smart51
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| posted on 13/11/08 at 07:21 PM |
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Vacuum forming help needed.
I've had a go at vacuum forming today but without much success. I heated the oven to the desired temperature (160° for acrylic) and waited for
the plastic to sag, the put the vacuum cleaner hose into the hole in the box I made to hold the mould and, well, not very much.
I pushed the plastic into the mould with the handle of a spoon that had been sat in a cup of boiling water and the plastic moved a bit but it
wasn't at all like you see on TV.
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Howlor
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| posted on 13/11/08 at 07:25 PM |
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What thickness acrylic were you using?
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smart51
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| posted on 13/11/08 at 07:27 PM |
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2mm. Quite thin really.
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Howlor
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| posted on 13/11/08 at 07:29 PM |
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I would say try 180ish, but I would have thought it should have gone at 160. Did you trap the outer edge of the acrylic to form the seal?
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smart51
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| posted on 13/11/08 at 07:33 PM |
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The acrylic is clamped between 2 plywood squares with the middle cut out using 6 bolts set into one of the frames and wing nuts to hold on the top.
The baby is in bed now but I'll have another go tomorrow.
How many holes should I have in the mould and how big should they be? For info, the box is 410mm x 425mm on the outside (just fits in the oven).
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Howlor
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| posted on 13/11/08 at 07:37 PM |
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You need enough holes to let the vac pull it's full vacuum. I would say 8 x 6mm spread across the tool to allow for even pull.
You could put a solid sheet in with say a small hole to put your finger over just to check that you have a good vacuum.
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SeaBass
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| posted on 13/11/08 at 07:43 PM |
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I'd suspect that your vacuum cleaner is not able to evacuate the box or you have a leak allowing equalisation of pressure...
James
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Howlor
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| posted on 13/11/08 at 07:57 PM |
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TBH I know of a lass that could do the job for you. I reckon she could suck golf balls through a hose pipe!
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nathanharris1987
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| posted on 13/11/08 at 08:48 PM |
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what what? how do you know my ex?
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emsfactory
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| posted on 13/11/08 at 09:18 PM |
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Probably not hot enough. You dont need much pull to draw over a buck if the plastic is hot enough.
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smart51
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| posted on 13/11/08 at 09:36 PM |
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How do you tell if the plastic is hot enough then?
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Hammerhead
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| posted on 13/11/08 at 09:44 PM |
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the plastic should sag, then re tighten in your frame, this means it is ready to form.
You need a lot of holes, I used 3mm drill bit.
Raise your mould off the board slightly with a spacer of a couple of mm, this allows air to get under the mould.
Make sure your frame seals with your base board, dont let air escape.
I used a shop vac which is a very powerful american vacuum cleaner, but my mould was 250mm deep.
Check that your vac doesn't have a safety pressure release valve, (dysons do) this safety feature stops people having their men bits sucked
clean off if they happen to 'fall on the vacuum cleaner whilst hoovering naked'
Hope that helps.
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trextr7monkey
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| posted on 14/11/08 at 12:35 AM |
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Hi Smart, we have a vac former at work what size is your mould, without frame etc? I fit will fit in we can prob knock you one or 2 out
atb
Mike
http://www.flickr.com/photos/14016102@N00/ (cut and paste this dodgey link)
Our most recent pics are here:
http://s129.photobucket.com/albums/p211/trextr7monkey/
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Mr Whippy
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| posted on 14/11/08 at 07:47 AM |
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I'm a bit confused what the spoon is for, never needed one or anything like that when I do this.
From what I can read, you may not have sufficient holes, an A4 sized area should have around 100-200. Plus it does not sound like you have put foam
draught seal around the edge of the box for the frame to press against, this is quite important due to the low flow rate of the air being drawn
through all the holes.
The sheet is hot enough when it is floppy when the frame is rocked, then press the sheet down on the mould in one go, till the frame seals against the
box with the draft seal foam, then the vacuum will completed the process. Even a small air leak will prevent it working so make sure the box and frame
are air tight.
A photo of what you have built would solve the issue very quickly btw
Don’t give up as you will find this process invaluable around the scooter in areas like the dash etc and its well worth learning how to do it.
Fame is when your old car is plastered all over the internet
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02GF74
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| posted on 14/11/08 at 07:55 AM |
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how do you know it was 160? did you rely on the cooker dial or use an accurate thermometer?
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Mr Whippy
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| posted on 14/11/08 at 08:22 AM |
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I find using a hot air gun far better than an oven, held about a foot away and moved more around the edge of the frame than the center. Its great if
one area is stiffer than the rest and if it starts to droop too much you can flip the frame over rather than the risk that the plastic might touch the
inside of the oven and get ruined. I sit the frame on the backs of two wooden chairs so I can heat the underside as well.
[Edited on 14/11/08 by Mr Whippy]
Fame is when your old car is plastered all over the internet
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smart51
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| posted on 14/11/08 at 04:10 PM |
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I've had another go with more sealing on the box. There are 2 problems. 1 is that the plastic sags so much in the oven that there is too much
material to be pulled into a shallow mould, so the edges are raised off the mould in places. 2 is that it doesn't pull into the corners of the
mould at all. The radius it forms too is quite large.
I now have a fairly large plastic bowl where I just let the scrap piece sink in the oven then let it cool.
The plastic didn't sag then tighten up, it just sagged. A lot. How do I get it hot enough without sagging too much?
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hellbent345
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| posted on 16/11/08 at 10:38 PM |
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just heat it less, the perfect temperature is when you can stab it with a finger (not too much) and its soft enough to absorb the blow, but soft of
hard enough to spring back to flatness
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