TOLERANCES & MANUFACTURING PLASTIC MANIFOLDS

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.

All linear dimensions are assumed to be ± 0.005” (125 μm). 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 ± 0.004” (100 μm).

Our bond alignment accuracy is generally within 0.004” (100 μm).

• At request, this can be improved to within 0.002” (50 μm).

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 0.004” (100 μm) of each other.

While plastics can be a less stable/malleable product, products can still need close tolerance holes on the order of ±0.0002” (or tighter). This is because alignment pins for components or manifold mounts sometimes require exact placement. Unlike metal products, an inspector can make a "no-go" pin fit with just a little extra push, but they would consider the part rejected due to the need for that small push.

We have developed an approach that demonstrates how meet these needs for intense precision in tolerances and fit. However, it is important to note that our method exhibits a functional test that involves checking bores with a CMM. This will often result in higher tolerance measurements, as they can be set to an interpolated circle as opposed to a minimum size circle. Close tolerance holes are mostly smaller in size and can be properly measured with a pin gage. Here's how we do it:

1. Measure the pins accurately. We find that a laser micrometer works best.
2. Go-pin should fall through or fall out of the target hole by its own weight and gravity
3. No-go pin should ideally not start through the hole, however, this can (and often does) with plastics.
4. Choosing whichever is lighter, either case should not happen. Neither the part should not fall off the no-go pin nor should the no-go pin fall out of the part during this test.
5. If the go-pin slides gently into the part, we would consider that "line to line" and meets exact size.

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.