Joining the CNC club!

[-MIKE-]

What do you used those for?

[Morris Dovey]

I'm working on a non-electrical solar pump to supply water for folks in under-developed areas. One of the outstanding problems is a DIY-able check valve that seals decently.

If interested you can see what I have so far at

drawing is only of the engine/pump without the solar heat source)

If the pop can flapper works out, I'd kinda like to send out "show-n-tell" check valves to the volunteer R&D teams so they'll have some to play with (and improve upon) :)

[-MIKE-]

I've seen your pump, I try to check in now and then to see how things are going.

I'm trying to build a shock for my out-feed table, so I can just let it go and it will glide down to its latch.

I tried a screen door closer, but those have a spring that gives quite a bit of resistance on the open throw.

I was thinking of some pvc water pipe and a check valve stopper of some kind. Maybe I could steal one from a bike tire pump.

[Morris Dovey]

Hmm - when I dropped in on a guy who's done some machining for me, he was rebuilding some auto and motorcycle struts. I wonder if a worn-out strut might be a good solution for you.

If not, I'd think that a UHMWPE or delrin piston with a "pop can" flapper would work with your PVC pipe approach...

...and if it works well enough that the table takes more than an hour to lower itself, you should send photos. :-D

[Robatoy]

Think automotive scrapyard. Hatchback gas cylinders van be had for next-to-nothing, Even new replacement ones at your PartBoys are sometimes reasonable. The dampening amount varies with the angle you mount it on. Some of them exert serious spring tension.... be careful.

[Robatoy]

idea for a flapper-valve seat which could be done for cheap and from local materials.

[-MIKE-]

LOL, literally. :-)

My first approach was simply a wood cylinder that fit as tight as it could into pvc, with a cap on the end. The air escaping around the wood provided a decent pad, but it was the same in both directions.

[-MIKE-]

Next on the list. :-)

My old minivan (I need to sell!) has two I may use as a proof of concept. :-)

[Han]

Robatoy wrote in news: [e-mail]:

Is there anything that for the valve could use a piece of bicycle inner tube as sealing material? Certainly in Asia bicycles are plentiful, and so must used up inner tubes. You should be able to get 2-3" diameter pieces out of that.

[Robatoy]

Playing with those gas cylinders is as much fun as that day my neighbour, years ago, was playing with one of those exercise spring things. You know the ones, you could hook springs between the handles and streeeetch them for exercise. You could add them as you needed them. He had two springs on, and his foot inside one of the handles and he was trying to push the other handle towards the ceiling. Well, he almost got the thing past his shoulder when it slipped out from under his foot, breaking his jaw in several places and electrocuting him as the whole mess destroyed some track lighting. Damn near blinded him for life from the heavy glass fragment of those old style flood lamps. 3 weeks in hospital. Never the same since. His co-workers bought him a Slinky for Christmas that year....bastards.

[Robatoy]

[e-mail]:

There you... stealing my idea...LOL. The Dutch made all kinds of fun things out of innertubes. I had a slingshot that could take out a bus.

[Han]

Robatoy wrote in news: [e-mail]:

That dates you, Robatoy!!!

[Robatoy]

[e-mail]:

How about paper blow-darts? Launched trough plastic electrical conduit. (That thought just shocked me.. we had our house re-wired in the mid-1950's...and we had plastic conduit....)

[Morris Dovey]

50mm/2" at present, perhaps 100mm/4" later, and possibly 200mm/8" after that. The 2" looks like it /should/ be easy, the 4" might be iffy, and the 8" is likely to be a real challenge (but that pump is going to offer a number of other challenges anyway).

[Han]

Robatoy wrote in news: [e-mail]:

We used Bic pens with the inkstraws removed. In high school class. But not in physics ...

[Robatoy]

[e-mail]:

In school we used a bent piece of solder and a strong rubber band. Those could draw blood. The 1/2" paper arrows had fantastic range and could take a small bird down.

I'll make some up when I have some time and post a video on its contruction and performance.

[Larry Jaques]

On Sat, 28 Nov 2009 12:45:31 -0600, the infamous -MIKE- scrawled the following:

You could either:

1) Install relief valves (one-way check valve) in it to let the air out during the outward stroke, as you put up the table.

or

2) Bore out the major length of the cylinder a bit larger, all but the final several inches. When the table comes out, the piston quickly hits the larger bore and that produces no damping. As you drop it, it glides down until the piston hits the tight cylinder and starts damping so it doesn't slam.

-- Some days, it's not even worth chewing through the restraints.

[-MIKE-]

I like that one.

[Larry Jaques]

On Sat, 28 Nov 2009 14:11:13 -0800 (PST), the infamous Robatoy scrawled the following:

innews: [e-mail]:

Bwahahahahaha! That's a good one.

We used to shoot unbent paper clips or loosened bobby pins. Those hurt like HELL! (There's where I date myself, too.)

Great!

-- Some days, it's not even worth chewing through the restraints.

[-MIKE-]

In jr. high, my older brother and his delinquent buddy's used to shoot those blow-darts at each other. I gave my brother a small metal tube from my first drum set, so he had an advantage.

We sat up most of one night, making arrows from sewing pins and the ends (aglets?) of shoe laces. We would cut the ends off, leaving about a 1/4" of lace, push the needles through the aglet, then fray the lace. We would then (not kidding) dip the needle points in Raid ant killer. When stuck with one of these tainted needles, you would get a welt that itched all day.

They used to go at it in the hallways during class changes. They would wear their shop goggles and run the halls, hunting each other down and shooting these blow-darts. Lots of civilian casualties led to confiscation and suspension for each of them.