5

I'm cutting a 900mm circle out of a 35mm thick hardwood panel using a router jig that I've built and a straight cut bit. That works very well for 90° degree sides, but I would also like to be able to bevel the edge, so that it has a ~15-30° angle to it all the way around. The exact angle isn't so important, though it would need to be less than 45°.

Side profiles

I have a 45° chamfer bit for my router, but the depth is only about 18mm, so that won't work on its own.

My current thinking is to cut the 45° using the chamfer bit, and then mount the circle on a pivot (probably using the same pivot the cutting jig uses), and use a belt sander to smooth out the transition from straight to 45° to an even ~30° all the way around - I can spin the circle and hold the sander fixed that way. I'm somewhat concerned that this won't be even enough though. A more geometrically precise method would be better, I think.

My other thought is to adapt the jig so that it can hold a jigsaw at an angle and trim the edge that way. It seems tricky, though, and I don't know if I trust my jigsaw enough.

Any other ideas?

  • Do you have a band saw? You could use a circle cutting jig for a band saw, with the table tilted to obtain the angle. Or, do you have a router table? I can imagine a ramped jig that would accomplish this task. – Charlie Kilian Jul 31 at 2:38
  • No band saw, I'm afraid. I have a home-made router "table", well, a big flat sheet with places to mount the router and a fence - but it's fairly basic and I don't know that it would cope with the weight of the circle (probably 20kg or so). – Beejamin Jul 31 at 3:50
  • Could you explain the ramped jig for a router table a little? Would you cut the circle with a straight bit first, and then apply the taper via the ramp? It's making me wonder if I can achieve the same thing by somehow angling the router on my circle jig with an adapter. – Beejamin Jul 31 at 3:53
2

belt sander

A belt sander is certainly one way this could be done and it's one of the methods I was just about to suggest1 after reading the first part of your Question.

I'm somewhat concerned that this won't be even enough though. A more geometrically precise method would be better, I think.

If the belt sander is fixed in place, has a hard platen and the pivot point doesn't shift there's no reason this couldn't be accurate enough. Circle-shaping is now often done via sanding, using jigs that allow the workpiece to rotate against a disk or belt sander.

Tip: start coarse! You don't want to try to remove this much wood with a 100-grit belt, for bulk material removal you want to begin at 60 or even coarser and work up from there. I know some users would start at 36 grit for something like this as extreme as that sounds (if doing this entirely by sanding).

My other thought is to adapt the jig so that it can hold a jigsaw at an angle and trim the edge that way. It seems tricky, though, and I don't know if I trust my jigsaw enough

You could remove the majority of the waste with your jigsaw. You'd want to cut well on the waste side of the line because of the expected wobble in the cut at certain areas along the perimeter (as the grain orientation relative to the cut changes).

But even if you could get the cut really neat you should expect to have to refine the sawn surface a lot afterwards. This doesn't argue against using the jigsaw — you'd have a very similar amount of cleanup to do if the cut were done on a bandsaw, which is the saw many would recommend most highly for this cut.

Hand sanding to finish
Regardless of whether you do this entirely by sanding or not, expect to have to do a fair amount of hand sanding to complete the job. Use a block to back the paper2. The two portions of the circle that are towards to ends of the boards will be tougher to sand than the sides as end grain is always harder than long-grain surfaces, so you'll need to concentrate more effort there.

In general there's no need to sand beyond about 180-220 grit, but for the end grain it's worth taking the time to go up higher, to 400 grit or a bit finer. End grain sanded to higher grits looks better anyway but it finishes better too (helping to avoid the usual tendency it has for going much darker than the rest of the wood when finish is applied).

Remember to slightly soften the top arris. Leaving it sharp would make the table surprisingly uncomfortable or even hazardous to sit at, press against or bump into3, plus finishes can creep away from sharp edges, so it's necessary to round them over slightly. I find a quick sand, just 2-3 swipes, with very worn 250 is often enough for arrises to stay looking sharp but be comfortable to handle. But you can give the edge a definite rounding if you prefer, it's entirely a matter of personal taste.


1 My main suggestion was going to be to do it using hand tools but I'm presuming you don't want to go there so I'm leaving that out :-)

2 If you don't own one make one now from a piece of scrap. You may find, as many have before you, that this 'temporary' sanding block will stick around in the workshop for many years! I still have the first sanding block I made, it's just a length of 1x2 with cork glued to one face that I had no expectation would last more than a couple of months and it's now over six years old.

3 I've cut myself a couple of times on 90° edges in harder woods like oak and this angle you're creating is more acute than that.

  • 1
    Thank you for this comprehensive answer! You're right about hand-tools: I don't have the luxury of unlimited time to spend on the project and am a novice in their use. Do you mind quickly outlining how you would do it by hand? I've worked on this today, and used the chamfer bit, then a power plane and belt sander mounted on an angle to refine the edge. It's not finished, but is looking promising! Good call on the end-grain and the top arris. My plan is to make a tiny bevel on the top edge, then soften those angles with sandpaper, which will hopefully protect against chipping somewhat, too. – Beejamin Jul 31 at 12:30
  • 1
    There are a number of different ways you could do this by hand. A drawknife or spokeshave could be used similarly to peel or shave off wood working 'downhill' (towards the end grain in both directions). One or more planes could be used to plane the wood away although that could be very slow if one doesn't have a plane set up to take off lots of wood. Re. time, shockingly and somewhat surprisingly this might actually be done faster using hand tools, not just because of the lack of setup time but also because some of the methods are inherently very efficient (esp. the drawknife if super sharp). – Graphus Jul 31 at 18:16
  • 1
    That's really helpful. I did eye my spokeshave when thinking about how to approach this, but I have really only used it for trivial things (shaving spokes, basically!). I don't doubt that hand-tools could be very efficient - the time for me would be learning and practice! In any case, I finished the bevel today with a flap disc on the angle-grinder: I found an angle and pressure that both steadily spun the disc and removed material quickly and evenly. I'll finish with a disc sander and then hand sanding - it's looking better than I expected. Thank you again for your knowledge and advice. – Beejamin Aug 1 at 11:07
  • 1
    "flap disc on the angle-grinder: I found an angle and pressure that both steadily spun the disc and removed material quickly and evenly." Nice one! Good to figure out little tricks like this that get the job done. – Graphus Aug 1 at 16:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.