daven

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This may sound like an odd question, but has anyone tried CNC cutting Plexi Glass as their mold material?

Just curious, it would seem like a good choice to me, but I'm not sure.

Campgems

I can think of a couple things that might prevent it from being a good mold material. First, in anything over a 1/4" thickness, it becomes expensive. That, in addition to the maximum thickness I've seen is about 1 1/2", you are limited to size. The other thing is that it is attacked by some solevents, IE acitone for one. Clean up could be a problem. Oh yes, it chips like crazy unless the mill is set for the right speed and feed and there is enough coolant, or it melts and sticks to the mill. The finish is not real smooth, it has to be sanded and then buffed out to get a good glassy finish and this can lead to imbeded polish if to much heat is generated. Some of the other plastics would be a better choice, IE acetal. However, you are still limited by rough sizes.

Don

diggs_74

I guess that answers that.. Luckily there are people who know about this stuff so others don't make an expensive mistake However, the plastic idea I think might be a desent one if the correct plastic was used.. Of coarse, if it costs as much as a block of aluminum then I guess it's not really worth it.

It was just something Daven and I were batting around earlier today... Thanks for the info Don.

Campgems

There is probably a hundred guys out there that use plastic without problems. I've not had good luck machining it.

If you were going to make a lot of an item, making a mold using the methods use in boat building may work. They make a hull and finish it out. That becomes the plug that they make the mold from. The plug can be made from about anything, plywood frames, lath and plaster is one way. Carving a big ole block of wood is another. Once you have a finished plug, you put the mold release on it and the lay up the mold surface and the add in the re-inforcements to keep the mold from twisting and such when it is set up. The good thing about doing the work this way is that you apply the finish first and the build up the glass after. It gives a great finish almost every time. You could do something like this on a small scale for stuff like wheel pants and cowlings. You could even make a fuselage if you wanted. I tried one way back when. It about cost me my mariage. I heard you could put the paint brushes you brushed the resin on with in plastic wrap and put them in the freezer and they would stay soft for the next days work. First, it didn't work and second everything in the refrigerator had to be thrown away as the fiberglass odor was every where. It took us a couple days of scrubing with everything we could find to get the smell out of the frig. One lives and learns and sometimes the cost of learing is high.

Don

dolanosa

How about using plexiglass as a parting board? wouldn't the smooth surface be good for that? I have some plexiglass here and I'm making a plug for a 27% plane. I was thinking about backing up the p-glass with some 1"x1" so it wouldn't bend. Thanks in advance.

B.P.R.

Hello Dave , i have build in this sistem the new F3D wing for my friend Paolo Mucedola ......i pholish the master with paper 1000 and after paper 2000...finisch with abrasive polish............only wax and you have a good relase , you have a very clear mould.

Ciao Paolo Pampana

B.P.R.

I am now waiting to finish milling the master (in this sistem) for my new Q40 model "STREGA" (for now have approved the first step of the approval proces)........hope Paolo Mucedola can fly in phoenix febbrary ......and also hope build one for my friend Frank Wong (i called he in F3D WC Muncie).
Paolo P.

Campy

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For smaller parts I vaccuum mold PETG over a plug, then use the PETG as my mold.

FWIW - When I am going to make a mold from PETG I try to use .080 (or in a pinch .060 ).

I put 2 coats of PVA Mold release inside the mold, then a coat of epoxy and finally layer in the fiberglass cloth. On smaller parts (wheel pants, 2 and 3 part cowls, etc ) I have had very good results.

daven

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Paulo,

That is very impressive, do you have any other info on your Strega model??

Glad to hear it is working well for you, let me know how it holds up..

B.P.R.

Daven,
This is the Strega design.....