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kirkster501

MESU/Sitech questions

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After an incredibly frustrating cloudy two weeks when I have been itching to get my MESU up and running I managed to get a few glimpses of stars through the murk this evening and so had a half chance to partly set up my polar alignment with my Pole Master and check out SGP Pro and moving the mount about.  I have done half the polar alignment on my Pole Master from QHY.  That is an amazing device.  I could not complete the fine tuning bit because the seeing was too bad and Polaris was jumping about all over the place.  Also, a bit frustrating Polar Aligning the MESU since I get the Pole bang on and then when I tighten up the main wingnut adn Azimuth post it moves the polar alignment slightly.....  So I need to have a play about on a better night to get a better feel for the movement of the mount upon tightening those bolts so I can predict it better when aligning Polaris.

When loaded with scopes and weights it is quite difficult to turn the altitude adjusters.....  Do you guys polar align with the mount unloaded?

Frankly I am blown away with the mount - or what I can glean from it so far.  I set up SGP last weekend (thick cloud since then). From SGP I moved to a random piece of sky, I hit blind solve and after 30s the mount sorted itself out and updated CdC as to where it was pointing. I then grabbed an old FITS of M101 solved and synced and the mount silently moved and it was bang in the middle of the frame when the test sub came in.  Amazing.

It was then getting very hazy with only Mag 2 stars visible so from the mosaic wizard I selected M37.  It downloaded an image of it, I centred it and mount  put it bang in the middle of the sensor.

I am amazed with it so far.  The mount is astonishing, silent, accurate.  But SGP and the mosaic wizard equally so.  You don't even need o do mosaics!

Need to report back its performance with guiding in ten years when we get a proper clear night.....

One thing.  When i did the blind solve something called "InitPoint" (i think that's the name) popped up.  It counted down and applied a sync.  I just let it and it all worked.  But what is that doing?

Edited by kirkster501
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Hi Steve

If you start Polemaster with the bar pointing down and the scope straight up (the classic home position), then things are quite easy, since everythng works as up/down and right/left.  Things do move when you tighten the locks back up, so the trick is to determine the correct direction you need to adjust; make a small adjustment and tighten; recheck; make another small adjustment and tighten; and so forth.  Trying to get it bang on and then tightening is an exercise in frustration.

Altitude adjustment is easy enough so long as you 'help' the mount.  By this I mean apply a bit of pressure in the correct direction on the weights bar.  This makes it easy to turn those wheels.  It is easier if you have someone to help.

Regarding 'Offset Init' - this is important.  You can leave it to count down the 30 seconds.  Or you can click the 'Offset Init' box followed by OK.  Another option is to go into SiTech Config and change the 30 second countdown to 5 or less.  Then just let SGP do everything.

Regards

Edited by gnomus
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9 hours ago, kirkster501 said:

......Also, a bit frustrating Polar Aligning the MESU since I get the Pole bang on and then when I tighten up the main wingnut and Azimuth post it moves the polar alignment slightly.....

I have to say that for me this is a real problem..... it is a real failing on a fantastic mount......I dislike PA intensely and with the Avalon it was a breeze compared to this system with the silly wobbly middle bolt that throws your PA out again when you tighten it :(  :( 

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If you use 2 large washers under the nut with a little bit of Silicone grease between them that should stop the mount trying to twist when you tighten it. 

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2 minutes ago, RayD said:

If you use 2 large washers under the nut with a little bit of Silicone grease between them that should stop the mount trying to twist when you tighten it. 

Just under the nut or between the mount and the plate? As maddening as it is, I'm not planning on taking the mount off any time soon :)

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I agree with you Sara.

I use Polemaster and do the same as gnomus , Look at my pc screen and polmaster alignment as I tighten.

You soon get the knack of how much and in which direction to compensate before tightening up.

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Just now, swag72 said:

Just under the nut or between the mount and the plate? As maddening as it is, I'm not planning on taking the mount off any time soon :)

Yes between the nut and the mount Sara. Just a smear of grease between the 2 and it should stop the problem. 

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Since I saw the pictures of the single nut I've already been working on a replacement lever/clamp system as I think a nut in the centre screwed down from the top (the moving part) is fundamentally flawed.  I'll post my solution here, but basically it's a locking lever that sticks out the front and pushes down in 2 points using the middle bolt only as a central leverage point (if that makes sense).

This is an issue I've seen loads of time in engineering, and in the short term is easily helped with the 2 washers and silicone grease.

Edit:

This is the fundamentals of my design, which is a cam lever, which will push down on a disc with a raised outer rim on the under side, so it clamps the mount down rather than spin it, and does so over a wider area.

Cam lever.jpg

Edited by RayD
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10 minutes ago, swag72 said:

Metal washers @RayD ?

Yes Sara.  If you have 2 large M12 "penny" washers, reasonably thick at say 2mm each, then take the nut off, don't apply any grease between the bottom one and the mount, put a bit of grease between the 2, then put the nut back on top of the 2 washers.

Basically as long as the friction is less between the 2 washers, which is why I would use silicone grease as it is very slippery, then the washers will be the point that move rather than the mount.  

I think the problem is possibly worsened a little if the friction is very low between the mount and mounting plate, such as where people are using PTFE tape, so possibly a little counter intuitive given the flawed design, but the simple addition of 2 greased washers will help.

Edited by RayD
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Thanks Ray - I'll pop to the local DIY shop and see what I can find :)

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36 minutes ago, RayD said:

Since I saw the pictures of the single nut I've already been working on a replacement lever/clamp system as I think a nut in the centre screwed down from the top (the moving part) is fundamentally flawed.  I'll post my solution here, but basically it's a locking lever that sticks out the front and pushes down in 2 points using the middle bolt only as a central leverage point (if that makes sense).

This is an issue I've seen loads of time in engineering, and in the short term is easily helped with the 2 washers and silicone grease.

Edit:

This is the fundamentals of my design, which is a cam lever, which will push down on a disc with a raised outer rim on the under side, so it clamps the mount down rather than spin it, and does so over a wider area.

Cam lever.jpg

 

You can buy them for £35...

http://www.wdsltd.co.uk/product/3566/eccentric-cam-lever-with-eyebolt-wds-358/

 

http://www.wdsltd.co.uk/images/10197/11/eccentric-cam-lever-with-eyebolt-wds-358

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Just now, Zakalwe said:

Thanks for that.  Yes I had planned to use a pre-made cam lever, actually from the same supplier you've linked, and then having an aluminium disc made to fit under that with a raised edge to the under side to push down further away from the centre to just increase the stability.

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54 minutes ago, RayD said:

Yes between the nut and the mount Sara. Just a smear of grease between the 2 and it should stop the problem. 

Grease or silicone (bath sealant)???

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Is the movement only due to the rotation of the mount as you tighten the nut, or could at least part of it be due to uneven-ness between the mount plate and the pier top which allows for a 'rocking' motion?  If so, then the slippy washers idea may not cure it.  Have you had the chance to try this Ray?

I have found the 'slow creep to the correct position' technique works fairly reliably.

Edited by gnomus

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Just now, kirkster501 said:

Grease or silicone (bath sealant)???

No silicone grease, definitely not silicone sealant.  You can get it in car shops such as Halfords etc.  Any very slippery grease should do though, so even general purpose grease should be fine, it's just when it gets very cold it can go a little hard, and silicone grease has a higher operating temperature range without affecting it.

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1 hour ago, swag72 said:

I have to say that for me this is a real problem..... it is a real failing on a fantastic mount......I dislike PA intensely and with the Avalon it was a breeze compared to this system with the silly wobbly middle bolt that throws your PA out again when you tighten it :(  :( 

Zakalwe's idea is very good but the other thing about using any kind of locknut in engineering is judging how tight to leave the it during the adjustment phase.  What I would do, Sara, is leave that central nut moderately tight as you are coming into the final iteration of azimuth adjustment. You will still be able to push it both ways, but against resistance. It's like that in all sorts of applications - adjusting tappets on engines, preloading bearings, etc etc. So never take the pressure off that central nut during adjustment, just ease it off.

I'm sorry to hear that folks are finding this troublesome. One of the things that struck me about ours was the incredible ease of PA adjustment. We first did it with two iterations per axis, literally.

Olly

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Just now, gnomus said:

Is the movement only due to the rotation of the mount as you tighten the nut, or could at least part of it be due to uneven-ness between the mount plate and the pier top which allows for a 'rocking' motion?  If so, then the slippy washers idea may not cure it.  Have you had the chance to try this Ray?

I have found the 'slow creep to the correct position' technique works fairly reliably.

Yes the movement is exactly that, and is because the friction generated between the nut and mount is higher than between the mount and plate.

I've not tried it myself as I don't have my mount yet, but as soon as I saw how it was fixed I suspected this would be an issue so have been looking at alternatives.

It could be an uneven mount which isn't helping, definitely, but you need to change the point where the movement is occurring, so reducing the friction at a suitable point (between the nut and plate) will help this.

For the cost of a couple of penny washers it is worth trying as from an engineering perspective, where you want to see no movement at all between the 2 parts, this design isn't great, and probably why most other mounts don't do it, with most pulling directly down from underneath.

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Im not a big fan of the single locking bolt, but in fairness most other solutions will have a bit of motion as you cinch the locking bolts down.

The problem is that the pier top and the underside of the mount won't be all that flat. Welding the uprights to the base plate will have distorted the base a small amount. Any slight distortion will result in a certain amount of "rocking" .

Having said all that, it's just a matter of practice to take the movement into account. When I PA (using Polemaster) I watch closely how the tightening of the altitude locking nut alters the star position. I then offset by that amount and lock it up. With the azimuth I don't open the central locking bolt...there's enough movement to tweak it back and forth. I then just lock it with the two opposing knurled nuts.

PA doesn't have to be bang on either, unless you are using a massive focal length. A little bit out can be helpful as the DEC guiding will only work in one direction. Not that that's so important with a zero-backlash mount like the Mesu.

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1 minute ago, RayD said:

Yes the movement is exactly that, and is because the friction generated between the nut and mount is higher than between the mount and plate.

I've not tried it myself as I don't have my mount yet, but as soon as I saw how it was fixed I suspected this would be an issue so have been looking at alternatives.

It could be an uneven mount which isn't helping, definitely, but you need to change the point where the movement is occurring, so reducing the friction at a suitable point (between the nut and plate) will help this.

For the cost of a couple of penny washers it is worth trying as from an engineering perspective, where you want to see no movement at all between the 2 parts, this design isn't great, and probably why most other mounts don't do it, with most pulling directly down from underneath.

Agreed, but it should be pulling donw from on top! Pulling down from beneath introduces the rat box or spindley bolt syndrome!

Olly

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2 minutes ago, ollypenrice said:

Zakalwe's idea is very good but the other thing about using any kind of locknut in engineering is judging how tight to leave the it during the adjustment phase.  What I would do, Sara, is leave that central nut moderately tight as you are coming into the final iteration of azimuth adjustment. You will still be able to push it both ways, but against resistance. It's like that in all sorts of applications - adjusting tappets on engines, preloading bearings, etc etc. So never take the pressure off that central nut during adjustment, just ease it off.

I'm sorry to hear that folks are finding this troublesome. One of the things that struck me about ours was the incredible ease of PA adjustment. We first did it with two iterations per axis, literally.

Olly

I now don't undo the central nut very much at all, it is still reasonably tight when I do the adjustment, but that final tweak, however gentle I try to do it always ruins my PA and it's back to the start. I have disliked this since the minute the mount went on... I'll give the washer idea a try!

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Just now, ollypenrice said:

Agreed, but it should be pulling donw from on top! Pulling down from beneath introduces the rat box or spindley bolt syndrome!

Olly

Oh yes I'm definitely not advocating the rat cage idea, that's for sure Olly.  No my point was a direct pull or push rather than twisting at the point the Mesu does, is a far better solution.  Of course it won't correct uneven mounts or mating surfaces, but it is definitely an issue.

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1 minute ago, swag72 said:

I now don't undo the central nut very much at all, it is still reasonably tight when I do the adjustment, but that final tweak, however gentle I try to do it always ruins my PA and it's back to the start. I have disliked this since the minute the mount went on... I'll give the washer idea a try!

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

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1 minute 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.

Good thinking. What do you think of the lapping idea?

Olly

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