Like everything manufactured, gaskets have tolerances on their key features. These are dictated by a combination of material characteristics and manufacturing process. It’s important to understand these tolerances if your new gasket is going to fit.
Key Features
Unless a gasket goes in a channel the outer dimensions aren’t usually critical. What does matter though are the bolt hole positions, bolt hole diameter, and the inner shape, (because the gasket should not intrude into the flow.)
Gasket Material Thickness
Tolerances are dependant on the type of material and industry standards. RMA commercial gauge sheet rubber tolerance chart shows typical tolerances.
Manufacturing Process Tolerances
Here at Hennig, gasket material is cut in four ways: die cutting, oscillating knife (flash cutting,) water jet and by hand. Die cutting, used for quantity orders, is probably the least accurate yet also the most repeatable. The oscillating knife and water jet machines provide excellent accuracy, and as they cut one gasket at time repeatability is about the same. Hand cutting is the least accurate.
Here’s some more detail on each process:
- Die cutting. Accuracy, defined as conformance to design, is set by the precision to which the steel rule is set into the mounting block. A laser-cut block can usually hold +/- 0.015” (+/-0.381mm) although this tolerance increases with the size of the tool. Larger tools are less precise. Softer, thicker material deforms more during cutting and a convex edge profile may result. Die-cut gaskets are very consistent, with the first piece identical to the last, (until the blade starts to wear.)
- Water jet cutting. Accuracy is set by the precision of the gantry and table motion. In general, this is around +/-0.007”.
- Oscillating knife. Machine repeatability is claimed as 0.010mm but in practice +/-0.003” (+/-0.076mm) is more typical. Softer and thicker materials can show greater variation.
Consider Tolerances When Ordering
Critical gasket dimensions influence the choice of cutting methods. In such cases, it’s important to let us know about these at the quotation stage.
