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Graham Rounce11/11/2012 17:33:47
28 forum posts
2 photos
Bazyle - Thanks for the drill-aligning tip! Simple when you know, huh?

In my brain, at least, the project is proceeding apace! - I'm now thinking of trying (if I don't jinx it by speaking in advance) to get a steel pipe supplier to chop off (say) a 6mm thick ring from a 7" dia pipe whose wall thickness is 6mm. This would give me a nice thin but fairly massive ring, hopefully pretty circular that I could either glue to a plywood disc as before or, more ambitiously, attempt to make spokes to a bush, and balance it somehow by attaching nuts & bolts in appropriate places.

Obviously, I do realise that this is making the recent Mars landing look like a sure thing in comparison! Luckily there's no rush.

As for the motor handling the load, my approach is going to be: if it doesn't, get a bigger one! The shaft sticks out a little at the other end, so I guess I could rest it on a little oiled "cup" somehow...
PS - Ian: I'll puzzle over all that, too - I like the idea of aerials as tube sources!
Graham Rounce11/11/2012 17:48:01
28 forum posts
2 photos
Michael - Of course I would! I'm not superstitious!
Terryd11/11/2012 21:38:06
avatar
1946 forum posts
179 photos

Hi Graham,

You are truly optimistic if you think that 6" diameter tube of those dimensions will be anywhere approximating round, good luck,

Regards

T

Graham Rounce12/11/2012 09:52:18
28 forum posts
2 photos
Hi - I was thinking that the tubes would be made to fit together with standard fittings, elbows etc, so would have to be pretty round. Well, one can only try - they may not sell it in 6mm lengths anyway !

Ian S C12/11/2012 11:51:08
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7468 forum posts
230 photos

The 7" ring will be approximately round, but you should be able to average it so it balances. I built a flywheel of a similar size, and you could too. Around the rim I drilled six holes to match the diameter of the spokes (I used old bike spokes). For a hub use a hex nut, with a bore that can be drilled to suit the shaft, drill six holes around the nut, but not into the center hole. Fix the nut to a board, and mark a circle for the rim. Using loctite, glue the spokes to the hub by poking them through the rim, let it cure, center it and put loctite on the spokes at the rim, and after it cures, trim the spokes to length. Ian S C

Graham Rounce12/11/2012 14:19:58
28 forum posts
2 photos
Ian - thanks for all that. I think I'll be using the hopefully precision-drilled-to-3.18mm Meccano bush wheel for the hub - I haven't heard back from him/them yet.

Any tips for balancing it? I was thinking of "hanging" it with the shaft horizontal, and adding weights or removing metal until it showed no preference for taking up any particular position, but that would be approximate at best...?
Andyf12/11/2012 17:53:24
392 forum posts

One way would be to put it on a longish and hopefully straight bar between bearings of some sort, then rev it up slowly (perhaps using an electric drill). If it's out of balance, the bar will flex towards the heavy side, and a felt-tipped pen mounted close to the wheel when static will mark it to show where weight should be removed. This would need a number of iterations at gradually increasing speeds, and a supply of different coloured felt tips so you can tell new marks from old.

Andy

Graham Rounce12/11/2012 21:17:33
28 forum posts
2 photos
Hi Andy - Past a certain speed the bar is going to bow anyway, but it sounds worth a try - hopefully it won't need to go up to that speed.. Now I wish I had a continuous speed control on the drill press! (Or a less heavy duty one of those amazing machines that garages use for car wheel balancing.)

Latest: The metal pipe supplier doesn't want to cut thin slices, unfortunately.
Terryd12/11/2012 21:49:32
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1946 forum posts
179 photos
Posted by Graham Rounce on 12/11/2012 14:19:58:
Ian - thanks for all that. I think I'll be using the hopefully precision-drilled-to-3.18mm Meccano bush wheel for the hub - I haven't heard back from him/them yet.

Any tips for balancing it? I was thinking of "hanging" it with the shaft horizontal, and adding weights or removing metal until it showed no preference for taking up any particular position, but that would be approximate at best...?

Hi Graham,

The standard way to balance is to insert a short close fitting bar into the hub and let it roll naturally on 'two razor' parallel edge supports, add small weights or drill out material from the rim to balance. If you drill out too much add lead shot into your drilled hole. I had two tyres fitted today on to my car and the balance machine was amazing smile - you could use one of those wink 2

Regards

Terry

Edited By Terryd on 12/11/2012 21:50:23

Les Jones 112/11/2012 22:17:25
2292 forum posts
159 photos

Hi Terry,
Here is a design for a tool to balance model turbine rotors that probably uses the same principal as the car wheel balancing machine.

Les.

Graham Rounce12/11/2012 23:20:34
28 forum posts
2 photos
Terry - Yup, that must be the way to go. Thanks.
Les - That's fantastic. I wish I was as well-directed, quick, single-minded or whatever as him! Most people would count their lives well spent if they successfully completed EITHER of those projects!

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