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I am trying to find a way to drill a 4" flat-bottomed hole without a forstner bit. I thought about using a router, but I guess I would have to build a large round jig that the router would fit in. Does anyone have any other ideas?

Post #814 by nimrod » Tue Nov 28, 2006 12:37 pm

The router with a circle cutter is probably your best bet.

Is this something you can make in 2 pieces? cut the hole in one, and glue another piece to it?

Post #818 by metzmail » Tue Nov 28, 2006 3:55 pm

Thanks for the reply. No, I cannot make it in two pieces. The hole has to go partially through the one piece of wood.

Flat Bottom Hole

Post #819 by berry » Tue Nov 28, 2006 5:16 pm

You didn't say how deep this hole had to be? But assuming it's fairly shallow, say less than an inch I think the router would work great.

You need a router, guide bushing, and a larger stright bit. First make a template that will give you the diameter you need plus the distance from guide bushing to the cutting edge of the router. mdf works great for templates.

Attach guide bushing to the router base. Attach the template to the stock to be routed and go to it. I know this works as I've used this process before.

IF the router base doesn't span your hole it gets more complicated because you have to make a oversize base, strong enough to support the router so it won't sag in the middle of the cut, and then attach the guide bushing to your new base. While I've made overside bases I've never attached a guide bushing. But I don't think it would be too hard?

Post #835 by metzmail » Wed Nov 29, 2006 1:40 pm

Thanks Barry,

I'm concerned about how to make the template exactly round. I thought about scribing a circle, cutting it close to size, and then using a drum sander to get it to final size, but I am afraid that any errors in the large template will be magnified in the smaller circle. Hmm...

Post #836 by Ed in Tampa » Wed Nov 29, 2006 2:17 pm

metzmail wrote:I am trying to find a way to drill a 4" flat-bottomed hole without a forstner bit. I thought about using a router, but I guess I would have to build a large round jig that the router would fit in. Does anyone have any other ideas?



Take a thin piece of ply 1/8-1/4 inch about ten inches long and about 1 or 2 inches wider than your router base. Remove the plate from your router base and place it on the ply, lined up at one end. Mark and drill the screw holes that hold the plate on, plus mark the center of bit opening and make a hole in the center at least as big as your router bit.

Now mount the ply to your router and mount the bit now measure from the outside of the bit back toward the other end of the ply 2 inches and put a nail there with the pointy end facing the same direction as the bit.

Now place the router on you work piece making sure the nail is in the center of where you want the hole to be and plunge the router in. push the nail into you wood enough to hold it from slipping. After you make a ful circle you have the outside of the perfect circle 4 inches in diameter. Now pull out the nail and use the router to clean our the rest of the circle.

Caution make sure you don't allow the router to dip into the circle or you will ruin the bottom. Perhaps you should leave the ply mounted to the router and just pull the nail out. The large ply will help you keep the router from dipping into the hole.


Another way requires a bandsaw. IF you have one mount a circle cutting jig,(board clamped to bandsaw table with nail exact distance from the side of the blade as the diameter hole you need aligned with the front teeth) and cut a circle the size you want minus 1/2 the diameter of a straight cutting patttern router bit. Now mount the cutout circle to the wood where you want the flat bottom hole and use it as a pattern to cut the outside of the hole you need. Again you will have to go back and clean up the inside by hand but as long as you keep the router flat on the wood and don't touch the outside edge you will end up with a perfect 4 inch hole.

Hope this helps
Ed

Making the template.

Post #842 by berry » Wed Nov 29, 2006 9:32 pm

metzmail wrote:Thanks Barry,

I'm concerned about how to make the template exactly round. I thought about scribing a circle, cutting it close to size, and then using a drum sander to get it to final size, but I am afraid that any errors in the large template will be magnified in the smaller circle. Hmm...


I think Ed answered your question but if you need to know more about using your router to make a circle template - post here and someone will help.

Post #846 by metzmail » Thu Nov 30, 2006 4:23 pm

Thanks to all of you for your input. That really helped.

Post #926 by froglips » Sat Dec 09, 2006 6:31 pm

Another thought, look at a 4" hole saw. Drill to depth to create the outline.

Then hog out the center how you see fit.

Then use a router with a top bearing flush cut trimmer bit to make it sweet.

Good luck,
Jim

Post #958 by army1ret » Sun Dec 10, 2006 10:09 pm

Hey Gents,

How about using a hole saw, 4 1/4" in diameter, and cut into a sheet of 1/4" ply or hardboard. Use a router with a guide bushing. Make sure your guide bushing is 1/4" larger than the router bit. Also, ensure your base is larger than the hardboard template. And finally, ensure the peice you are working on is secured. Route your hole. If the hole needs to be deeper than your template, route the hole first using the template, then switch to a template bit and finish the cut.

There are other variations to this same theme so I don't expect this to be the "best" idea. It depends on what you have in your shop.

Good luck!

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[font="Comic Sans MS"]Shannon Fields
CPT, FA
US Army Retired![/font]
[font="Comic Sans MS"]Bryan, TX :rolleyes:[/font]

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