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*UPDATE: For those interested in how I achieved the design, skip to 'CONSTRUCTION'.

I've constructed the following circular cutting board out of hexagonal sections of plywood and I'm trying to get the smoothest possible sides. As you can see based on this design, the grain is in all different directions.

Cutting board

I've tried straight flush trim bits but they result in a lot of tear out. I've also tried making a jig which allows me to rotate the piece so the side brushes past a belt sander but I end up with flat spots. I was thinking about spiral up/down cut bits or compression bits but my understanding is they focus creating a smooth edge as opposed to solving the problem of cleanly cutting through wood where the grain goes in all directions like in my case.

What are some recommendations?


CONSTRUCTION

I copied someone's design from TikTok. I used baltic birch plywood and cut pieces on a 60 degree angle using the table saw:

Baltic birch on 60 degree angle

I then glued sets of 3 pieces together to form hexagonal rods:

Hexagonal rods

I then cut the rods into pieces:

Hexagonal pieces

And glued the pieces together to form a board:

Hexagonal board

I then glued all the pieces together to create a large enough form from which I could get a circle of the desired diameter. Due to sloppiness in cutting the hexagonal rods I had pieces of varying heights and required planing:

Big enough board pre-planing

I then made a very basic planing jig and used a router with a surfacing bit:

Planing jig

...which resulted in a board of uniform thickness from which I cut a rough circle with the bandsaw using a templating router bit and a template which I double-sided taped to the cutting board:

Router bit

Board with template

Resulting in:

Planed board cut to circle

As the previous process resulted in a lot of tearout (due to my poor gluing and wood grain going in many directions) I made a simple jig to rotate the board against the belt sander to try and further smooth the edges. This process left flat spots because I used a sanding cylinder with WAY too large a diameter:

Sanding jig

And that's when I posted this question.

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  • Age old situation. A sharp cutter and do 2 passes. fill and sand. Your to critical on this. Not so important, it's wood ! Make it smooth and move on. Nov 14, 2022 at 3:22
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    Huh... that's a really cool design! Trying to wrap my head around how to make the cuts to get the pieces and thicknesses necessary. scurries off to do math and stuff
    – FreeMan
    Nov 15, 2022 at 17:16
  • Have you considered trying a bandsaw?
    – gnicko
    Nov 19, 2022 at 2:17
  • @FreeMan I updated the question with details and photos about the construction.
    – Matthew
    Nov 21, 2022 at 21:32
  • @gnicko Yes - I used a bandsaw to cut the rough shape before routing the circle. But even with the smallest bandsaw blade and a jig to rotate the piece against the saw you'll never get a smooth circle.
    – Matthew
    Nov 21, 2022 at 21:32

2 Answers 2

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I'm trying to get the smoothest possible sides.

TBH if the results in this one photo are fairly representative, what you're achieving already is pretty darned good :-) Many would be happy with this and maybe would apply filler1 followed by a last router pass and/or a couple rounds of sanding to finish off.

I've tried straight flush trim bits but they result in a lot of tear out.

A certain amount of breakout may have to be accepted with this material, however you may be able to reduce it noticeably.

One of the ways to minimise or avoid breakout (and burning) from any routing operation is not to do it in a single pass. If instead of the norm you take off the bulk of the material with one or two initial cuts and then go for what some call a 'dust pass' you can greatly improve results. See What is a "dust pass"? for more detail.

However, since you have access to a belt sander that may offer a competitive and possibly superior method, once you're set up right to do the sanding.

I've also tried making a jig which allows me to rotate the piece so the side brushes past a belt sander but I end up with flat spots.

I think this indicates that your jig doesn't work as it should — the whole point of such a jig is to semi-automate the process, avoiding the possibility of flat spots. A firm pivot point (moveable or fixed depending on how many diameters you need to produce) seems to be the key feature of any circle jig for router table, bandsaw, sander or table saw.

It's probably worth noting that given the multitude of grain directions in the plies there's no guarantee you won't still get some breakout here and there when belt sanding!

I was thinking about spiral up/down cut bits or compression bits but my understanding is they focus creating a smooth edge as opposed to solving the problem of cleanly cutting through wood where the grain goes in all directions like in my case.

I believe you're correct here.

In addition such a bit wouldn't help with the roundovers! And again if the photo is representative this is where it seems a lot of your breakout is occurring.

What are some recommendations?

In addition to the above, it could be worth looking at the videos and/or writing of people who do a lot with "patterned plywood". On YouTube Michael Alm could be the best person to start with2.


1 And this could be a good candidate for a DIY version, made from glue and fine sanding dust (or fine dust sifted out from your router waste).

2 But that might just be based on my viewing history; since I don't look at a lot of videos of this type and don't do related searches what is being shown to me in my feed could well be a 'content bubble' that hides other channels, something YT is notorious for. So there could easily be any number of other content creators worth hunting for — including by searching externally, rather than relying entirely on the internal YT search engine.

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  • Part 1 of 3: Your comments are gold! << what you're achieving already is pretty darned good :-) >> Thank you. << ...would apply filler >> I am indeed doing this. Depending on how big a chunk the router took out, I'm cutting out a bigger section of hexagon, sticking in a whole new one and then cutting it down again. B/c some big chunks were taken out, which leads me to... I realized one reason why my tear outs are so bad (in some cases I had like 10% of a hexagon flying off): it's because I did a poor gluing and clamping job. Solving next time will resolve a lot.
    – Matthew
    Nov 15, 2022 at 21:50
  • Part 2 of 3: << One of the ways to minimise or avoid breakout...is not to do it in a single pass. >> Such a great point. I realize now I was too aggressive even when trying to take off just a little bit. About the sanding jig: << I think this indicates that your jig doesn't work as it should >> I now see my issue. I'm using an oscillating belt sander and should have used the smallest cylinder. I went way too wide so even if it slightly kisses the surface it's going to leave a flat spot. I'll redo with a smaller roller.
    – Matthew
    Nov 15, 2022 at 21:50
  • Part 3 of 3: << In addition such a bit wouldn't help with the roundovers! >> I've been too afraid to even address the roundovers so far. Your recommendation to search for "patterned plywood" is great.
    – Matthew
    Nov 15, 2022 at 21:50
  • "I realized one reason why my tear outs are so bad (in some cases I had like 10% of a hexagon flying off): it's because I did a poor gluing and clamping job. Solving next time will resolve a lot." Yes, definitely will help! Don't skimp on glue and do not be afraid to clamp hard. PVA glues benefit from high clamp pressures to achieve the strongest possible joint. Also, in case you're not already doing this refreshing the surface of the ply before glueing could help enormously (old wood surfaces don't glue as well as fresh wood).
    – Graphus
    Nov 15, 2022 at 22:51
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If smoothest is your goal, then gloves, 1/2 sheet of fine grit sandpaper and work it. Too much work? Try a very very flexible rubber 6" drill mounted sanding disc start with 220 or 400.

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    Your first sentence could use an edit for some additional clarity. What do gloves have to do with anything? Also, most folks have moved beyond drill mounted sanding to using dedicated random orbit sanders - RO gives a much better finish.
    – FreeMan
    Nov 21, 2022 at 18:51

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