What Type Of Plastic Are Coils/skid Plates Made From?

[jasong]

@GoodAmount Does it help the cover stay on if you angle the vertical edges in towards the coil some small amount like 0.5 or 1mm to keep the edges on the coil in tension? 

A solid TPU skid plate might be interesting too - it's flexible so you could angle the lip in quite a lot or put a locking ridge on the top, and pop it over a coil with no tape at all - just like a cell phone case. And it would be way quieter to detect with. TPU is tough enough that it would be interesting to get rid of the skid plate altogether and see if just a layer of it on the sides and bottom of a coil would be sufficient. I think I could actually print a layer onto existing coil bottoms with some kind of glue or bonding agent, too bad the sides aren't really doable. 

Watching some vids on it last night, I think oven/water annealing might get a 3d printed coil to closer to the same toughness as a vacuum formed or injection molded. Between that and a good material selection, I'm thinking now it's probably possible to make an equal if not better coil housing/skid (in some cases) on a 3d printer than the commercially available ones if done with annealing and using tough plastics. 

[Aureous]

Everyone uses just 3 types, ABS, PET and PC. PET is the worst wearing (recycled ice-cream containers ?) like Minelab decided to use with their 6000 coils. ABS is commonly used but skid plates are now more often made with PC (polycarb) for longer lasting use. The 'heavy duty' Nuggetfinder skid plates are thicker polycarb and last 3x the time that ABS does to my mind.

[GoodAmount]

12 hours ago, jasong said:

@GoodAmount Does it help the cover stay on if you angle the vertical edges in towards the coil some small amount like 0.5 or 1mm to keep the edges on the coil in tension? 

A solid TPU skid plate might be interesting too - it's flexible so you could angle the lip in quite a lot or put a locking ridge on the top, and pop it over a coil with no tape at all - just like a cell phone case. And it would be way quieter to detect with. TPU is tough enough that it would be interesting to get rid of the skid plate altogether and see if just a layer of it on the sides and bottom of a coil would be sufficient. I think I could actually print a layer onto existing coil bottoms with some kind of glue or bonding agent, too bad the sides aren't really doable. 

Watching some vids on it last night, I think oven/water annealing might get a 3d printed coil to closer to the same toughness as a vacuum formed or injection molded. Between that and a good material selection, I'm thinking now it's probably possible to make an equal if not better coil housing/skid (in some cases) on a 3d printer than the commercially available ones if done with annealing and using tough plastics. 

You could certainly play with the angle of the lip to give the skid plate a tight fit. Or just globally scale the whole part for a tight fit according to the extrusion tolerances of your 3D printer. The coil housing will have a bit of draft on it anyway, so given there’s a perpendicular inner wall on the skid plate file, it will have the same effect. I’ve uploaded the stl btw if you want to mess around with it. 
 

I love the idea of a flexible skid plate that lips up over the top of the coil like a sock. I’ve never had much luck printing TPU though - it’s very temperature sensitive and I end up with either a globby mess if it’s too hot or a part that delaminates easily if not hot enough. Getting the right balance is tricky. I’ve been wanting to design a two-part clam shell version where the top shell protects the top of the coil cover when scraping the scoop over it, but I was planning to just make it out of ABS. A flexible one would be great though.

I usually anneal parts with a heat gun, but it’s better to do it in a more controlled way. I’ve had a few disasters where I’ve melted parts in the oven beyond recovery, so I’m reluctant to do it that way until I have an industrial oven with better temperature control. I haven’t tried hot water - I’ll give it a go. ?

[fourtyniner]

It would be great if someone came up with a coil top cover to protect it from scratches from the scoop. Does anyone have any ideas on what to use to protect the coil top?

[Redz]

19 minutes ago, fourtyniner said:

It would be great if someone came up with a coil top cover to protect it from scratches from the scoop. Does anyone have any ideas on what to use to protect the coil top?

Glue on a thin piece of polycarbonate sheet in the area of interest

[GoodAmount]

1 hour ago, fourtyniner said:

It would be great if someone came up with a coil top cover to protect it from scratches from the scoop. Does anyone have any ideas on what to use to protect the coil top?

I just use pvc duct tape (pictured in my earlier post in thread). Works a treat. 

[GoodAmount]

…just don’t use cloth tape - it will leave adhesive on your coil when it comes time to replace it.

[jasong]

10 hours ago, GoodAmount said:

I haven’t tried hot water - I’ll give it a go. ?

I saw another vid where they were using salt to maintain the shape, it left grain imprints though. I have a bag of hot mud (drywall compound) that is ultra fine powder, I might give that a try in an oven too to hold shape during annealing. 

I kinda want to try experimenting with printing TPU directly onto a coil, then get rid of coil skid plates entirely if possible but yeah like you experienced, bonding probably will be the problem. I use Amazing Goo on some of my old ones instead of skids, and it worked great, never wore through, and it's kinda similar to TPU, I'd love to be able to just replicate that in nice controlled, even layers to save on weight and make it look nice. Other problem though is my print bed is small so I'm limited to the small coils like a Sadie or maybe 8" X Coil. 

But like you, I've not figured out a good way to print it yet, mine just turns out all stringy and messy, not professional looking. I'm still very much learning here. Thanks, snagged your .stl. That's another thing I'm still learning, using Fusion 360. 

[Geotech]

@Aureous is correct. At White's the coil housings and skid plates were made with an ABS/polycarbonate blend, don't recall the ratio but maybe 50/50. ABS alone wears quickly, PC alone wears well but is brittle.