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BlindSquirrel
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Joined: 01 Jun 2006
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PostPosted: Fri Jul 21, 2006 9:08 am    Post subject: Test pulls Reply with quote

I plan to buy some plastic today for some test pulls. Do I buy something thin (.04) to save money while I work out problems or do I buy .08 to test what I'll probably pull in the future? How much of a difference does the thickness of the plastic make in the process?
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ANH trooper
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PostPosted: Fri Jul 21, 2006 11:30 am    Post subject: Reply with quote

I personally would get the thinner plastic to test with.If your oven heats .040 then it will heat .125 just as well.I started out using .040 for all my test pulls,then once I was happy with my moulds I used thicker plastic.The thicker plastic usually takes a little longer to heat,but not much in my experience.Hope that helps Very Happy

-paul.
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jegner
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PostPosted: Fri Jul 21, 2006 11:33 am    Post subject: Reply with quote

I started with a sheet of .060, a bit thinner than what I ended up using. For strictly practice, you can use .060 but I would not go lower than that. The thinner stuff is hard to hold on my frames. If you plan to use .080, get a sheet of that too. If you plan thicker, say .093 or .125, you will need some to test with as well.

The differences between .060 and .080 are small, but the thinner stuff will show you mold flaws, and will perform similar to your final intended thickness, but again, sort of depends on what it is your are test pulling. Flat pieces are good test subjects for .060, but if you part has depth, the .060 will go thing or form a hole, so it sort of depends.

IMHO

Jim
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AlterEgos
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PostPosted: Sat Jul 22, 2006 11:52 pm    Post subject: Reply with quote

Yep, it all depends on what your pattern model is and the results you're looking to get.

For example, I usually use .060 to pull my archival molds and .080 to pull armor. But, since the need for better detail in my archival molds is of great importance at this stage, I'm going to try using .030 or .040 for them. Wink
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BlindSquirrel
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PostPosted: Wed Jul 26, 2006 12:00 am    Post subject: Reply with quote

Thanks for the advice, everyone. I picked up some .06 Styrene for my testing.

The GOOD news is that I got everything assembled and ran my first test on my new machine.



I suffer from limited storage/working space so I opted for the over/under design. 95% of it is exactly to Jim's tutorial specs...My variations include: Wooden canvas stretching frames (since I can't weld!) to hold the plastic, sash locks to allow variable pressure on the frames, pillow block bushings to slide the frame up to the oven and a concrete board oven cover that slides in place.

The oven takes about 45 minutes to get to 350ºF and the .06 plastic was ready in 3 minutes. For the first pull I wanted to try a variety of items to see what I would get: a BIG bowl shape of unfinished MDF, a small flat sided primered and sanded MDF and a small round edged unfinished MDF. And to fill in spaces, a pocket knife and wrench.



Although I got some webbing, everything actually worked! I was very surprised to see how MUCH detail was visible in the final piece. I guess I have some sanding to do!

Much thanks to Jim and everyone else who responded to my (stupid) questions! I would never have attempted this build without the tutorial and this great board!
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jegner
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PostPosted: Wed Jul 26, 2006 6:32 am    Post subject: Reply with quote

WOW!

Looks great. Yes, .060 will show you all sorts of detail! The webbing can be fixed with some mold placement experimentation.

45min to heat? That seems a bit long, but then again, I use a cover to help hold the heat in. You might want to make one from some scrap HardiBacker, and place that where your plastic holding frame would go, at least during your pre-heat cycle. My guess, is you are loosing a lot of heat, hence the long warm up time.

Great job, I really like your design. Can you post some pics of your frame and clamps?

Thanks

Jim
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AlterEgos
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PostPosted: Wed Jul 26, 2006 12:15 pm    Post subject: Reply with quote

That's excellent, Squirrel!!! There's nothing more exciting than your first successful pull, eh? Very Happy

I'm not sure why your heat up time is so long (mine is about 20 minutes, but I have the flip-flop design). The cause may be from any number of factors such as voltage regulation to poor insulation on the oven, but I'm sure you'll eventually figure it out and have that machine popping out flawless pulls in no time!

The whole thing about garage vacuforming is that it's not an exact science so, there's always something which will hinder progress. The good news is we have this forum to help take some of the guess work out of the equation. Wink
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crashmann
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PostPosted: Wed Jul 26, 2006 12:52 pm    Post subject: Reply with quote

Fantastic!

Even a blind squirrel gets lucky and finds a nut occasionally Razz

I love the windows sashes for the plastic clamping frames. That's a great way to accomodate different thicknesses of plastic! I also like the hook to hold the frame in place while heating. Nice engineering!

I'm curious about your oven setup. I just finished assembling a small over under design using a Sunbeam electric grill for the oven (report with pictures to be posted later). This will be for doing small prototype parts for my friends. I'm going to let them keep it, and build another one using nichrome wire in the oven. Can you shoot a few photos from below and post them?

Thanks!

Charlie
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BlindSquirrel
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PostPosted: Wed Jul 26, 2006 11:12 pm    Post subject: Reply with quote

Perhaps my slow heat up time is due to heat loss from above...can someone recommend insulation that I can use that will resist that kind of heat?

I had to crimp the sash locks to get them tighter, but they hold great. I had to forgo the hinge side for extra clamps just to keep the equal pressure. Hopefully the wooden frame will hold for a while but I suspect I'll eventally have to replace it with metal.

I ran out of daylight, but will be sure to post requested pictures tomorrow.
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BlindSquirrel
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PostPosted: Fri Jul 28, 2006 12:13 am    Post subject: Reply with quote

Here are a few detail photos. I added a support on either side of the frame so I could load up plastic if I had forms already on the table. It locks into place using the slots on the Gorilla Rack supports. Not terribly strong but sturdy enough.





This is the upper frame (The lower is attached to the pillow block bushings). I had to flip the sash locks so that the flat side is on top for a snug seal with the oven. I also added a wooden strip and weather stripping to prevent heat loss.



This shows the sliding oven door and the Dollar store oven thermometer I embedded in it. Don't look at the sloppy caulk!



Alook inside the oven. It has the tutorial's angled concrete board sides, supported by a wooden frame.

[/img]

I still need to insulate above the oven and paint the modifications but at least it works!
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drcrash
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PostPosted: Thu Sep 28, 2006 8:50 am    Post subject: over-and-under experience? Reply with quote

Blind Squirrel,

I'd be interested in hearing any updates about your over-and-under, which looks like a nice design.

Some questions:

Did you try insulating the oven? Did it speed up preheating? I'm wondering if over-and-under ovens need a bit more wattage than flip-tops, because the hottest air rises to the top of the oven. (Harley Guy cranked the wattage way up by shortening his coils a lot, but for most of us that might flip some circuit breakers.)

How did you mount and align the vertical shafts that the pillow blocks (and frames) ride on?

Do you have any problems with the pillow blocks binding? I'd think more vertical displacement would be stabler and more self-correcting, but maybe I'm overly concerned about that.

How are your wooden frames working out?

From reading some pro thermoforming handbooks, it sounds like metal frames often contribute to cold edges, by acting as heat sinks. (I'm not sure if that's mostly because of conduction, or mostly an indirect effect via cooling the air near the edges.) The pro machines often preheat the frames before clamping the plastic, or actually have heaters inside the frames.

This makes me think that wooden frames may be better than metal ones, at least in that respect. (Or that even a little bit of insulation between metal frames and the plastic might go a long way to reduce the problem. Maybe a little silicone would do it.)
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BlindSquirrel
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PostPosted: Thu Sep 28, 2006 10:33 pm    Post subject: Reply with quote

I have not found insulation for the top yet. I'm sure I'm losing heat up there but there seems to be ample heat below for the plastic. It takes a while to pre-heat but once it does it only takes 3 minutes before it's ready to pull!

The shafts and pillow blocks were lined up by running the frame up to the top and then securing the shafts. REAALLLY scientific! I am getting a bit of binding due to flexing of the wood frames but this small delay doesn't seem to affect the pulls.

Flex aside, the wood frames have worked out really well. I painted them with barbeque (heat resistent) paint so they've shown no deterioration. The sash locks have been great too, as I can put just about any thickness of plastic in this thing and it holds like a bear!

I haven't done a lot with the machine but it has performed flawlessly. I'm very happy!
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drcrash
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PostPosted: Fri Sep 29, 2006 1:29 am    Post subject: Reply with quote

Thanks, Blind Squirrel.

Sounds pretty sweet.

About insulation: you may want to consider mineral wool. It's really cheap and can handle 1200 degrees.

McMaster-Carr has 24 x 48 sheets of 1" thick mineral wool for about four dollars. (1 1/2 & 2" thick are about 6 and 8 bucks.) You can get it with chicken wire on one or both sides, but then it costs about ten dollars more.

How hot does the wood around your oven get?

(I wouldn't put insulation around the wood; you want it between the oven and the wood.)
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Mattax
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PostPosted: Sun Oct 01, 2006 8:28 pm    Post subject: Reply with quote

Very nice! And good ideas in getting the other item bugs worked out of my over/under design.

Yes, definitely insulate the outside of the oven box. The box I had made is slightly larger than 24 x 24 and 12 inches deep/tall. Now from reading this forum I am thinking that I will need to make an inner plate to mount the niachrome wire and spacers in order to bring the heating element down closer to the plastic frame holder which will stop right below the oven and then 1-1/2 inches below it due to the frame holder hitting the bottom of the oven.

What caulking will seal and withstand the heat of the elements/oven?

I guess I need to post elsewhere so as not to hi-jack this thread. http://www.tk560.com/phpBB2/viewtopic.php?p=1792#1792
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BlindSquirrel
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PostPosted: Sun Oct 01, 2006 11:11 pm    Post subject: Reply with quote

Mattax wrote:
What caulking will seal and withstand the heat of the elements/oven?


I found some furnace caulk that seems to be working pretty well. I think it's rated for 1200ºF (some temperature over DOUBLE what I can get!). Ace or Home Depot should have it in stock.
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