Quarter circle with forstner bit?


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I want to cut the corner off a 1x4 (that's ~9" high) with a radius that's approximately 1.5" wide and high, something like this:

14b427cc6d920f36efac61113e037000.jpg

 

My idea was to use a 3" forstner bit and drill press, but have some concerns about the bit shifting around since the center spur would need to be right on the corner of the board.

 

Any suggestions for how to do this that's relatively quick and easily repeatable?  I'd need to make.... a lot, so I don't want to use my jig saw or anything. Thanks!

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I think you will find that a Forstner will not perform well in this application.  The point wants to be fully engaged in wood or the bit will walk.  And a 3" Forstner is a BIG bit so you can expect that "walking" to be forceful and with purpose.  Indeed you may find (as I have) that it is difficult to drive a 3" Forstner as it keeps slipping in the chuck.  

Could you drill a three inch hole in a larger piece of wood then saw the circle in quarters to create 4 pieces at once.  Your quarter circles will be a trice small due to the saw kerf, but I doubt it would be noticable.  

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On 7/8/2021 at 8:21 PM, Coop said:

Or use a hole saw and a fence and a stop block on your drill press that will locate each board in the same position each time.

This was kind of my idea. Was going to build a simple jig with stops and clamp it to the table. The stops wouldn't be wide enough to get under the drill press though the sacrificial board they'd be screwed/nailed to would be. Then I could just butt each new working piece against the stops, drill, remove and repeat.

But the bit walking because the center isn't engaged in the wood seems like it will be an issue so I'll probably have to reconsider.

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As most Hole saw bits are 1/4”, make your jig where it barely receives the bit each time. With your piece clamped or probably just held firmly in place, you shouldn’t have a problem.

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Something like this. A 2 1/8” saw is the largest I have but same principle. First pic is the stop block in place after cutting the first hole. Second pic, the results after the first cut. Third is the 1x4 flipped with the stop block remaining in place. Fourth, second cut with no problem.

BA98550D-BA20-4D95-9824-4AA52D239191.thumb.jpeg.075462827da3a34cb44fac7b25dcb2c7.jpegE9A3E80C-9C84-43F1-AA8B-3F1199FC321D.thumb.jpeg.3b9cfada9f2131cf4cfdaff27f3373ad.jpegFD8D3240-D44D-4534-ACFE-9E9236F41C27.thumb.jpeg.e2436ff1327ad6fc742988ea59c47aad.jpegB2C76507-F6D5-447E-BDF9-6BBCC8C6B0F0.thumb.jpeg.00018e4e303a894d2bf6de75dace7632.jpeg

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I don’t have issues with Forstner bits walking with a drill press. In fact, they are one of the best options for off axis cuts as the rim typically cuts first to prevent tear out. If you hold the pieces in a jig, I think the biggest issue is the torque required to spin that large a bit. My press couldn’t do it. Forstners cut like planes, shaving a lot at the same time. A hole saw would cut faster and cause less torque. If you jig it right, that takes care of not having the center also.
 

On the other hand… Hole saws tend to not cut as cleanly. That means clean up of some kind. I don’t see a magic shortcut button. A lot of those means a lot of work. 

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Excellent illustrations, @Tpt life!

Have to agree, I've never made a clean cut through 3/4" stock with a hole saw. Flipping the work when the pilot emerges helps, but negates the use of such a jig.

I still think a router cut is the way to go. Jig the work similar to how it is illustrated above, but include registration blocks or pins to allow a circle / partial circle cut-out template to overlay the work, the cut with a bearing guided bit. Make 2 templates, with first about 1/16" less radius. Cut with that, then apply the larger template for the final cleanup pass.

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On 7/8/2021 at 8:11 PM, Tpt life said:

On the other hand… Hole saws tend to not cut as cleanly. That means clean up of some kind. I don’t see a magic shortcut button. A lot of those means a lot of work. 

I didn’t have any sacrificial hardwood and just used 3/4 ply and the cuts are darn clean with a relatively new hole saw. 

Top side and bottom side.

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With the hole saw, I cut only a small perimeter kerf with minimal dust and I suspect them to be a bunch cheaper than a Forstner bit of the same size that eliminates the entire circle with bags of mulch. Just my suggestion. 

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On 7/8/2021 at 9:11 PM, Coop said:

Something like this. A 2 1/8” saw is the largest I have but same principle. First pic is the stop block in place after cutting the first hole. Second pic, the results after the first cut. Third is the 1x4 flipped with the stop block remaining in place. Fourth, second cut with no problem.

BA98550D-BA20-4D95-9824-4AA52D239191.thumb.jpeg.075462827da3a34cb44fac7b25dcb2c7.jpegE9A3E80C-9C84-43F1-AA8B-3F1199FC321D.thumb.jpeg.3b9cfada9f2131cf4cfdaff27f3373ad.jpegFD8D3240-D44D-4534-ACFE-9E9236F41C27.thumb.jpeg.e2436ff1327ad6fc742988ea59c47aad.jpegB2C76507-F6D5-447E-BDF9-6BBCC8C6B0F0.thumb.jpeg.00018e4e303a894d2bf6de75dace7632.jpeg

I love this! Thank you!

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On 7/8/2021 at 9:14 PM, wtnhighlander said:

Excellent illustrations, @Tpt life!

Have to agree, I've never made a clean cut through 3/4" stock with a hole saw. Flipping the work when the pilot emerges helps, but negates the use of such a jig.

I still think a router cut is the way to go. Jig the work similar to how it is illustrated above, but include registration blocks or pins to allow a circle / partial circle cut-out template to overlay the work, the cut with a bearing guided bit. Make 2 templates, with first about 1/16" less radius. Cut with that, then apply the larger template for the final cleanup pass.

I was looking up how I would do this last night, something like this? (Though this has the template below the working piece and uses toggle clamps.)

template-routing_5F00_thick-parts-1.jpg

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On 7/9/2021 at 5:43 AM, wtnhighlander said:

Coop, your hole saw cuts are much better than mine. Do your run a particularly low speed, or have some other technique for clearing the kerf and avoid burning?

I don’t know if it’s the design that makes it cut so clean but I prefer the Milwaukee Hole Dozer over the Lenox that I used for years. 

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Yes that photo is along the lines of what wtnhighlander is suggesting.

I think template routing is a good solution.  If you go with the drill bit approach, then Coop's idea looks good to me.  You could use either a hole saw or Forstner with this method, but as the owner of a 3" Forstner I have to say it's next to impossible for me to drive with either lathe or drill press as the bit just spins in the chucks no matter how tight I make it.  

I see a couple of keys to success with drilling.  First is to use a drill press and second have the hole's center within the jig marerial as Coop did.  

I would also offer this suggestion for modification.  Make the jig thicker than the working stock.  That way either bit you use will be partially guided as the asymmetric cut is started.  

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+1 to the compass and bandsaw. You'll never be able to see any small inconsistencies. Faster than the router method bout the same as the hole saw. I've done all 3 ways.

If you want them all exactly the same double stick tape them all together cut and sand them all at once.

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when I need to drill a hole in something where the forstner bits center is at the edge of the piece I clamp a sacrificial scrap or the opposing piece then I drill with no problems, or you can make it as complicated as you wish. I've done this hundreds of times try it with some scrap if you have doubts.

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