Identifying various Screws, Bolts and Washers

One thing that I found a little confusing was that several of the washers intended for different purposes were contained in one bag, and even held together on one particular bolt, and it wasn't until after a bit of fiddling and experimentation, and reference to the parts list, that it became apparent what the purpose of each item was. So I think it's wise to familiarise yourself with some of these items first.

Bolts and WashersThe main Azimuth axis hex-head bolt (length 2.25 inches), and the Azimuth Bearing Brass Bush are shown in this picture.

The bolt can be seen exactly as it was shipped to me, with 5 washers slid onto it, followed by the lock-nut to keep everything safe.

At first sight I thought these were all intended for use on the azimuth bearing, but actually the 3 washers to the right-hand end are intended as spacers for the Vertical Stop, because they are different thicknesses and are used in combination to fine-tune the vertical alignment.

From left to right: 2 x Fender Washers (largest), 2 mid-size washers (for optional use on the Vertical Stop), 1 x small/thin washer (for optional use on the Vertical Stop).






Vertical Stop Knob and Spacing Washers

Vertical Stop BagLeft: This bag contains the Vertical Stop Knob, and the 5 circuit board mounting wood screws.

Vertical Stop WashersRight: the Vertical Stop Knob with its 3 washers.

I needed only one of the mid-size washers to make my OTA tube exactly vertical.





Eyepiece Rack and Carrying Handle

HandleLeft: The 4-Hole Eyepiece Holder Rack (3-hole on the XT6) has 2 x 3/4" wood screws in their own bag. If you do up the screws loosely in the slotted mounting holes, this allows the rack to be removed. Personally I prefer the rack permanently mounted, so did up the screws good and tight.

Right: The Carrying Handle with its 2 x Hex-head bolts and washers.


Rack and HandleBase On Its FrontTip: The Instruction Manual leaves the fitting of the Rack and the Handle until later, but I found it was better to fit them before the azimuth bearing and baseplates because it helps make the base more steady when laid on its front.

With the rack screwed into place this makes it more solid, and laid on its front it angles the base conveniently so that the Magnetic Disc can be sat upon the Brass Bush prior to inserting the bolt, and this in turn makes for much easier assembly of the brass bush, magnetic disc, and Ground Baseplate on the azimuth bearing. Doing it the way the manual suggests (on the floor, lowering the top baseplate onto the ground baseplate) is much more difficult!

This will become clearer in a moment, but the photo here shows the base laid on its front, resting on the bottom edge of the circular Top Baseplate, and the flat edge of the Eyepiece Rack (the left photo shows the final assembled base, with the triangular shaped Ground Baseplate held in place by the main Azimuth axis bolt).


Azimuth Axis Bolt Assembly Order

Bolts and WashersIn the photo to the right I have re-arranged the items to group them with their respective partners.

Top left is the Computer Controller Port circuit board with 4 of the encoder board mounting wood screws (small screws). The 5th of these screws (not shown) is used to mount the Azimuth Bearing circuit board (not shown).

Top middle is the Vertical Stop Knob, and the two mid-size washers.

Bottom shows the Azimuth Bearing Axis bolt, and the order that the parts go together, which is as follows:-

Bolt-> fender washer-> magnetic disc-> brass bush-> fender washer-> lock nut (ignore the last small washer, I got it wrong in this photo, it belongs with the Vertical Stop).


The following 3 photos show how the Magnetic Disc and the Brass Bush register together when the main Azimuth Axis bolt is passed through them. Notice that the hole in the disc is considerably larger diameter than the bolt (see left and middle photos).

Now pay attention to the slightly raised "notch" on the wider flange end of the Brass Bush (shown upside down) in the middle photo. This registration feature is exactly the same diameter as the hole in the Magnetic Disc, into which it is placed so as to make firm contact with the disc (right hand photo).

When the main axis nut and bolt are tightened, the pressure squeezes the Brass Bush down onto the Magnetic Disc, so holding the disc tightly against the upper surface of the Ground Baseplate. This ensures that the magnetic disc remains completely stationary against the ground baseplate (which sits on its feet, on the ground), while the telescope and Azimuth Encoder Board in the Top Baseplate rotate above the disc when the telescope is moved around.

Magnetic Disc Magnetic Disc and Brass Bush 


Attach the Azimuth Encoder Board

Now that you have an idea of how things slot together we can begin putting it all together.

Azimuth RecesAzimuth Encoder BoardThe Azimuth Encoder Board is offered up to the underside of the Top Baseplate, and its connector socket goes into the square hole, with the round hole of the circuit board lining up exactly with the central hole in the top baseplate.

One of the small size wood screws and washer are used in the pre-drilled pilot hole to hold the circuit board in position.

The screw should be done up just tight, be careful not to squeeze or crack the circuit board. The screw only needs to hold the board securely in position, because when the brass bush and main axis bolt assembly are done up, they will hold everything secure.



 Azimuth Encoder Board


Insert the Brass Bush

Now the Brass Bush can be inserted into the hole of the circuit board and pushed through the hole in the Top Baseplate. This is a very snug fit, and a very light coating of 3-in-1 oil on the brass bush will aid smooth rotation in the hole (keep oil away from the sensors, you don't want it attracting any dust).

Now you can see from the middle photo how the flange on the bush seats against the circuit board, and then the Magnetic Disc can be carefully placed upon the flange registration feature, which is possible due to the slight backward angle of the top baseplate laid on the work surface as described earlier.

Notice that it is the depth of this flange (middle photo) that ensures the critical distance is maintained between the hall-effect sensors on the circuit board, and the magnetic surface of the disc. Any changes to this critical gap may prevent the digital encoder from working properly! However it is this location that people are sometimes tempted to add "milk bottle washers" to make the central axis bear some of the weight of the scope so that the Teflon bearings have a lighter load so that the telescope can be rotated more freely. Just beware that this distance is crucial, and any additional washers should be added between the Ground Baseplate and the Magnetic Disc, not between the Brass Bush Flange and the Circuit Board.

With the Magnetic Disc carefully balanced on the Brass Bush (right photo), you are ready to put the whole assembly together.

Azimuth Bearing Brass Bush Azimuth Bearing Brass Bush Azimuth Bearing Brass Bush


Putting it all Together

GroundPlateBoltTake one of the Fender Washers and put it onto the long Azimuth Axis Bolt, then thread the bolt through the bottom (feet side) of the Ground Baseplate.





The Instruction Manual says that putting the top and ground baseplates together should not be done with them on their side, but I am suggesting otherwise. The reason the manual says this is because you risk the magnetic disc becoming dislodged from the brass bush registration feature while you do up the bolt.

As long as you understand why I am explaining this and the importance of getting it right, I believe doing it this way is easier, and a little more "hands free". I have dismantled and re-assembled the whole base several times over, and it is definitely a more simple approach.

However, if you prefer to follow the instruction manual exactly, please do so. I take no responsibility if you are too ham-fisted to get this part right!

Ground BaseplateMake sure you have two 7/16" wrenches handy for this part (or an adjustable spanner and some pliers). Fingers are not good enough because the nylon insert in the lock-nut makes a very good lock-fit!

Very carefully, so as not to knock the Magnetic Disc off the Brass Bush, offer up the Ground Baseplate and push the bolt through the bushing, then gently push the Ground Baseplate until it butts up against the Magnetic Disc. The best way to do this is to grasp the triangular baseplate with one hand at the bottom straight edge, fingers curled round supporting the bulk of its weight, with your thumb pressing the bolt head to keep it in place, and the other hand supporting the top corner, then standing in front and looking over the top gently and accurately guide the bolt into the brass bush.

NutIt all slots together very easily, there should be no need to force anything.

The bolt will protrude through the top baseplate where you can put the second Fender Washer, then the Lock-Nut, and then using the wrenches do them up, until just tight enough to stop the top Fender Washer moving freely.

VERY IMPORTANT: While assembling these and doing up the nut and bolt, do not let the parts become slack, because if you accidentally knock them, the Magnetic Disc might come off the registration feature on the Brass Bush, so you would have to take it apart again to put the disc back on properly. You must not tighten the bolt if the disc has slipped off, because there is a danger of distorting the disc or damaging the registration feature.

If you are happy with the initial tightening, and that the disc is properly seated on the bush, you can tighten the Lock-Nut just a further 3/16 to 1/4 turn beyond that to give it a little bit of torque. This ensures proper spacing between the Magnetic Disc and the Azimuth Encoder Board. Do not overtighten.

As long as you are steady and careful this procedure is quite easy (this method is certainly easier than attempting to do it on the ground as described in the manual, when you need 3 hands to hold everything together, and keep the bolt held in place, and try holding the wrenches to do up the nut/bolt).

Gaps That Go Clunk In The Night

Another small point: Look carefully at the right hand photo above of the Lock-Nut, and you will notice a gap where you can see the top end of the Brass Bush showing between the upper surface of the Top Baseplate and the Fender Washer. This gap is about 4mm, and deliberately allows some play between the parts. They are NOT supposed to be tight together. However this gap explains why you might hear a "clunk" when you pick up the dobsonian base, because the Ground Baseplate will drop by those 4mm before the washer and nut take the weight of the ground baseplate as you lift it. This might be a little disconcerting at first, but there is nothing wrong. Simply lift it more gently!

Be warned though! If you decide (like I did) to add a nylon washer between that gap to lessen the clunk sound, make sure the washer is not so thick that it takes up all the slack or more, because then when you tighten the nut down it could actually start to squeeze the Top and Ground baseplates together. This can have two detrimental effects, which I learned by experience;

  1. Stiction: It will create a turning friction because the washer will act like a clutch-brake against the top baseplate. This will increase the likelihood of "stiction" causing jerkiness when rotating the telescope, and at high eyepiece magnifications this is a most annoying problem.
  2. Incorrect Sensor Readings: It could squeeze the magnetic disc, brass bush, and circuit board assembly together and this could affect the critical gap between the disc and the sensors, so causing inaccuracy in the digital readings or preventing them working properly altogether.

Critical Gap


Fitting the Carrying Handle

For completeness the following photos show the Carrying Handle being bolted into position. I placed the washers, then did the bolts up good and tight with the thought that the handle is intended to carry the weight of the telescope.

HandleHandle BoltsTo be perfectly honest with the XT10 the handle is really more of a decorational feature than functional. Maybe the XT8 or XT6 scopes are more manageable, and can be lifted by the handle, but the XT10 is so hefty it is very difficult to lift as one complete unit by the handle - I tried and nearly broke my back!

I much prefer to do it in two more manageable and safe trips.

First I undo and lift the OTA off the Dob base, and set it aside on the ground.

Then I lift the base and carry it to its viewing location.

I find it more convenient to carry the base by putting my hands through the openings in the side panels, than by using the handle.

Then I return for the OTA and carry that out and carefully place it back in the waiting base, straightaway screwing the Altitude Tensioning Knobs back in to secure the OTA to the base again.


Vertical Stop Knob

Handle BoltsThis photo shows the bolts of the handle on the inside of the front brace board.

In the middle can be seen the Vertical Stop Knob which the bottom end of the telescope tube butts up against when vertical.

The intention of the Vertical Stop Knob is to ensure the tube is exactly 90 degrees from horizontal as taken from the horizontal surface of the Top Baseplate, and this fact is used during the first step of alignment for the IntelliScope Computer Object Locator.

For now, simply screw the knob into place with all its washers. After the telescope is fully built you will make the "one time" adjustment for proper vertical setting.








Next section: Assembling the Altitude Bearing and IntelliScope Altitude Sensor

Other Topics in the Assembly section: