Building a Trailer Axle

NOTE - Building your own axles should only be undertaken by a skilled and proficient welder. Good weld penetration with no porosity or undercut is required to ensure the strength and integrity of the axle is not compromised. If you have any doubts about your skills, leave axle building to the professionals, poorly built and poorly welded axles can cause accidents and kill people.

Axles for offroad or extreme use trailers should always be professionally manufactured and ideally be of solid construction.

Trailer Axle Parts and Materials

Selecting the right kind of hub and stub axle for your trailers gross loaded weight is relatively straight forward although care needs to be taken to get the best possible quality for all the components from the axle steel type, and quality cast hubs, through to branded bearings, marine grade seals and quality wheels studs and nuts. Most suppliers will have their own branded hubs and stubs and will have a designated load rating.

Hubs and stubs are subjected to the extremes of the road conditions, overloaded trailers, water, dust and everything else flung up from the road so getting the best quality hub /stub set you can afford should give you a long and trouble free trailering experience.

Look for quality branded bearings to suit - Timken, SKF & NTN, NSK, Koyo, INA, & FAG are among the better manufacturers and are normally European or Japanese made. Steer clear of bearings without a manufacturers stamp or markings.

The same goes for seals - preventing water and dust getting in, and keeping the grease from getting out of the hubs and bearings is a priority to prevent bearing failure. Double or triple lipped seals need to be fitted at a minimum.

Stub axle steel varies from low grade mild steel to a higher grade medium tensile steel like AISI 1045 and come in both solid round & square. High tensile steels are not ideal for stub axles as they do not have the flexibility to handle the stresses placed on a trailer. Along with your bearings, check the quality of the axle steel and if the supplier can’t tell you what grade it is, go elsewhere.

Stub axle back end diameters for standard trailers range from 39mm (700kg up to 1500kg), 45mm (1500kg up to 1750kg), 50mm (2000kg) up to 60mm diameter (4000kg+).

If you are welding your own axles, finding a suitable axle tube or receptacle to contain the stub axles without compromising strength and accuracy can be tricky.

Axle Tube Material

For 39mm round axles, you cannot go past a good piece of 40NB Schedule 80 line pipe. The overall diameter is 48.30mm with a wall thickness of around 5mm. The cut to length pipe will need to be sent to a machine shop to be internally bored out to suit the axle, but in doing so hugely reduces the time setting up the axles for true running. 40NB heavy ERW pipe can also be used although there will be clearance around the stub that will need to be equalised to ensure the axle is central – see shimming detail below

Round stub axles are commonly welded into square hollow section (SHS) and 50 x 50 x 4.0 or 5.0 are suitable. Finding a suitable axle material for 45mm round and square axles is a bit more difficult and most people use this size stub axle in a stepped/overlay setup on top of 50 x 50 x 5.0 SHS or heavier.

For 50mm round and square diameter stub axles, 65 x 65 x 6.0 SHS can be used. For a straight beam axle with a 50mm round stub axle, 50NB Schedule 80 line pipe can be machined out to suit. Again this method ensures the most accurate and true axle alignment and setup.

Axle Setup and Building

There are a couple of relatively easy methods of setting up stub axles for accurate, true and straight running if you are not using machined pipe/tube.

The Shim Method is one of the easiest, and can be accomplished in almost any home workshop - This method uses shims fitted around the stub axle to centralise it within the axle tube. Click here to go to the Shim Method Page.

The Weld and Machine Method is also a simple method which requires building up the stub axle with weld before being machined to the right size for the axle tube. Click here to go to the Weld & Machine Page.

For information on measuring axles - Click here.