Wanted: advice regarding my plug

[rtfm]

Hi

 

I have reached the point with my plug preparation where I am just about ready to wax on, wax off. I.e. start making my molds. However, I would really like an experienced eye to give my plug the once over and provide me with a sanity check before I carry on.

 

I have reached the 150grit stage, all the blemishes have disappeared and as far as I can see all is ready. But what do I know?

 

So, if you live in the Brisbane area and have a half hour to spend this weekend, I'm looking for some assistance.

 

Regards

 

Duncan

 

 

[Guest Maj Millard]

Do a quick lay up in it (doesn't have to be a structural one to just check finish) and have a look at the product finish.........Maj...

 

 

[turboplanner]

He's using foreign language; I think he means a pattern, and he is about to make a mould, so he would be laminating over it.

 

So the surface correction opportunities are ideally on the pattern, but when the mould is laminated, recesses on the pattern will sit proud on the mould and can be sanded off, and recesses on the mould can be filled.

 

More importantly, if checking the pattern, the mould part line(s) should be drawn on with a pencil chinagraph, and very close attention should be paid to ensure the mould shap does not undercut the pattern in any way, or you'll have a permanent garden ornament.

 

 

[skeptic36]

I have reached the 150grit stage, all the blemishes have disappeared and as far as I can see all is ready. But what do I know?

A little more than T.P me thinks.........

 

 

[turboplanner]

I notice that you haven't offered him any advice at all Skeptic.

 

If it's so important to qualify knowledge, I was employed for five years by one fibreglass company and four years by another as a draftsman, production planner, salesman and sales manager.

 

I mainly worked on the design and production drawings of large transport equipment which included refrigerated vans, semi vans and truck cabs, and mainly in FRP.

 

I also did a lot of personal design and laminating

 

The advice I gave above is based on my own experiences with laminating

 

The attached photo, about 48 years old shows the first set of US mag style wheel covers in Australia.

 

I made the pattern by pulling an aluminium section around a mandrel and adding dental plaster to get the round base wheel and hub shape, then laminating five FRP spokes and setting them on to the plaster with plasticene internal radii.

 

The mould was just a lay up over the pattern.

 

My comments about looking for undercuts to prevent a lock up once the parts are laid up in the mould was based on many experiences with screwdrivers, crow bars, and on one occasion chaining the mould to the floor and trying to pull the part out with a 6x4 truck.

 

Although the mag wheel covers had the minimum radii and withdrawal angle required, they locked up in the mould.

 

FRP tends to shrink very slightly when it goes off, shrinking out of concave shapes, but draping over convex shapes and gripping them.

 

I eventually solved the problem by laminating a garden hose fitting on to the mould so full mains water pressure seeped in and gradually melted the PVA between the surfaces until enough hydraulic force was generated over enough area, and the part came out with a big "pop" about 30 minutes later.

 

These wheel covers are also a little unusual in that I used a clear gel coat with aluminium powder filler, and got a metallic appearance.

 

Hence my advice to look for undercuts etc.

 

 

[skeptic36]

I notice that you haven't offered him any advice at all Skeptic..

No, that is because I don't have any to offer, Nor do I have any criticism .

My comment was aimed at the one you made, that the guy must be speaking a foreign language. I guess that was because he called a plug, a plug and not a pattern as you would like it to be known.

 

He should be taken to the edge of town and stoned for that, as he was for his question about Jab skin thickness.

 

I know nothing about anything so you won't get any advice from me ( unless you want to know what a plug is, I could give you a layman's description if you need it) ;-).

 

Regards Bill

 

 

[bexrbetter]

Everybody but everybody uses the term "plug" while only engineers generally use the pedantically correct term - type 'fiberglass plug' into Google Images then try 'fiberglass patterns' for confirmation. Duncan's molds are not at high risk from undercuts as his plug/pattern is made from plaster and can simply be washed away later if it came to it.

 

150 sounds a bit course to me, for gelcoat anyway, and I would be using 400 by hand or 240+ with an orbital sander and as Maj says, do a foot square test.

 

I'm not going to get into the PVA or wax release agent debate as i don't want to be responsible, but i notice a lot of people have had from mildly stuck pieces in molds to molds being thrown away using PVA whereas as I have used McQuires Mold Release wax all my life and never had the slightest of issues - again, personal experience only and not a recommendation.

 

 

[Kyle Communications]

He's using foreign language; I think he means a pattern, and he is about to make a mould, so he would be laminating over it.So the surface correction opportunities are ideally on the pattern, but when the mould is laminated, recesses on the pattern will sit proud on the mould and can be sanded off, and recesses on the mould can be filled.

More importantly, if checking the pattern, the mould part line(s) should be drawn on with a pencil chinagraph, and very close attention should be paid to ensure the mould shap does not undercut the pattern in any way, or you'll have a permanent garden ornament.

Its either a plug or a mould...its that simple TP

 

 

[Kyle Communications]

RTFM Is it a plug or a mould you have made? and finish sanding you NOT have any 150grit anywhere near it....finish on the plug should be 1200 paper wet and dry not 150

 

 

[Kyle Communications]

DOH

 

its ok I see you are doing the plug....work tomorrow not in the right headspace

 

 

[cscotthendry]

Duncan: The finish you make on the plug will be the finish you get in the mold. Generally it is easier to put a high finish on the outside of a plug than the inside of a mold, just because it's a convex surface and it's easier to see what you're doing, and also easier to reach around. Generally, I would say that 150 grit is pretty coarse surface finish. If you want a nice glossy part to come out of the mold, then the mold has to have a glossy surface and the easiest way to get a glossy surface in a mold is to have a glossy surface on the plug.

 

Also, if you're in Brissy, the Gateway TAFE used to run a fibreglass course. I went on that course when I was in the process of buying a large(ish) fibreglass cruiser. For mold release, they used to reccommend 3 coats of car wax in the mold every time you do a layup in it. This would also apply to the plug before making the mold around it.

 

 

[turboplanner]

Here's a photo of it.

 

http://rtfmaero.wordpress.com/construction/

 

 

[David Isaac]

FFS guys, layoff Turbo will you. It is bloody obvious he is trying to help RTFM.