tight latitude screws on EQ6Pro

[DJDD]

Hello,

using EQ6Pro- white

I attempted my first drift alignment on the weekend and experienced some problems.

1. I found that the screw at the 'back' is very very tight and once it reaches about 52 degrees i need to use my other hand to hold the mount and take opressue off the system. I did loosen the other screw to give the problem screw room-to-move.

2. moving the latitude tended to move the mount/tripod so that the alignment star shifted drastically. Contrast this to the azimuth adjustment, which is smooth.


I do not want to force the latitude adjstment, and in fact, i do not think I can force it much more.

I notice someone else had added new handles for the latitude adjustment to make it a lot easier but I cannot seem to find the photo anymore.

I am also concerned that my entire setup moves when i change latitude.

Has anyone else experienced these problems?

cheers,
DJDD

[33South]

I have the older style black EQ6 and once loaded with the OTA and balance weights the bolts are indeed difficult to turn. They can also end up bent. They need to work together - loosen one - tighten the other, but you shouldn't need to move them much if you set your latitude as close as possible before adding the OTA etc.
Its recommended to replace them with stainless hex bolts or custom made with handles.

Pictures you were referring to
http://www.iceinspace.com.au/forum/showthread.php?t=39806

One local supplier

http://www.starstuff.com.au/eqaccessories.html

[iceman]

It's normal to have to undo one to tighten the other, as Chris said. They need to work together.

I replaced mine with 10mm (I think) bolts from bunnings. I just use a small rachet with the right sized socket for adjusting them. The rachet stays in my kit.

[DJDD]

Thanks, 33South and iceman.
The pictures were on Hagar's EQ6pro. How could I not remember that? I just read the ad the other day!

I have been turning one and lossning the other, in fact loosening both before starting. It just seems extremely hard to move, near impossible. I am just concerned abotu benindbreakign the bolts OR damiging the mount...


I should investigate replacements, or at least look at the bolt option.

Thanks for the tips.

cheers,
DJDD

[Aster]

The first and most important thing you should realise is that cast aluminium, most aluminium for that matter, is a damn side softer than steel.

It is very easy to force the steel bolt/screw and strip the thread in the aluminium casting.

The more weight the EQ6 carries, including counterweights, the harder the bottom bolt will be to turn, as all the weight rests on that bolt.

My EQ6 is pier mounted and carries a 10" F6 Newtonian and a SWED100. The only way I can adjust, move, the bottom bolt without damaging/stripping the aluminium thread, is by removing the end cap and pole finderscope, inserting a wooden or steel bar, undo the top bolt slightly, take the weight of the bottom bolt by lifting the bar enough to relieve the pressure on the bottom bolt and do the adjustment required.

Remember, life wasn't meant to be easy :)

[DJDD]

Thanks, Alexander.

I was not sure how to hold the mount up to take the weight, make the adjustments, etc., with only two hands. I like your solution usign the bar.




every step brings me closer...

cheers,
DJDD

[bmitchell82]

Ill chime in here too. your not alone buddie, i picked up my eq6 last week, and i too experience that the thred/bolt combo is stupidly tight and i had NO weight on my at the time (i use a digital angle meter to get it almost spot on) and i was at my limit of pushing harder for fear of stripping thred or bending the little twistie handle.

on the up side unless your going 10's of km's away from your normal viewing sight, its going to be pretty much the same every time.

[DJDD]

Hi Brendan,

yes, it is insanely tight (especially the back bbolt), even without weight.
I probably will not be going anywhere with the mount, although, is something astronomy-related is happening around melbourne over the long weekend I might have to go there. An inclinometer (?) would be useful.

cheers,
DJDD

[bmitchell82]

In the tool section in bunnings, its a little cube about 50mm x 50mm by 25mm, you can measure absolute angle or set a referance angle and then measure from that, also has a level feature and will tell you which side is up which side is down. 39 bucks :D

I still keep in handy the level to get rough guide straight up but then use that to get it dead eye d1ck! and its correct to the 0.1 degree aka, 32.01 deg :P yay

basis is that it uses a accelorometer (i think it is) and the gravity moves some liquid or something inside (its a jesus box) and gives a output in Degrees.

[TrevorW]

Did you find the EQ6 scale to be out by much

[bmitchell82]

I cant say that i have really taken too much notice of it all. but i from memory, its pretty accurate. Definately not something you could set grenich mean time on :D but it will land you somewhere in the ball park

[ozstockman]

Hi DJDD,

Be very carefull with these screews. I wasn't and I bent one of them. Then when I was trying to to get it out for replacement (http://www.axio35.dsl.pipex.com/astrodev/Synta%20cables.htm) I stripped a thread. As a result I had to buy Keysert Key Lock Thread Inserts just to repair the stripped thread first.

cheers,

Mike

[DJDD]

Thanks, ozstockman.
I will be sure not to eat any vegemite or weatbix before-hand. :lol:

cheers,
DJDD

[bojan]

The problem with latitude screws (especially back one) is that they are not ending perpendicular to the surface of internal post which they are supposed to hold in place. The front one is not loaded much (for our latitudes that is.. because the the centre of gravity is well in front of the vertical axis of the mount. It has to be tightened a bit just to keep the whole thing not moving, but in principle we could live without one)... (see drawing attached).
The result of this is the screw is skewed and the thread is under stress downwards (looking from inside of mount), which results in bending or even damaging thread(s) as a worst case.

My solution to this problem-issue was two-fold:
- Replaced original screws with M10 high tension screws (shortened such that they do not protrude more than 15mm from the mount, I do not intend to travel to the equator or Pole so I do not need them to be un-necessary long.
- I added counter nuts and spring-loaded washers, which hold the screw perpendicular into its threaded hole.
- Installed high sensitivity bubble-level (instead of crappy one, supplied by Sinta), so that I adjusted the screws only once. From now on the latitude I adjust by levelling the whole thing with bubble-level, by inserting plastic wedges under two legs (those things that go under the door to keep them open), or simply by placing the mount always in the same place, in the three water-pipe tubes hammered into the ground (later I plan to do it properly by making three concrete slabs, one for each leg.. before I build the concrete pier.
There is no need to align the mount every evening if I use the same observing spot (in the corner of my backyard). Small errors in alignment from night to night (which are smaller than overall PE BTW) will be taken care of by auto-guiding anyway.

EDIT:
At some stage I will re-design the elevation mechanism by welding much thicker post. This will inevitably reduce the mount ability to adjust for any latitude.. but this is not important at all.
Also, I will use M12 screws, driven into steel threaded nuts, inserted from inside of mount, so that there will be no thread into aluminium (very bad idea, Sinta..)

[ozstockman]

My EQ6 scale is 2 degrees off. It shows almost 40 while the gauge displays 37.80. I'm using the same angle gauge device with only difference that I've bought mine from ebay. Found them after that in bunnings for the same price I paid for mine.

[bmitchell82]

Mine is slightly more accurate than yours, though its still out by a bit, I know i set it to 32d00" now i know that my location is 31d52" (explains the edge of ep :) ) on the actual mount head its saying 30d50" approximately. Hence the digital angle meter is happy gets me right online.

Oz stockman whats your setup procedure?

-i have made a piece of wood that comes out from the headmount using the location pin for the head mount to get my bearings for true south

-raise the legs 50mm, put the bubble level on 3 different angles associated with the legs, then put the DAM to get it right on.

-Put the head mount on and shoot a level for the Dec of 31.52 degrees

-scope on power up drift align

-3 star align then go for it?

[DJDD]

Thanks, bojan. your technical info is welcome.
After reading ozstockman's and your replies have made me wonder about 'replacing' the aluminium thread as you mention. Spring loaded washers sound like the go, as well.

brendan, is the difference of 8 minutes noticeable in images or will further drift alignment for latitude be required?

cheers,
DJDD

[bmitchell82]

Im not imaging yet, though it places the object on the edge of my ep. Drift aligning will eliminate this problem to some extent, and further accurate initial alginment.

As for your screws and what not unless you are changing them all the time i don't see a major issue with leaving as is. if your that worried about it you can but untill it presents a major issue i will be leaving mine as is.

I see where bojan is coming from but i would more likely suggest that the cutting of the teeth was extremely tight, as when i lay the head unit on its side, both screws are tight and they don't have any weight or stress on them.

[bojan]

Brendan,
When you un-fasten the screws and then leave your mount lay on the side, are the screws tight then?
Mine were not - they were actually reasonably loose, as it should be expected of tapping properly done.
Then, what I saw as a potential problem was the fact that adjustment of the screw that was pressured by the mount under load (back screw) was changed with tightening of the opposite one, which should not happen and what I saw as a clear indication that the screws are not perpendicular to the surface of the post, so they were stressed radially, with the potential of damaging the threads by load weight (and even bending the screws under load.. remember, there is potentially 50 kp of load (telescope + counterweight) on one side of the the 200mm lever, held by that screw only 50mm away from pivot point.. which means more than 200kp load on post and screw thread.. a lot, especially if you have additional lateral stress.
So I decided to stiffen the whole thing a bit by adding the nuts. I simply like to have details done properly, no matter how simple or complicated they are

[bojan]

As for handles on latitude scale you can do something like this (vernier):
http://groups.yahoo.com/group/EQ6/photos/album/1030565234/pic/532520954/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc
However, I do not see the point.. polar finder is much, much more accurate, and as said before, once you adjusted the latitude, there is no need for re-adjustment if you have good bubble level.

[bmitchell82]

Yes they are still tight, im very handy with a spanner, and i know that they are too tight to be normal. Considering that we all brought our mounts within the last few months ide say they are the same batch. Im not too fussed as at most im only going to have to give it a few turns or a bit of a tweak here or there. and if i notice that the thred is being damaged its not a great deal of worry, as you can either tap it out again into a bigger thred (even a coarse thread though this might make fine adjustment harder) or resleave it with something like a SS thread.

What unit of measurement are you using bojan, kP is Kilo pascal, unit of pressure of fluids. Do you mean Newtons (N) (Force) or Newton meters (N.m)(Moment Force). and further more how did you measure the force, as you would have had to of known the angle of the bolt in relation to the perpendicular thus giving a moment force at the point of interation with the mount head. Damage could be caused to the thread but if you have loaded it up enough to do so then quite likely you have exceeded the manufactures load limits as it would be fracturing the cast alloy mount head as goes for the bolt.

I thought the reason why you would change it is the dickky little handle they give you bends like butter and has no screw/hex head to do your tweaking. and generally they give you a tougher material aka SS or Steel (stainless doesn't rust and looks all shiny)

In any rate relating kP to kN that would indicate this bolt would have in excess of 500kgs on it. and if it was just N would be 5kgs. I want to know as i might have missed something and have a chance to learn something new, but my knowledge i thought to be reasonably sound in this area as i am a student of civil engineering with my focus on Structural and lifting engineering in particular.

[bojan]

:-) I was using kiloponds, sorry :-)
Started with kg, and was lazy to change the numbers. That is the reason for confusion.
The force I estimated as a possible maximum... you have 25kg of telescope, 25 kg of counterweight and all that 200mm away - that is the rough distance of DEC axis from pivot point in the base of the mount. It reality it will be lower because the load will not be that much and second, the latitude angle is 37° so we have reduction of momentum here by factor of 0.8 (cos (37°)). However, I saw some people using EQ6 as alt-az mount, so it is a possibility.
The distance of where screw is in contact with the post inside mount is ~50mm. So the max net force to a screw is 3.2x the load [ (200mm x 0.8)/50 ]. That makes ~1400N on the single screw. Or, 142kg.

[bmitchell82]

sorry bojan, your rational still doesn't make sense, as if you have the telescope balanced it doesn't matter how much you put on it because the net moment force is 0 this classified as a static system if the mount can stay in a particular spot without moving then there is enough forces to cancel it out and make the sum of the net for = 0 N.

If manufactured correctly the bottom weight bearing bolt (what gives us our dec of 30 something degrees) should be perpendicular to the surface when the mount is at 0 degrees. if it is not then the measurement would have to be made. Problem with it staying perpendicular is that the actuall thread would have to pivot to mate the face at 90deg. In all fairness you could estimate the angle of deviation but that doesn't give you a "factor" amount. it will give you a definate force F or N.m.

Force is just the mass * gravity
N.m is Newtons * Meters

when you split things into right angle triangles all you are doing is giving a Force in the X and the Y direction as its extremely complex to be able to deal with a force in one direction.

So theres only one factor that you need to consider here, and that is in the Positive Y direction and if the bolt is capable of accepting such stress.

Also remember that any calculations that you are doing must be in standard SI units eg, Seconds Meters Kilograms, or you will have erronus results

first draw a FBD free body diagram making sure to split each area up to work out the net force transfered to each element, ending up with a foce amount placed on to the bolt in question. a quick split of the x and y components will see you with the amount of N applied in the Y direction and the of moment of inertia needed by the bolt itself to counteract this

[bojan]

Sorry for possible mistakes, I think I've made a few minor ones... But we are thinking in the same directions I would say.

So, lets go this way... and I will try to be more careful and exact with my calculations from now on :-)

A cross-section drawing of the mount is attached, and it illustrates my direction of thinking....
The mount on the sketch is set to 45° latitude, but I wanted to explore the worst case, which is 50kg of load (telescope + counterweight) and as used on equator.

If we assume the mount is used on equator, we have momentum (pivot point is latitude bolt) on the load side expressed as M1=F*D1*sin(alpha).
The angle alpha between D1 and F can vary from 75° (if we are on equator) to ~-15° (near pole.. then the load is on the other side of the pivot point, so I used "-" here).

This momentum is held in balance by M2= F2*D2. The angle between D2 and F2 is close to 90° for the purpose of estimating the axial force on screw, however the radial component is also present and significant since the screws are designed for axial component primarily and they can not hold much radial (side) force (they bend, or they damage the thread in the case of excessive force and if material is not thick enough) .
You must excuse my English here, I went to grammar school in Europe (non-English) and it was long time ago so the terminology I use here may not be quite right, but I am trying my best to make myself as clear as I can :-)

If we assume the worst case, that is the use of this mount on equator, D1 is at roughly 75° (discussed above) so we have load momentum M1= 98.1Nm*sin(75°) = 94.75Nm.

From the above, we have:
F2 = M1/D2 = 94.75Nm/.05m = 1895N


For our latitudes (~37°) this force will be lower, since the angle between D1 and F1 is ~20°, so F2 is around 650N [F2 = 1895N * sin(20°) = 648.128N] but still significant.

There is no force on screws for latitudes around 75° (if my estimate of 15° angle between D1 and F1 is correct).

I hope there are no more mistakes here :-)

[bmitchell82]

Kinda close but not really, tonight if i get a bit of time ill sit down draw some drawings and do a bit of measurements and calcs then you can see how it should work.

Ultimately you should have 3 diffrent Free body diagrams, using the worst case like you said and in our case would be at lower dec like myself which im close to 30 degrees.

[Shawn]

I have found this too yo be an issue, particularly at 17S, Now Im looking at the casting thickness and wondering why iy cant be drilled out to a reaonable sized fine thread, OK this doesnt change the sums, but a greater contact area would be better equiped to deal with it...TCW