Grade-specific tooling
Cavities sized for the shrinkage of your chosen grade.
Silicone manufacturing guide
Tolerances in moulded silicone and rubber parts.
Rubber moves. It shrinks as it cures, flexes when you measure it and relaxes in the bag. Specifying it like machined metal leads to rejected parts and arguments. Here's a better approach.
The starting point
A flexible part doesn't have one size. It has a size under certain conditions.
Silicone and rubber shrink as they cure, by amounts that vary with grade and process. They flex under the measuring tool. They relax slightly after moulding. A caliper pressed firmly on a soft seal will read differently from an optical measurement of the same part.
None of that makes rubber imprecise. It makes it a material where the measurement method matters as much as the number.
That's why we don't publish headline tolerance figures. What's realistic depends on your grade, geometry and how the feature is measured.
Common problems
Three patterns we see on drawings.
Metal tolerances copied over
A title-block tolerance written for machined parts applied to a soft seal.
Everything is critical
Every dimension tightly toleranced, raising cost without improving function.
No measurement method
A tolerance with no note of how or in what state the part is measured.
What we recommend
Four steps to a workable specification.
The aim is a specification both sides can measure the same way and agree on.
Identify critical features
The few dimensions that affect fit or function.
Describe the function
What each critical feature has to do, so we can suggest a realistic band.
Agree the method
Instrument, fixture, free-state or constrained, and conditioning time.
Confirm on first articles
Measure first articles together and adjust the tool if needed.
In production
Four controls that keep sizes steady.
Process windows
Temperature, pressure and cure time held and recorded.
Batch measurement
Critical features measured per batch and trended.
Tool maintenance
Wear caught early. See tool refurbishment.
Keep reading
More guides from the workshop.
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Read the guideScaling a silicone part to volume
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Read the guideWhen to switch from HCR to LSR
Many silicone parts start life in HCR, compression or injection moulded. As volumes grow, LSR starts to look attractive. Here's…
Read the guideDesigned and developed in the UK. UK moulding capability, with some higher-volume production placed with trusted partners where that's the right commercial answer.
Get in touch
Tell us the part, the volume, and the timeline.
Rough annual volume, target unit price, and any deadlines. That's enough to work out whether compression, LSR injection or something else is the right tool.
Real people, a real workshop
You deal with the people who make it.
No call centre and no middlemen. When you contact TCI Products, you speak to the team who design, build and check your mould.
- A real Warwickshire workshopUnit 15, Waterloo Park, Bidford-on-Avon, Alcester B50 4JG.
- Real people on the phoneCall the team on 01789 224228, Monday to Friday.
- The same team on every jobDesign, production and aftercare come from the people you see here.
- Part of TCI GroupFive specialist brands, one engineering team. Visit TCI Group.
Thomas LaneManaging Director
George PrestonDesign & Project Manager
Kelly BallingerHead of Partnerships
Jim AndertonProduction Manager
TheodoreEmployee Welfare