Clearance: Small Number, Big Consequence
Why clearance is a range, not a number
The pillar-bush pair needs running clearance for lubrication and thermal growth, but tight enough to stop plate misalignment. Standard mould base practice fits guides with a small, controlled clearance defined by the guide class.
As a rule of thumb, larger moulds and higher moulding temperatures need the upper end of the clearance band to avoid seizing during thermal expansion.
Reading the symptoms
Wear shows up as galling lines on pillars, plate rock during closing, or parting-line mismatch that wanders between shots. Too tight a fit shows the opposite way: heat at the guides and sticky opening.
Once wear marks are measurable with a micrometer, replace the pair. Re-machining a worn bush in place usually loses the original alignment reference.
FAQ
Can I replace just the bush and keep the pillar?
Possible if the pillar measures within tolerance, but replacing both as a matched pair keeps the fit geometry predictable.
Does guide lubrication matter?
Yes. Dry guides wear fast and can seize. Follow the base maker's grease spec and interval, especially in hot-runner or high-cycle moulds.
Why does my plate still misalign with new guides?
Check the pocket positions in the plates. If pockets have worn or were cut off-centre, new guides cannot recover alignment without pocket repair.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.