PMF and Foamie Fillets?

[stepcut]

Hello,

If I was working with fiberglass, epoxy, and plywood, I would likely use thickened epoxy to fillet the inside edges before laying up the fiberglass. (sorry the image is so wide).

Screenshot_2020-04-08 Duckworks - Liquid Joinery.png (359.07 KiB) Viewed 1042 times

I could, of course, still use epoxy and a filler -- but that seems like a lot of money when bonding to foam.

Has anyone had success making fillets by mixing cabosil fumed silica with TBII? Gripper? Something else?

Or maybe I can use Loctite® PL® 300 Foamboard Construction Adhesive with no filler? Or with a filler?

Thanks!

[John61CT]

Great Stuff, Dow 2-part even better

precisely applied not overfilling the "mold", which does need to be stronger than you think.

Or do it rough then cut it back.

Whole point of PMF is No Epoxy IMO

[Pmullen503]

Are the fillets structural or just for looks?

For something small, like 1/4" even 1/2" radius you could use thickened epoxy.

For anything larger, I'd use hot wired foam fillets glued onto place. Not easy, I thought about that on my foamy, 2x2 quarter rounds.

[stepcut]

Are the fillets structural or just for looks?

Both looks and structure. I have something like 42 feet of edges I'd like to fillet, so 'fast' and 'affordable' would be nice. Thickened epoxy would be fast, but expensive. Creating some sort of custom jig for creating foam fillets to glue in place would be affordable, but time consuming.

The idea of creating a mold and pouring an expanding foam in it sounds like it could generate a good result, but also be fairly time consuming.

I do have a Ryobi Powerfile. So I have considered gluing in foam or using 'great stuff' to add extra material and then trying to use the powerfile to sand a fillet into the material. Sounds very messy and imprecise.

ryobi-powerfile.jpg (4.21 KiB) Viewed 982 times

I am looking to do a pretty big fillet if I can. Perhaps the radius of an American Quarter?

The idea of using a thickened glue or thickened something that is not epoxy is appealing because it could also be useful for fairing surfaces before/after laminating. For some of my foamie projects I definitely have gouges and other imperfections I'd love to fill in and sand down.

[OP827]

What thickness of foam and size of fillets do you have?

Maybe make the fillets out of foam with a circular saw or a hot wire jig and glue them with Epoxy or PL Premium glue (NOT the PL400 construction adhesive as it will dissolve XPS foam). With fillets you will need less glue and it will be faster then making the fillets with thickened epoxy. You can do your own testing, but I feel that TBII with a thickener may not work well as a fillet. If fillet is small then it is probably better to cut a fillet our of soft wood and glue it with TBII or PLP or Epoxy. The challenge here could be the holding of the glue up together until it dries. What is your plan to hold the assembly together?

If it were me I would consider foam fillets and PLP glue, but need to figure out how to hold the glueup in its final position. I can think of two options.
One option is to use some removable plywood strips covered in packing tape and use drywall screws of suitable length to be "fast" and "affordable".
Another option is to use nylon or wire ties like in stitch gluing. Just make holes along the joint in each piece near the joint to hold the fillet and walls together, but will need to have plywood pieces under the ties to prevent the ties sinking into the foam while tightening. To reinforce the joint I would consider gluing a thin 2-3mm plywood or wood strip on top of the foam fillet, then such joint will be much stronger and possibly easier to make.

Epoxy does not really need to be clamped, while PLP and TBII require a decent holdup for good results.

PLP also needs moisture from air to cure so it is only suitable for relatively small non-porous surface glueups. I would not water mist PLP as it will then have too much bubbling and expansion. It is better wait longer for it to cure than have bubbled glue surfaces IMHO. For larger non-porous surfaces epoxy is the ticket. In any case I would do some test pieces to proof the concept before going with a production piece.

I prefer PLP for work with wood and foam because it has a long working time comparing to TBII, less toxic than epoxy, can glue at a lower temperature, and it is more "affordable" than epoxy and similar to TBII when it comes to cost.

Would be nice to see your build and method you selected. Good luck with the build!