Tolerances & Manufacturing Plastic Manifolds

Origin Location

For inspection purposes and dimensioning, it is best practice to locate the origin at a corner or hole. By creating a feature-based origin, we can directly measure the dimensions as defined on the drawing. The practice of creating an origin at the center of the part requires dimensions to be adjusted mathematically, reducing accuracy.

Center - Not preferred

Corner - Preferred

Hole - Preferred

Geometric Tolerances

All linear dimensions are assumed to be ±.005” (125 microns). We can provide tighter tolerances if needed. Please note: tighter tolerances raise the cost of the manifold. Be sure that performance requirements benefit from it.

Size of holes are held to within ±.004” (100 microns).

Our bond alignment accuracy is generally within .004” (100 microns).

  • At request, this can be improved to within .002” (50 microns).

Dowel pin holes for mounting will be held to a medium slip fit. For stress sensitive plastic, light slip fit is preferred.

Valve patterns will be placed within .004” (100 microns) of each other.

How To Measure Close Tolerance Holes In Plastic Manifolds 

While plastics are a less stable/malleable product, there still is need for close tolerance holes on the order of +/- .0002” (or tighter). Alignment pins for components or manifold mounts sometimes require exact placement. Unlike metal products however, an inspector can make a no go pin fit with just a little extra push and consider the part rejected. Controlled Fluidics has developed an approach that shows consistently good measurements.

It is important to note that our method demonstrates a functional test. Bores checked with a CMM will often show higher, as they can be set to an interpolated circle versus a minimum size circle. Close tolerance holes are mostly smaller in size and can be properly measured with a pin gage. Method:

  • Measure pins accurately, preferably with a laser micrometer.
  • Go pin should fall through or fall out of target hole by its own weight.
  • No go pin ideally should not start, however it often does in plastics
  • Choosing whichever is lighter, the part should not fall off the pin or the pin should not fall out of the part.
  • If the pin slides gently into the part, it is considered line to line and exact size.

Fixturing Requirements

A common concern for customer is fixturing cost and engineering charges. We utilize universal fixturing where ever possible to control costs and improve turnaround time. This approach applies to machining as well as bonding.