Author Topic: Question about angles of venturi (Read 7991 times)

greasemonkey · « **on:** August 08, 2014, 09:03:07 PM »

On the Wiki page on Venturi, it states the angles as 10 degrees inclusive, and 60 degrees inclusive.
Would I be right in thinking, that if there was a line running horizontally, through the middle of the pipe, then the angle of the edge of the pipe would be 5 degrees one side, and 5 degrees the other?
To put it another way, if I was to turn down a wooden plug, for casting, I would find the axis of the wood, and turn down a taper, that would be slopping out 5 degrees from the axis?

Julian · « **Reply #1 on:** August 08, 2014, 09:09:05 PM »

Correct.

Julian · « **Reply #2 on:** August 08, 2014, 09:09:47 PM »

Try drawing one in Sketch-up!

kamaangir · « **Reply #3 on:** August 08, 2014, 09:25:50 PM »

Drawing things in sketchup is the new printing stuff with 3d printer!

greasemonkey · « **Reply #4 on:** August 08, 2014, 09:29:00 PM »

Magic, thank you.
I think this one will be a fag packet design, or at least a piece of printing paper.

Another question for the more experienced metal casters. When it comes to the suction hole, what would it be like to make a sacrificial plug, out of clay or something, the exact right size, and pour with that, rather than trying to drill the hole afterwards. Or is that not practical.
I haven't calculated he size of the hole yet mind. If it happened to be exactly 6mm, than there would be no question but to drill it.

Ahh, no, that's not going to work.......

Jamesrl · « **Reply #5 on:** August 08, 2014, 10:00:31 PM »

Right, first things first.

What pump will you be using with the venturi as that will determine the throat diameter.

Throat diameter will govern the vacuum diameter, I use 3 x 6mm diam holes on an 8mm throat.

We need more info.

greasemonkey · « **Reply #6 on:** August 08, 2014, 10:05:24 PM »

IIRC, my pump is rated at 70LPM, but I will have to check that.

Jamesrl · « **Reply #7 on:** August 08, 2014, 10:22:20 PM »

Quote from: greasemonkey on August 08, 2014, 10:05:24 PM

IIRC, my pump is rated at 70LPM, but I will have to check that.

You'll need an 8.7mm diam throat but you could get away with 9mm, it might slightly reduce the vacuum but it's a nice round figure to work to.

With a 9mm throat you can use a 9mm vacuum hole, IF you can drill it accurately.

greasemonkey · « **Reply #8 on:** August 08, 2014, 10:28:05 PM »

Cheers, that was my next question, how much difference would the extra 0.3 mm make.
I can probably get it in the lathe to drill it, somehow.
Cheers, I update when I get on with it. Hopefully soon.

Jamesrl · « **Reply #9 on:** August 08, 2014, 10:51:13 PM »

Quote from: greasemonkey on August 08, 2014, 10:28:05 PM

Cheers, that was my next question, how much difference would the extra 0.3 mm make.
I can probably get it in the lathe to drill it, somehow.
Cheers, I update when I get on with it. Hopefully soon.

I was referring to the accurate vacuum hole drilling as the throat will be formed during the casting.

Julian · « **Reply #10 on:** August 08, 2014, 10:56:50 PM »

If you are going to drill the throat in a lathe, be careful you don't get a jet effect from it.

There's a bit on the wiki about it here ... http://www.biopowered.co.uk/wiki/Venturi#Installing_a_venturi

greasemonkey · « **Reply #11 on:** August 08, 2014, 11:30:22 PM »

I can see what you mean about the jet effect. I presume that is caused by the parallel walls of the throat. once it's been drilled.
I was going to cast that bit anyway, and drill the vacuum hole. I was thinking I'd clamp the piece, and spin the drill.
I will have to do a bit more pondering, and work out what way is best, given what tools I have access to.
I'm also considering spinning it.

Been watching a few Utube vids, and it looks like it might spin not to bad, but I'd have to make a few tools for the lathe, and possibly spin it in two parts, and join them.

Something to mull over.

Thanks for your help Gents.

Julian · « **Reply #12 on:** August 09, 2014, 12:25:43 AM »

I've made a couple of spun venturis. I only have a little ML7 lathe and it puts way too much stress on the components.

I had some photos I posted on the VOD a while back, but I can't find them now. They showed damage to the tool post (very heavily burred edges) just from the pressure of leavering the tool.

It was a really interesting exercise, and produced good venturis, but didn't do the lathe any favours at all.

greasemonkey · « **Reply #13 on:** August 09, 2014, 09:32:32 AM »

Did you anneal the copper?
The lathe here is a horse of a thing. It took two of us to lift the bed, without the feet and motor. It's only 4 ft long.
Bit of a bargain father had off an old boy who was clearing out.

Julian · « **Reply #14 on:** August 09, 2014, 10:04:04 AM »

Yes, annealed the copper several times, but it soon work hardened.

I was using 22mm copper pipe which I shrunk to a turned mandrill. It may not have been the best type of copper to use, but it was readily available.

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Question about angles of venturi