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Hi,  I've been pondering for for sometime as to how to make a ring onto which rollers could rotate my homemade dome. 

I've seen people  use professional cut /welded steel pipe rings,  laser cut bearing sheets and rollers on flat wooden rings with extra rollers for lateral location. 

All a bit expensive and or complicated. 

How about using 50mm ish  MDPE (medium density polyethylene)  pipe as used for water pipes..... It's very flexible, easily formed into a ring, rust proof and if used with polyethylene V rollers would give silent operation, all rust proof and with the V rollers provides lateral location as well.  The MDPE tube ring could be fixed in position with crossed wood screws passing through the  tube leaving the top surface clear for the rollers. 

Hope this gives food for thought. 

Jim

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If your dome is very heavy, the pipe will probably deform with time, and could take a set when the dome is parked for an extended period. That might make rotation and loading somewhat uneven. PVC pipe gets brittle over time as well, more quickly at elevated temperatures. I don't know how MDPE would behave, but also probably something to investigate before committing to a structure.

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MDPE pipe does not become brittle,  that's why it's used for water and gas supplies underground.  A decent diameter has very thick wall thickness to withstand quite high internal pressures.  If deformation  (from a parked heavy dome)  is perceived as a potential  problem,  then the tube could be filled with sand before the tube ring is fixed in position. 

Jim

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43 minutes ago, Kev M said:

Maybe you could use the base ring from a trampoline.......cheap and readily available ?

I can see a dual purpose emerging, something for the cloudy nights?      😀

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Interesting idea. :thumbsup:


Heavy wall plastic pipe is certainly sturdy but would rely entirely on the load applied and how well the pipe itself was supported.
You cannot assume that your pipe's base is dead flat and likely to remain so.
How would you "restrain" the pipe? Bolts through the middle? How would you ensure a true, level circle?

I used large, 180mm/7", industrial truck wheels with roller bearings on my heavy, plywood, 3m/10' dome.
The base ring of the dome itself, on which they ran, was laminated marine plywood but did NOT remain flat.
While watching the base ring rotation it is easy to see gaps appearing over different rollers in turn.
Which means the load falls only on the few. Rather than the total number of rollers.

I am building a new 4.3m [13'] GRP dome and have invested in a 360° green laser level for the [laminated marine plywood] base ring.
I have already used the laser tool on my present dome and found the base ring wanting in flatness.
After two years of utterly wasted time, repeatedly trying to check the level of the base ring, the laser gave me the true answer in seconds!
The thin, green, laser line can be easily seen on the lower edge of the dome's base ring.

Note how I have added restraining disks on top of the steering rollers to hold the dome down in gales.
No danger of ever forgetting to set storm latches. Not that the dome has ever shown any signs of lifting.
Most dome failures are probably due to wind penetration followed by catastrophic inflation.
 

P1440688 rsz 600.JPG

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Steel angle, approx 45/50mm, rolled to the correct diameter, then neatly welded at the join, forms the base.
Another piece carries the dome.
The size difference between the rings is chosen to take a standard fixed castor. You fit quite a few so they don't take much strain - and hold back  some spares for the life of the dome.
Turnbuckles or latches stop the dome from flying away when not in use and keep the thieves out.

Many steel fabricators have the rolling machines and all have the welding skills.

I used to have an 8ft set, bought 2nd hand for when I moved house and planned a home build.
As it happened I went for roll off roof instead.
I advertised the rings on SGL a couple of years back but there were no takers so they went into a skip.

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I used a 50mm angle ring and 100mm rollers.

Worked very well no real issues.

You can see them in the background supporting a Octodome......

canopus320_1984.jpg

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