It was $32 and one day shipping from mcmaster and I needed a pile of other nonsense from them as it was. I should have some time to play this weekend.
That or an oven. I've used both - heat gun is for more localized bends but for that skidplate i'd probably use an oven.
does HDPE/Seaboard/Starboard relax enough when heated in an oven to form compound curves if a mold is used? if used as a skidplate, what is the recommended minimum separation distance to the exhaust?
My experience was with Seaboard: Yes, but getting to the exact temp. is tricky and at that temp. the mold may distort/indent the plastic. I accidently over heated a sheet and it squeezed out of the mold at the edges. You need to get all the bends in one shot in the mold. If you reheat the sheet for the second bend it will go back to flat. I've tried heating the sheet in the mold and at 240/270 the wood was fine. Run some trials before committing the whole project sized sheet. From the photos of my rack you can see the plastic is very close to the muffler and there were no issues with there.
What you might do is to make two molds. Make the first break and leave the sheet clamped in the mold. Re - heat both together then place the first mold with sheet in a second mold to make the second break.
I would use stainless slotted countersunk screws and set them just below flush. This gives you some room before a gouge in the soft plastic gets to metal. Remember the plastic will not support the screw. Hit the screw on a rock and it will bend sideways. HDPE is not nearly as abrasion resistant as UHMW-PE, which would have been my choice (and you can get cheap cutting boards at the thrift store to cut up) The allen fastener packs up with crap and in stainless they are strip monsters. Stainless is soft stuff. The slotted head is easy to clean and get a tool on, especially in the field. For impact, Kydex is tops. The polyethelenes cold flow, don't store on edge.
TAP does a lot of custom fabrication. if you know what you want, the way to score is to walk in and go through the scrap bin. usually sold by the pound. Don't use lexan. Chemically fragile.
Well, I did this on a whim sort of. The hardware I had on hand. I will likely recess the front two M6 bolts like you said, and the rears will never see contact, or I'm in big trouble ripping off the rear shock linkage. I went with the Starboard from McMaster as it was UV stable, and mold/mildew resistant.