Tolerances and Finish

See Design for Waterjet for suggested fastener and assembly clearances.

Taper, edqe quality and tolerance:

Waterjet cuts have a slight tapered edge - parts are typically within a few thousandths of an inch of your CAD at the top side of the material, where the jet enters, and thicker at the bottom/exit side. The slower the cut, the less taper, but at higher cost.

The taper is typically a difference of .003" to .010" in part width at the top vs. bottom of the cut edge. That's per edge, so twice that difference measuring edge-to-edge across a part. The taper not a specific angle - it's more for thin parts, e.g. 5 degrees for 1/16" material, but only 0.5 degree for 1" material. That's for a fast/low cost cut; the taper is less for higher edge quality cuts.

Waterjet cuts in our world are coded with an edge quality specification of Q2 (roughest, most taper) through Q5 (smoothest, most precise, least taper). Most cutting is done at Q3 - a "good" quality tradeoff of cutting cost vs. accuracy. A Q3 cut edge is typically .003" undersize at the top surface and .003" oversize at the bottom/exit side of the cut. Double that for hole diameters - for a Q3 hole cut to a certain diameter, the largest round pin the hole passes is typically about .006" smaller than the hole drawn in your CAD. (Add .006" diameter to a Q3 hole to ensure fit.)

Cutting at Q2 typically saves 10-20% and is recommended for fabrication work - in general any situation where you're going to further finish the edge anyway, or it's welded, or hidden, or the edge condition just doesn't matter. A Q2 cut edge is typically .006" oversize at the exit side, and shows some jaggies, but is still far smoother than the best plasma cut. Q2 is a good choice for bolt clearance holes where some taper is OK and you can generously oversize the holes (add .02" diameter) to ensure fit.

Q4 is typically used for more precise holes - tap pilot holes, clean rectangular slots for tab-slot joinery. Q5 is occasionally used for the smoothest cuts in thick material, e.g. 1/2" steel or 1" aluminum.

Our standard practice, when not otherwise specified, is to quote and cut using a mix of features that result in your best overall value - typically a mix of Q3 and Q4 for machine parts, or Q3 holes/Q2 perimeter for fabrication parts. Sometimes we'll quote options. You're welcome to specify what you want up front. Please indicate if you've already adjusted hole sizes for desired cut quality and clearance.

Part condition and finish options:

Waterjet parts typically have sharp cut edges, and some burr on the exit side - typically more for ductile materials such as aluminum, less for steel; none for brittle material such as tile.

Parts heavy and/or large enough to stay put in the tank are typically cut free and left to sit on the slats until the job is complete. Smaller and thin sheet parts are programmed leaving them attached to the stock by a small tab.

If you're doing your own fabrication, your best value is to receive raw parts as they come from the waterjet, and not pay us to trim the tabs or deburr your parts.

In general, if we're sending a finished part not subject to further machining or fabrication, we'll quote based on us doing the basic finishing work - let us know.

There's no simple silver bullet for finishing. Hand sanding, or a sanding disc with a random orbit sander, is expedient for deburring, but leaves an swirl finish on the back side of the part. Smoothing or actually rounding over edges is best done using a power brush finishing tool, or a Scotchbrite power disc, or sandblasting.

In general, the top side of your part is clean and free of blemishes, except for slight frosting around all the cut edges.

Where appearance matters, we can power brush finish one or both sides of your parts. This creates a uniform professional appearing finish, and also slightly rounds over sharp edges.

Sheet material gets blemished on the back side from the table slats scratching under it. Soft materials, in particular plastics and composites, are often gouged where the jet crosses over a table slat and is reflected back into the material. Where it's likely to matter, we cut your parts over a sacrificial layer to keep both sides of the material clean.