Carbon fibre undercarriage layering

[Steve Houghton]

Hi All,

 

I'm attempting to mould my first carbon fibre/glass laminated undercarriage, for a Sssshhwept by Geoff Dallimer (as updated by Shaun Garrity).

 

My first attempt set fine, but it was too thick and heavier than I wanted, at 28g. I managed to laminate my planned 10 layers (4 carbon interleaved with 6 glass) just before the resin started setting.

 

Second attempt, using the same 10 layers again, I refined the process using thinner cloth. This time I mixed up the resin in three batches and applied them without letting the previous layers set. I ended up with the middle layer not setting. Is this likely to have be caused by not letting the layers set before applying the next?

 

The other possibility is an incorrect ratio of resin to hardener in one mix. I'm using some very old Ripmax SP113, but all my trial mixes have set correctly, in the ration 3:1.

 

Any ideas from the experienced moulders, please?

 

Thanks, Steve.

[Andy Stephenson]

Some epoxies have to be mixed by weight rather than by volume and when mixing small amounts it can be quite difficult to get the mix as accurate as it needs to be for laminating resins. I use a jeweller's digital balance that reads down to 1mg.

As far as the non-setting layer is concerned, I wouldn't ascribe that to adding other layers on top, as I have never had this problem. It may yet go off if left for a while or under the effect of heat.

Interesting note, epoxies set better in the absence of oxygen, especially at its surface.

[Steve Houghton]

Thanks, Andy. Useful to know that you have used 'wet' layering successully.

 

I used 2ml and 10ml syringes for measuring by volume, mixing approx 6ml resin to 2ml hardener each time. I strongly suspect I got the ratios wrong for the second mix.

 

I left it in the warm since last Sunday night, and finally pulled it apart tonight, to find that layers 1 to 5 had set but layers 6 to 9 hadn't.

 

[Andy Stephenson]

I should add, it's also necessary to thoroughly mix the two parts, so going above and beyond in the stirring process can't be stated too strongly.

[Steve Houghton]

Thanks. I'm making a third attempt today, concentrating on thorough mixing, and will show how I got on in due course.

 

[Engine Doctor]

Did you keep the layup in a warm dry atmosphere while it cured ? I had some finishing resin that wouldnt cure as the temp fell too low. Once the cure stalls I find it wont start again even if warmed up.

[Jason Channing]

21 hours ago, Steve Houghton said:

Hi All,

 

I'm attempting to mould my first carbon fibre/glass laminated undercarriage, for a Sssshhwept by Geoff Dallimer (as updated by Shaun Garrity).

 

My first attempt set fine, but it was too thick and heavier than I wanted, at 28g. I managed to laminate my planned 10 layers (4 carbon interleaved with 6 glass) just before the resin started setting.

 

Second attempt, using the same 10 layers again, I refined the process using thinner cloth. This time I mixed up the resin in three batches and applied them without letting the previous layers set. I ended up with the middle layer not setting. Is this likely to have be caused by not letting the layers set before applying the next?

 

The other possibility is an incorrect ratio of resin to hardener in one mix. I'm using some very old Ripmax SP113, but all my trial mixes have set correctly, in the ration 3:1.

 

Any ideas from the experienced moulders, please?

 

Thanks, Steve.

SP 113 is a vile resin with very bad amine bloom, bin it and use any other brand, West, Poly fibre, Easy composites etc , It never hardens correctly in a mould or as a laminating resin and cannot be over coated with out a lot of work, very similar to polyester flowcoat. I do a lot of mouldings and have never had an issue with the major brands other than SP113.

[Steve Houghton]

ED: Thanks for your tip. As far as I know it was warm enough - just room temperature but inside the house rather than an outhouse/shed.

 

Jason: Thanks for the heads up. I thought I'd try the SP113 just to see what happened, with nothing to lose by trying. I have mixed up 7 or 8 batches of resin now, and each has set well except for the one mentioned above. I strongly suspect I used an incorrect quantity of hardener.

 

I'm pleased to report that my third attempt was successful. I managed to lay up 11 layers altogether, using two separate mixes of resin laid on top of each other.

 

Lay it on: Layers as below, with the uppermost layer of c/f cloth (when viewed from the top) at the bottom of the picture. The underside (top of picture) was finished with a layer of glass, since earlier attempts left the bottom c/f surface rather rough since I didn't use any press to smooth it down:

 

Mould: My mould was made from ply and scraps of balsa for spacers. Two coats of sanding sealer, then 8 coats of release wax each buffed up:

 

Let me Out: Since the mould tapers toward the feet, I made the front surface of plasticard removable so that I stood a chance of removing the product:

 

Drying Out: After drying for 18 hours it felt hard enough to release. The front popped off nicely:

 

Free at Last: The main moulding needed a little persuasion to release, but finally it popped out cleanly without bring any of the mould with it - Phew!

 

Voila: It won't win any concours prizes, but I'm quite happy with the result. All the resin dried nicely and the layers seemed to hold together. I haven't mastered the art of getting a shine on the top surface yet - the surface against the release wax is smooth but matt finish.

 

It just remains to be seen whether it is strong enough and how easily it can be drilled without breaking. Approx thickness 3mm. Unfinished weight before sanding is 20g.

 

Thanks to everyone who has chipped in.