4

In a question about routing MDF & HDF, an answer suggested:

when routing conventionally use a second "dust pass"

What is a "dust pass"?

1
  • I'm having way more difficulty tracking down references than I would have expected! I'll try to add an Answer in the morning (the gods of search permitting).
    – Graphus
    Sep 16 at 22:34
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A "dust pass" is a second (or last) machining pass that removes just a tiny amount of material — sometimes literally producing only dust as the name suggests — to improve surface finish and/or remove burn marks.

In a router context I believe it's most commonly utilised for improving edges when pattern routing and when using a fence, either the fence on a router table or one attached to the router itself. But it can also be done to improve the bottom of a cut, or the surface left after router planing as the following tip mentions.

Flawless-surface tip
Tip #5 from 14 Fuss-free router-bit setup on Wood Magazine's site.

This should probably be done more in routing since it can dramatically reduce the need for sanding, and on occasion may even prevent it entirely.

It's on the table saw1 where this process is used more widely, where it is sometimes referred to a "skim cut" but more commonly a "dust cut". Despite it being more common I only became aware of its use in a table saw context relatively recently; I've been unable to locate the reference, so I suspect it may have been mentioned in passing in a video on YouTube (likely during an episode of Shop Talk Live from Fine Woodworking).


This basic principle is quite widely used in woodworking, very light cuts (and occasionally a succession of them2) being used to give the best surface possible3. Here's a reference to the same idea on a thickness planer:

"Set the depth of cut for a 1⁄64 "-or-less “skimming cut” on the final pass for the same reason [to get a smoother surface]"

No-fail Routines for Jointing and Planing on Wood Magazine's site.

...

1 Although presumably will work equally well on other rotary saws. But bear in mind this is only important if no other process will be used to finalise the sawn surface, such as planing to final length in a shooting board or running a cut edge over the jointer.

2 Q.v. the related incremental routing.

3 Not unlike the final wispy shavings taken by a smoothing plane, or the even finer and wispier shavings taken by a scraper.

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  • Basically a "pass over the jointer" for the types of cuts that can't be jointed. Of course, it looks like the implication is that a jointer wouldn't be needed at all if you've got a good blade and make the final cut that just takes off the thickness of some masking tape.
    – FreeMan
    Sep 17 at 13:51
  • @FreeMan, yeah for sure, for edges a jointer is absolutely not a must-have. You can joint very well with a router using common bits (even without a router table, although since you can just poke it through a hole in plywood really nobody needs to be without a router table if they want one), and go from live-edge al the way to two jointed, and dead parallel, edges with very nice surface quality on any decent TS. And obviously there are hand planes...
    – Graphus
    Sep 17 at 14:31
  • There was a fine woodworking podcast recently where they discussed doing this without changing your setup (or rather forgetting to do it), in order to ensure that a groove that was being cut didn't come off the fence and end up a little shallow in spots. The second pass just ensures that nothing was missed.
    – lnafziger
    Sep 22 at 2:00
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    @lnafziger, not quite the same thing but that's also worth doing routinely for some setups (e.g. not necessary if using a featherboard or guide blocks on the router table). Definitely for freehand routing using the fence!
    – Graphus
    Sep 22 at 6:14

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