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Need some advice

 
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Lortan



Joined: 06 Apr 2014
Posts: 4

PostPosted: Wed Apr 09, 2014 3:40 pm    Post subject: Need some advice Reply with quote

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
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Joined: 21 Mar 2007
Posts: 251
Location: Kingdom of Nye Area 51

PostPosted: Wed Apr 09, 2014 5:25 pm    Post subject: Reply with quote

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..... Wink
ps use the vac pump if you've got a good seal on the edges of the platen..
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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

PostPosted: Wed Apr 09, 2014 7:43 pm    Post subject: Reply with quote

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
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Joined: 21 Mar 2007
Posts: 251
Location: Kingdom of Nye Area 51

PostPosted: Thu Apr 10, 2014 10:06 am    Post subject: Reply with quote

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

PostPosted: Thu Apr 10, 2014 10:12 am    Post subject: Reply with quote

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
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Joined: 20 Oct 2005
Posts: 305
Location: UK

PostPosted: Sun Apr 13, 2014 5:19 pm    Post subject: Reply with quote

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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