Mechanical installation and polar alignment
In this chapter
- 3.1 Installation preparation
- 3.2 Install the tripod or pier
- 3.3 Install the mount
- 3.4 Install the telescope and accessories
- 3.5 Payload and counterweight setup
- 3.6 Latitude and azimuth adjustment
- 3.7 Polar alignment
- 3.8 Cable routing and movement clearance
3.1 Installation preparation
Choose a support that remains stable with the mount, telescope, accessories and counterweights installed. Its rated payload alone does not establish stability: height, leg spread, ground firmness and off-center load also matter.
Prepare the correct mounting screws, compatible adapter or extension, and manually operated hex keys. Inspect threads, clamp surfaces and dovetails. Identify the coarse latitude setting before adding the optical payload.
Carry the mount by supporting its body. Keep hands clear of adjustment joints. A mount set away from the vertical position can tip when left unsecured on its base; hold it until it is attached to a stable support.
Do not grip, squeeze or lift the mount by the black cylindrical section between the mount body and the base. Pressure on this section can deform it and impair its dust protection. Support the mount by its solid body and base instead, keeping clear of adjustment joints.
3.2 Install the tripod or pier
For heavy imaging setups, prefer a suitably anchored fixed pier or a rated folding pier with a rigid top plate and secure joints. A carbon-fiber tripod's mass rating alone does not establish stiffness: leg extension, joints and platform flexure can affect vibration settling and guiding. Keep extensions low and assess rigidity with the complete equipment installed.
Keep the complete setup's center of gravity inside the support footprint throughout telescope travel, including on both pier sides and at Park. An off-center load or raised extension can overturn the support. Use a suitable counterweight arrangement where it improves load distribution, and recheck stability after adding each weight. Counterweights also increase total load and cannot compensate for an unsuitable footprint or insecure footing.
Support examples
Support and adapter structures are illustrative. Confirm the actual support's fit, mounting hardware and load rating for your setup.
Set up the support
- Set the tripod on firm ground, spread the legs fully as specified by its manufacturer, and secure the spreader and leg locks.
- Keep the center column low where possible. Level the mounting platform.
- If using a pier, check its base attachment and top plate.
- If using an extension, attach and secure the extension to the support before placing the mount on it. Check both joints independently.
- Check that the telescope and camera will have sufficient clearance from the support through the intended travel.
An extension can improve clearance but increases the height of the load. Reassess stability after installing it.
3.3 Install the mount
Inspect the underside of the mount base to identify the connections. The current WD-20E drawing shows a central 3/8-inch attachment and three M6 mounting holes, spaced 120° apart. For heavy loads, use the three-point M6 arrangement with a compatible adapter, rather than relying on a single central attachment. Secure all three mounting points; do not substitute one M6 screw for the complete arrangement. Select screw length and engagement for the actual adapter and mount.
The screw's insertion depth into the mount base must not exceed 10 mm, for either the central 3/8-inch connection or the M6 mounting arrangement. Excessive insertion can damage the base or jam the mechanism. Select screw length for the actual adapter thickness and any specified washers: insertion depth is the portion entering the base, not the screw's overall length. Use compatible hardware with sufficient engagement within this maximum; do not force a screw that bottoms out.
- Confirm the adapter is designed for the WD-20E hole pattern. Check each screw's length and its resulting insertion depth into the base: 10 mm maximum.
- Position the mount on the adapter while supporting it continuously.
- Start the screws by hand. If a screw does not turn freely, remove it and check alignment and thread compatibility.
- Secure all required fasteners with the correct hand tool. Follow the adapter's tightening instructions.
- Check for rocking, loose joints and interference with the azimuth mechanism.
Current WD-20E drawing. Open the full-resolution PDF for dimensions and thread positions. All dimensions are in millimeters.
3.4 Install the telescope and accessories
Keep the telescope supported until both saddle clamps are secure. Do not use the mount's motors to compensate for a partly engaged or unsecured dovetail.
- Complete the coarse latitude setting before installing the telescope.
- Check the dovetail is a compatible Vixen or Losmandy profile and its own attachment to the telescope is secure.
- Loosen the two saddle clamp knobs enough to seat the dovetail in the appropriate channel.
- Place the dovetail fully in the channel. Keep the telescope supported, with adequate plate engagement on both clamps.
- Tighten both clamp knobs by hand and verify that the plate cannot lift, rock or slide.
- Position the optical assembly so its center of gravity and accessory clearance are suitable. Support it before loosening the clamps for any repositioning.
- Fit the camera, guider, focuser and remaining accessories. Recheck payload assessment and clamp security after the final configuration is installed.
Use compatible plate stops or retention features where available. Do not assume that a clamp can securely grip a nonstandard dovetail because it looks similar.
3.5 Payload and counterweight setup
Include the entire telescope assembly: tube, rings, dovetail, camera, filters, focuser, guide equipment and attached hardware. Check both the published mass limit and the torque produced by the actual center-of-gravity offset.
For a static estimate of gravitational torque:
Torque (N·m) = mass (kg) × 9.81 × perpendicular lever arm (m)
= mass (kg) × 0.0981 × perpendicular lever arm (cm)
Use the worst relevant orientation. The lever arm is measured from the RA axis to the load's center of gravity, not just from the top of the saddle.
| Example | Approximate RA torque |
|---|---|
| 10 kg at 25 cm | 24.5 N·m |
| 20 kg at 25 cm | 49.1 N·m |
| 20 kg at 30 cm | 58.9 N·m |
These examples explain why a light but bulky telescope can place a substantial load on the drive. Keep normal operation within 50 N·m recommended, and never exceed 60 N·m maximum. Also respect the published mass ratings and support-system limits.
Manufacturer load-geometry reference: L1 is measured from the dovetail plane; L2 is measured from the RA axis. Torque-derived values in the illustration do not override separate mass, bearing, tripod or brake constraints.
Counterweights
The shaft connection is M12 × 1.75. Use a compatible shaft and weights with suitable locking and end-retention hardware. Attach the shaft securely, install each weight while supporting it, and fit/check the end stop before operating.
The combined counterweight mass must not exceed 10 kg. This limit protects the M12 shaft-attachment thread from damage and applies independently of payload mass and net RA torque. If several weights are fitted, add their masses together. Do not add more than 10 kg to obtain a favorable torque calculation; instead reduce the optical load or its offset, or reposition the telescope safely.
A counterweight on the opposite side can reduce net RA torque. It also adds weight, inertia and another collision path. For a static estimate, subtract opposing torque from payload torque and consider the magnitude of the resulting torque across the working orientations. Do not use the subtraction to justify an arbitrarily large total load.
The RA brake is rated at 45 N·m, below the 60 N·m maximum powered torque. A load acceptable for powered slewing may therefore be unsafe to leave unbalanced when power fails. Arrange the load conservatively, use suitable counterweights where necessary, and support the equipment before power-off, removal or servicing. Do not depend on uninterrupted power as the sole safeguard.
Counterweight-free operation does not remove the need to assess tripod tipping, wind loading or equipment retention. Recheck the complete arrangement after changing a camera, adding a guide scope or moving the dovetail.
Estimate your setup
Enter the complete optical payload and the perpendicular distances from the RA axis to the corresponding centers of gravity. If several counterweights are used, enter their combined mass (10 kg maximum) and mass-weighted mean lever arm. Evaluate the worst relevant orientation; the estimate assumes the counterweight torque directly opposes the payload torque.
WD-20E static RA torque estimator
Example values are editable. Use actual measurements in the worst relevant orientation. All distances are perpendicular lever arms from the RA axis, in centimeters.
- Payload torque
- 24.5 N·m
- Opposing counterweight torque
- 0.0 N·m
- Residual RA torque (magnitude)
- 24.5 N·m
- Load direction
- Payload side
- Optical mass: Within the published 22 kg rating for operation without counterweights.
- Powered torque: Within the 50 N·m recommendation for this static estimate.
- RA brake: Below the 45 N·m holding rating in this static estimate; this does not confirm safe load holding.
Added counterweight mass: 0.0 kg. Include the mount, shaft, adapters and all equipment when checking the support's load rating.
This estimate covers opposing static gravitational torques only. It does not assess tripod tipping, inertia, wind, stiffness, cable drag, bearing loads or clearance, and does not certify a setup as safe. Respect every independent mass, torque and support limit.
3.6 Latitude and azimuth adjustment
The full 0–90° latitude range is divided into three coarse positions. Each position provides 30° of fine adjustment, with a small overlap between adjacent ranges. Set the polar-axis elevation approximately to the absolute value of your observing latitude for GEM use; aim toward the north or south celestial pole as appropriate.
Coarse latitude setting
Choose the coarse position whose 30° fine range includes the observing latitude. The small overlap between neighboring ranges allows a suitable position to be selected near a range boundary. Do not try to cover the entire 90° range using the fine adjuster alone.
Remove the telescope and attached loads before loosening the coarse range fastener. Secure the mount to its support and hold the body so it cannot drop when the range mechanism is released.
- With the telescope and attached loads removed and the mount secured to its support, identify the range-setting fastener and access opening. Support the body and slightly release both latitude locks. Turn each lock counterclockwise when viewed from its own outer end.
- Use the fine adjuster, within its available travel, to bring the range-setting screw hole fully into alignment with its access opening. Align the holes completely before unscrewing or reinserting the range-setting screw.
- Use a correctly fitting manual hex key to remove the range-setting screw while keeping the body supported.
- With the body supported, select the appropriate coarse position and align the screw hole and access opening completely again.
- Start the screw by hand and screw it fully in and secure it. Stop if it does not engage freely; do not force misaligned threads.
- Secure the latitude locks and check that the range setting is stable before adding the telescope.
Misaligned holes or partial screw engagement can damage the threads or leave the range setting insecure. Keep the body supported throughout the coarse-range change. After selecting the range, ensure the range-setting screw is fully screwed in and secured before moving or carrying the mount, commanding axis motion or adding the telescope. Do not operate the mount with that screw partly inserted.
If access or engagement is unclear, stop rather than forcing the screw.
Latitude fine adjustment
One full turn of the latitude fine-adjustment handle changes the polar-axis elevation by approximately 1°. This is an approximate adjustment guide; use the polar-alignment measurement for the final result. The available fine travel is 30° in each selected coarse range.
For routine fine adjustment, generally leave the latitude-lock handles locked. This avoids disturbing polar alignment when the handles are loosened and tightened again.
For a latitude correction greater than 2°, release the latitude-lock handles before turning the fine adjuster to avoid adjustment-screw wear. Secure the handles after the correction and remeasure polar alignment. Stop if you encounter unexpected resistance; do not force the mechanism.
Do not keep turning with force after the fine adjuster reaches the end of its travel; this can damage the adjustment mechanism. If the required latitude is outside the available range, stop, remove the optical load and follow the coarse latitude setting procedure to select another range. Never force the fine adjuster to extend its 30° travel.
- Determine the correction required from your polar-alignment method.
- Generally keep the latitude-lock handles locked for routine fine corrections. If the required correction is greater than 2°, release them before adjusting.
- Turn the fine adjuster gradually while watching the polar-axis position or alignment result.
- If you released the latitude-lock handles, secure them again. Remeasure alignment after the correction.
Viewed directly from the fine-adjustment handle end, clockwise rotation raises the polar-axis elevation; counterclockwise rotation lowers it. Verify the response with a small movement on your hardware before making a large correction.
The arrows show direction, not a required adjustment amount. For routine fine corrections, generally leave the latitude locks locked; release them before corrections greater than 2°, as described above.
Azimuth fine adjustment
The azimuth fine range is ±8°. One full turn of an azimuth fine-adjustment handle changes the azimuth by approximately 1°; use the alignment measurement for the final correction. First aim the entire support sufficiently close to the celestial pole that the fine mechanism can complete the correction. Do not force an adjuster beyond its travel.
- Slightly loosen the azimuth locks. Do not remove them.
- Back off the opposed adjuster on the side that must provide clearance.
- Turn the other adjuster gradually to move the base in the desired direction.
- Bring both adjusters into suitable contact without forcing them against each other.
- Secure the azimuth locks and recheck alignment.
The direction diagram identifies the two opposed adjusters as A and B. Read each knob's clockwise/counterclockwise direction from that knob's outer end; read the mount's azimuth rotation from above.
| Desired mount rotation, viewed from above | Back off first | Then advance |
|---|---|---|
| Counterclockwise | B counterclockwise | A clockwise |
| Clockwise | A counterclockwise | B clockwise |
If an adjuster requires unexpected force, stop. Check the lock and opposed screw before continuing. Excessive force can wear or damage the mechanism and shift the installation.
3.7 Polar alignment
Polar alignment physically aims the RA axis at the celestial pole. It is different from synchronizing coordinates, centering a target, finding Home or parking.
- Confirm GEM mode, approximate polar-axis direction and latitude, and correct observing data.
- Choose a supported plate-solve polar-alignment routine or another established alignment method for your equipment.
- Before any software-controlled rotation, inspect the required travel, cables and safety limits. Choose a routine whose travel is clear.
- Follow the routine's image capture and solving steps. If a solve is implausible or motion is unexpected, stop and investigate.
- Apply the requested corrections with the mechanical latitude and azimuth adjusters, not with ordinary GoTo or Sync.
- Secure any adjustment locks you released and repeat the measurement; routine latitude fine corrections generally leave the latitude-lock handles locked. Aim for a measured polar-alignment error below 2 arcminutes (2′), and verify it with a fresh pass.
- Confirm Home/pointing state as required by your controller before returning to normal GoTo operation.
In the northern hemisphere aim toward the north celestial pole; in the southern hemisphere aim toward the south celestial pole. A compass is only a rough orientation aid, because magnetic north and true north differ and nearby metal can affect the reading.
Optical-tube center of gravity and polar-axis stability
The latitude-adjustment mechanism uses a low-clearance design. Its latitude-lock handles primarily prevent loosening and rocking; they are not intended to provide the entire gravitational support for the optical tube assembly (OTA). Tightening them harder is not a substitute for arranging the load correctly.
A heavy OTA can shift the load's center of gravity toward the front or rear of the mount as the axes rotate. This changing load can move the latitude mechanism and affect polar-axis stability, even if alignment was correct at the initial position.
Best practice: reposition the OTA on its dovetail, with the telescope fully supported while the clamps are loosened, so its center of gravity remains toward the front of the mount through the intended observing positions. If needed, use compatible counterweights to keep the combined load's center of gravity toward the front and reduce front-to-rear load changes. Counterweights change the combined center of gravity, not the OTA's own center of gravity. Respect the 10 kg maximum combined counterweight mass, RA torque, brake holding, support stability and clearance limits.
After securing the load and latitude locks, check polar alignment at more than one representative axis orientation using clear, supervised movement. If alignment shifts, correct the load position or counterweight arrangement and repeat the measurement; do not simply apply more force to the lock handles.
Recommended camera-based methods
Use a plate-solving polar-alignment routine where your camera and control platform support it. Focus first, confirm a reliable solve, and follow the chosen routine's tracking and rotation requirements. Ordinary plate solving and Sync calibrate pointing; a dedicated polar-alignment routine measures the physical polar-axis error.
| Platform | Method | Practical check |
|---|---|---|
| N.I.N.A. | Three Point Polar Alignment plugin | Configure camera/optical parameters and a working solver; inspect the complete RA sweep before starting. |
| StellarMate / Ekos | Polar Alignment Assistant | Set a clear rotation direction and travel; use the refreshed plate-solving error during mechanical correction. |
| ASIAIR | Polar Alignment workflow in the ASIAIR user manual | Verify solving in Preview, then follow the alignment workflow and refresh the error while adjusting the base. |
Two passes and fresh measurements
For this WD-20E workflow, aim to finish each live fine-adjustment pass within about two minutes, once the routine has acquired its reference measurements. This is a practical adjustment target, not a two-minute limit on focusing, initial capture, solving or the complete software procedure. Do not rush the mechanical checks or force an adjuster to meet the target.
Avoid continuing a prolonged adjustment against an old reference. Tracking drift and changes in the observed field can affect the displayed correction; if a pass takes much longer, restart the measurement for a fresh fine pass. The N.I.N.A. plugin's FAQ also recommends a fresh pass when final adjustment takes a long time.
Complete two independent measurement passes: use the first to make the main correction, secure any locks you released, then start a fresh second pass to verify the residual error. Correct any meaningful change and recheck after the correction and any necessary relocking. Repeatedly viewing the same unrefreshed result is not an independent verification.
The high-precision RA encoder measures and corrects RA-axis rotation; it cannot correct a physically misaligned polar axis. A large polar-alignment error can produce slow tracking drift even when RA rotation is accurately controlled. Aim for a measured polar-alignment error below 2 arcminutes (2′), then verify with a fresh second pass after locking and check for changes as the load rotates. This recommendation is not a guarantee of guiding or exposure performance; focal length, seeing, flexure and guiding conditions still matter.
3.8 Cable routing and movement clearance
Anchor cables so connector ends are not carrying their weight. Provide a controlled service loop for each moving axis, keeping cables away from saddle clamps, adjustment joints and the tripod spreader.
Route the loops so neither axis winds a cable around the mount, counterweight shaft or support. Check both slew directions, both pier sides, Home and Park; a loop that is clear at the starting position may tighten later. Secure the cable on the stationary side and leave the moving section enough slack to flex without wrapping or pulling on a plug.
Avoid large or repeated rotation of the DC plug relative to its socket during mount movement. Route and secure the power lead close to the stationary mount body so movement is absorbed by a controlled loop, rather than twisting the connector. Relative rotation or side loading can cause intermittent power contact. With power off, check full seating and strain relief; if movement produces dropouts, correct the routing or replace a damaged cable before continuing.
Inspect all of the following:
- Camera, focuser and filter-wheel clearance near the tripod/pier.
- Telescope and guide-scope clearance at either pier side and near Home.
- Counterweight shaft, weights and end-stop travel.
- Cable slack during slewing, guiding, homing, parking and a meridian flip.
- The actual planned Park position and any movement used for AEB Auto Tune.
For a first powered check, use short, low-speed commands and remain at the mount. Stop before reaching uncertain clearance. Revise the physical arrangement and safety limits before increasing the tested travel.
Do not use a telescope striking the tripod to test EC HA Limit or AEB. A protective response occurs under specific conditions and does not guarantee that a collision will cause no damage.