Losmandy GM8 DEC Axis Upgrade — No Motor

Product Overview

This is the GM 8 declination axis sold on its own. Losmandy lists it as the part that converts a G-11 to GM811 configuration — the lighter 2.8-inch, 180-tooth DEC axis paired with a G-11 RA — and as a straight replacement or spare GM8 DEC. It ships with the spring-loaded worm installed and with the convertor cone for attaching a GM8 DEC to a G-11 RA. No motor is included; the servo motor from your existing axis transfers across.

Who It's For

The GM811 configuration exists because of where periodic error shows up. Tracking happens in right ascension, so that is where a large, slow-turning gear earns its cost; declination only holds position between guide corrections, so a smaller gear there costs little in performance and saves real weight. Putting the GM8 DEC on a G-11 RA is how you get most of the G-11's tracking behaviour on a head roughly seven pounds lighter.

Key Features & Design

• 2.8-inch, 180-tooth 7075 aluminium worm gear.
• Spring-loaded worm, installed — mesh is held by the spring, with nothing to adjust after fitting.
• Dual-supported, ball-bearing-housed stainless steel worm, heat treated and ground.
• One 2.10-inch and one 2.00-inch thrust bearing plus two 1.50-inch needle bearings.
• 1.25-inch centreless-ground shaft.
• Convertor cone included for G-11 RA to GM8 DEC attachment.
• Motor not included. Your existing DEC servo motor fits.

Mechanical Design

The gear is smaller than the G-11's, and that is the whole point of it. Diameter and tooth count drive both weight and the angular size of a tooth error. In declination the mount is not tracking, so the tooth-error argument that justifies a 5.625-inch gear on RA largely falls away, while the weight saving is immediate and permanent — it applies every time the head goes on the tripod.

The worm is spring-loaded, which is what keeps the pairing honest. Mesh is held against the gear through the full revolution by the spring rather than set by moving bearing blocks, so a mixed-gear head does not need the owner adjusting one axis differently from the other.

Recommended Uses

Converting a G-11 to GM811 configuration to save head weight. Replacing a damaged or worn GM8 DEC axis. Building a GM811 from parts alongside the G11 RA axis. Keeping a spare motorised DEC axis for quick swaps between configurations.

Compatibility and Accessory Notes

• Fits: GM8 and GM811 mounts as a replacement DEC axis, and G-11 RA axes as the DEC half of a GM811 build — the convertor cone for that attachment is included.
• Motor: your existing servo axis motor attaches to it. A second motor is worth adding only if you want both DEC axes left motorised so you can swap in minutes.
• Motor coupling: the GM8 motor-to-worm coupling joins motor to worm on the GM8 DEC and RA axes.
• RA extension: Losmandy offers quick-release RA extension options for swapping between a G-11 and a GM811 without tools. We stock the G11 RA extension dovetail and the RA extension kit.
• Saddle: the GM8 saddle plate takes Losmandy D-series and Vixen-style V-series dovetails and also fits Takahashi mounts.

Good to Know Before You Order

• No motor in the box. The upgrade assumes you are moving the motor from the axis you are replacing.
• This is the lighter axis, not the stronger one. Fitting it to a G-11 trades declination gearing for head weight. If you want the opposite move, the G11 DEC axis is the part.
• The convertor cone for G-11 RA attachment is included, so a GM811 build does not need it ordered separately.
• Specifications are Losmandy's published figures for the GM 8 axis.

Frequently Asked Questions

Is it difficult to set up?

No. The old DEC axis comes off, this one goes on with the supplied cone where needed, and the motor and coupling move across. The spring-loaded worm arrives set, so there is no mesh to adjust.

Why would I put a smaller gear on my G-11?

Weight. Declination is not tracking, so the large gear does less work there than it does on RA, and the GM8 axis takes meaningful weight off a head you have to lift onto a tripod.

Does it come with the cone for a G-11 RA?

Yes — Losmandy supplies the convertor cone for the G-11 RA to GM8 DEC attachment with this axis.

Can I swap back and forth?

Yes, and Losmandy's RA extension options are designed for exactly that. A second motor left on the spare axis makes it a quick job.

What capacity does it give me?

That depends on the whole head rather than one axis. Losmandy publishes 40 lb imaging for a full GM 8 and 50 lb for a GM811 — send us your configuration and we will tell you which figure applies.

Bottom Line

In short: the GM 8 declination axis on its own, spring-loaded worm installed, convertor cone included, motor not included — the lighter DEC half of a GM811 and the replacement axis for a GM 8.