Tutorial - Making a small o ringed piston on a drill press

[saefroch]

Of course, I had access to a lathe, so I was able to machine clean faces. That being said, it would be worth a shot, as if there is no rubber sealing face, it can never be blown out the barrel!

No precision machining needed. I cut a section of UHMWPE with a hacksaw blade on a drill press, then when the seal blew off once, it sealed anyway. Only trouble is that it didn't pilot, since the entire front of it was sealed to the port and my check valve wasn't fully working yet.

[Matt_NZ]

I have been considering it.

Same. There is a wide range on eBay, but they charge alot to post to NZ. I'm also looking for a quite a large piece (2.5").

Another idea I had was to buy a cheap plastic chopping board then use tech's technique to get your designated size.

[Technician1002]

The same stuff milk jugs are made of.
I wonder if anyone has tried molding a milk jug to make a block of HDPE?

I tried it and it didn't work very well. Milk jugs have some kind of mold release contaminate on the surface, so even though it melts, the resulting rubbery goo does not flow into a solid mass, but instead is full of cracks holes and such.

If you look at the plastic planking made from used shopping bags and recycled plastic, you get about the same result. It does not turn into a nice solid chunk of plastic.

Look up "Recycled Plastic Lumber" to see what the stuff will be like. It's OK for a park bench or decking, but lousy for building pistons.

http://www.theparkcatalog.com/itemdesc. ... ce=Froogle

EDIT;

Molten HDPE can best be described as having the consistancy of a cross of melted cheeze and gummy bears. It feels like rubber much like gummy bears. You need to get it up to about 375-425 degrees F do do this. You won't want to touch it with your bare hands. The stuff is hot when melted.

They will squish together with lots of pressure, but they won't become a solid mass simply by putting a bunch in a jar. I used clamps to laminate the piston. Simply stacking the melted faces toghther does not work. Melting a bunch of cut up milk cartons provides the same poor results.

[Matt_NZ]

You need to get it up to about 375-425 degrees F to do this...

They will squish together with lots of pressure, but they won't become a solid mass simply by putting a bunch in a jar. I used clamps to laminate the piston.

Ok , so when you melted this stuff with your custom thermostatically controlled heating unit, would it not just stick to the pan?

[Technician1002]

It did melt and stick to the pan. That is why I used a custom heating unit from Goodwill instead of using one from the kitchen. This removed some of the surfaces contaminates from the plastic surface as well as adding some of the Teflon non stick surface to the plastic. You can see the contamination on my finished piston. Getting the plastic to fuse to plastic required the squish, other wise very little of the surfaces bond well and can be snapped apart when cooled.

I think it was JSR who laminated some the other direction and air pressure seperated the layers of his piston because the bonding was poor. I feared this in my piston so I laminated in the other direction so air pressure hold the piston together instead of ripping it apart.

I can't find the photo of the broken piston at the moment.

Edit;

Found the post.. It was Ranger.. I got JSR from the following post in that thread. Still makes me smile.

I make these pistons by cutting 2" circular holes with a holesaw in a cutting board and then heat them up and press them together. Then turn them down on a drill press. I guess when I heated and pressed them together, I didnt do it good enough.

[Matt_NZ]

I make these pistons by cutting 2" circular holes with a holesaw in a cutting board and then heat them up and press them together. Then turn them down on a drill press. I guess when I heated and pressed them together, I didnt do it good enough.

I'll do my best not to turn up like this guy.

Lucky enough, I've got an old "custom thermostatically controlled heating unit" in the garage. Lets see how this turns out. 8)

[Selador]

There must be -some- way to melt milk jugs together, consistantly.

A few years ago, I saw a program that devoted some time to how some people in India, or Pakistan, or somewhere else in that region... Were making prosthetic limbs from old milk jugs.

They actually showed part of the process.

I believe they added some chemical to it, like acetone or MEK.

They made a 'soup' of the plastic, (actually showed them stirring it up), then poured that into a mold.

I have been googling to try to find the info, but so far have been unsuccessful.

[cannon monkey]

where can i find this UMWHDPE or HDPE stuff? looking to make a 2 inch piston

[jackssmirkingrevenge]

I think it was JSR who laminated some the other direction and air pressure seperated the layers of his piston because the bonding was poor. I feared this in my piston so I laminated in the other direction so air pressure hold the piston together instead of ripping it apart.

I can't find the photo of the broken piston at the moment.

Edit;

Found the post.. It was Ranger.. I got JSR from the following post in that thread. Still makes me smile.

JSR would have just cast it out of epoxy, but thank you for automatically associating him with FAIL

[Technician1002]

Sorry JSR..

@ cannon monkey, HDPE rod and sheets can be purchased from any good plastics supplier. I used Tap Plastics.

Many white cutting boards are made of HDPE.

http://www.tapplastics.com/shop/category.php?bid=39&

McMaster-Carr has HDPE rod. Here it is in 2 inch.
http://www.mcmaster.com/#plastics/=axu5j9

[jackssmirkingrevenge]

Sorry JSR..

No need, anyone who refers to himself in the third person deserves some level of mockery

[wyz2285]

I made a video about this "how to"
[youtube][/youtube]
Oh, and I made a chamber seal piston valve repeater 8)
Sorry for bumping this thread but I thought it´s relevant

[bravootome]

what is the maximum pressure you charged that propane red tank you got in your picture. I got one on my QeV and i put 25 bar, But i want more, like 30-35......

[Technician1002]

Highest pressure tested is 125, the highest a borrowed compressor could provide. It was a Hydrostatic test for safety. Safe to use now at 100 PSI.

[MightyBlue]

Great tutorial! will try this later!