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Skywatcher EQ8 Mount pre-orders

FLO

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Gina

Gina

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Considering we are aiming to get within a couple of arc minutes PA and may be using a 1000mm scope and 5 micron pixels, I think it could be significant.  Mind you I guess guiding would take care of it.

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Zakalwe

Zakalwe

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Considering we are aiming to get within a couple of arc minutes PA and may be using a 1000mm scope and 5 micron pixels, I think it could be significant.  Mind you I guess guiding would take care of it.

I sincerely doubt it.  I doubt if you would be able to measure the compression in a thin plastic sheet under the weight of 30Kg. Possibly, if you used a 5mm thick sheet of rubber, but not a thin sheet of nylon.

As for affecting the images? Not to any measurable amount, especially when the whole shooting match is supported on a mass produced mount with lots of gears, cogs and what-not.

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1parsec

1parsec

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I sincerely doubt it.  I doubt if you would be able to measure the compression in a thin plastic sheet under the weight of 30Kg. Possibly, if you used a 5mm thick sheet of rubber, but not a thin sheet of nylon.

As for affecting the images? Not to any measurable amount, especially when the whole shooting match is supported on a mass produced mount with lots of gears, cogs and what-not.

I think Gina is right with the thinner washer. :icon_salut:

PTFE is quite soft and the compression of a thick washer would be noticeable. Maintaining PA wouldn't be the issue but more down to

the overall rigidity of the mount where it is attached to the pier adaptor puck.

Here are some rough scribblings :icon_scratch:

Assuming -

1. PTFE disc is 180mm dia with a 100mm hole in the centre with full contact with the base plate of the mount.

2. Modulus for PTFE 500MN/m2

3. Weight of mount 30Kg + 15Kg scope + 15kg of counter weights = 60 Kg  I'm talking about a fully operational setup, not just the mount .

I calc the compression of the 1.0mm thick PTFE washer would be 0.068mm and the 0.25mm thick washer 0.017mm 

The thinner washer would be prefered as it would be more rigid. The thicker the washer is, the more it would act like a spring .

As mentioned above, acetal might be a better choice as it has about 5 times the compressive strength than PTFE and probably do the job sufficiently well.

But you've got to ask that if the mount is to be permanently mounted, do you really need all the fancy low friction adjustment surfaces ?

I'd go for a rock solid attachment, no need for a puck, and tap the 3 or so holes straight on to the pier top instead :smiley:    

Cheers, Dave.

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Zakalwe

Zakalwe

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Posted

I think Gina is right with the thinner washer. :icon_salut:

PTFE is quite soft and the compression of a thick washer would be noticeable. Maintaining PA wouldn't be the issue but more down to

the overall rigidity of the mount where it is attached to the pier adaptor puck.

Here are some rough scribblings :icon_scratch:

Assuming -

1. PTFE disc is 180mm dia with a 100mm hole in the centre with full contact with the base plate of the mount.

2. Modulus for PTFE 500MN/m2

3. Weight of mount 30Kg + 15Kg scope + 15kg of counter weights = 60 Kg  I'm talking about a fully operational setup, not just the mount .

I calc the compression of the 1.0mm thick PTFE washer would be 0.068mm and the 0.25mm thick washer 0.017mm 

Nice work Dave, but at the end of the day we are talking about a hundredth of a millimetre. That's as near to nothing as you are going to get. Plus you havent factored in that the mount would be bolted down thus compressing the washer.

Anyhoo, it looks like spending £90 of a puck is probably not needed for anyone purchasing these mounts. :icon_salut:

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1parsec

1parsec

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Nice work Dave, but at the end of the day we are talking about a hundredth of a millimetre.

Yes it's 'only' 0.01mm but that can translate in to a large pointing error.

For example if you were to tip one side of the base of the EQ8  0.01mm relative to the other you'd be pointing 11.5 arc seconds in a different position :eek:

So in practise we can be often looking at microns not 100ths when the goal is to point and track to arc-sec accuracy.

Dave.

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Steve 1962

Steve 1962

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Looks nice (and pricey!). Whats to stop someone from drilling and tapping 3 holes in the pier top plate (one for the azimuth pin, two for the mount securing holes). The base of the mount is flat, isn't it, so no need for stepped pier adapter (unlike the EQ6)?

From the manual - it looks to me as though the mount attaches to the pier / tripod using a bolt treaded upwards into the mount as per the eq5/6's. Are we saying that this bolt can be dispensed with .....or have I read that wrong? I'm asking because I have a solid concrete pier with a 10mm steel cap plate.

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JamesF

JamesF

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You're not thinking of buying one as well (as Gina), Steve?  Another one down that way and the Blackdowns could end up sinking below sea level.  And this end of the county might end up as the UK's first all-year ski resort.  Hmmm.  Suddenly that doesn't look quite so bad.  As you were...

James

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Steve 1962

Steve 1962

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You're not thinking of buying one as well (as Gina), Steve?  Another one down that way and the Blackdowns could end up sinking below sea level.  And this end of the county might end up as the UK's first all-year ski resort.  Hmmm.  Suddenly that doesn't look quite so bad.  As you were...

James

Just mulling the options James, that's all - honestly (cough)! Skiing? Sorry - I'm lost now.

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Zakalwe

Zakalwe

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Posted

From the manual - it looks to me as though the mount attaches to the pier / tripod using a bolt treaded upwards into the mount as per the eq5/6's. Are we saying that this bolt can be dispensed with .....or have I read that wrong? I'm asking because I have a solid concrete pier with a 10mm steel cap plate.

I *think* that you'd still need the central bolt to allow the mount to pivot when making adjustments in azimuth

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Gina

Gina

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I *think* that you'd still need the central bolt to allow the mount to pivot when making adjustments in azimuth

Yes, I agree.  That is the pivot for PA azimuth adjustment.  What a shame the central hole in my pier plate is 30mm in 10mm mild steel that took me an age and extreme effort to bore out with a hand pillar drill - the only thing I have that was up to the job - the electric pillar drill wouldn't touch it! :(  Now I need a 12mm hole.  12mm holes in mild steel present no problem - the 16mm x4 ones around the edge took a little longer.  The 250mm (or it might have been 254mm/10") x 10mm mild steel discs I got before are no longer available from ebay. 

I could do something like I did before when I made the fitting for my NEQ6 - a 5mm aluminium plate 200mm x 200mm with the corners rounded off (or thicker).

EDIT  Been trying to use the "Full Editor" to add a diagram but it's not working :(  So please see the following thread post #15 :- http://stargazerslounge.com/topic/197002-pier-designsplanmeasurements/#entry2071608

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stephen_usher

stephen_usher

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I very much doubt that the thin parts of the casting where the two side bolts lock the mount would be strong enough to hold the whole mount anyway without fracturing, so you'll need the central bolt.

The way around this would be to have a "floating" plate held above the top plate of your pier on three or six bolts. This plate would have the central bolt hole, the pin and the two locking bolt holes. The main bolt would then be placed through this to secure the mount.

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FLO

FLO

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Any sign of the next batch of these on the horizon, Steve?

The October delivery has arrived so we'll be dispatching yours Monday for delivery Tuesday  :smiley:

I'd rather like to know as well...

Olly

We have two EQ8 mounts available from the delivery due November. 

HTH, 

Steve 

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FLO

FLO

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We have two EQ8 mounts available from the delivery due November. 

We now have 'one' EQ8 available from the November delivery :smiley:

We have sold out :smiley:

New orders placed from this point onwards will be fulfilled from the first delivery of 2014. 

A big thank-you to everyone who entrusted us with their EQ8 pre-order  :icon_salut:

Steve 

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Sp@ce_d

Sp@ce_d

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We have sold out :smiley:

New orders placed from this point onwards will be fulfilled from the first delivery of 2014. 

A big thank-you to everyone who entrusted us with their EQ8 pre-order  :icon_salut:

Steve 

Thank goodness for that.. finger been hovering over the button all morning.. been sooo close but need to hold back for the Esprit 80 first !! :eek:

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