MESU/Sitech questions

[Zakalwe]

34 minutes ago, ollypenrice said:

What about lapping the plates together with a suitable lapping compound?

No chance. The only foolproof way would be to mill/surface grind the mount plate after welding and use a machined surface on the pier. That's just too expensive to correct a minor inconvenience.

[RayD]

37 minutes ago, ollypenrice said:

Yes, the washer idea is good. It also makes me think that the teflon strips idea is bad and precisely what you don't want. What you do want, as Ray and Zalalwe are saying, is less friction between the nut and the top plate and more fricition between the pier and mount plates.

What about lapping the plates together with a suitable lapping compound? Maybe ours works because it happens to have a good flat fit between the plates.

Olly

Yes I personally think it's a little counter intuitive Olly as you are right, you actually want slight higher friction between the mount and plate.

The mating surfaces should be as flat and matched as possible, so lapping is a great idea if you have the time as it can take ages.  I think the aluminium plate from Mesu appears quite good, but of course even tightening that to the pier top can move things a touch.

[Star101]

Once a mount is polar aligned on a static pier does one have to perform a PA often?

[RayD]

6 minutes ago, Zakalwe said:

A 51101 thrust bearing under the tommy nut would be the solution to preventing the mount from twisting when the bolt is locked.

http://www.bearingboys.co.uk/Thrust-Ball--Budget/51101-Budget-Thrust-Bearing-679-p

If it's rocking from a slightly uneven base then you're going to have to live with it.

Yes another great option.  Anything really to move the friction point from between the nut and mount.

[RayD]

4 minutes ago, Zakalwe said:

No chance. The only foolproof way would be to mill/surface grind the mount plate after welding and use a machined surface on the mount. That's just too expensive to correct a minor inconvenience.

Definitely agree.  Ideally the 2 surfaces would be machined as a pair, but this I suspect would be negated when you bolt the adaptor plate to the pier top.

Unfortunately as you pointed out earlier, if there is unevenness between the mount and plate, that is something entirely different and maybe something you will have to live with, but adapting the way the nut has a natural tendency to twist the mount when tightening is definitely something that can be easily helped.

[Zakalwe]

To lap two surfaces you have to move them back and forth. Good luck with trying to do that with a heavy lump like a Mesu.

Bear in mind that the base is also painted/powdercoated. Stripping that off should be a consideration if you are trying to achieve a good mating surface.

[RayD]

3 minutes ago, Star101 said:

Once a mount is polar aligned on a static pier does one have to perform a PA often?

I don't think it has to be done very often, but the great thing about devices such as PoleMaster, is that it makes the process so quick and easy that you can check it periodically, and actually fairly often.

[Zakalwe]

6 minutes ago, Star101 said:

Once a mount is polar aligned on a static pier does one have to perform a PA often?

In a perfect world, no.

Even though I have a cubic metre of concrete in my pier base the ground that I am on is very poor. When I had a house extension built some years ago we had to drive the foundations piles down to 9 metres before hitting solid ground. I get a little bit of movement when the water table rises. Also loading and unloading scopes can knock the mount a little bit.

[RayD]

1 minute ago, Zakalwe said:

we had to drive the foundations piles down to 9 metres before hitting solid ground

Holy cow!!!  That's practically a swamp!

[Star101]

Thanks Zakalwe and RayD,

Reading this thread I was beginning to wonder if I will be having to PA every night before imaging!

Thank heaven its only if I have an earthquake

[Zakalwe]

Just now, RayD said:

Holy cow!!!  That's practically a swamp!

Thats exactly what it is. I live in a coastal region...3 metres above sea level. The land is basically a massive tidal plain. All the houses are built on concrete "rafts" so when I had the extension built we had to make sure that the foundation ring-beam was fixed to the main house raft otherwise the two would settle at different rates.

Probably the worst place in the world to take up astro imaging.  Lancashire coast- constant cloud, crummy seeing, lots of moisture in the air. A bit like taking up surfing if you lived in the Sahara. Still...nowt like a challenge!

[RayD]

Just now, Zakalwe said:

Thats exactly what it is. I live in a coastal region...3 metres above sea level. The land is basically a massive tidal plain. All the houses are built on concrete "rafts" so when I had the extension built we had to make sure that the foundation ring-beam was fixed to the main house raft otherwise the two would settle at different rates.

Probably the worst place in the world to take up astro imaging.  Lancashire coast- constant cloud, crummy seeing, lots of moisture in the air. A bit like taking up surfing if you lived in the Sahara. Still...nowt like a challenge!

All of a sudden the problem of the nut seems pretty insignificant 

[RayD]

4 minutes ago, Star101 said:

Thanks Zakalwe and RayD,

Reading this thread I was beginning to wonder if I will be having to PA every night before imaging!

Thank heaven its only if I have an earthquake

Definitely not 

Personally I've got so used to going it with my PoleMaster on my AZ-EQ6, and it is so quick, that I plan to include it in to my routine on a weekly basis anyway, and any time I add or remove equipment.

[ollypenrice]

28 minutes ago, Zakalwe said:

Thats exactly what it is. I live in a coastal region...3 metres above sea level. The land is basically a massive tidal plain. All the houses are built on concrete "rafts" so when I had the extension built we had to make sure that the foundation ring-beam was fixed to the main house raft otherwise the two would settle at different rates.

Probably the worst place in the world to take up astro imaging.  Lancashire coast- constant cloud, crummy seeing, lots of moisture in the air. A bit like taking up surfing if you lived in the Sahara. Still...nowt like a challenge!

Echoes of the Hersonceaux disaster. When the RGO relocated to Hersomnceaux they had not factored in the effects of the tide which conserably affected the aligment of their mount and so made a mess of any positional astronomy they might have wanted to do.

My ground is boulder in clay over limestone. It isn't the most stable but I find I go about two years before needing a PA tweak.

OK, the lapping wouldn't work. I had forgotten that it needed to be back and forth. In that case how about ditching the flat-to-flat principle behind the design and bonding three thin circular stainless steel shims set 120 degrees apart on the base plate to make it three points of contact? Would there be a danger of the centre nut bowing the top plate downwards?

Olly

[Zakalwe]

13 minutes ago, ollypenrice said:

 In that case how about ditching the flat-to-flat principle behind the design and bonding three thin circular stainless steel shims set 120 degrees apart on the base plate to make it three points of contact? Would there be a danger of the centre nut bowing the top plate downwards?

Any engineering solution is a compromise between all sorts of mutually exclusive requirements. Cost vs profits. Efficiency vs effectiveness and so on. A three-point support would introduce other issues as you've pointed out.  What we have is a relatively minor inconvenience that can be overcome with a bit of experience of how your individual mount reacts to tightening the bolts. Of course a solution could be engineered, but it would increase the costs. Is it really worth machining the mount base and having to purchase a matching pier top plate to correct what is really a minor issue? For me, the answer would be a resounding "no".

Personally I liked the EQ8 solution- a central bolt with two outrigger bolts. Even that can rock a bit due to the pier top.

I think Paramount use something similar?

[ollypenrice]

40 minutes ago, Zakalwe said:

Any engineering solution is a compromise between all sorts of mutually exclusive requirements. Cost vs profits. Efficiency vs effectiveness and so on. A three-point support would introduce other issues as you've pointed out.  What we have is a relatively minor inconvenience that can be overcome with a bit of experience of how your individual mount reacts to tightening the bolts. Of course a solution could be engineered, but it would increase the costs. Is it really worth machining the mount base and having to purchase a matching pier top plate to correct what is really a minor issue? For me, the answer would be a resounding "no".

Personally I liked the EQ8 solution- a central bolt with two outrigger bolts. Even that can rock a bit due to the pier top.

I think Paramount use something similar?

Agreed, but I hate to be beaten! I think a lot of this is 'feel' which comes from a mis-spent youth fiddling about with mechanical things on which one later tries to kill one's self...

Olly

[Zakalwe]

9 minutes ago, ollypenrice said:

 I think a lot of this is 'feel' which comes with fiddling about with mechanical things (which I no longer do, it must be said.)

The age old art of fettling. Keeping men busy in sheds since 1549

[ollypenrice]

56 minutes ago, Zakalwe said:

The age old art of fettling. Keeping men busy in sheds since 1549

What happened in 1549? The invention of the shed?? 

Olly

[gnomus]

There may be potential Mesu purchasers reading this thread who are concerned that adjuting the PA on a Mesu is a very tricky business.  I don't find that to be the case.  Yes, there is the issue of slight shift when locking down (and some of the suggestions here may be helpful in alleviating that), but it is fairly easy to work around.  Certainly adjusting the PA on a Mesu is magnitudes easier (and more precise) than adjusting my CGEM is.  

As has been said, in an observatory you don't have to do this very often.  I imagine that the majority of Mesus (though not all) are in observatories.

[RayD]

32 minutes ago, gnomus said:

There may be potential Mesu purchasers reading this thread who are concerned that adjuting the PA on a Mesu is a very tricky business.  I don't find that to be the case.  Yes, there is the issue of slight shift when locking down (and some of the suggestions here may be helpful in alleviating that), but it is fairly easy to work around.  Certainly adjusting the PA on a Mesu is magnitudes easier (and more precise) than adjusting my CGEM is.  

As has been said, in an observatory you don't have to do this very often.  I imagine that the majority of Mesus (though not all) are in observatories.

I've certainly not got that impression Steve.  

I think as an engineer I just looked at it and thought I could improve on the design at a very low cost.  My points were raised simply in response to @kirkster501's query about the mount moving when tightening the bolt, and certainly not intended to highlight reasons that people should fear buying a Mesu.  I've ordered one myself so I'm keen for it to be as well engineered as it appears.

As you say most are going to be in observatory's anyway, so it's not a big issue.  For me it's just a niggle that I think I can work around.

Added to this as well is the accuracy of PoleMaster also highlighting any tiny movement in real time, which historically I guess we never had. 

[gnomus]

1 hour ago, RayD said:

...

Added to this as well is the accuracy of PoleMaster also highlighting any tiny movement in real time, which historically I guess we never had. 

Actually that is bang on.  In the bad old days, we had to drift align.  This meant measuring, making an adjustment (locking down), and seeing what has happened.  You wouldn't have known that the thing moved a bit on lockdown.  It is only because we can see it on screen with the Polemaster that we know it happens.  

[kirkster501]

5 hours ago, ollypenrice said:

Yes, the washer idea is good. It also makes me think that the teflon strips idea is bad and precisely what you don't want.

Olly

With the PoleMaster last night I gave up on the fine alignment section at the end because tightening the central wingnut just wrecks the fine alignment you just struggled so hard to achieve.

Yes indeed Olly.  I am starting to think this too and well for that very reason.  However, you could also counter-argue that the PTFE has some "give" to cater for unevenness between the two mating surfaces.

The Penny washer idea is fabulous.  I have a load of those kicking about - they shall be on my mount within the hour.  I will report back how it works (in ten years when we get another clear night).

Also guys do you polar align with a loaded mount or the mount "on its own"?  I;d imagine if you dod this on its own the addign of 30Kg of stuff and weights will throw it out again?  I could try it I suppose.

 

[AstroBruiser]

13 hours ago, kirkster501 said:

With the PoleMaster last night I gave up on the fine alignment section at the end because tightening the central wingnut just wrecks the fine alignment you just struggled so hard to achieve.

Yes indeed Olly.  I am starting to think this too and well for that very reason.  However, you could also counter-argue that the PTFE has some "give" to cater for unevenness between the two mating surfaces.

The Penny washer idea is fabulous.  I have a load of those kicking about - they shall be on my mount within the hour.  I will report back how it works (in ten years when we get another clear night).

Also guys do you polar align with a loaded mount or the mount "on its own"?  I;d imagine if you dod this on its own the addign of 30Kg of stuff and weights will throw it out again?  I could try it I suppose.

 

I will give this a crack tonight and let you know if the PTFE does the trick 

[Zakalwe]

18 hours ago, kirkster501 said:

Yes indeed Olly.  I am starting to think this too and well for that very reason.  However, you could also counter-argue that the PTFE has some "give" to cater for unevenness between the two mating surfaces.

Very, very unlikely. How thick is is the PTFE? Less than a millimetre, I'd wager. How much do you think that will compress and how much difference would it make? Thermal expansion/contraction in a steel pier would be more I would think.

We tend to obsess in this game about stuff, but in a lot of cases I don't think that it stands any scrutiny. The classic is the whole concern about "rat's cages" which was started by a certain manufacturer selling snake-oil. How many people with Avalon mounts find this a problem??

Not much evidence of problems with the images produced by that setup....

http://www.lightvortexastronomy.com/astrophotographs.html

[RayD]

2 hours ago, Zakalwe said:

Very, very unlikely. How thick is is the PTFE? Less than a millimetre, I'd wager. How much do you think that will compress and how much difference would it make? Thermal expansion/contraction in a steel pier would be more I would think.

We tend to obsess in this game about stuff, but in a lot of cases I don't think that it stands any scrutiny. The classic is the whole concern about "rat's cages" which was started by a certain manufacturer selling snake-oil. How many people with Avalon mounts find this a problem??

Not much evidence of problems with the images produced by that setup....

http://www.lightvortexastronomy.com/astrophotographs.html

Yes I tend to agree re. the PTFE tape.  I don't think there would be an issue with movement or compression of the PTFE tape, it's too thin, but it would just be making a very slippery surface where you actually don't necessarily want one (in this instance with the single nut clamping arrangement).