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Author Topic: machining down a nylon / polypropylene wheel  (Read 6248 times)
acresswell
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« on: December 22, 2015, 07:52:19 PM »

For a mad project I'm planning (a rotary sieve/ trommel to separate out the stones from our veg plot), I need about 8-10 fixed castors with wheels that are about 12mm wide.  I can't find any, so I'm thinking about using ordinary castors like http://www.screwfix.com/p/fixed-castors-swivel-50mm-pack-of-4/69497 and then turning down the outer edges of the wheels.

I don't have a lathe, so I'm wondering whether I stand a decent chance of success if I clamp a wheel between washers/nuts on a piece of studding, and hold the studding in a drill that's clamped to a bench...

Will an ordinary wood chisel do the trick? I can rig up something to lean it against so that the chisel isn't flapping around in the air...  I can also re-grind it to whatever angle would be best...  Alternatively I have an old cold chisel that's about 18 inches long (so it might give me more control) and I could have a go at grinding it to give a sharp edge...
Would it be better to hold an old plane against the wheel?

Will I have a better chance with nylon or polypropylene wheels? 
The other possibility is rubber wheels, but I'm suspicious that the chisel will just dig in or rip chunks out of rubber rather than cutting...

I'm thinking of wheels somewhere between 50mm and 100mm diameter.  Obviously if I use smaller wheels I'll have to remove less material.  Larger wheels would be better for the project (but also more expensive). Will one size be easier to machine?

I have a choice of 2 drills - a mixer one which is 2-speed but turns relatively slowly with high torque, or an old hammer drill (with broken reversing switch, but the variable speed still works) which turns much faster.  I'm not willing to risk my "best" drills!  Which speed will give me the best chance of success?

Any/all thoughts appreciated!
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knighty
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« Reply #1 on: December 22, 2015, 07:59:23 PM »

I'd clamp/screw the bracket down to a bench, then let them spin while I sanded them down with a flap wheel on an angle grinder

they'll spin fast enough that they'll end up nice an even, plus it's easier and you should have more control
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acresswell
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« Reply #2 on: December 22, 2015, 08:10:22 PM »

Knighty, do you mean one of these?
http://www.screwfix.com/p/erbauer-zirconium-flap-disc-115mm-80-grit/7448G

Like the idea of doing it without disassembling the thing.  I could stick a bit of scrap wood in the vice and bolt the brackets to it...

Thanks
« Last Edit: December 22, 2015, 08:12:56 PM by acresswell » Logged

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knighty
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« Reply #3 on: December 22, 2015, 08:49:33 PM »

yep one of those :-)


probably a good idea to oil the bearings in the center of the wheel a bit before you do it too, they might not have much lube on them when they come!

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smegal
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« Reply #4 on: December 22, 2015, 09:38:12 PM »

What about using scooter or rollerblade wheels. They have an ID of 8mm so you can just make the axles as required to support the trommel
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roys
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« Reply #5 on: December 22, 2015, 11:17:26 PM »

Send them to me and I will stick them on my lathe and turn them down for you if you want.
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Nickel2
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« Reply #6 on: December 23, 2015, 12:38:56 AM »

Silly question time.  Wink
Do they need to be 12mm wide, or can you amend your design to suit a ready-made item?
I'm a firm believer in repurposing ready-made items with the minimum of modification, so if one breaks or fails, you just buy another box of 4 and swap out the broken one without having to do any mods.
Can you post a pic of a scribbled drawing?

N2
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acresswell
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« Reply #7 on: December 23, 2015, 03:12:52 AM »

Silly question time.  Wink
Do they need to be 12mm wide, or can you amend your design to suit a ready-made item?
I'm a firm believer in repurposing ready-made items with the minimum of modification, so if one breaks or fails, you just buy another box of 4 and swap out the broken one without having to do any mods.
Can you post a pic of a scribbled drawing?

N2

I think the wheels do need to be 12mm wide, because I'm matching ready-made items that are harder to modify (cycle wheel rims).  The rim (with spokes removed) forms the shape of the trommel drum. The castors then run inside the rim to hold the drum in the right (horizontal, with a slight downward slope) position.  The trommel probably needs to run for about 2 days to sieve all the soil in my veg patch, then it will probably be taken apart in any case, so as long as the castors last for about 10 hours of operation, I'll be happy.

There are various examples on youtube, like this one:


There are couple of people hiring out the proper scheppach rotary sieves (on ebay), but I can't find one locally...

The only other thought is whether anyone can suggest where I can get 2 old mountain bike rims, which would be a bit wider and take the unmodified castors.  I tried a couple of local bike shops with no luck. Have kept my eye on ebay, but the only bike wheels being sold seem to be rather higher spec (and price) than I need. Have even looked on ebay for a scrap bike, but nothing suitable has come up locally. The blokes at the tip were quite aggressive when I enquired about a bike wheel from one of their skips... !

The rims I have came from my sister's garage - they were hanging there when she bought the house, but unfortunately they're from a racing bike so they're a bit narrow.
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DaveF
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« Reply #8 on: December 23, 2015, 09:03:07 AM »

Try the link below. I know the wheel has a 35mm thick edge but this is just a 'lip'. Might be easier to take a wheel similar to this and use a 70mm hole saw in line with wheel the axle will go through and just saw a slightly smaller and thinner wheel out of the hub material.

http://uk.rs-online.com/web/p/solid-wheels/0387919/

Regards,

Dave
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smegal
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« Reply #9 on: December 23, 2015, 09:34:14 AM »

You really are best off using something like this:

http://www.ebay.co.uk/itm/291504984328?

Where abouts are you? I have a couple with badly drilled holes in the side that you can have.
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smegal
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« Reply #10 on: December 29, 2015, 11:28:22 PM »

If you're still looking, drop me a PM and I'll send a few wheels your way.
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guydewdney
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« Reply #11 on: December 29, 2015, 11:40:15 PM »

i have a fully built vibration table, that we used for soil sieving. just a frame with some mesh on it, and a motor with an offset weight. v simple to build.

its in somerset.....
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acresswell
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« Reply #12 on: December 30, 2015, 08:33:12 PM »

If you're still looking, drop me a PM and I'll send a few wheels your way.

Smegal,

thanks for the kind offer.  Having raided my Dad's garage junk store, I think I'm now ok for the smaller wheels/castors.  I reckon the ones I've found were some of the first prototypes made by the bloke who invented the wheel, but the size is right!

Thanks again

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acresswell
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« Reply #13 on: December 30, 2015, 08:47:50 PM »

i have a fully built vibration table, that we used for soil sieving. just a frame with some mesh on it, and a motor with an offset weight. v simple to build.

its in somerset.....
Thank you, Guy.

Unfortunately, I'm a fair way from Somerset, and I'm not convinced that a vibrating table design will work for us.
I looked at vibrating table designs before deciding to go for a trommel instead... a test run with a sieve suggests that more than 50% of our "topsoil" is really gravel, so I'd end up emptying the vibrating frame after every bucketful.  A trommel is undoubtedly harder to build, but the process can run continuously rather than in batches.

Thanks again

PS
The gravel that is separated out will be a useful by-product-- I'm going to use it to form the paths between the raised beds.  Any excess will get dumped by the trailer load onto a boggy bit of track. Luckily there's no shortage of soil to process... we live on quite a steep hill, so the vegetable patch needs to be terraced as I go along, and of course I don't care if the paths between the raised beds don't have any topsoil under the gravel.  If we already had flat land, I'd probably be thinking about just importing some decent topsoil, but since I've got to dig it all anyway to make it vaguely flat, it seems sensible to try and get some useable soil at the same time.  Getting imported soil up the hill wouldn't be easy, either!
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mike7
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« Reply #14 on: December 30, 2015, 11:47:58 PM »

I made a rotating sieve last year to clean up the muddy gravel on my driveways. it worked a treat. I didn't need any wheel rims or castors for it as I had a central shaft and just a few spokes to support some curved metal flats - the equivalent of your rims. I'll see if I can get and post a photo in case it's any help. For sure the design of such things depends very much on what you happen to have available to you, though.
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