Making a mould...

[JohnMarc]

Okay so beginning with the wooden mould....(sorry plug...JamesG123) this morning. I am of course on a different timezone to most of you guys. But I have done a set of little sketches which will (I think) put my concerns out there although with all of your help I think I have it sussed. My main reason for doing this is when I do the "real" bits and pieces for my actual project it will act as a reference for me.

Any comments would be appreciated, (be nice I am very new to this)

 

[JohnMarc]

BTW should I go the epoxy or poly route for the mould? if epoxy (which I am assuming is the way to go) then how do I get the gelcoat equivalent finish on the female mould which I am told does not work with epoxy?

 

[tpenfield]

Looks like you added 8 mm to one dimension and 3 mm to the other (?). The thickness of the female mold does not affect the dimensions of the part, if that was a concern.

The finished part will be 238mm x 323mm outside dimensions. Looks like you were concerned about the inside dimensions in the original post. . .

You mentioned the hatch being strapped down, not hinged. Is there going to be a lip on the opening to hold the hatch in place? . . . not much room in your dimensions for the hatch to slide around without exposing the opening.

Poly will be quicker, but epoxy will give more time for bagging and resin flow.

I am curious as to what graphics software are you using? Sketchup? images look good.

 

[JohnMarc]

Looks like you added 8 mm to one dimension and 3 mm to the other (?). The thickness of the female mold does not affect the dimensions of the part, if that was a concern.

The finished part will be 238mm x 323mm outside dimensions. Were you concerned about the inside dimensions in the original post?

I am curious as to what graphics software are you using? images look good.

Yes it is the inside dimensions I am concerned about, these are shown in image #4..... I think I have achieved it with my little drawing exercise. The software I used is SketchupMake. Free to download .... be careful when you download it, they have set many traps in the process to get you to click on the Pro version, but an awesome little package. I designed my ultimate project using this programme and I would highly recommend it.

 

[JohnMarc]

Looks like you added 8 mm to one dimension and 3 mm to the other (?). The thickness of the female mold does not affect the dimensions of the part, if that was a concern.

The finished part will be 238mm x 323mm outside dimensions. Looks like you were concerned about the inside dimensions in the original post. . .

You mentioned the hatch being strapped down, not hinged. Is there going to be a lip on the opening to hold the hatch in place? . . . not much room in your dimensions for the hatch to slide around without exposing the opening.

Poly will be quicker, but epoxy will give more time for bagging and resin flow.

I am curious as to what graphics software are you using? Sketchup? images look good.

I think I mentioned earlier that the hatch is just held down by a bungee cord stretched over the hatch. Picking up on your point of epoxy versus poly .... can one thin down (maybe by warming slightly) the epoxy to mitigate the risk of not achieving the required saturation.

 

[tpenfield]

Yes it is the inside dimensions I am concerned about, these are shown in image #4..... I think I have achieved it with my little drawing exercise. The software I used is SketchupMake. Free to download .... be careful when you download it, they have set many traps in the process to get you to click on the Pro version, but an awesome little package. I designed my ultimate project using this programme and I would highly recommend it.

My apologies for not fully understanding the dimensions that you were trying to achieve. I always look at the process as the plug and the part come out with equal dimensions. The mold just has to account for flange and cut-off margins.

I thought it was Sketchup. I have the Sketchup 2017 free version, which preceded Sketchup Make. It seems to be a bit more independent from the Pro version than SketchupMake. SketchupMake is fully browser based? or is there an installation on the PC/Mac? (I have the Mac version)

 

[tpenfield]

I think I mentioned earlier that the hatch is just held down by a bungee cord stretched over the hatch. Picking up on your point of epoxy versus poly .... can one thin down (maybe by warming slightly) the epoxy to mitigate the risk of not achieving the required saturation.

There are low viscosity versions of the resin, which would be good for infusion. You can only thin resin down by a small amount (3-5%) without adverse effects.

 

[JohnMarc]

My apologies for not fully understanding the dimensions that you were trying to achieve. I always look at the process as the plug and the part come out with equal dimensions. The mold just has to account for flange and cut-off margins.

I thought it was Sketchup. I have the Sketchup 2017 free version, which preceded Sketchup Make. It seems to be a bit more independent from the Pro version than SketchupMake. SketchupMake is fully browser based? or is there an installation on the PC/Mac? (I have the Mac version)

Yup on a mac as well. I have the 2017 version and refuse to upgrade..... they will find a way to make us pay .... I think the that is where they are going with the web based version.

 

[tpenfield]

Warming the resin will make it set up (harden) faster, particularly poly resin. I usually cool the resin down if I need to extend the working time.

 

[JohnMarc]

There are low viscosity versions of the resin, which would be good for infusion. You can only thin resin down by a small amount (3-5%) without adverse effects.

There is something that I have read a lot about and maybe too worried about, removal of air or degassing. With vacuum bagging should I focus on the degassing? Do the air bubbles weaken the finished product?

 

[tpenfield]

There is something that I have read a lot about and maybe too worried about, removal of air or degassing. With vacuum bagging should I focus on the degassing? Do the air bubbles weaken the finished product?

Seems like we are Instant Messaging . . . I'm not an expert on the finer points of vacuum bagging or infusion, only have done it a few times over the past 10 years . . . but it is a relatively small part, with an easy task, so I would not be overly concerned. Others may offer more detail.

 

[JohnMarc]

It might well be small but as a precursor to a much larger project I am hoping to learn all I can irrespective how small.

 

[fallguy]

Your finished part does not reflect the radius formed by filleting and radiusing the plug.

It may be a drawing limitation or irrelevant, but you asked for nitty details.

I would draw a section picture of the final part to verify section detail accuracy. The section drawing is more important than the big 3D imo.

 

[tpenfield]

Having just made the molds for the 2 hatches on my extend swim platform project, I can add a nitty detail that you will want a slight taper to the sides of the plug, so the mold can come off easily from the plug.

The hatches that I am making are 380 mm x 460mm x 50mm (15" x 18" x 2") and one of the molds had a death grip on the plug. It took a bit of prying on the flange area to get the mold to come loose. One the second one, I added some additional PVA to the sides of the plug before making the mold. It came off easier, but still could have been better.

My hindsight is that I should have given the sides a slight taper (2-3 mm) so the mold would want to 'pop' off of the plug.

 

[Heimfried]

Like tpenfield I would recommend a slight taper to the sides. And I think it would be better to round off the short vertical edges of the plug also - assuming this will not create issues with sharp edges of the lip of hatch opening.