Gear design with the correct involute profile
A gear is defined by module, number of teeth and pressure angle. The module m gives the tooth size in millimetres, and the pitch diameter is the module times the number of teeth. The standard pressure angle is 20° to ISO 53, and two gears that mesh must have the same module and pressure angle. The centre distance is half the sum of the pitch diameters.
We model the teeth with an exact involute profile, not with circular arcs, which often cause noise and rapid wear. With fewer than about 17 teeth, undercut occurs at a 20° pressure angle, which is solved with a profile shift. From a worn gear we work out the module from the tip diameter and number of teeth: without profile shift, the tip diameter is m × (z + 2). Sprockets are drawn to the chain pitch and roller diameter to ISO 606.
Gears in POM or PA run more quietly and need no lubrication, but take lower loads and less heat than steel. In a gear train with mixed materials, the smaller gear is often made of metal and the larger of plastic, because the small gear's teeth mesh more often. When a steel gear is replaced with plastic, the face width is often increased slightly.
Shafts, fits and bearing seats
Fits to ISO 286 define how hole and shaft go together. H7/g6 gives a sliding fit with a small clearance for moving parts. H7/h6 is a location fit that can be assembled by hand, and H7/p6 an interference fit for hubs that must stay put without a key. We choose the fit by function and state it directly at the dimension, for example Ø25 H7.
Bearing seats are sized from the bearing manufacturer's tables. With rotating load on the inner ring, the bearing often sits on k6 on the shaft and H7 in the housing, but load and bearing type decide. Keyways are drawn to DIN 6885 with key width and depth according to the shaft diameter. Shaft shoulders get a fillet radius smaller than the bearing's chamfer, so the bearing sits flat. A common mistake on home-made shaft drawings is giving every dimension the same tight tolerance, which makes the part expensive without making it better. We specify fits only where parts meet and let the rest follow general tolerances.
Bushings, wear parts and materials
Agricultural and forestry machines contain many plain bearings and bushings that wear quickly in dirt and moisture. A POM or PA bushing can be a good alternative to bronze where the load is moderate, because it can run without lubrication. Plastic swells with moisture, though, PA in particular, and therefore needs more running clearance than metal. Dirt is often a bigger problem than load. A bushing exposed to soil and sand can wear faster when greased, because the grease binds particles. A seal or guard in front of the bearing then does more good than a harder material.
For one-off wear parts, a 3D print in carbon-fibre-reinforced PA can serve as a quick stopgap until a metal part is in place. We assess the load and say plainly when a printed part is only a temporary solution. For recurring failures we redesign rather than copy – see also obsolete spare parts.
Brackets, covers and guards
Brackets for hydraulic valves, work lights, cameras and accessories are among our most common jobs. We start from existing hole patterns and design the bracket in sheet metal, profile or machined aluminium. A bent sheet metal part is often both the cheapest and the strongest, and we then deliver a DXF with the flat pattern. Brackets on implements are exposed to shocks and vibration that are hard to calculate exactly. We therefore avoid sharp corners and welds in highly loaded zones and prefer a bent tab to a welded one. Bolted joints get a good margin and a locknut or threadlocker.
Guards and covers over moving parts must stop anyone reaching chains, shafts and belts. We design openings and distances to the safety distances in EN ISO 13857 and use fixings that need a tool to release. Responsibility for the machine's CE marking stays with the manufacturer or with whoever modifies the machine. Covers that are opened for servicing get hinges or guides, so they are easy to refit and do not get left off.
Machine part design with drawings for the workshop
A machine part is never better than the data sent to the workshop. We deliver STEP for CNC programming and a PDF drawing to ISO 128 with views, sections, dimensions, fits and threads. General tolerances are given to ISO 2768-1, usually class m, and surface roughness is given as Ra values where the function needs it, for example Ra 0.8–1.6 µm on bearing seats.
Geometric tolerances to ISO 1101 are used where they make a difference, such as coaxiality between two bearing seats or perpendicularity to a mounting face. We avoid tight tolerances where they are not needed, because every unnecessary hundredth costs machine time. More on drawings is under technical drawings and in the guide tolerances and fits.
The drawing gets a title block to ISO 7200 with part number, material, revision and scale. Changes are recorded in a revision table, so the workshop always knows which version applies.
Guide values for machine parts
| Parameter | Guide value or standard |
|---|---|
| Pressure angle, gears | 20° (ISO 53) |
| Pitch and tip diameter | d = m · z, da = m · (z + 2) |
| Minimum number of teeth without undercut | approx. 17 at 20° (approx. 14 with slight undercut) |
| Sliding fit, moving parts | H7/g6 (ISO 286) |
| Location fit, hand assembly | H7/h6 |
| Interference fit for hubs | H7/p6 |
| Bearing seat with rotating inner ring load | often k6 on the shaft, H7 in the housing – per bearing manufacturer |
| Keyed joint | parallel key to DIN 6885, sized by shaft diameter |
| General tolerances | ISO 2768-1, usually class m |
| Surface roughness on bearing seat | Ra 0.8–1.6 µm (ISO 21920) |
Guide values for common cases. Load, material and the bearing manufacturer's instructions decide the final sizing.
What we need from you
- The worn or broken part, or photos with dimensions
- Make, model and serial number of the machine
- Dimensions of mating parts: shafts, bearings and hole patterns
- Load, speed and operating environment (dirt, moisture, temperature)
- For gears: number of teeth on both gears and centre distance
- Preferred manufacturing method or a workshop you already use
- Quantity and how quickly the machine needs to be running again
Typical projects
- Gearbox gear for an older machine
- Sprocket for a conveyor
- Shaft with keyway and bearing seats
- POM bushings and plain bearings
- Bracket for a hydraulic valve or work light
- Guard over a chain or belt drive
- Adapter between implement and three-point linkage
- Wear strip for a muck spreader or conveyor belt
- Hydraulic blocks and adapters for pipe fittings
- Camera mount for a forestry machine
What affects price and lead time
- Number of fits, threads and geometric tolerances
- Gears and other profiles that have to be calculated
- Whether the part is to be improved or copied as is
- Scope of the drawing: views, sections and tolerancing
- Need for a simplified strength check
- Whether there is an existing part to measure
What you get
- STEP file for CNC programming
- PDF drawing to ISO 128 with fits and tolerances
- DXF with flat pattern for sheet metal parts
- Bill of materials with bearings, keys, O-rings and screws
- Simplified load check where needed
- Printed test part for fit (optional)
Frequently asked questions
Can you model a gear from a worn original?
Yes. We count the teeth, measure the tip diameter and the centre distance and work out the module and any profile shift. The teeth are modelled with an involute profile, so the gear meshes with its mating gear.
What does H7/g6 mean on a drawing?
It is a fit to ISO 286. H7 is the tolerance for the hole and g6 for the shaft, and the combination gives a small clearance so the parts can slide against each other. H7/p6 instead gives an interference fit where the parts are pressed together.
Can you calculate the strength?
We carry out simplified checks and design with a margin. Calculations that must be verifiable, for example for lifting equipment, are done by a stress engineer who takes responsibility for the result.
Can a gear be 3D printed?
Yes, at low to moderate loads. Carbon-fibre-reinforced PA or PETG works in many mechanisms. For high torque and high speeds we design the gear for steel or POM.
Do you help find a workshop?
Yes. We manufacture by 3D printing ourselves and help you on to workshops for turning, milling and sheet metal. With a complete drawing it is easy to compare quotes.
Which files does the workshop need?
Usually a STEP file for programming and a PDF drawing with tolerances. Sheet metal shops also want a DXF with the flat pattern and bend information.