Joined: 22 Feb 2013
Posts: 96
Location: Dekalb, IL
Can you use HDPE for a polyurethane molds?
Mon Oct 14, 2013 12:06 pm
maddox
Joined: 21 Dec 2006
Posts: 786
Location: Belgium
Yep, I didn't find a compound that bounded to HDPE.
Still I would advice loseningwax in the mould.
Mon Oct 14, 2013 12:41 pm
Nick Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
HDPE will work fine. I have used UMHW and Delrin to make molds. I started out using a soft wax as a mold release, which worked OK, but switching to a proper silicone release agent made releasing the wheels MUCH easier. Making your molds as smooth as possible is important; the urethane might not chemically bond to the mold surface but it will definitely mechanically key itself into every imperfection.
Mon Oct 14, 2013 7:07 pm
Valen Experienced Roboteer
Joined: 07 Jul 2004
Posts: 4436
Location: Sydney
if you can a slight taper will help release too.
Otherwise cut a block in half, then bolt it together then machine the wheel mould out of it, so you can just pull it apart. _________________ Mechanical engineers build weapons, civil engineers build targets
Wed Oct 16, 2013 12:35 pm
dyrodium Experienced Roboteer
Joined: 24 Aug 2004
Posts: 6476
Location: Sydney
Yeah that silicone mold release is magic, you only need a tiny spray of it too. Worth the cost! _________________ ( •_•)
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
I went with the split mold for my wheels but it was much more complicated than a one piece mold block with a backing plate. Unless you are making a wheel with a very wide face, a one piece mold with a proper release agent should be fine.
Wed Oct 16, 2013 4:30 pm
Valen Experienced Roboteer
Joined: 07 Jul 2004
Posts: 4436
Location: Sydney
sorry i should have been more clear, yes generally a one piece mould should do fine.
if you are doing fancier stuff, wider, softer/whatever then it might be an idea to go multiple pieces. _________________ Mechanical engineers build weapons, civil engineers build targets
Wed Oct 16, 2013 7:54 pm
tetraPark
Joined: 07 Oct 2013
Posts: 62
Location: Brisbane / Ipswich
Hey guys,
currently working on the test rollers for my mecanum wheels. Rollers are very small (about 3cm diameter or so, 5cm wide). Am using silicone sealant I had available mixed with a small amount of corn starch poured into a plaster mold... Very ghetto. Seems to set up real nice; quite tough but still rubbery. Havent really had a chance to test grippiness yet, but i'm optimistic.
Has anyone else used silicone for wheels before, and have any tip's / pro's / con's / omgdontdothat's to share?
thx
Sun Nov 03, 2013 12:38 pm
danjr1
Joined: 02 Jun 2012
Posts: 30
Hey,
Just wondering how well the wheels worked out in a featherweight? Im looking at doing something very similar.
Nah I never used them, but Nick has a lot of experience casting his own urethane wheels and they have been very successful. I don't think you can get away with a 3D Printed hub though, Nick uses machined UHMW. _________________ ( •_•)
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
Happy to answer any questions about casting wheels, hubs or making moulds. If you have a 3D printer, the moulds that Angus invented are very hard to beat. The urethane wheels I made worked very well, but in the end, it was cheaper & easier to buy Colson wheels.
EDIT: I actually use polycarbonate hubs, not UMHW. They have taken plenty of direct hits and there have been zero failures. I like the combination of fairly low weight, high impact resistance, high hardness and the rough surface finish I can get. It all makes for a hub that won't break or move when it is pressed or cast into a wheel.
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