JMI Triangle-Style Wheeley Bar — Dobsonian Dolly for 8″, 10″ & 12″ Telescopes

Product Overview

The JMI Triangle-Style Wheeley Bar is a Dobsonian dolly built as a welded steel triangle, open at the centre, with a locking caster at each of its three points. It carries the ground board of an 8″, 10″ or 12″ Dobsonian and rolls the assembled telescope out to the observing spot in one piece. The frame accepts a centre-of-foot to centre-of-foot span of 12.21″ to 20.87″ (310 to 530 mm), which is the measurement that settles fit. JMI builds it in the USA, and the vendor lists it at 20.0 lb.

Who It's For

This is a good match if you keep an 8″, 10″ or 12″ Dobsonian assembled indoors, in a garage or in a shed, and your observing spot is a driveway, patio or garage apron a short roll away. The three-point triangle is the lighter and simpler end of the JMI dolly range, so it suits a flat, hard route out rather than a long haul over rough ground.

Key Features & Design

• Triangular welded steel frame: Three-point layout, open through the centre, matching the three feet under a Dobsonian ground board.
• One locking caster per point: A caster at each corner of the triangle, each one lockable at the observing position.
• Wide fit range: Accepts a foot spacing of 12.21″ to 20.87″ (310 to 530 mm) centre-of-foot to centre-of-foot.
• Covers three popular apertures: Specified by JMI for 8″, 10″ and 12″ Dobsonian telescopes.
• Published caster options: JMI lists 2.5″ locking casters as the standard fitment, and a 5″ locking caster set as a separate upgrade that raises the mount 6-3/8″ off the ground.
• Leveling screws available separately: JMI publishes a leveling screw and hardware set as its own add-on.
• Built in the USA: Manufactured by JMI.

Mechanical Design

A Dobsonian ground board stands on three feet, and this frame answers that directly: a steel triangle with a caster under each point, so each foot of the telescope loads a corner of the frame rather than sitting on a rectangular platform that has to be sized to the board's diameter. Leaving the centre open keeps the steel out from under the azimuth bearing and keeps the weight down. Because the geometry is set by where the feet land rather than how wide the board is, one frame covers a span from 12.21″ to 20.87″ — which is how the same dolly takes an 8″ Dob and a 12″ Dob. The caster choice sets ride height: the 2.5″ standard casters keep the telescope low and the eyepiece close to its usual height, while the 5″ set raises the mount 6-3/8″ off the ground and clears more of what is underneath it.

Recommended Uses

• Rolling an assembled 8″, 10″ or 12″ Dobsonian from a garage out onto a driveway or apron
• Shed-to-patio and indoor-to-deck roll-outs over a short, flat, hard route
• Keeping a medium Dob on its dolly between sessions so the rocker box is not lifted
• Repositioning the telescope on a paved surface during the night to clear an obstruction
• Storing a Dobsonian assembled rather than separating the tube and rocker box each session

Compatibility and Accessory Notes

The triangle frame is specified by JMI for Dobsonian telescopes in the 8″, 10″ and 12″ classes, with fit decided by the centre-of-foot to centre-of-foot distance under the ground board — the straight-line distance between any two of the three feet — which falls between 12.21″ and 20.87″ (310 to 530 mm). That measurement, rather than the aperture on the tube, is what determines whether a given Dob sits on this frame. JMI also publishes two separate add-ons for it: a 5″ locking caster set that raises the mount 6-3/8″ off the ground, and a leveling screw and hardware set. This frame carries a Dobsonian ground board; tripod-mounted telescopes and equatorial mounts are served by the Universal Wheeley Bars, and larger Dobsonians by the Sky Trekker range. Tell us your telescope model, the distance between two of its feet, and which caster height suits your setup, and we'll confirm the fit and the configuration before you order.

Good to Know Before You Order

• Fit is set by foot spacing, not aperture. The published span is 12.21″ to 20.87″ (310 to 530 mm) centre-of-foot to centre-of-foot, and a Dob outside that range sits outside the published fit.
• Caster size is a configuration choice. JMI lists 2.5″ locking casters as standard and a 5″ locking caster set as a separate upgrade — we are glad to confirm which casters are on the unit you are looking at.
• Leveling screws are a separate item. JMI publishes them as their own add-on rather than as part of the frame.
• The casters suit hard, flat surfaces. Garage floors, paved driveways and patios are the surfaces this frame is built around; rough ground, gravel, grass and stairs are where the pneumatic-tired Sky Trekker models earn their keep.
• This is a manual dolly. It rolls under hand power; the motorized drive unit is a separate product built for the Heavy-Duty Universal Wheeley Bars.
• The vendor lists the frame at 20.0 lb on its own, before the telescope is added.
• Larger Dobsonians have their own models. The Sky Trekker 300, 350 and 400 cover apertures above this frame's range.

Frequently Asked Questions

Is it difficult to set up?

The frame is welded steel, so setting up means lowering the Dobsonian's ground board onto the triangle with each of its three feet over a corner, and locking the casters once the telescope is positioned.

What is cof-to-cof distance, and how do I measure it?

It stands for centre-of-foot to centre-of-foot — the straight-line distance between any two of the three feet on the bottom of your Dobsonian's ground board. For this frame that figure falls between 12.21″ and 20.87″.

Which casters does it use?

JMI publishes 2.5″ locking casters as the standard fitment, with a 5″ locking caster set offered separately that raises the mount 6-3/8″ off the ground. We are happy to confirm the caster configuration on a given unit.

Will it work with a tripod-mounted telescope?

The triangle is shaped around a Dobsonian ground board and its three feet. Tripod-mounted telescopes and equatorial mounts are covered by the Universal Wheeley Bars instead.

What surfaces does it suit?

Hard, flat, smooth ones — garage floors, paved driveways and patios. For grass, gravel and uneven ground, the Sky Trekker models ride on 10″ pneumatic tires.

When would a Sky Trekker suit better?

For Dobsonians larger than the 12″ class, for a route that crosses rough ground, or where more ground clearance is wanted than a caster provides.

Bottom Line

In short: the Triangle-Style Wheeley Bar is the simple, light Dobsonian dolly in the JMI range — a welded steel triangle with a locking caster at each point, taking a foot spacing of 12.21″ to 20.87″ across the 8″, 10″ and 12″ classes, listed at 20.0 lb and made in the USA. Tell us the distance between two of your ground board's feet and we will happily match it for you.