside the urethane castings. That's the plan, anyway.

I made a jig to attach the castings to this frame, but my measurements seem to be off in a couple of points. Gotta go back to the drawing board.

Check and re-check.

 

[joberg]

Wow! Love that Bondo trick of turning those with that metal profile Looking very good and eager to see your next update

 

[JimmyB]

I concur with joberg on your Bondo "lathe" trick. Genius.

Do you use epoxy to bond the brass to the styrene like you did with the aluminium?

 

[Bondo Fett]

Thanks for the kind comments! Actually, I used CA to bond the brass strips to the styrene. Not sure which approach would be stronger, probably epoxy, but the CA sets way faster, and besides, the ends of the brass will be captured by the urethane pieces. Might even be able to get to it this weekend!

 

[JimmyB]

Great stuff. Thanks for the info I'm looking forward to seeing this progress.

 

[Bondo Fett]

After some life distractions I was able to make some movement with the mounting bracket. The plan was/is to to encapsulate the armature inside the urethane castings using epoxy for the fill. The epoxy I have is a product I use at work called Masco Hi-mod gel. It's a two part masonry product and it has the consistency of creamy peanut butter. It sets up hard as stone.

I didn't take enough pictures unfortunately. For the armature I added a loop of aluminum wire CA-ed to the ends to wrap around the pivot point and- presumably- provide more reinforcement for the fine screws I'm planning to use for the axles (pivot rods?). If you use your imagination you can sort of see the wire buried in the epoxy.

I also included an aluminum tube passing through the pivots to act as a cast-in-place bore hole for the screws. I released the dickens out of it before I captured it in the epoxy- goodness knows if I can work it back out later. I'm making it all up as I go.

This will cure in a nice toasty shop all weekend then I will find out if I've made a mistake. If so I will have to build all these bits over again so fingers crossed! This is as square and true as I can make it, it's too small for clamps.

 

[joberg]

Beauty all around

 

[Bondo Fett]

A little bit of movement- got the arms of the support frame goobered together finally. Then a very, very dry fit:

 

[TazMan2000]

Very nice looking. Perhaps because it's because everything is sitting flat on your workbench, but it seems with the armature's placement, the gun won't be able to rotate on its axis.

TazMan2000

 

[Bondo Fett]

Very nice looking. Perhaps because it's because everything is sitting flat on your workbench, but it seems with the armature's placement, the gun won't be able to rotate on its axis.

TazMan2000

Because the parts are just sorta strung along like that none of the axes are true. It’s not a very good picture. The concave shape of the window should give it the room it needs to orbit- I hope. However, if it only fits in its resting/neutral position I’ll be satisfied. I’m not drawing this with 3D, but on paper, so I might have missed something.

 

[TazMan2000]

Because the parts are just sorta strung along like that none of the axes are true. It’s not a very good picture. The concave shape of the window should give it the room it needs to orbit- I hope. However, if it only fits in its resting/neutral position I’ll be satisfied. I’m not drawing this with 3D, but on paper, so I might have missed something.

I just wasn't sure if you were planning on making things movable, or just have the gun in the stowed position as a display.

TazMan2000

 

[IzzyMel]

Awesome work. I’ve been working on a 1/6 scale version( printed not scratch build though)

 

[joberg]

I just wasn't sure if you were planning on making things movable, or just have the gun in the stowed position as a display.

TazMan2000

I think it all depends on the depth of that concave window, how high the guns will rest, even on a stowed stance, above said window...I believe it could be done