One Last Shorty

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rmac
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Re: One Last Shorty

Post by rmac »

So once you got into a rhythm, how fast could you make these parts? Maybe 3-4 per hour?
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Dick_Morris
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Re: One Last Shorty

Post by Dick_Morris »

A brand of resin I used a few years ago was Alumilite. I had good luck with it. They probably have a product line similar to Smooth-On.

3D printing with a resin printer is an alternate way to make windows and doors, but having used both processes I might leans towards castable resin if I had to make a lot of them to make. If I only had a few, the cost for the mold material and the short shelf life would drive towards 3D printing. 3D printing is also a good way to make the patterns, but the castable mold material doesn't play well with some materials.
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Steggy
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Re: One Last Shorty

Post by Steggy »

Dick_Morris wrote: Thu Jan 26, 2023 11:22 pm A brand of resin I used a few years ago was Alumilite. I had good luck with it. They probably have a product line similar to Smooth-On.

The nose and cab section of my F-unit’s body, as well as the number two end bulkhead was cast in Alumilite. Alumilite is chemically similar to the Smooth-On product Carl is using, but has a somewhat-longer pot life, plus has higher density and mechanical strength. The better mechanical properties come with higher product cost.
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ccvstmr
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Re: One Last Shorty

Post by ccvstmr »

rmac wrote: Thu Jan 26, 2023 10:17 pm So once you got into a rhythm, how fast could you make these parts? Maybe 3-4 per hour?
RMAC...you're pretty close. Once I got going, I could get maybe 4 or 5 castings per hour. Of course, by the time I got going and was "in my groove"...had to stop for a lunch break. And then, pick up the pace after lunch.

The rush took place during the de-mold process, mold cleaning and prep the mold for the next pour. Then, mix the resin and hardener. Stir a little bit and pour. Plug in the "vibrator" and then...wait 10 minutes until the madness started once again. Carl B.
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ccvstmr
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Re: One Last Shorty

Post by ccvstmr »

Dick_Morris wrote: Thu Jan 26, 2023 11:22 pm A brand of resin I used a few years ago was Alumilite. I had good luck with it. They probably have a product line similar to Smooth-On.

3D printing with a resin printer is an alternate way to make windows and doors, but having used both processes I might leans towards castable resin if I had to make a lot of them to make. If I only had a few, the cost for the mold material and the short shelf life would drive towards 3D printing. 3D printing is also a good way to make the patterns, but the castable mold material doesn't play well with some materials.
Hi Dick...I am familiar with Alumilite. Steggy commented about this material in a post right after yours. While Smooth-On has metal flakes in some of their resins...wasn't sure if Alumilite was that thin...or at least thin enough to flow into .062" thick cavities. The nose and rear bulkhead pieces on Steggies F unit are alumilite castings. On the cross sections used for the nose...that stuff was not light weight.

3D printing...have a friend that experimented with 3D printed windows for his own 2.5" scale equipment. Nothing fancy, just a basic rectangular window frame. I thought the printed surface was too "grainy"...but that could have been due to program or printer parameter settings.

No doubt, if someone wants window frames...there's now several ways to get from start to finish. Thanks for sharing. Carl B.
Life is like a sewer...what you get out of it depends on what you put into it!
I don't walk on water...I just learned where some of the stepping stones are!
I love mankind...it's some of the people I can't stand!
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Dick_Morris
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Re: One Last Shorty

Post by Dick_Morris »

Concerning 3D printing, there are two processes available for consumer units. One uses a plastic filament and deposits thin layers of molten plastic to build a part. The other uses UV setting resin and layers are made by passing UV light through a UV resisting mask that is a lot like a cell phone screen. I found that the resin is more precise and gives better detail. The filament leaves more noticeable lines and a surface that isn't as smooth. Both have advantages and disadvantages and each has its place, but I have found the resin printers better meet my model building needs, mostly to create "waxes" for investment casting.

With the urethane resins like you are using a trick it to put a layer of spray paint on the mold. When the resin hardens and is removed from the mold, it stays on the part and you don't have to paint it.
ccvstmr
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Re: One Last Shorty

Post by ccvstmr »

Dick_Morris wrote: Fri Jan 27, 2023 10:33 pm With the urethane resins like you are using a trick it to put a layer of spray paint on the mold. When the resin hardens and is removed from the mold, it stays on the part and you don't have to paint it.
Hello Dick...not sure I want to invest in 3D printing equipment. Will add, however, might be interesting to do a Chaski series on those methods if there was a reasonable way to share the process from conception thru to a completed print.

Your idea of painting the mold is an interesting. You're assuming there's no clean up work to do on the casting that would expose the resin/color underneath. More than likely, some paint touch up work would be needed. I know Smooth-On does sell a line of color additives that can be added during the mixing stage. One would be limited by the colors available. Not sure you'd want to experiment with color-matching AFTER the two parts come in contact and the pot life clock is ticking. Still, a neat idea. Thanks for sharing.

Carl B.
Life is like a sewer...what you get out of it depends on what you put into it!
I don't walk on water...I just learned where some of the stepping stones are!
I love mankind...it's some of the people I can't stand!
ccvstmr
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Re: One Last Shorty

Post by ccvstmr »

WINDOW PAINS - Part 5

Would appear the photo posting/previewing issue in Chaski has been resolved (thanks Mike).

Okay, let's finish up the window casting process. After a while, a stack of cast window frames starts to build. Some frames came out perfect! Used a fingernail file board to clean up the "inside" surfaces. Can use those fingernail boards to clean up the outside surfaces too, but found a piece of 220 grit sand paper on a drill press table or other flat surface worked well...and fast. The resin "powders" easily and even with a 220 grit sand paper, need to make sure you don't remove too much of the cast resin.

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Sadly, there were several frames that experienced air entrapment. Damn...hate that when that happens! Thought some of those window frames could be saved. Some frames needed too much effort.

My solution...used a Dremel tool with a burr tool and roughed up the casting void. Kind of like what a dentist does when preparing a tooth for a cavity. Used a couple strips of masking tape to "dam up" both sides of the frame in the affected area. Mixed some Harbor Freight 5 minute epoxy to fill the void. Unwound a paper clip, mixed the epoxy and used the end of the clip to take an epoxy blob to "wet" the window frame surfaces being filled...pushed out the air and kept adding epoxy until the void was filled.

In the next photo, did my best to save the left and right window frames. Let the center frame go to the scrap pile.

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Next photo shows some attempted window repairs. When the epoxy cured, the epoxy could be sanded and finished just like the resin. Before any painting or priming is done on the window frames, cleaned the window casting. Choices are: a glass bead blast, a gentle grit blast or even a good scrubbing with kitchen cleanser. Should remove residual foot powder on the casting before priming or paint finishing.

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Let's talk some window glazing. Knew from the start, I wanted some "color" in these windows. The shorty cars are painted Hunter Green. Decided to "up the game" and use some green acrylic for the half moon and clerestory windows. Looking on line, found (2) types of green glazing material: 1) translucent and 2) transparent. Contacted the supplier to find out the difference. Found out translucent glazing is opaque. Wasn't sure how that would allow lighting to shine thru the window. Selected the transparent green acrylic...and was glad I did.

The main area of the windows would get clear acrylic glazing. Used the "score 'n snap" method to cut this material to size. If starting with a large piece of material, would be best to get another pair of hands to assist. Else, despite the scoring...acrylic sometimes likes to break where IT wants to break. Don't ask how I know. An alternative...clamp the acrylic material before snapping along the break line.

The next question...how would the half round windows get cut? Once again, out came the hole saw. Drew a grid on the acrylic surface paper. But, the pilot hole in most hole saws is 1/4". Too large! Made a new pilot drill for the hole saw with a piece of short 1/4" diameter steel rod and a 1/16" diameter drill bit. Silver soldered the drill bit in place. Lined up the NEW hole saw pilot drill on a grid drawn on the backing paper and clamped the acrylic material in place. Used a pumping action with the drill press to cut thru avoid over heating the acrylic material.

Once the hole saw made several round windows...used a centering square to line up the center of the glazing circle, scored the acrylic a few times and then snapped that in half. So each round piece of glazing would hopefully produce (2) half round windows. Note to self...cut a few extra round windows. The pilot drill would leave a small center hole that would be removed with a disk sander as part of the glazing fitting.

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Readers are probably wondering how this was going to look in the window frame. Well, I was liking the end result here!

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Lastly, how would the half round window be secured? For other windows, I made basswood angle cleats from a couple pieces of strip wood. Something that could be glued to the inside car/roof walls with a short "leg" to push up against the glazing and hold the glazing in place.

There was no way to do that with the half round windows. Luckily, there was a wide enough shoulder on the window frame interior that a 2-56 hole could be drilled and tapped for a 3/16" long screw. Made an aluminum sheet metal template to locate and drill the glazing mounting holes. A bottoming tap was used to get a few threads in the hole. Will admit...for a guy with small fingers, working with these screws was a challenge (read PITA). In the end, stubbornness won!

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At this point, it's time to get back to the car body for car #7. What's next? Think it's time to cut the openings for these windows. See you soon. Carl B.
Life is like a sewer...what you get out of it depends on what you put into it!
I don't walk on water...I just learned where some of the stepping stones are!
I love mankind...it's some of the people I can't stand!
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Harold_V
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Re: One Last Shorty

Post by Harold_V »

Hmmm! The void issue.
Some time ago I made tooling so I could rewind one of the (electromagnetic) clutches in my Graziano. Once wound, it had to be potted, for which I chose epoxy. The clutch was hand poured until full, then placed in a bell jar with a vacuum pulled to ensure good penetration of the epoxy and removal of air. I was shocked to see the amount of epoxy that had to be added to compensate for the displacement.

Armed with that, is it possible you could do something similar with your castings? Pulling a vacuum pretty much assures that there would be no voids.

H
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djjh87
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Re: One Last Shorty

Post by djjh87 »

I'm digging those green windows .. awesome job.
Jim
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ccvstmr
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Re: One Last Shorty

Post by ccvstmr »

Harold_V wrote: Sat Jan 28, 2023 5:00 pm Hmmm! The void issue.
Some time ago I made tooling so I could rewind one of the (electromagnetic) clutches in my Graziano. Once wound, it had to be potted, for which I chose epoxy. The clutch was hand poured until full, then placed in a bell jar with a vacuum pulled to ensure good penetration of the epoxy and removal of air. I was shocked to see the amount of epoxy that had to be added to compensate for the displacement.

Armed with that, is it possible you could do something similar with your castings? Pulling a vacuum pretty much assures that there would be no voids.

H
Harold...that's interesting. Yep, when the air gets sucked out...it's replaced by...whatever. Epoxy, resin, varnish, other. Only problem, when dealing with short pot life resins...don't have much time to de-gas. Use longer pot life resins, and it takes longer to wait for curing, de-molding and prepping for the next pour. And then, not every shop has a vacuum pump and chamber.

Smooth-On suggests de-gassing the silicone rubber mixes. But we never had any problems with bubble/holes in the rubber molds. As such, we didn't worry about de-gassing the rubber. Using the foot powder as a release agent perhaps helped more in this area than we thought.

My opin...the problem with the window frame air pockets was simply not enough "tilt" in the mold to allow the resin to push the air out the nearest opening. Another possible approach...after the resin is poured...squeeze the rubber mold a few times like "pumping" and try to push the air pockets out before the resin starts to set up.

No matter what course of action is taken...it's a hoot to pour resin into a mold and a few minutes later pull out a part ready for clean up and use in out models. Carl B.
Life is like a sewer...what you get out of it depends on what you put into it!
I don't walk on water...I just learned where some of the stepping stones are!
I love mankind...it's some of the people I can't stand!
ccvstmr
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Re: One Last Shorty

Post by ccvstmr »

djjh87 wrote: Sat Jan 28, 2023 5:28 pm I'm digging those green windows .. awesome job.
Jim
Thanks Jim. Stand by...cause I think you'll be "digging" some more things I did with car #7. Carl B.
Life is like a sewer...what you get out of it depends on what you put into it!
I don't walk on water...I just learned where some of the stepping stones are!
I love mankind...it's some of the people I can't stand!
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