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Hub For PVC Blades
By Slingshot, Section Mechanical Posted on Fri Feb 10, 2006 at 11:58:00 PM MST
How do you handle the curvature at the root

Does anyone have details on building a hub for a 3-blade PVC rotor? How do you handle the lack of flat surfaces? I'd like to see some pictures, if you have a link.

Hub For PVC Blades | 9 comments (9 topical)

Re: Hub For PVC Blades (3.00 / 0) (#1)
by wildbill hickup on Fri Feb 10, 2006 at 06:22:52 PM MST

I've never had a problem. I just lay the trailing edge as flat as possible on a disk usually plywood and attach with 3 screws set in glue.

Never had one come lose. Consider that this is a small blade though only about 30", don't know if I'd trust screws with a longer blade.

Not the best drawing but I think you can see what I mean. I don't have any photo's handy but I can get some tomorrow.

Wildbill

Re: Hub For PVC Blades (3.00 / 0) (#2)
by georgeodjungle on Fri Feb 10, 2006 at 08:36:29 PM MST

i use old fan blades from trucks.
this one is off a 71 corn binder.
aready curved !
kind of a drag grinding the rivets.
just bolt it to gether.

Re: Hub For PVC Blades (3.00 / 0) (#3)
by domwild on Fri Feb 10, 2006 at 11:43:19 PM MST

Hi,

My method was done as follows:

Two SS "Jerry-type sandwich" supports around the root with four 5mm bolts one inch in from the end to stop the blade from flying off. Size of sandwich about 3 inch x 3 inch.

Two of one inch wide SS bar connected to the root in longitudinal fashion and the two straps were then connected to the flange (hub).

Search (Google) this site for PVC and you will see pictures similar to my setup. What I have not done as yet is prime the blades with PVC primer and then paint a reflective colour over the primer to stop the dastardly UV rays from zapping the life out of the blades.

dom We only ever use the best fencing wire for our repairs!

Re: Hub For PVC Blades (3.00 / 0) (#6)
by dastardlydan on Sat Feb 11, 2006 at 06:12:29 PM MST

HAY lets watch how we sling some words around.
++++++++++++++++++++++++++ DastardlyDan . This is only a test, had it been the real thing , you would have got instructions.
[ Parent ]

Re: Hub For PVC Blades (3.00 / 0) (#4)
by wooferhound on Sat Feb 11, 2006 at 08:52:28 AM MST

You could make a onepiece PVC blade and the hub would be built in.
http://www.fieldlines.com/story/2003/11/11/172721/53

W o o f -={(

Re: Hub For PVC Blades (3.00 / 0) (#7)
by Slingshot on Mon Feb 13, 2006 at 08:26:52 AM MST

Yes, I've done a one-piece blade very similar to this, for my AMETEK motor. That was before the high-performance carbon-fiber blades were available cheaply from hydrogenappliances.com - now I'd just run store-bought on a small generator.

A one-piece (two blades) has built-in centering if you just drill a hole on the line common to both leading edges.

What I'm looking to do now is create a larger PVC rotor for a (planned) homebuilt alternator, having three blades. The problem I see is that, with individual blades, it would be easy to get the "setting angle" a little bit off due to the curved mounting surfaces. It wouldn't have much effect on performance at the root, but at the tips it seems that the difference in +2 deg and -2 deg angle of attack might be a big deal.

thanks!

[ Parent ]

Re: Hub For PVC Blades (3.00 / 0) (#5)
by DaveW on Sat Feb 11, 2006 at 09:13:00 AM MST

I'm not certain of the approved method, but one way that works if you're working out of the scrap pile behind the barn - cut some pieces from old 4 or 5 inch pipe. Using a rosebud tip heat them and gently tap them down flatter until they match the curvature needed to support the PVC. Then carefully clamp them in place on the hub at the angle you want to support the blades. Weld in place and drill holes to mount the blades. A few pointers to the process. Never place the PVC on the pipe piece to check for fit without first cooling the hot metal, especially if you have onlookers. This will gain you a certain reputation at odds with the impression you were trying to cultivate. (stop and build a new blade) Don't drill holes in the blades without first checking to see where they will be on the pipe and hub after welding, you may not be able to get a bolt and nut to that location and again your reputation will suffer. And finally, balance the hub before adding blades. Don't assume that with most of the mass so close to the center and those light weight blades it will work out fine. Otherwise once it is high up in the air for everyone to see and spinning like crazy it will remind several people of the story of the dog and the peach seed. This time, the bearings will suffer along with your now tattered reputation. Pictures? I'm just glad that none were taken.
DaveW

Re: Hub For PVC Blades (3.00 / 0) (#8)
by Slingshot on Mon Feb 13, 2006 at 08:31:26 AM MST

Dave,

That's a pretty good idea, using weld-on steel-pipe sections that match the curvature. Not sure how I'd go about cutting them, though, maybe with an air-powered cutoff tool?

I could see using a curved piece on top as a "washer" also. You could even slot the holes in the PVC, so that you'd have some fine-tune control over the setting angle.

thanks!

[ Parent ]

Re: Hub For PVC Blades (3.00 / 0) (#9)
by hvirtane on Mon Feb 13, 2006 at 11:34:13 AM MST

That's a pretty good idea, using weld-on steel-pipe sections that match the curvature. Not sure how I'd go about cutting them, though, maybe with an air-powered cutoff tool?

A normal electric angle grinder will do the job.
Just go slowly, not to burn the machine.

- Hannu

Hub For PVC Blades | 9 comments (9 topical)

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