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Lortan
Joined: 06 Apr 2014 Posts: 4
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Posted: Wed Apr 09, 2014 3:40 pm Post subject: Need some advice |
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Hi guys. I built a machine last week so I could form some molds for my concrete business. It is 2'x4' based on some pictures I saw on here and other sites. It seems to work descent enough but I can't quite get the definition I want. I have a robinair vacuum pump that I borrowed from a friend and I am using an old, long empty 100lb propane cylinder for a holding tank. The vac pump can only get to 20-21 mercury. The molds I have are actually cement pavers. Approximately 20" in diameter - they're hexagon shaped. They have a slate style appearance on the surface.
The first pull I tried using 0.056" ABS sheet. It pulled fine around the mold but did not pick up the slate design.
I removed the vac pump and went directly to my 6 hp shop vac and then tried using a sheet of 0.110" HDPE as I was out of the ABS, it seemed to get the definition i need but opposite. I suspect that my molds need to be warmer. I think the HDPE shrank away from the cold mold rather than setting in place.
Should I be warming up the mold or cooling it more? ( the first couple tries i did were when the molds were room temp.)
Should I cast a new paver from plaster and then drill some holes in it to get the vacuum to pull though the paver/mold?
Is there a casting material I should use that is porous for the vacuum to pull though?
Any advice here would be great. I will try to post some pics below.
Machine Pic
Mold Pic
HDPE test
ABS test
Original Mold for concrete paver - one I am trying to recreate
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Fredo Master
Joined: 21 Mar 2007 Posts: 251 Location: Kingdom of Nye Area 51
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Posted: Wed Apr 09, 2014 5:25 pm Post subject: |
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After you pour and drill a new paver, trim a piece of felt to fit under the paver. That'll hold the paver up enough to pull air through the holes you've drilled.....
ps use the vac pump if you've got a good seal on the edges of the platen.. _________________ If someone has a gun and is trying to kill you,
it would be reasonable to shoot back with your own gun...The Dalai Lama..Seattle 2001 |
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Lortan
Joined: 06 Apr 2014 Posts: 4
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Posted: Wed Apr 09, 2014 7:43 pm Post subject: |
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So you say I should pour a paver using plaster instead of the cement? I have had some issue with the seal on the edge of the platen but I used a foam tape to seal the edge of the sheet frame to the platen. I made the platen 24" x 48" and the frame rests on top of the platen. I think this may have been a mistake - after looking at the other machine designs I think I will make the platen smaller so the frame will pass and the plastic sheet will seal on the platen better. Any thoughts? |
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Fredo Master
Joined: 21 Mar 2007 Posts: 251 Location: Kingdom of Nye Area 51
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Posted: Thu Apr 10, 2014 10:06 am Post subject: |
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Since you can't very easily drill the cement and you need better definition, the grout lines can be made a little deeper in the plaster and can be drilled, 1/16 inch drill is what I'd use in the grout lines.. After you're happy with the plaster mold pull, you can make a cement paver that might pull with the deeper grout lines you've added without drilling holes.... The plastic being pulled hard into the deeper grout lines give you better def.
There's little chance that trying to do a straight copy will work well enough to suit you...
PS I recommend Hydrocal 30 if you can find it, so much stronger and harder than regular plaster... If your platen doesn't seal well it will always be an up hill battle.... _________________ If someone has a gun and is trying to kill you,
it would be reasonable to shoot back with your own gun...The Dalai Lama..Seattle 2001
Last edited by Fredo on Thu Apr 10, 2014 10:15 am; edited 1 time in total |
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Lortan
Joined: 06 Apr 2014 Posts: 4
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Posted: Thu Apr 10, 2014 10:12 am Post subject: |
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That clears it up a lot. Thanks for the help Fredo. Ill get to the plaster mold right away. |
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ANH trooper Master
Joined: 20 Oct 2005 Posts: 305 Location: UK
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Posted: Sun Apr 13, 2014 5:19 pm Post subject: |
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Using the original paving stones as forming tools are going to get you the best results. Simply drill breather holes in the joints using a thin masonry bit (2mm) and you will be fine. The pavers will hold up to much more abuse than Hydrocal or Plaster in my opinion. |
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