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My 2 X 3 Design (pic heavy)
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felixx
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PostPosted: Wed Sep 30, 2009 9:50 am    Post subject: Reply with quote

thanks for that, i think i will also go with MDF instead of plywood for the spacer and supports.

When I look at

thanks againTHIS machine, you can see a thin spacer, and this is a 4 x 4 table. I have seen the video of that one in action, why do you think they went what looks to be 1/8 vs an inch as you suggest?
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jegner
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PostPosted: Wed Sep 30, 2009 12:05 pm    Post subject: Reply with quote

According to Thurston James' book The Prop Builder's Mold and Casting Guide, page 188, a 1/4 inch spacer is all that is needed.

1 inch means more cavity air to evacuate. 1/8th inch might restrict flow. 1/4 inch is a known working thickness.

http://www.amazon.com/Prop-Builder%C2%92s-Molding-Casting-Handbook/dp/1558701281/ref=sr_1_1?ie=UTF8&s=books&qid=1254333905&sr=8-1
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jdougn
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PostPosted: Fri Oct 02, 2009 8:12 pm    Post subject: 1/8" spacers Reply with quote

When I reset my molds for the commercial vac former they wanted at least 1/4" spacer. I've not used anything else just because that's what I started with. But, doesn't the Proto-form design use hardware cloth as the spacer under the perforated metal top sheet?
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felixx
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PostPosted: Fri Oct 02, 2009 8:28 pm    Post subject: Reply with quote

Thats an interesting question doug, I was just planning on using the sheetmetal right on top of my platen when i drill my 1/8 inch holes.

Im curious to know what the purpose is of having something between the top pulling surface and the sheetmetal.
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spektr
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PostPosted: Sat Oct 03, 2009 8:39 am    Post subject: Airflow. Reply with quote

The reason the hardware cloth is there is to provide for vac airflow. As the plastic seals off against the platen, all those holes are occluded and will not flow. This means that the cfm drops very quickly at the time you need it most, finishing the part. The reason you space tools off the platen face is the same, to get the holse under the mold to work for you at the completion of the pull. Otherwise things slow down dramatically and the sheet can lock prior to getting the edges of the part to completely mold. It's pretty simple if you think it thru..

Scott..
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jdougn
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PostPosted: Sat Oct 03, 2009 12:57 pm    Post subject: crazy spacers Reply with quote

felixx wrote:
Thats an interesting question doug, I was just planning on using the sheetmetal right on top of my platen when i drill my 1/8 inch holes.

Im curious to know what the purpose is of having something between the top pulling surface and the sheetmetal.


Not exactly sure how your planten is being assembled. I think the Proto-form uses a perforated aluminum top sheet, hardware cloth spacer, MDF core, then aluminum bottom sheet with one hole for vac line hookup.

When I retooled for the commercial vacuum former they had me set the molds up on a top sheet & bottom sheet of 3/4" cabinet grade plywood with 1/4" spacers between. A 1 1/2" galvanized pipe plumbing flange was used to attach vac lines. (I've had the fitting pull or break out of MDF.) The edge spacers were siliconed in place. Two center spacers were also used on a 21"x45" planten. Thompsons Paste Wax was used on the backside perimeter of the top sheet to prevent the silicone from permanently bonding to the top sheet. This allows for removal of the top sheet when needed. I'm not sure this exact method would work with a perforated top sheet though.

Forgive me if this is over-kill but since I get confused by dualing terminologies let's use pictures! These picts are all from the Proto-form build by TK1035. http://www.tk560.com/phpBB2/viewtopic.php?t=1162&postdays=0&postorder=asc&start=45


The aluminum sheet for the top, perforated and ready to mount to MDF with hardware cloth spacer.


Here is the perforated top sheet with the hardware cloth being attached.


Bottom sheet with single hole. Siliconed to MDF core. MDF is porus enough that air will actually move through it so seal all exposed surfaces with silicone.

I believe the MDF core is there primarily for structure. The hardware cloth creates a void through which vacuum can flow to all the holes in the topsheet.
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felixx
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PostPosted: Sun Oct 04, 2009 1:10 pm    Post subject: Re: Airflow. Reply with quote

spektr wrote:
The reason the hardware cloth is there is to provide for vac airflow. As the plastic seals off against the platen, all those holes are occluded and will not flow. This means that the cfm drops very quickly at the time you need it most, finishing the part. The reason you space tools off the platen face is the same, to get the holse under the mold to work for you at the completion of the pull. Otherwise things slow down dramatically and the sheet can lock prior to getting the edges of the part to completely mold. It's pretty simple if you think it thru..

Scott..


Does anyone have a link for this "cloth"?

So its my understanding (as im building my platen today) that before i place the sheetmetal down and drill my 1/8 holes, place the cloth down? Or is this something i put on after before i seal the sheetmetal to the platen?

thanks

EDIT: here is my platen concept. so far i have the the mdf and sheet metal. i was going to use 1/4 mdf for the spacer. the supports are 3/4 square


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jdougn
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PostPosted: Sun Oct 04, 2009 1:50 pm    Post subject: Reply with quote

Harward cloth is just heavy duty screen, almost like fencing materials. It's available at probably any hardware store. At the big box stores it's usually with the fencing products.

hth, dn
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felixx
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PostPosted: Tue Oct 06, 2009 2:11 am    Post subject: Reply with quote

jdougn wrote:
Harward cloth is just heavy duty screen, almost like fencing materials. It's available at probably any hardware store. At the big box stores it's usually with the fencing products.

hth, dn


THIS was pretty much the only site i could find any info on the stuff. ill look around other places like home depot to see if they carry it. is there a specific type i should look out for? like copper, stainless, fine mesh etc.,
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jdougn
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PostPosted: Tue Oct 06, 2009 8:35 am    Post subject: Reply with quote

felixx wrote:
THIS was pretty much the only site i could find any info on the stuff. ill look around other places like home depot to see if they carry it. is there a specific type i should look out for? like copper, stainless, fine mesh etc.,


Hardware cloth is a fairly universal fencing product used for things rabbit cages. It is at Home Depot here: http://www.homedepot.com/h_d1/N-5yc1vZ1xj7/R-100081535/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

I would again suggest getting plans for your build. Trying to reverse engineer a vac former will get very frustrating and expensive due to failed ideas. For example, just on the planten, if the spacers aren't the right size and spacing it can create numerous problems that are difficult to fix.

In your drawing, if hardware cloth (or 1/4" thick strips) were used under the metal top sheet this would eliminate the perforated center piece of MDF and the little spacers on the bottom sheet. You would still need to carefully & completely seal the bottom sheet to control vacuum leaks.

Hope this helps.....
DougN
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felixx
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PostPosted: Tue Oct 06, 2009 9:05 am    Post subject: Reply with quote

it does help, because in the previous post, it was called "Harward cloth"
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felixx
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PostPosted: Fri Oct 09, 2009 1:39 am    Post subject: Reply with quote

Hello,

I purchased a sheet of 1/4 MDF for my spacer and cut it to shape and size (just like in my drawing a post up)

I was looking at THIS pic from the tutorial and was wondering what would the best way to assemble the platen be.

Should i use tack nails then simply use the flashing around the inseam? Or place the sealing directly on the spacer then place it on the top half of the platen then tack nail it to gether, then use my screws to bring together all pieces.

Im just looking for the best way to make a tight seal.

thanks!
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spektr
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PostPosted: Fri Oct 09, 2009 6:52 am    Post subject: Platen construction. Reply with quote

I'll sit on the sideline on this one, after all, I really try to discourage platens and promote the use of seperate mold bases.....
I find that they provide better sheet utilization for parts.

Then again for simple small stuff, tossing molds on the platen
and making a shot or 2 it has advantages. I just dont have requirements
tha tallow me to do that.......

Scott.
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felixx
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PostPosted: Fri Oct 09, 2009 11:17 am    Post subject: Re: Platen construction. Reply with quote

spektr wrote:
I'll sit on the sideline on this one, after all, I really try to discourage platens and promote the use of seperate mold bases.....
I find that they provide better sheet utilization for parts.

Then again for simple small stuff, tossing molds on the platen
and making a shot or 2 it has advantages. I just dont have requirements
tha tallow me to do that.......

Scott.


i am sorry, i dont understand your response. making this platen has suited the friend who let me use his table and pulls 100s of sets of armor. He is two hours away otherwise i would bug him more.

Being that this is crucial, i just may ask him on this one.
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jdougn
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PostPosted: Sat Oct 10, 2009 11:53 am    Post subject: perforated plantens are good for prototypes Reply with quote

felixx wrote:
.......Should i use tack nails then simply use the flashing around the inseam? Or place the sealing directly on the spacer then place it on the top half of the platen then tack nail it to gether, then use my screws to bring together all pieces.....


I tend to use screws for everything so it can be taken apart if needed. But as you plan, just do whatever necessary to hold the spacer in place.

On the issue of plantens, Scott (Spektr) does production work and permanently fastens all molds to a unique, purpose built planten. On the other hand, if you are doing mostly one-offs or proto-type work then a perforated planten is, IMHO, indespensible. For example, in the development stages of the fender flares that I make it would've been impractical to have made a unique planten for each prototype.

You are headed in the right direction. You have first hand experience with your friend's vac former and that should be a good source of information. This process is so much more "art" than "science" and many different techniques will end with the desired results!

Good luck and continue to keep us posted on your progress!

HTH, DougN
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