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jdougn
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PostPosted: Sat Feb 04, 2012 9:38 am    Post subject: Reply with quote

I've used PP before and found that it is also very sensitive to variations in mold density. For example, the mold was made from about 6 stacked layers of 3/4" MDF and each layer telegraphed through the .187" PP as a large scallop. Places where bondo had been used telegraphed through. The mold was perfectly smooth so all of this was a total surprise to me!
Hope the heating situation with your oven works out.
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spektr
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PostPosted: Sat Feb 04, 2012 3:57 pm    Post subject: Reply with quote

The problem isnt the coils, the issue with polypro is the RATE you heat it. If you dump a ton of BTU's/Second at it, it gets unhappy. You need to heat it up at less than the rate you are using. Throttle the oven back if you have controllers on it, or increast the distance to the oven face by not raising the shuttle all the way up on a protoform style carrier.
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ANH trooper
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PostPosted: Sat Feb 04, 2012 5:04 pm    Post subject: Reply with quote

I tried having the plastic a few inches lower than the first attempt and it did help, but still burned through on the edges. I will try it even lower next time and see how it goes.

I don't have any controllers on my oven. It's either on or off. It's been great for ABS over the years though, but was hoping to make something that has controlled areas like hotter center and cooler outer edges or vice versa if I need to.

Everything else on my machine works perfectly, but now I want to use PP and need to get it to heat properly. Funny thing is I got it to form when my oven was under the plastic before I made the over head design. It wasn't perfect though and I got a thin spot in the middle due to the plastic sagging into it (or I didn't pull it early enough).
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jdougn
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PostPosted: Sat Feb 04, 2012 9:18 pm    Post subject: Reply with quote

My experience with PP is a bit limited but was the same as yours on the sagging. It didn't need to sag nearly as much as ABS. I started going by feel instead of sag and when it felt about the same as ABS then it was ready to pull. I probably only did 8-12 test pulls though.
dn
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ANH trooper
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PostPosted: Sun Feb 05, 2012 1:10 pm    Post subject: Reply with quote

What kind of heater did you use and was it over or under the plastic?
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jdougn
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PostPosted: Mon Feb 06, 2012 7:52 am    Post subject: Reply with quote

ANH trooper wrote:
What kind of heater did you use and was it over or under the plastic?


Proto-Form with the heat on top. Modular oven with nichrome wire and hardibacker. Oven uses range top burner controls but it's been long enough that I don't recall what the settings would've been.
dn
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ANH trooper
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PostPosted: Tue Feb 07, 2012 2:45 am    Post subject: Reply with quote

Sounds good.

Do you have a link to your build thread or oven design?
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jdougn
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PostPosted: Tue Feb 07, 2012 8:38 am    Post subject: Reply with quote

ANH trooper wrote:
Sounds good.

Do you have a link to your build thread or oven design?


I don't have anything on my vac former on the internet. However, the ProtoForm design and modular oven in this thread are the same as what I did except that he used the ProtoForm oven kit which, to me, is a good idea. http://www.tk560.com/phpBB2/viewtopic.php?t=1162
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ANH trooper
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PostPosted: Wed Feb 08, 2012 4:10 am    Post subject: Reply with quote

Thanks for the link Smile

I remember that build now...really nice!

I also have the build plans on a CD from Doug but there was no mention of building the oven yourself (at least I don't recall there being) with this modular oven. I really like the design and could pull that off on my 2' x 2' oven if I knew the coiled lengths needed and resistance for each section?
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jdougn
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PostPosted: Wed Feb 08, 2012 8:17 am    Post subject: Reply with quote

ANH trooper wrote:
Thanks for the link Smile

I remember that build now...really nice!

I also have the build plans on a CD from Doug but there was no mention of building the oven yourself (at least I don't recall there being) with this modular oven. I really like the design and could pull that off on my 2' x 2' oven if I knew the coiled lengths needed and resistance for each section?


Yes, that is a really nice build by TD1035. I have the Protoform plans but couldn't afford the oven kit at the time. It's not hard to reverse engineer the modular design.
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Fredo
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PostPosted: Wed Feb 08, 2012 7:41 pm    Post subject: Reply with quote

ANH, you could still configure your oven same as a tj oven if you went to a three segment oven. If you isolate the third segment from the first two, you have control of the center third of the oven. Go to the oven calculator and enter, say 4800 watts,240 volts, [same power level as proto-form] , 3 segments, 24x24 oven base, now you have the amount of coiled wire you need and the spacing. The spacing changes, but that isn't a problem. http://www.tk560.com/ovencalculations.html You can select the watts you want, I used 4800 as an example................Fredo

PS Make the changes in the first column, the third column wont show the floor layout.
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ANH trooper
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PostPosted: Thu Jan 02, 2014 6:36 pm    Post subject: Reply with quote

Hi guys,

It's a new year and I want to tackle this oven again. I have the oven wired in 2 segments and I am looking to try infinity switches so I can have the centre section hotter then the outer section of the oven. I believe I have found what I am looking for here: http://www.ebay.co.uk/itm/140546738082?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

Can you more experienced guys take a look to make sure I am buying the right controllers please?
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jdougn
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PostPosted: Thu Jan 02, 2014 7:51 pm    Post subject: Reply with quote

ANH trooper wrote:
Hi guys,

It's a new year and I want to tackle this oven again. I have the oven wired in 2 segments and I am looking to try infinity switches so I can have the centre section hotter then the outer section of the oven. I believe I have found what I am looking for here: http://www.ebay.co.uk/itm/140546738082?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

Can you more experienced guys take a look to make sure I am buying the right controllers please?


I'm certainly not the most experienced electrician around here but here's my .02. The voltage and amperage look okay. It may take some doing to figure out the purpose for each terminal unless it's supplied with a diagram. Are you thinking this controller will provide variable heat or is it a percentage controller that controls heat by being on part time then fully off part time?
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ANH trooper
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PostPosted: Fri Jan 03, 2014 1:02 pm    Post subject: Reply with quote

I am looking to control the heat with these switches. They are designed for oven hobs so I think they should work. I am hoping there will be a wiring diagram for the terminals or it could be fun trying to work them out (not!)

I believe these are the UK equivalents of infinite switches since all my searches have come up blank looking for them here. I really want to be able to regulate the heat better than just having my oven constantly on hot.
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jdougn
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PostPosted: Fri Jan 03, 2014 6:20 pm    Post subject: Reply with quote

These simmerstats appear to be a percentage timer based on information on the net: http://en.wiktionary.org/wiki/simmerstat
The oven on my vac former uses this type of thermostat and it seems to work fine with ABS plastic varying from around 1/16" up to almost 1/4". I'm not sure how well it'd work on thinner plastics or more difficult plastics. This thermostat will simply cycle the heating element on then off to maintain an average temperature. Real interested in seeing how your build works out!
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