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MDR
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Joined: 22 Nov 2011
Posts: 49
Location: Missouri
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 Posted: Thu Dec 01, 2011 7:04 pm Post subject: ... |
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Last edited by MDR on Thu Mar 01, 2012 2:14 pm; edited 1 time in total |
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spektr
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Joined: 07 Jan 2008
Posts: 425
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| Posted: Fri Dec 02, 2011 2:37 pm Post subject: |
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Yes, its just a version of vacuum snapback forming. Instead of blowong a bubble with positive pressure and vacuuming it all out, youre just allowing the sag to happen by gravity. I dont like it because of the loss of controll you get over some process variables, but it will work with a bit of effort.
But you might ask the question...... Why doesnt the industry use sag instead of bubbles.....
http://www.youtube.com/watch?v=NPLWxxyIJcE |
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MDR
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Joined: 22 Nov 2011
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Location: Missouri
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| Posted: Sat Dec 03, 2011 6:32 am Post subject: |
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| Thanks for the reply. I came up with this design after I got a wrinkle in my plastic at the top of the mold, which only happen once. The bubble idea would work real good. Im going to start my new former after the first of the year, and looking for new ideas. My mold is 33" long, 13" wide, and 12" tall. It's a male mold with minor detail.[/url] |
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MDR
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Joined: 22 Nov 2011
Posts: 49
Location: Missouri
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| Posted: Tue Dec 06, 2011 8:36 am Post subject: |
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| Ok, I went ahead and ordered the plans. They were acouple of things I wasn't sure about. As for the over, I might just try to build it myself, I can get alot of supply pretty cheap, just need the list. |
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MDR
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Joined: 22 Nov 2011
Posts: 49
Location: Missouri
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| Posted: Thu Dec 08, 2011 12:04 pm Post subject: |
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MDR
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Joined: 22 Nov 2011
Posts: 49
Location: Missouri
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| Posted: Thu Dec 08, 2011 12:06 pm Post subject: |
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| This is my mold, all the holes were a mistake, as you would have guessed. |
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MDR
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Joined: 22 Nov 2011
Posts: 49
Location: Missouri
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| Posted: Fri Dec 09, 2011 7:43 am Post subject: |
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| If I vacuum form this mold, can I then pour epoxy in the mold to create a new mold? I really wanting to round the edges a little bit, and round off the top, plus this mold is made with sheetmetal and lots of bondo. All the holes will be filled up. Any suggestion on epoxy, or if this could be done. |
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MDR
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Joined: 22 Nov 2011
Posts: 49
Location: Missouri
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| Posted: Fri Dec 09, 2011 8:34 am Post subject: |
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The fenders is what I'm wanting to make. |
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MDR
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Joined: 22 Nov 2011
Posts: 49
Location: Missouri
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| Posted: Sun Dec 11, 2011 10:08 pm Post subject: |
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| Well, finally got the plans in and printed off the supply list. WOW a bunch of supplies |
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crashmann
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Joined: 27 Sep 2005
Posts: 501
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| Posted: Mon Dec 12, 2011 1:08 am Post subject: |
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Wow, that looks really cool!
I've had great success with BCC BC-8001 Kwik-Kast and BC-8009 Slo-Kast:
http://www.bccproducts.com/castingmaterials
You're idea of using the first pull to cast the resin production mold is exactly the technique that I use. With a part that large, you will need to support and clamp the plastic before pouring the resin. I use a jigsaw to cut a "riser" with a 45 degree beveled edge out of 3/4" MDF to place under the mold to ensure the plastic is pulled all the way to the finished edge of the mold (there can be some flaring out of the plastic where the mold meets the platen).
Save the leftover MDF with the hole cut out. You will put your first plastic pull in the hole, and fasten it to the MDF with clamps. Now when you pour in the resin, the plastic will not become twisted or warp from the weight of the material.
The size of your part has me a little concerned. That would be a ton of resin, and be extremely heavy! Ideally, your production mold would have a 1" thick skin of resin, a vertical wood support frame inside, and some type of filler to resist collapse. I've thought about trying this, but haven't yet...
Good luck!
Charlie |
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MDR
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Joined: 22 Nov 2011
Posts: 49
Location: Missouri
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| Posted: Mon Dec 12, 2011 5:40 pm Post subject: |
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| Thanks for the reply, I was lookin at the slo-kast, I think that would work.(I hope anyway) As anybody ever put anything like tiny wire in the mold before it cures for small suction holes going threw the mold. (I'm not sure if I'm explaining that right or not) I'm wanting to be able to put small molds on top of the mold, if that makes any sense. |
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jdougn
Guru
Joined: 18 Mar 2009
Posts: 714
Location: Louisville KY area
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| Posted: Tue Dec 13, 2011 11:07 am Post subject: |
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| MDR wrote: | | Thanks for the reply, I was lookin at the slo-kast, I think that would work.(I hope anyway) As anybody ever put anything like tiny wire in the mold before it cures for small suction holes going threw the mold. (I'm not sure if I'm explaining that right or not) I'm wanting to be able to put small molds on top of the mold, if that makes any sense. |
Interesting project! Is that a sand rail this is going on?
Crashman is right about the BC8009 High Temp Urethane. It works well for large molds. The 8009 sets up more slowly which makes it easier to mix & pour in large batches. His suggestions on how to cast by using the first plastic pull are good too. One disadvantage is that the plastic shrinks as it cools so the first pull is slightly smaller than the original mold. When casting, it is important to get the plastic level, straight, and well supported before pouring the 8009. BCC also has a mold release product that I like using on the plastic to make sure the casting pops out easily.
On the stuff I do, I make a plug of MDF to fill most of the cavity but keep it away from the finished surfaces so that the 8009 is about 3/4" thick on all faces. Much less than around 1/2" and the 8009 seems to separate from the MDF. The MDF plug is just supported and braced from above before pouring the 8009. The last pour I did this way still used 4 gallons so it's heavy.
The 8009 will quickly dull cheap carbon steel bits but high speed steel or carbide does okay. It is much harder than wood but using 40 grit in the random orbit sander cleans up the surface fairly quickly. For fine details using a sharp chisel as a scraper will work too. I've also ground metal tools to shape to use as scrapers to handle certain contours.
Is your mold going to be fixed to a platen base or sitting freely on a vented platen? If it's sitting on a vented platen you might not need any vent holes. If you think you do, remember that it doesn't take very many. I would suggest to just start with a few around the perimeter and see how it goes. Some of my molds have deep pockets for mounting hardware in the finished plastic so each pocket has a vent hole
To drill the vent holes, a small drill bit will do okay. If it's not long enough make a drill bit using a section of the wire designed to support fiberglass insulation under the floor in a house. This wire is real springy so it doesn't bend real easy. Always drill from the finished side since the 8009 is brittle and will probably chip if drilled from the back.
You could probably suspend wire or weed eater line in the mold but I personally think it'd be a hassle. If the line was very long it may be hard to get out even with mold release.
hth,
DougN
http://www.napierprecisionproducts.com
_________________
DougN - Just in case you're wondering, I got my "rating" legitimately... by posting aimless drivel, useless advice, and pointless questions. |
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jdougn
Guru
Joined: 18 Mar 2009
Posts: 714
Location: Louisville KY area
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| Posted: Tue Dec 13, 2011 11:24 am Post subject: |
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| MDR wrote: | | The fenders is what I'm wanting to make. |
I make fender flares for the Jeep Cherokee XJ. Different than fender flares for what you're doing but similar in overall size and shape.
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DougN - Just in case you're wondering, I got my "rating" legitimately... by posting aimless drivel, useless advice, and pointless questions. |
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MDR
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Joined: 22 Nov 2011
Posts: 49
Location: Missouri
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| Posted: Tue Dec 13, 2011 12:36 pm Post subject: |
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| Yes they are a atv based sand rail. As for mounting the mold to the platen is a real good idea, but I'm in the process of making a few more designs, the will all have the same characteristics with a little different look. I will try to come up with some kinda holding device. Man I sure do appreciate all the suggestion. |
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jdougn
Guru
Joined: 18 Mar 2009
Posts: 714
Location: Louisville KY area
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| Posted: Tue Dec 13, 2011 1:17 pm Post subject: |
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Are you getting the ProtoForm plans? And, what type of plastic do you plan on using for the fenders?
dn
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DougN - Just in case you're wondering, I got my "rating" legitimately... by posting aimless drivel, useless advice, and pointless questions. |
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