Newbie with design question- multi-layers vs kerfing

[Shanfam]

Hello, everyone. I have so enjoyed spending hours reading your posts. I just purchased some of my foam today to start my foamie build. I have absolutely no exerience or knowledge, except what i've leaned reading here. I am starting with a deconstructed jayco pop up trailer and want to build a foam pop up standie. I'm inspired by the foam crank up HYBRID (has more wood than i would like due to weight) standie built by tsmyth, but am concermed about height when towing. My first question is this...in order to make it more aerodynamic, i am thinking about more curves. I may not be talented enough to kerf. So, what is the disadvantage of using many thin sheets of foam (maybe 1/4"), bending it, then using something (gg or latex caulk) to apply another thin sheet and repeating? Thank you all for sharing all you knowledge and experience!

[jondbar628]

Shanfam, The lamination technique for bending has been used on several builds, both foamies & plywoodies. Sometimes kerfing AND laminating. My impression is that it is considered more labor intensive, but sometimes necessary for tight bends. I kerfed my bends (mostly just to see if I could successfully do it), so I can't give you anything first-hand on laminating problems. I'm sure others will have more help for you. Good luck with your build..

[Shanfam]

Thank you, Jondbar , I'll continue playing with foam and drawing....

[ghcoe]

On my front radius I kerfed two sheets of 1" foam and laminated the kerfed sides together. I liked doing this method because I did not have to fill and fair the kerfing slots later. On my rear radius I found out just how much a pain in the ___ it was to fill a fair kerfing slots on a inside curve. Needless to say it still is not perfect, but I am done with that.... . This is the page that shows the kerfing on my build. http://tnttt.com/viewtopic.php?f=55&t=54099&start=120

[Shanfam]

Thank you, I had run across your build previously. How did you make the cuts? Are the cuts made in a v shape with foam removed? They look good.

[ghcoe]

I used a hot wire jig that I made. Most of my cuts are with a hot wire. I love how clean the cuts are and the jigs are easy to make. Look on the previous page there is some info on the jig I built http://tnttt.com/viewtopic.php?f=55&t=54099&start=120 . I did not bother making V cuts, just straight cuts spaced closer together to make sure there was enough give for the bend.

[Shanfam]

That was a terrific idea. I re-read more of your build thread but need to do more research on the hot wire cutting method. I really like the profile and aerodynamic properties of the curved sides, but still not sure I can pull that off. Thanks again- beautful work.

[ghcoe]

Thanks again- beautful work.

Thanks.

[Andrew Herrick]

I've also noticed, when shopping for foam, that the 1/2-inch XPS foam costs almost as much as the 1-inch foam. So if you're concerned about cost, kerfing will prove notably cheaper.

There are lots of calculators to help you with kerfing calculations. Here's one: http://www.bloggingwv.com/bending-wood- ... f-formula/

[GPW]

viewtopic.php?f=55&t=44081

[KCStudly]

For me, laminating two layers of 3/4 foam was a lot more work than kerfing one layer of 1-1/2 would have been. Some of my curves did require kerfing but the bigger issue was the time and money it took fitting and gluing. Double the work and double the PL300. There is also a problem laminating large areas of foam and making sure the adhesive cures. To get air into the middle I ended up using shallow kerfs just to act like vent passages.

1/4 inch would only be worse doing everything that many more times.

If you have a circular saw or router... better yet a good table saw with ample out feed table, kerfing is simple. Easier than building a TD (i.e. if you can build a TD, you can kerf). Having a respirator and a shop vac goes a long way toward managing dust, too.

[GPW]

... we’re still testing the idea of heat bending the foam instead of kerfing .... We know it works from other successful efforts , but the problem is heating the bend area without melting the foam ....which takes a bit of skill ... ( being careful) The industrial heat blanket idea is most feasible but expensive for making a single camper... for “production “ it would be very practical ... Two people with heat guns working together heating the area to be bent works , but requires teamwork and some type of bending form ......
Here’s a link to our previous bending efforts on a smaller scale ... http://www.rcgroups.com/forums/showthre ... t=Bendfoam ( WARNING: )... this site contains a reference to “model planes made of foam” ... some people have an aversion to these .... for some reason ...


Ps. We think ( JMHO ) kerfing is Great if done properly ( mathematically) so each kerf closes completely ( and can be glued) when bent , otherwise the only foam left is the thin bit remaining on the outside ... There’s a thread here (somewhere) that shows how to kerf perfectly so if glued lightly between the walls of the kerf slot , the foam forms one continuous solid layer ( Thick layer) .. And if you’re worried about the foam sheet cracking when bending the kerfed panel , just cover the Outside with the outer fabric ( tension side) and you can bend it into a tube if you want . ( so , Yes OP ! ) We can do like the Wooden Teardrop guys do and make indivitual panels , finished on the inside and outside , and just assemble them together at the end ...

[lthomas987]

...

Ps. We think ( JMHO ) kerfing is Great if done properly ( mathematically) so each kerf closes completely ( and can be glued) when bent , otherwise the only foam left is the thin bit remaining on the outside ... There’s a thread here (somewhere) that shows how to kerf perfectly so if glued lightly between the walls of the kerf slot , the foam forms one continuous solid layer ( Thick layer) .. And if you’re worried about the foam sheet cracking when bending the kerfed panel , just cover the Outside with the outer fabric ( tension side) and you can bend it into a tube if you want . ( so , Yes OP ! ) We can do like the Wooden Teardrop guys do and make indivitual panels , finished on the inside and outside , and just assemble them together at the end ...

If you want help with the math I can do it for you pretty quickly. Basically to get your kerf spacing right you calculate the circumfrence of the inside of the curve and the circumfrence of the outside of the curve. Subtract inside from outside, then divide that by your circular saw kerf (1/8" probably unless you have a fancy blade) to get the number of cuts you need to get your kerfs to close. Then space them evenly over the length of the outside of the curve. I managed to pull 2" foam into a 12" inside radius curve (only for 90 degrees) but it worked just exactly like the math said it would. In the kerf post linked eariler with the super awesome graphics and pictures I posted a spreadsheet you can use to do most of the math for you. http://www.tnttt.com/viewtopic.php?p=1092779#p1092779 Here's the spreadsheet. https://docs.google.com/spreadsheets/d/1Kk7c9hEz1XWNd5RT-SXk2GimpYZOMOlkoKAXUTULIHs/edit#gid=0