Cut, then Sand? Or Vice-versa

Question

I have a rough-sanded red oak panel (120 grit). I need to make a small circular cut with a jigsaw for a grommet. I plan on sanding the panel with 150, then 180 grit, in preparation for either staining and sealing, or just sealing.

I was planning on using blue painter's tape on the panel, and some on the foot of the jigsaw, to help prevent any scratching.

Should I cut this hole before doing my 150 and 180 sanding? The hole is about 100mm (3.9") in diameter.

I worry that I'll get better sanding results without the hole in the way, but that I could have to re-do some sanding if the foot of the jigsaw scratches the surface.

Which is the tried-and-tested best practice here?

Answer 1

As Daniel B. mentioned, a jigsaw isn't the ideal tool if you want a smooth cut.

If you have a drill press, you can use a circle cutter for a smooth cut.

You can also use a small router and circle cutting jig to get a nice, smooth cut.

In either case, use a sacrificial piece of wood on the exit side of your workpiece to prevent blowout.

Just to be safe, I would cut the hole then finish sanding but it probably won't make much difference if you use a cutting method and technique that produces a clean cut straight off the tool.

Answer 2

Unless your hole is too large, you should use a hole-saw bit for your drill rather than a jigsaw. If you can't, then make sure you're using a fine-toothed blade and some sacrificial scrap to prevent tear-out.

If you like extra work, you could sand first and make your cut, but no matter the precautions you take, you're likely to have a little-touch-up work to do. For any project, finish sanding should be the last step: You should cut your wood to its completed shape, then sand.

Answer 3

Since your finished hole is going to lined with a grommet, it seems that a little tear out can easily be tolerated. I think that with your use of masking tape to limit the tear out you are on the right track and can reasonably use your jigsaw.

Circle cutters are kind of tricky and you would want to make several practice cuts before you commit to using it on a cherished project.

If you decide to use a hole saw, you can eliminate the tear out by drilling from both sides of the panel. Again practice cuts would be advisable.

Cut the hole, finish sanding, insert the grommet.

Answer 4

I don't know that there's a single best practice here. Different woodworkers tackle certain things in different ways and we have a good example here of the differences in philosophy between one maker and another — the resistance to the idea of using a jigsaw for the cut in the first place. This despite curved cuts being one of the things a jigsaw is primarily intended for, coupled with the fact that they make blades specifically for wood, one could say that a jigsaw is a perfect choice for this job.

Hole-saws are obviously purpose-made for this too, but they aren't immune to tearout either. Especially on a fibrous wood like red oak.

With the right jigsaw blade used at the right speed you should normally get minimal tearout on at least one side of a board (depending on the blade this can be the entry or the exit side). With a particularly good blade such as the Bosch Extra Clean both sides of the board can end up equally free of tearout.

However, even if you are using a blade that won't give a perfect entry side, there is another way to help prevent tearout and that is with a zero-clearance plate or insert. This offers the same advantages as a sacrificial board, without the added cutting effort and the waste of the sacrificial material. The zero-clearance can be left in place for all vertical cutting, only removed for angled cuts.

I worry that I'll get better sanding results without the hole in the way

I think you're right to be concerned, but with just finish-sanding still to go you should be OK.

I would actually use a card scraper instead of sanding for this (faster, no dust, better results), but either way I would smooth the wood prior to cutting and then examine the hole edges, hoping I wouldn't have to but prepared to do touch-ups if needed.

I could have to re-do some sanding if the foot of the jigsaw scratches the surface.

I think your plan to tape the foot of the jigsaw with tape is a very safe way to go, done right even on softer wood like pine you nearly remove the risk of light surface scratches. But if you make a zero-clearance insert from a material such as hardboard which is softer than the red oak you will have even greater assurance that you won't scratch the workpiece.