Losmandy G11 DEC Axis Upgrade — No Motor

Product Overview

This is the G-11 declination axis sold on its own, as an upgrade for a GM811 mount. Fitting it puts the 5.625-inch, 360-tooth G-11 gear on DEC alongside the G-11 gear already on RA, which turns a GM811 into a mount running the large gear on both axes. It ships with the spring-loaded worm installed. No motor is included — the GM8 DEC servo motor already on your mount transfers across.

Who It's For

This is the second half of the GM811 story. A GM811 already carries a G-11 RA axis against a GM8 DEC, which is the right way round if you are buying one mount: periodic error shows up in right ascension, where the sky is actually moving, and DEC only has to hold position between guide corrections. Fitting the G-11 DEC afterwards is what you do when the mount has earned its keep and you would rather carry more instrument than change mounts.

Key Features & Design

• 5.625-inch, 360-tooth 7075 aluminium worm gear — the full G-11 gear, in place of the GM8's 2.8-inch, 180-tooth.
• Spring-loaded worm, installed. The spring maintains mesh, so there is no worm adjustment to set after fitting.
• Dual-supported, ball-bearing-housed stainless steel worm, heat treated and ground.
• One 3.75-inch and one 2.00-inch thrust bearing plus two 1.50-inch needle bearings, as on any G-11 axis.
• 1.25-inch centreless-ground stainless steel shaft.
• Clutch rather than a lock — you set the friction you want and move the telescope by hand.
• Motor not included. The existing GM8 DEC motor fits the G-11 DEC.

Mechanical Design

Gear diameter and tooth count set how fast the worm has to turn for a given rate of sky motion. A 5.625-inch gear with 360 teeth turns slowly, so any single tooth error contributes a smaller angular movement than the same error on a 2.8-inch, 180-tooth gear would. In declination that matters less than in RA, because DEC is not tracking — but it matters for load. The larger gear, the larger thrust bearing and the heavier shaft are what carry a longer, heavier instrument without the axis flexing between guide corrections.

The spring-loaded worm is the part worth understanding. On a fixed-mesh worm, backlash is taken out by moving the bearing blocks closer to the gear and then living with whatever high spot the gear has. A spring holds the worm against the gear through the full revolution instead, so mesh stays constant and there is nothing for the owner to set.

Recommended Uses

Converting a GM811 to G-11 gearing on both axes. Carrying a heavier or longer instrument in declination than the GM8 axis was sized for. Building a second head from spares, alongside the G11 RA axis. Replacing a damaged G-11 DEC axis.

Compatibility and Accessory Notes

• Fits: GM811 mounts, as the DEC half of the pair. It is also the replacement DEC axis for a G-11.
• Motor: your existing GM8 DEC motor attaches to this axis. If you would rather keep the old axis complete and motorised so you can swap between configurations, a second motor is the way to do it — send us your mount's vintage and drive type and we will confirm which one it takes.
• Motor coupling: the G11 motor-to-worm coupling is the part that joins motor to worm on a G-11 DEC or RA axis.
• Spacing between axes: Losmandy sells this axis with spacer and RA-extension options depending on whether your mount already has an RA extension fitted. We stock the G11 RA extension dovetail and the RA extension kit — tell us what is on the mount now and we will work out which piece you need.
• Clutch knobs: the clutch knob set fits the new axis if you want the handled knobs.
• Saddle: the G-11 saddle plate takes both Losmandy D-series and Vixen-style V-series dovetails. We stock the D-series universal plates in 14", 19" and 24" lengths.

Good to Know Before You Order

• No motor in the box. The upgrade is designed around reusing the motor already on your DEC axis.
• Which adapter you need depends on your mount as it stands today — specifically whether an RA extension is already fitted. This is the one detail worth settling before ordering; send us a photo of the mount between the axes and we will tell you which piece to add.
• The worm arrives spring-loaded and set. Fitting is mechanical assembly, not gear timing.
• Specifications are Losmandy's published figures for the G-11 axis.

Frequently Asked Questions

Is it difficult to set up?

It is a bolt-together job rather than a rebuild: the DEC axis comes off, the new one goes on with the appropriate spacer or extension piece, and the motor moves across with its coupling. Nothing inside the axis needs adjusting, because the spring-loaded worm arrives set.

What does this actually change on the mount?

It puts the large G-11 gear on declination. On a GM811 that means both axes then run the 5.625-inch, 360-tooth gear rather than only RA.

Do I need a new motor?

No. The existing GM8 DEC motor fits. A second motor is only worth buying if you want to keep the old axis motorised for quick swaps.

Can I go the other way?

Yes — the GM8 DEC axis is the same part in reverse, for putting the lighter DEC on a G-11.

Will my dovetail plates still fit?

Yes. The saddle interface is unchanged, and D-series and V-series plates fit as before.

Bottom Line

In short: the G-11 declination axis on its own, spring-loaded worm installed, motor not included — the part that takes a GM811 to the full 5.625-inch, 360-tooth gear on both axes.