Precision couplings
A torque-carrying rotating part: the coaxiality of the two bores matters more than the outside diameter.
Part family · Precision components
Connecting stems and link rods
A slender rod where straightness and the coaxiality of both threaded ends are the two things that decide fit.
What it is, and where it usually goes wrong
A stem is a long thin rod, often threaded at both ends. Two things decide whether it fits: whether it is straight, and whether the two threads share an axis. Both are lost the moment the part deflects under tool pressure and is then measured while still clamped.
How we machine it
- Rough between centres, then finish in a second pass so the part is supported along its length.
- Use a travelling steady or a follower rest on anything longer than about five diameters.
- Thread both ends from the same datum; re-chucking on the outside diameter on a slender rod repeats the error, not the axis.
- Let the part cool before the finish pass — a long rod grows measurably as it warms.
Where it is used
Linkages, fixture pull rods, adjustment screws, sensor extension rods, cylinder fittings.
What we check before it ships
- Straightness over the full length, on a surface plate
- Coaxiality of the two thread axes
- Thread gauge fit at both ends
- Length between reference shoulders, not between thread tips
Measured against your drawing and written on the inspection sheet that ships with the parts. First article reports are available on request.
What to send for a quote
- Overall length and the diameter at the thinnest point
- Thread specification and how much of the length is threaded
- Straightness tolerance over the full length
- Whether the rod carries load in tension, compression or both
A STEP file plus a drawing is ideal; a PDF with tolerances also works. Quantity, material and finishing are enough to give you a real price instead of a range.
Questions we get on this part
How long can you turn without a support?
As a rule of thumb we use a steady beyond about five diameters of unsupported length, and a follower rest beyond ten. Below that the deflection is small enough that the finish pass removes it; above it, the rod pushes away from the tool and the middle comes out oversize.
Can a bent stem be straightened?
It can be pressed straight, but the material remembers it: the straightness will drift again under load or heat. We would rather control it in machining, with a steady and a light finish pass, than correct it afterwards.
Other precision components we machine
Aluminium profile parts
Second-operation work from extrusion or plate, where datum choice and the anodising dimension chain are the risk points.
Earphone housings
Small, thin and curved: cosmetic consistency and the assembly shoulder are where parts usually fail.
Send a drawing, get a price within 24 hours
STEP, IGES, DWG, PDF or a dimensioned sketch — plus material, quantity and finishing. We reply with a price and any questions in one message.