Plastic sheet - material/source?

Make your own gear? Talk about it here!

Moderators: Bearbonesnorm, Taylor, Chew

Post Reply
jameso
Posts: 3405
Joined: Tue Nov 06, 2012 1:48 pm
Location: Chilterns

Plastic sheet - material/source?

Post by jameso » Fri Mar 27, 2020 8:35 am

Had a quick read of the plastic sheet seatpack posts here and it got me thinking. Can anyone tell me what sort of plastic is used for guard flaps like these? Same stuff as an Asssavers guard.

https://rawmudflap.uk/gallery/

I've got a couple of Rawflaps -yeah, I know :grin: - so, wanting something else to do now my riding hours are down.. I made an extended front flap for my Brompton from truck tarpaulin but it's too flexy/flappy for the guards on my all-road bike, want to make something for the front that Rawflaps don't offer. The Rawflaps stuff is really good btw, recommended kit.

User avatar
Bearbonesnorm
Posts: 18311
Joined: Sun Jun 05, 2011 8:53 pm
Location: my own little world

Re: Plastic sheet - material/source?

Post by Bearbonesnorm » Fri Mar 27, 2020 8:51 am

James, remind me of your address and I'll stick you some int' post.
#corporate shill for hire

mfezela

Re: Plastic sheet - material/source?

Post by mfezela » Fri Mar 27, 2020 4:36 pm

Ass Savers are 0.8mm polypropylene.
Here's one online source. There's bound to be someone close to you.
Steelexpress, Hindleys, ebay. Signwriters and outdoor advertising companies sometimes use the same.

https://www.kitronik.co.uk/materials/po ... heets.html

jameso
Posts: 3405
Joined: Tue Nov 06, 2012 1:48 pm
Location: Chilterns

Re: Plastic sheet - material/source?

Post by jameso » Sat Mar 28, 2020 7:57 am

Great stuff, thanks to you both. Will PM, Mr BB.

Cyclepeasant
Posts: 186
Joined: Sun Feb 04, 2018 9:56 am

Re: Plastic sheet - material/source?

Post by Cyclepeasant » Sat Mar 28, 2020 7:38 pm

Any of you guys in the building trade?
I have been using damp course to make mudflaps for years.
Rigid with give if caught on a root,rock etc.
Use cable ties or existing screw holes etc.
Not posh,just functional.
Cheap as chips!
Insanity over vanity

oreocereus
Posts: 95
Joined: Mon Nov 04, 2019 10:20 am

Re: Plastic sheet - material/source?

Post by oreocereus » Tue Mar 31, 2020 12:03 pm

To hijack this thread, I'm looking for a plastic to make a rough handlebar harness with. Without being able to go into a store and feel different materials, and knowing little of plastics, i feel a little blind (most DIY guides refer to US specific materials).

Anyone who's more MYOG oriented have a good idea of what to aim for in terms of balancing stability/stiffness with the right amount of flexibility to wrap around a dry bag?

User avatar
Bearbonesnorm
Posts: 18311
Joined: Sun Jun 05, 2011 8:53 pm
Location: my own little world

Re: Plastic sheet - material/source?

Post by Bearbonesnorm » Tue Mar 31, 2020 12:13 pm

Anyone who's more MYOG oriented have a good idea of what to aim for in terms of balancing stability/stiffness with the right amount of flexibility to wrap around a dry bag?
Roughly what size of piece do you need?
#corporate shill for hire

oreocereus
Posts: 95
Joined: Mon Nov 04, 2019 10:20 am

Re: Plastic sheet - material/source?

Post by oreocereus » Tue Mar 31, 2020 12:46 pm

Hmm, probably minimum 30cm x 40cm.. larger in either/both of those dimensions give me a bit of room to play a little with the design.

User avatar
Bearbonesnorm
Posts: 18311
Joined: Sun Jun 05, 2011 8:53 pm
Location: my own little world

Re: Plastic sheet - material/source?

Post by Bearbonesnorm » Tue Mar 31, 2020 1:57 pm

I've got a piece of 2mm HIPS here but it's only 22cm x 30cm. Yours if it's any good to you?
#corporate shill for hire

mfezela

Re: Plastic sheet - material/source?

Post by mfezela » Tue Mar 31, 2020 4:47 pm

High Impact Polystyrene, HIPS is less flexible and more brittle than Polypropylene, PP.

PP allows for cold creasing and repeated (but not infinite) bending at that crease, whereas HIPS requires heat to crease successfully and repeated bending will quickly cause cracking.
Both can be cut by knife, but HIPS requires more careful treatment at sharp corners to prevent tearing. Ideally there aren't sharp corners for either material, try for rounded corners instead.

A useful comparison site.

https://www.makeitfrom.com/compare/High ... omopolymer

oreocereus
Posts: 95
Joined: Mon Nov 04, 2019 10:20 am

Re: Plastic sheet - material/source?

Post by oreocereus » Tue Mar 31, 2020 8:21 pm

Bearbonesnorm wrote:
Tue Mar 31, 2020 1:57 pm
I've got a piece of 2mm HIPS here but it's only 22cm x 30cm. Yours if it's any good to you?
Oh thanks, that's very kind! Having not handled it, do you reckon it's about the right stiffness for a handlebar harness for a bigger drybag (I use synthetic sleeping insulation)?
My other thought is that it might be a touch too small in dimension to be able to wrap effectively enough on a bigger drybag, and I don't want to take it off your hands if it'll be wasted on me. I gather you've probably enough experience using and making bikepacking stuff to advise there?
mfezela wrote:
Tue Mar 31, 2020 4:47 pm
High Impact Polystyrene, HIPS is less flexible and more brittle than Polypropylene, PP.

PP allows for cold creasing and repeated (but not infinite) bending at that crease, whereas HIPS requires heat to crease successfully and repeated bending will quickly cause cracking.
Both can be cut by knife, but HIPS requires more careful treatment at sharp corners to prevent tearing. Ideally there aren't sharp corners for either material, try for rounded corners instead.

A useful comparison site.

https://www.makeitfrom.com/compare/High ... omopolymer
Thanks for this! I was planning to cut with a fresh scalpel blade and sand the edges a little - would this be suitable?

mfezela

Re: Plastic sheet - material/source?

Post by mfezela » Wed Apr 01, 2020 12:00 pm

Re: Corner treatment of thin sheet polymers.

External corners should be rounded, not for strength but to reduce sharp edges.

Slits cut into the material, e.g. for fixing straps, must be rounded. If not, the acute corners are very prone to splitting (jagged line on sketch). For narrow slits a larger than slit width hole is recommended.

For DIY purposes, external rounded corners are easiest cut with scissors. Use a hand drill (or any very slow speed drill) with brad point wood bit for internal corners. Drill holes first, straight cuts with modelling knife thereafter.
Attachments
IMG_20200401_114600394_1_1.jpg
IMG_20200401_114600394_1_1.jpg (87.77 KiB) Viewed 913 times

oreocereus
Posts: 95
Joined: Mon Nov 04, 2019 10:20 am

Re: Plastic sheet - material/source?

Post by oreocereus » Wed Apr 01, 2020 12:18 pm

Excellent tips. Almost certainly would've omitted to round internal corners without that comment.

jameso
Posts: 3405
Joined: Tue Nov 06, 2012 1:48 pm
Location: Chilterns

Re: Plastic sheet - material/source?

Post by jameso » Fri Apr 03, 2020 9:40 am

Bearbonesnorm wrote:
Fri Mar 27, 2020 8:51 am
James, remind me of your address and I'll stick you some int' post.
Arrived, thanks - got more ideas now. Lightweight roadpacker seat pack rolls.

jameso
Posts: 3405
Joined: Tue Nov 06, 2012 1:48 pm
Location: Chilterns

Re: Plastic sheet - material/source?

Post by jameso » Thu Apr 16, 2020 2:51 pm

https://www.cad4designs.com/polypropylene-1

Good place for 0.8mm polypropylene sheet, £1.50 for A4 and low postage costs.

jameso
Posts: 3405
Joined: Tue Nov 06, 2012 1:48 pm
Location: Chilterns

Re: Plastic sheet - material/source?

Post by jameso » Fri Apr 17, 2020 1:22 pm

Material science-ists ... "HDPE Sheet Black - High Density Polyethylene PEHD Thermoplastic Polythene" - would this be suitable for slotting and loading in the way a lightweight bike bag would be?

I have a random bit of plastic here, 1.5mm thick, flexible but not showing signs of whitening along a crease line so not a styrene (?), it's ideal for what I'm trying to do. Just need a bigger piece. Can't get hold of polypropylene in 1.5mm so wondering if this High Density Polyethylene might do the trick.

What was the stuff we used to use for vac-forming in CDT class? Acrylic I think. Don't want that anyway.

jameso
Posts: 3405
Joined: Tue Nov 06, 2012 1:48 pm
Location: Chilterns

Re: Plastic sheet - material/source?

Post by jameso » Fri Apr 17, 2020 1:27 pm

Cyclepeasant wrote:
Sat Mar 28, 2020 7:38 pm
Any of you guys in the building trade?
I have been using damp course to make mudflaps for years.
Rigid with give if caught on a root,rock etc.
Use cable ties or existing screw holes etc.
Not posh,just functional.
Cheap as chips!
Oh yes, just to add, I found a 40cm strip of this stuff in 0.5mm thickness, perfect for a better Brompton flap :-bd (the list of lockdown jobs is getting thinner and less important now, but more 'fun')

oreocereus
Posts: 95
Joined: Mon Nov 04, 2019 10:20 am

Re: Plastic sheet - material/source?

Post by oreocereus » Fri Apr 17, 2020 2:54 pm

If you can get two sheets of the 0.8mm stuff, that might be worth doing? They could be bonded together with glue (something suggested on the limberlost handlebar harness I loosely referenced making my own the other day). If you're putting them inside a material, they could just be sewn in place without any bonding.

oreocereus
Posts: 95
Joined: Mon Nov 04, 2019 10:20 am

Re: Plastic sheet - material/source?

Post by oreocereus » Fri Apr 17, 2020 2:57 pm

mfezela wrote:
Wed Apr 01, 2020 12:00 pm
Re: Corner treatment of thin sheet polymers.

External corners should be rounded, not for strength but to reduce sharp edges.

Slits cut into the material, e.g. for fixing straps, must be rounded. If not, the acute corners are very prone to splitting (jagged line on sketch). For narrow slits a larger than slit width hole is recommended.

For DIY purposes, external rounded corners are easiest cut with scissors. Use a hand drill (or any very slow speed drill) with brad point wood bit for internal corners. Drill holes first, straight cuts with modelling knife thereafter.
Thanks again for this. For anyone who might read in the future, the 2mm HIPS was just way to thick to cut with any of my modelling knives or scalpels. After some reading around, the material seems popular with model makers, but any reference to cutting with a knife is for sheets under 0.5mm thick. In the end I just made some loops with some old shock cord through drilled holes as my webbing slits. It's not super elegant, but it works.

User avatar
Bearbonesnorm
Posts: 18311
Joined: Sun Jun 05, 2011 8:53 pm
Location: my own little world

Re: Plastic sheet - material/source?

Post by Bearbonesnorm » Fri Apr 17, 2020 3:28 pm

Thanks again for this. For anyone who might read in the future, the 2mm HIPS was just way to thick to cut with any of my modelling knives or scalpels. After some reading around, the material seems popular with model makers, but any reference to cutting with a knife is for sheets under 0.5mm thick. In the end I just made some loops with some old shock cord through drilled holes as my webbing slits. It's not super elegant, but it works.
I just use a Stanley knife. usually I find 3 - 4 passes is all that's required.
#corporate shill for hire

oreocereus
Posts: 95
Joined: Mon Nov 04, 2019 10:20 am

Re: Plastic sheet - material/source?

Post by oreocereus » Fri Apr 17, 2020 4:05 pm

Bearbonesnorm wrote:
Fri Apr 17, 2020 3:28 pm
Thanks again for this. For anyone who might read in the future, the 2mm HIPS was just way to thick to cut with any of my modelling knives or scalpels. After some reading around, the material seems popular with model makers, but any reference to cutting with a knife is for sheets under 0.5mm thick. In the end I just made some loops with some old shock cord through drilled holes as my webbing slits. It's not super elegant, but it works.
I just use a Stanley knife. usually I find 3 - 4 passes is all that's required.
Ta. The blades we had for the stanley at home weren't sharp enough, then - maybe they were cheaper generic ones. My other knives are more intricate modelling knives and weren't enough.

Maybe I'll pick up some better blades for the stanley when shops reopen

jameso
Posts: 3405
Joined: Tue Nov 06, 2012 1:48 pm
Location: Chilterns

Re: Plastic sheet - material/source?

Post by jameso » Fri Apr 17, 2020 4:42 pm

oreocereus wrote:
Fri Apr 17, 2020 2:54 pm
If you can get two sheets of the 0.8mm stuff, that might be worth doing? They could be bonded together with glue (something suggested on the limberlost handlebar harness I loosely referenced making my own the other day). If you're putting them inside a material, they could just be sewn in place without any bonding.
Yes good point on doubling up within material, that would involve sewing though and I've not got the kit or skills for much more than sewing webbing straps into place. With free-time like this I wish I had a sewing machine, I have bag designs but not the ability to try them out. The idea with this system was using mainly slotted plastic as a harness base. I think ergonomically it's destined to fail though, the test run of the mock-up earlier with bivi gear in place still puts it too close to my legs. Straps into place beautifully.. just into the wrong place :grin:

oreocereus
Posts: 95
Joined: Mon Nov 04, 2019 10:20 am

Re: Plastic sheet - material/source?

Post by oreocereus » Mon Apr 20, 2020 8:53 am

Thanks again for the sheet, worked well (ignore my scratchy cutting - will try address with a better knife down the line) :-bd

Image

User avatar
Bearbonesnorm
Posts: 18311
Joined: Sun Jun 05, 2011 8:53 pm
Location: my own little world

Re: Plastic sheet - material/source?

Post by Bearbonesnorm » Mon Apr 20, 2020 9:24 am

Glad it was of use.
#corporate shill for hire

Post Reply