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Author: Subject: making a mould from a buck
smart51

posted on 16/12/08 at 08:55 AM Reply With Quote
making a mould from a buck

I've almost finished making a body panel but it's been hacked about so much that it weighs about 3.5 tonnes because of all the filler. I've decided that it is now a buck so I'll take a mould from it and remake the pannel from the mould. The surface is almost entirely filler and will be sanded nice and smooth.

How do I make a mould? Gel coat and GRP, but how much? How do I prepare the buck's surface? Wax? How many coats of wax do I need to guarantee separation?

Thanks in advance for any useful suggestions.

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fesycresy

posted on 16/12/08 at 08:58 AM Reply With Quote
You need some carbon

Have a look at this, may help:

Carbon Mods Video

I was just about to post a thread on this link (may still do )





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Howlor

posted on 16/12/08 at 09:08 AM Reply With Quote
Good vid, now let me see what I can make! Litle lad will be the first at school with a carbon lunch box!
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Mr Whippy

posted on 16/12/08 at 09:23 AM Reply With Quote
Why did he do so many layers in one go? Surely it would have been easier to do the first, let that cure then do the others. That way he'd have known the top outside layer was completely pushed into the corners. I'd have used glassfiber for the inside layers too.

Also is there much in a loss of strength when not curing these mouldings in the usual vacuum bag, autoclave setup. GRP never seems to need this treatment, why is it just carbon???

Fozzie? You do this stuff all the time, can you shed some light on this?


[Edited on 16/12/08 by Mr Whippy]






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Triton

posted on 16/12/08 at 10:24 AM Reply With Quote
First you have to make sure that the mould can actually come off the plug..say for instance you moulded have a ball but went too far round then that wouldn't come off..5 or 6 wax coats then pva to make sure it doesn't stick but no quarantee it won't especially taking mould from filler.
Best option is to paint or laquer then wax etc.

CF needs vac bagging to ensure the resin is forced into the material and all air is removed because you can't really go at it with rollers as distorts the weave. Too many layers in one hit will create too much heat and distort the mould and the part.
Gel coat then put too layers down making sure it's ALL down, let it cure then gritty paper to key it then start all over again with the resin...4 o 5 times the thickness of the part you intend to make but thicker the better for moulds if you want them to last.

Easy really





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twybrow

posted on 16/12/08 at 10:29 AM Reply With Quote
For making a mould, vacuum bagging is overkill. Simple GRP hand layup is sufficient for the sort of parts we might make. If you need to chase the highest mechanical properties, and minimal weight, then vacuum bagging, infusion, prepreg etc come into play.

To make a mould, start off thinking about any flanges etc you need to add. Also think about the draught angle (release angle) - minimum of 3degrees is good. It is best to add those to the buck now, before you get going. Once you have added these, use plastercine to radius any nasty corners, then you are ready to start....

Seal the surface to ensure it is not porous - wax can help here, alternatively PVA solution works well. Once you have at least 5 coats of wax put on, and buffed off, try an adhesion test - stick some masking tape to your released part (it shouldn't stick at all).

Next, apply your gelcoat (tooling gel, or gelcoat + wax solution). this needs to go on in 2 even layers - don't be tempted to wack a load on at once. Once this has gone off, I would look at using a fine glass tissue, or very lightweight csm to back up the gelcoat. This will help stop 'print through' from the other materials. Once this has gone off, begin layup of your csm. I like to work with 450gsm - any more and it wont take a radius without a lot of work. For your first layer, apply resin to the part, then add the mat, then work the resin up through the mat. Pay particular attention to radiused corners, flanges, edges etc. Then continue to build up thickness, but not too much at once. If your part exotherms (excess build up of heat caused by the reaction), then you can end up with an awful surface finish (pre-release), or even a fire!

Once you have built up sufficient thickness, you would need to add some support/stiffeners to your mould. USe steel, or wooden battens, and brace the backside of your mould. Again allow it all to go off. Once it is good and hard, you can look at demoulding the buck from the mould, and admiring your handywork....!

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Mr Whippy

posted on 16/12/08 at 11:16 AM Reply With Quote
I once left a glass bowl full of unused resin, got so hot it started steaming and shattered the bowl, didn't catch fire but made heaps of volcanic like noise






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scootz

posted on 16/12/08 at 11:49 AM Reply With Quote
Good wee video... never realised it was that straightforward... !

Does anyone have a good vid for larger GRP laying techniques?

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smart51

posted on 16/12/08 at 12:32 PM Reply With Quote
Should I use polyurethane varnish on the filler, then wax then PVA? I've used varnished and waxed MDF to good effect before. Never on filler though.
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Richard Quinn

posted on 16/12/08 at 12:55 PM Reply With Quote
quote:
Originally posted by Mr Whippy
Why did he do so many layers in one go? Surely it would have been easier to do the first, let that cure then do the others. That way he'd have known the top outside layer was completely pushed into the corners. I'd have used glassfiber for the inside layers too.

Also is there much in a loss of strength when not curing these mouldings in the usual vacuum bag, autoclave setup. GRP never seems to need this treatment, why is it just carbon???

Fozzie? You do this stuff all the time, can you shed some light on this?


[Edited on 16/12/08 by Mr Whippy]

It's more to do with the resin than the reinforcement. Epoxy should be laid up in one go if poss as epoxy is not very good at bonding to cured epoxy. The only way around this is to abrade the surface of the cured epoxy to get a mechanical bond.
Wet lay up will generally be inferior to vac bagging as mechanical strength is dependent on the correct fibre to resin ratio which is difficult to achieve without vac bagging.
If you are going for aesthetics (2x2 twill being the bit of a giveaway in the video), reasonable results can be achieved using the technique in the video. Patient stippling with the brush can remove a lot of the air bubbles.
If it is structural or the stiffness is important then plain weave should be used with different layers at different orientations (you will quite often see lay ups described as 0/45/0 etc which is the orientation). This is less pretty but superior strength/stiffness.
HTH

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Ross SA

posted on 16/12/08 at 01:27 PM Reply With Quote
Hi All,
I made a mould for a nose cone as the ones you can buy here in SA are really not good. I would advise against waxing directly on to body filler, far better to use 2K primer followed by top coat. On the plug for the nose I flatted the 2K with 1200 to give a smooth uniform but flat finish.
Whilst the mould released from the plug it wouldn't come off because of the shape, so eventually I had to split the mould to get it off the plug. I ended up with a nose that I'm more than happy with. As a release agent I used Meguiars mould release wax, 8 coats allowing the wax to dry completely before buffing, worked a treat.
Ross

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Dick Bear

posted on 16/12/08 at 02:37 PM Reply With Quote
Smart51 .... Perhaps this will help you get started.

Here's how I did it for a part I made (nothing to do wit a car)

Bondo buck ... created over simple cardboard rough form sanded smooth and to correct shape.

Dick Bear

[Edited on 12/16/0808 by Dick Bear] Rescued attachment Bondo buck.jpg
Rescued attachment Bondo buck.jpg






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Dick Bear

posted on 16/12/08 at 02:40 PM Reply With Quote
#2
Laid-up fiberglass and fiberglass pad over the buck

Dick Bear Rescued attachment fiber mold 1.jpg
Rescued attachment fiber mold 1.jpg






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Dick Bear

posted on 16/12/08 at 02:42 PM Reply With Quote
#3

Same image but on the unit in the back you can see the bracing I bondo(ed) to the mold to hold its shape.

Dick Bear Rescued attachment fiber mold 2.jpg
Rescued attachment fiber mold 2.jpg






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Dick Bear

posted on 16/12/08 at 02:46 PM Reply With Quote
#4
Turning the mold right side up and filling, sanding and preparing the surface smooth .... gel-coat, and release etc.... ready to lay-in fiberglass for the part.

Dick Bear Rescued attachment Ready mold.jpg
Rescued attachment Ready mold.jpg






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Dick Bear

posted on 16/12/08 at 02:49 PM Reply With Quote
#5

Primer painted finished part.

Sorry I couldn't figure out how to place more than a single photo per post.

Dick Bear Rescued attachment Primered part.jpg
Rescued attachment Primered part.jpg






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fesycresy

posted on 16/12/08 at 03:29 PM Reply With Quote
quote:
Originally posted by Mr Whippy
Why did he do so many layers in one go? Surely it would have been easier to do the first, let that cure then do the others. That way he'd have known the top outside layer was completely pushed into the corners. I'd have used glassfiber for the inside layers too.

[Edited on 16/12/08 by Mr Whippy]


Time is money in business, he's a pro, and I suppose the real answer is, because he can and still get the finish





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scottc

posted on 16/12/08 at 06:44 PM Reply With Quote
quote:
Originally posted by fesycresy
You need some carbon

Have a look at this, may help:

Carbon Mods Video



What did he make though?

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Ross SA

posted on 16/12/08 at 08:07 PM Reply With Quote
Hi,
Can someone help me by telling me how to upload images as attachments?
ross

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smart51

posted on 16/12/08 at 10:35 PM Reply With Quote
quote:
Originally posted by Ross SA
Hi,
Can someone help me by telling me how to upload images as attachments?
ross


When you reply there is a box between the word attachment and the button browse. Click the browse button and navigate to the picture you want to post. Click OK and the pic is uploaded to the message. I think it takes jpg files but not bmp files.

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Ross SA

posted on 17/12/08 at 08:06 AM Reply With Quote
Thanks, I'll give it a go.
Ross

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Ross SA

posted on 17/12/08 at 11:01 AM Reply With Quote
Ok,
I clicked on the browse button and it opened up my pictures, I selected the image I wanted to load but I didn't see an "OK" to click.
Ross

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smart51

posted on 17/12/08 at 11:22 AM Reply With Quote
Sorry, the button is called "Open" not "OK".
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Ross SA

posted on 17/12/08 at 12:43 PM Reply With Quote
Thanks, I'll try again.
Cheers,
ross

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Ross SA

posted on 17/12/08 at 12:45 PM Reply With Quote
It looks like it worked this time, this is a picture of my nose cone.
Ross

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