Lifting the Lid

[Demonperformer]

Sounds great. Hope the test goes well.

[Alan White]

Simple wins the day......I like simple,
it's often the best solution to many things.
Complicated and multiple steps often goes wrong as each step is a potential failure point.

I hope the Milliput is up to the job required.
 

[tteedd]

Mmm. Having given advice I'd better get on and do mine now!

I'm getting closer to finally powering rotation so it would be better if it didn't sound like Clapham junction.

 

[hughgilhespie]

Well, the results are in on my attempts to achieve smooth rotation. Yes - it is a lot better but overall I'm a bit disappointed. It is not as smooth as I had hoped. The Milliput putty worked very well but my attempts to make it smooth  - the wet finger method - weren't so good so now I have bumps rather than holes. It is going to take another lift. I have sent off for a set of abrasive flap wheels that should help to finally get a genuine flat surface. Unfortunately one essential component in my lifting method ( one strong neighbour) has taken himself of to France for a week so final repairs are on hold until his return. 

So - some pics of the first try. The middle pic shows the original gap on the left with the putty filling to the right of the rubber drip strip.

[ACross]

Well done Hugh, very useful pics; I don’t think I am alone in watching how your efforts pan out before having a go myself.

[Oddsocks]

4 hours ago, hughgilhespie said:

I have sent off for a set of abrasive flap wheels that should help to finally get a genuine flat surface.

Hi Hugh.

From my experience with boats, abrasive flap wheels are not the appropriate tool to use on fibreglass for this particular job. You will not have sufficient hand control over the power tool and as the resin surface heats and melts with the friction of the flap wheel the tool will dig itself into the surface and you will end up with a series of concave dips.

The trick with sanding fibreglass resin to a flat finish is to keep the surface and the abrading tool cold.

When you have the lid raised up on blocks again use a piece of medium grade grit (P160-P180) wet-and-dry abrasive paper wrapped around a small piece of wood block around 4" x 3" x 1" (~100mm x 75mm x 25mm), take a bucket of water with you to the work and dip the wet-and-dry wrapped block into the bucket to wet it, press the block against the surface and make half a dozen passes over the seam then dip the block back into the bucket to cool and re-wet the abrasive plus wash the resin out of the abrasive to keep it cutting. Move to a medium-fine grade grit as the surface becomes flatter (P220-P280) and then finish with fine grade wet-and-dry (~P600) to a polished surface.

Be careful not to abrade through the existing gel-coat and expose the inner glass fibre matting, if this happens environmental water will wick along the exposed fibres under the surface over time, freeze in the winter and split the top-coat from the fibre glass mat core. If you do expose the glass fibre core matting you will need to paint over and seal the exposed fibres with a two-part gel-coat mix which you can find in yacht chandlers, car-body repair kits for GRP shells, etc. 

Resin fibreglass is soft and easy to sand with wet-and-dry paper, used wet, and wrapped around a wood block, each seam should take ten-fifteen minutes or so to flatten by hand and the resulting 'bridge' across the seam will be as flat as you can achieve by any other method.

You will need to remove and then replace the drip-strip to gain proper access to the work. The drip-strip is just regular self-stick closed-cell door frame draught excluder for external doors that you can find in most DIY shops. Clean the surface of the fibreglass with acetone before applying the new strip. I had to replace the drip strip on my Pulsar dome after just a few months, I don't think they cleaned all the mould release agent off the dome before sticking the drip-strip on and it fell off in several places allowing rain water to track inside the observatory but a quick clean with acetone and then a new bit of drip-strip fixed that easily and the fresh strip has remained firmly attached.

HTH

William.

[Gina]

Yes, I was going to suggest wet-n-dry abrasive paper used wet.  Beat me to it ?

[hughgilhespie]

More excellent advice! Thanks to William and Gina!

I will replace the drip-strip all round. A spring clean is overdue to get all the algae off and following that I will put on new strip.

Regards, Hugh

[ACross]

Just a quick note to follow on Williams excellent point about seals. I found a self adhesive seal in white here: http://sealsdirect.co.uk/shopping.asp?intDepartmentId=1#77  that can  be purchased by the meter so that the entire rim is one piece, with only a single joint. I also ordered enough to go around the door and across the top of the door.

[hughgilhespie]

1 hour ago, ACross said:

Just a quick note to follow on Williams excellent point about seals. I found a self adhesive seal in white here: http://sealsdirect.co.uk/shopping.asp?intDepartmentId=1#77  that can  be purchased by the meter so that the entire rim is one piece, with only a single joint. I also ordered enough to go around the door and across the top of the door.

Brilliant! Ordered!

Hugh

[tteedd]

Hmm,

Drip-strip. My ancient model does not have one. Perhaps it was never fitted. What was fitted when we dis-assembled it was a strip of stainless steel around the lower edge. I did not re-fit this but just taped the holes. I had assumed that in the wilds of yorkshire the wind had been blowing rain in. I have not had water [drips or rain] in by this route and need to fill and gell paint the holes some time.

I'll fair the surfaces at the same time. Then look more into adding a drive.

 

[hughgilhespie]

Finally,

Just to finish off this topic. Another lid-lift was done using the tried and tested wooden block technique. Then final smoothing of the epoxy putty using 120 - 240 - 400 wet and dry wrapped around short wooden blocks. No power tools in sight!

Lower, test - bingo!! Rotation was comme le derriere du bebe!!

Also have done a good spring clean and replaced the drip strip all round.

My grateful thanks to everyone who gave me much needed advice. It really was a team effort.

Hugh

[Davey-T]

Well done Hugh, it's great when a plan comes together 

Dave

[ACross]

Well done Hugh, a great write-up and solution.

This is my next project over the summer as I can’t bear the thud of the dome as it rotates. Last week I used the wooden beam technique to lift the entire dome and walls assembly without any concerns, so that a vinyl floor could be laid over my table base. It was fiddly to unroll the vinyl with limited space but worth it to add a layer of insulation and deaden the sound of anything dropping.

Are you considering adding a rotator to your dome? I have been thinking of ways this could be done as the Pulsar module is very expensive.

[hughgilhespie]

On 27/06/2018 at 07:22, ACross said:

Well done Hugh, a great write-up and solution.

This is my next project over the summer as I can’t bear the thud of the dome as it rotates. Last week I used the wooden beam technique to lift the entire dome and walls assembly without any concerns, so that a vinyl floor could be laid over my table base. It was fiddly to unroll the vinyl with limited space but worth it to add a layer of insulation and deaden the sound of anything dropping.

Are you considering adding a rotator to your dome? I have been thinking of ways this could be done as the Pulsar module is very expensive.

Hi,

I have motorised my dome, both rotation and shutter. Like you, I thought the Pulsar modules were ridiculously expensive - as they indeed are. But - and it is a big but - it has taken me a very long time, over 3 years and in that time I am fairly sure I have spent far more on the project than the cost of the Pulsar modules. So, had I bitten the bullet 3 years ago, I could have saved money and been imaging at least two years earlier.

That said, the upside is that I have enjoyed the challenges along the way and it has kept me from hanging around street corners, not to mention making me learn lots of stuff about practical engineering, electronics, etc.

My final solution for Dome rotation is the tried and tested Lesvedome method using toothed timing belt glued to the inner flange of the dome and driven - in my case only - by a stepper motor. Again, were I starting again I wouldn't use a stepper motor, just a simple 12 volt geared DC motor (think vehicle windscreen motor). There are some pics in my gallery if you are interested.

Regards, Hugh

[Gina]

But then you'd need an encoder or some way of showing which way the slot is pointing.

[hughgilhespie]

38 minutes ago, Gina said:

But then you'd need an encoder or some way of showing which way the slot is pointing.

I managed to get the worst of all worlds! Lesvedome requires an encoder, so I had to incorporate an encoder in with my stepper design even though step counting gave me ridiculous levels of precision. Then I found that the Bourns encoder I was using was too fast for the Velleman board that is used by the Lesvedome system so then I had to use software to generate a pseudo-Gray count (quadrature signal) to keep Lesvedome happy!

What joy!

Hugh

[ACross]

Your setup looks very impressive, clearly you have an engineering background.  My own abilities are far behind but I had wondered about using a Raspberry Pi Zero & small environmental HAT to provide a compass heading and fixing this to the top of the dome. Then a second RPi used to control a repurposed 12v power drill, taking a heading feed from the mount and matching the dome heading to it.

I suspect there are a whole bunch of potential issues with this simple version, not least of which the inaccuracy of the heading reading could cause the drive to be constantly changing direction. Perhaps the Lesvedome is the route, shame the simple wheel encoder component seems to be no longer available.