Reply To: Cutting a circular depression – how to?
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Larry,
I realised that I already had some similiar as yet unused Forstner bits but only up to a diameter of 40mm, so I took them for a test drive.
The results are sobering.
Yeah, which type of Forstner bit you use matters if you try to use them by hand or with an electric hand drill.
They are really intended to be used in a stationary machine.
A drill of the Forstner style that worked really well was called a Stanley Powerbore®. They are alas no longer made. And I don’t think they ever came as large as 95mm. I only have a couple left.
It has a long center point, so for bottomed holes you really need two, one with the point ground down to finish the hole. Or use a block of wood with a predrilled hole in it clamped to the work as a guide and a ground off tip. The power bore really needed the long spur tip because it only had one cutter and would run off to the side otherwise.
There is a two cutter version that chair makers use with a brace that is purported to work well made by Stern in Austria
I don’t know where to get them in the Eu, but it is made there. They have a shorter guide point.
In the USA you can get them from Diefenbacher tools it is aggressive enough to use by hand.
https://www.diefenbacher.com/Drills.htm
Note that both bit styles are more aggressive than Forstner bits made to be used in a drill press.
There is a discussion on how to use them with an extension here:
http://www.greenwoodworking.com/UniversalBitForChairMaking
They only are offered at Diefenbacher to to 1”, which is why I didn’t mention them before.
And chair makers use them with a long extension with a level bubble hung on it to get a steadier bore.
as I think of it, I always used a Powerbore in the field with an extension even with an electric drill.
- This reply was modified 5 years ago by Larry Geib.