Which worm geared motors can be built with custom hollow output shaft sizes?

Our BGW worm gearbox range, sizes 30 to 90, is built around a hollow output shaft, and it is the range we configure when a customer needs a hollow bore to suit their machine. Each size has a standard bore from 14 mm to 35 mm. When the standard bore does not fit the driven shaft, we can customise the hollow bore to almost any size, wherever the requirement is feasible for the gearbox and the load. Paired with an IEC motor through an IEC adapter, the BGW becomes a compact worm geared motor that mounts directly onto the shaft it drives.

This article explains which worm geared motors take a custom hollow output shaft, the standard sizes to start from, and what we need from you to engineer the right fit.

Why the hollow output shaft matters

A hollow output shaft lets the gearbox slide straight onto the driven shaft of a conveyor, mixer, screw feeder or gate. There is no coupling, no separate bearing block and no alignment to set. A torque arm stops the housing rotating, and the drive is held in place by the shaft itself.

That saves space and parts, but it only works if the bore matches the shaft. A bore that is too large gives a loose fit and fretting wear. A bore that is too small means the machine shaft has to be turned down, which weakens it. Getting the bore right at the design stage is what keeps a shaft mounted drive running for years rather than months.

Which worm geared motors take a custom hollow bore?

The BGW range covers six sizes, with ratios from 5:1 to 100:1. Every size is supplied with a hollow output as standard, which makes it the starting point for any custom bore request.

BGW size	Standard hollow bore (mm)	IEC motor frames accepted
BGW30	14	56, 63
BGW40	18	56, 63, 71
BGW50	25	63, 71, 80
BGW63	25	63, 71, 80, 90
BGW75	28	71, 80, 90, 100/112
BGW90	35	80, 90, 100/112

IEC adapters are available in B14 for every frame listed and in B5 from frame 63 upwards, and the largest frame a size accepts depends on the ratio. The gearbox mounts in any orientation from B3 to V6.

The part code tells you the bore at a glance. In BGW50/7.5/80B14/H25, the gearbox is size 50, ratio 7.5:1, with an 80 B14 IEC adapter and a 25 mm hollow bore. A non-standard bore is specified in the same H position, so it stays traceable through quotation, build and spares.

The same hollow shaft can also be converted for other mounting styles. We supply plug-in single output shafts for every size, along with output flanges and torque arms, so one gearbox body can be shaft mounted, flange mounted or given a solid output.

When a custom hollow bore makes sense

Most requests for a custom bore come from one of three situations. An OEM is designing a new machine and wants the drive to suit a shaft size already fixed elsewhere in the design. A maintenance team is replacing an older drive and needs the new unit to fit the existing shaft without modification. Or a reseller is supporting an end user whose shaft sits between two standard bore sizes.

In each case we can customise the hollow bore to almost any size where there is a feasible requirement. Very little in engineering cannot be undertaken. What decides feasibility is the gearbox size, the torque required and the wall thickness left around the bore, and our engineers confirm it against your application rather than a catalogue.

What to tell us

To confirm a custom hollow bore quickly, send us:

The driven shaft diameter and tolerance
The keyway or locking arrangement on the shaft
The output torque and speed the machine needs
The motor power and IEC frame, if already chosen
The mounting position and how the torque reaction will be taken
The operating environment, for example washdown, outdoor or continuous duty

With that information our engineers can select the right BGW size, confirm whether the bore is achievable and give you a clear part code to order against.

How we engineer it

We design, assemble and supply gearboxes and geared motors from Victory House in Chatham, Kent. Our worm reducers are built with configurable inputs, shafts and flanges, and every gearbox can be supplied with bespoke adaptations where the application calls for them.

For new OEM designs we work alongside your engineering team, share CAD models and can build prototypes before production starts. For replacements and reseller enquiries, we give a fast, honest answer on whether the bore can be built and what to order. Data sheets and drawings are available for the whole BGW range.

If you are specifying a worm geared motor and the standard bore is not quite right, talk to us before you modify the machine. Call 01634 201110 or email sales@browngeartech.com with your shaft details, and one of our engineers will come back to you with a clear recommendation.

Frequently Asked Questions

Which worm gearboxes have a hollow output shaft as standard?

Every size in our BGW worm gearbox range, from BGW30 to BGW90, is supplied with a hollow output shaft as standard. Standard bores run from 14 mm on the BGW30 to 35 mm on the BGW90.

Can I order a worm geared motor with a non-standard hollow bore?

Yes. We can customise the hollow bore to almost any size where the requirement is feasible. Our engineers check the gearbox size, output torque and wall thickness around the bore, then confirm the right BGW size and part code for your shaft.

What are the standard hollow bore sizes on BGW worm gearboxes?

BGW30 has a 14 mm bore, BGW40 18 mm, BGW50 and BGW63 25 mm, BGW75 28 mm and BGW90 35 mm.

What ratios are available?

BGW worm gearboxes are available in ratios from 5:1 to 100:1. The ratios offered vary slightly by size.

Can a hollow shaft worm gearbox be converted to a solid output shaft?

Yes. We supply plug-in single output shafts for every BGW size, so the same gearbox can be used with a solid output when the machine needs one.

How is a hollow shaft gearbox stopped from rotating?

A torque arm fixed to the gearbox housing takes the reaction torque and anchors it to the machine frame. Torque arms are available for every BGW size. Alternatively, an output flange can be fitted for flange mounting.

Which motors fit a BGW worm gearbox?

Any IEC motor of a frame size the gearbox accepts, fitted through an IEC adapter in B14 or B5 form. BGW gearboxes accept IEC frames from 56 up to 100/112, depending on gearbox size and ratio.

What information do you need to quote a custom bore?

The shaft diameter and tolerance, keyway or locking detail, required output torque and speed, motor power or frame, mounting position and operating environment.