Plug building

Hello

I am about to dive head first in to the construction of some plugs and tooling for a 5.5m powerboat the old fashioned way(without CNC ).
My questions is about the main material for the plug.
For the frames and the strip planking of the hull would MDF be best or would a good grade plywood be better?
Which of the two will provide a stable base and is the least effected buy moisture and humidity changes in the air? Stability is key here.
Also dose anyone know how Styrene effects polyester base car body filler? I have had troubles in the past with excess shrinkage even after a full cure of filler is met. I have heard it is the styrene in the tooling gel effecting the filler?

Any help will be much appreciated
Regards
Nick

 

Those around here seem to prefer MDF over plywood 'cause it doesn't move as much. We tried both and it seemed to us that the MDF was better.

As for car body filler, It works fine in plugs as long as you get enough hardener in it. Trouble happens when people start cutting back on the hardener to get a longer working time. "No grey Bondo!" Body filler with not enough hardener tends to shrink.

We've had good luck using MDF & Bondo (car body filler). Then coating everything with a layer of Duratec as the finish layer. We like to release with about 6 or so coats of wax and one layer of PVA rubbed on with a rag.

Hope this helps.

Good luck!

-jim lee

 

Indeed undercure can cause shrinkage. One could also opt for regular polyester putty, available from your resin or gelcoat supplier. Usually a longer working time.

Here I see some boat plugs being built from MDF and coated liberally with epoxy (also fairing in epoxy putty), then painted in 2K PU paint. (which needs 1 week to fully cure).

 

Thanks for the responses guys. I new deep down MDF is best but heard some one mention ply wood and got me thinking.
Jim: I have been following your boat project, it looks like its thrown every thing it can at you! did you ever find out what was the reason for the plug cracking? Also did you seal the MDF with resin or anything before your first layer or dura tech?

I have had problems with bondo recently when I was making a composite roof for a race car. The original roof had a sunroof in it so we welded this in and bondo the gap. we duratek the roof and faired it up. The mold was complex and was make up of 7 parts the last part to be mold was the part with the sunroof. (4-5 weeks after duratek and polishing) we checked the roof before spraying the tooling gel and it looked perfect. but when we demolded the bondo had shrunk and there was a line were the sunroof was. Presumably this line can only occur after gel coat is sprayed and before the first laminate is cured. how dose this happened I though we had heat cycled it enough to make the bondo reach full cure and we checked 20min before spraying. I am a bit lost on this one. some one told me that styrene effects bondo even after it is cured?
not sure.

Nick

 

The plug that cracked was plywood and cedar. That thing danced all over! I also think that when the rains came, the floor moved a tad causing more grief.

Sometimes we pre-coated with resin before Duratec. I never really saw a difference either way. Seemed to me like more work with no visible benefit. Could be wrong.

As for the styrene attacking the Bondo. I wouldn't say it can't. It seems to attack everything. I'd watch the heat though. What are you using to build the mold? Any of that fancy non-shrink stuff?

It probably threw the regular things at us, we just were so ignorant that we ran into every little pitfall possible.

But in the end? Here's a little preview from last Thurs. & Friday.


Launching. Foils wet at last!


Look it floats!!


Sailing with the kiddies.

It turned out to be a really cool little boat. The faintest wisper of wind and it scoots!

So in the end, I'm all happy!

Now if I could get faster at building these silly stereo units..

-jim lee

 

for what its worth - I find applying PVA with a smooth sponge gives better results than a rag. Use single light straight line sweeps from centre to sides with slight overlap...

 

Jim. Wow she certainly look great when its all done! I bet your pleased. Again it seamed to be this love hate relationship we have with boats! I bet it is worth all the pain and effort when you set out on her for the first time.

 

I was a firm hater of PVA when all this started. As far as I was concerned it was nothing but snake oil.

Seeing you've read the Dart blog, you can see how much trouble we've had getting molds off plugs. Mostly its been picking bits of plug out of molds. We followed all sorts of black magic release formulas. 175,000 coats of wax, burn an offering in the dumpster and only shoot resin during a full moon.

When we were doing the bulkheads we had all these plugs complete at one time, ready to make molds. The first one we did with a bunch of coats of wax, full moon, what have you. Stuck like glue. We had to chip the plug out of the mold.

The second one, we did the wax, then wiped it down with a wet rag of PVA. Mold popped right off the plug. From then on we've wiped all the plugs down with PVA and all the molds have all popped right off.

From a hater of PVA I'm now a big proponent of the stuff. Its also the only thing I've found that works repeatedly with the aluminum molds I use for the simple stereos. Heck I'm coating the inside of my shoes with it. Now in the evening when I get home, they pop right off!

P.S. Thanks and yes, I'm really pleased!

-jim lee

 

In fact Jim, I use PVA on every molding we pull from a mold. Do not trust wax only and also had expensive damage to molds in the past. PVA is magic and as you said, moldings just pops out.
If a bit sticky, we just make and small a few openings somewhere between mold and molding with small wooden wedges, get the hosepipe and feed water into the mold and the moldings just pops loose and floats. (for those who does not know, PVA is water soluble) This method we use with every molding that has many curves, angles etc like canoe decks for example.

 

Still no brand names of release systems used.

In the USA, contact Zyvax. They have some great release systems, which basicly are 3 step:

-clean the plug / mould
-seal the mould (most important step, this is where 90% of the problems comes from, especially with glass and aluminium)
-put release on.

I sell a similar system from Ferro in Europe (Ferro FS-10) and have not seen any problems in release. Most release systems these days are so slippery, that pre-release is more of a problem then no release. (A coat of paste wax will solve that)

 

Jim, why sponge on PVA and not sprayed. Not that spraying has been eazy to do without a little texture but seems like a sponge would leave more "tracks". BTW Thanks for posting your trials and tribs, you give us little infusors hope. Dan

 

Professional Boatbuilder had a good article on spraying PVA, long, long time ago.

It is supposed to be on a CD which holds all issues up till a given moment, when they stopped making the CD.

I do have the article, though. (and still would be interested in the CD...)

Using the hints and tips in the article, I managed to spray PVA flawlesly on a plug. I do recomment a heavy charge of ink though, otherwise you have not a clue of what you are doing.

And applying a thin layer of wax on the PVA supposedly would create a very smooth surface again (never tried myself)

 

We wipe it (PVA) on because we get a smoother surface, more glossy. The amount we put on there, you can't even see. Spraying made the part's finish look dull. Also, it seems a lot easier to just have a jar with a wet PVA rag in it than setting up some spray equipment.

I can't see how you could wax PVA. Seems to me like that would rub the stuff right off. We try not to touch it once its on the mold.

Little infusers? I bet I'm the smallest. My two longtime employees took off for open ended christmas break, MikeC & Norm. I'm the only one left. Trying to catch up on paperwork and stereo orders. (And messing about posting here.) But thank you, posting them actually was fun.

-jim lee

 

I too have had trouble in the past with spraying. I could not get the PVA to atomize nicely. it seamed to spray in droplets rather than a even film so to get even coverage I was putting on a large amount but indoing this it would take a long time to dry leaving in open for foreign matter to contaminate the finish. when released it would leave a dull and slightly textured finish meaning lots of sanding and polishing.
I tried everything room temp and humidity, thinning (although not recommended buy PVA manufacture) still no good.
I haven’t been wiping long and so far good results. as Jim said when wiped you cant even see there is a coat of PVA on there.

Jim: Did you find it polished up as well as when you did not use PVA?

 

It seemed fine to us. But we infuse our molds onto the plugs. So there is print through issues that are going to mask the PVA issues.

-jim lee