saw flat bottom forstner bits advertised and first thing i thought of was all forstner bits are flat bottom but i wonder if that is true
- posted
7 years ago
saw flat bottom forstner bits advertised and first thing i thought of was all forstner bits are flat bottom but i wonder if that is true
It's not true. I would guess that most Forstner bits are *not* flat bottomed, as shown here. The center brad is used to get the bit started without wandering.
I have heard of (but never seen) the technique of using 2 Forstner bits to get a flat bottom hole. Grind the center brad off of one bit. Start the hole with the center brad of the "full" bit and when the hole gets deep enough to hold the other one centered, switch bits and finish the hole.
That's exactly what I've done when I need a totally flat bottom hole.
Actually a true Forster bit has no saw teeth and does not require a center brad point to guide it. I have drilled numerous quarter circle holes with only 1/4 of the bit cutting into the wood. The perimeter of the bit does the guiding. This is all done however with a DP, not a hand held drill.
Yes true Forster bits drill flat bottom holes. They also leave a small dimple and often an indention around the perimeter of the bottom of the hole, but the bottom is flat.
-MIKE- wrote in news:ndcpvh$err$ snipped-for-privacy@dont-email.me:
I'm curious why you would need a totally flat bottomed hole.
Like this one...no center point.
If you are using a bolt/nut/screw and flat washer in that hole the washer makes better contact with the bottom of the hole.
But the emphasis (as I read it) was why a TOTALLY flat bottomed hole? I understand what you're saying, Leon, but if I'm using ANY Forstner bit to drill say, a 1" hole in a board so I can insert a small fender washer and a bolt or screw what difference will that slight pip in the dead center make? If it's a screw the pilot hole will be there, if it's a bolt, there will be a hole rather than the pip.
...or a thrust bearing. BTDT
There's one at the bottom of the steering shaft for this Soap Box Derby car:
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However, I think we have a slight disconnect here. Doug used the word "totally" in his post. Your flat washer (and my bearing) will both work in the hole created by a Fortsner bit with a center point, which does not create a totally flat hole. (I believe that that is what EC is actually asking about)
The only reason I can think of for a totally flat bottomed hole would be for decorative purposes.
You're right, Leon. But I would add one caution. If you're drilling a full round hole, the force of the bit is equal in all directions. If you're drilling half a hole, the force is all in one direction. If you don't have the work secured, the bit can pull the work (and your hand) into it - DAMHIKT!
They're really fond of those bits aren't they? Four times or more the price of a Freud or Bosch with a center point!
I'm letting some coffee work on my brain to fire up the correct synapses in order to recollect the past projects I've needed them.
However, on a recent cabinet rehab, the client wanted cup hinges on her existing doors which were abnormally thin. Not only did I have to scour the globe/google to find euro-hinges with the shallowest cups, but I had to grind off the pilot point on my 35mm forstner to keep it from piercing the outer edge of the cabinet.
Yes, it was a butt-pucker job as there was less than 1/16" outer veneer left after the cup holes were drilled. Client wants, client gets. :-)
I'm trying to find some pictures for one project I did. It's more for looks than purpose. I needed semi-cylindrical shapes, think: round mortise. Except these would show. I could think of no easier or accurate way to cut the shapes I needed. I experiment with a hole saw, first. But they don't exactly cut clean holes, then there's the task of removing the core that's still attached on a non-through bore. That means having chisel out a clean, flat bottom inside a semi-circle. Not easy.
So that gets us to the subject of this thread. :-)
....and to what advantage!?
So, a center point leaves a little dimple at the bottom of the cut. How is this detrimental to the flat bottom? I could see the added expense of pointless bits if the bit point left a protruding dimple on the bottom, but it does not. A flat washer will lay jes as flat with a negative dimple under it as without. Or am I missing something? ;)
nb
Totally flat does not mean every spot on the bottom is solid, it simply means that the bottom is flat. Even though pegboard has holes in it, it is flat.
If there is any portion that is not flat the washer will not make full contact, if the bottom funnels toward the center the fastener head can deflect the washer and then only the edge/perimeter of the fastener head is making contact. Why is this a problem? The fastener can loosen over time. Now this is all being picky but flat bottom for these type flat washers and fasteners need to be flat for the same reasons that you use a tapered type countersink with flat head screws. It simply distributes the load of the fastener more evenly.
And just to add a touch for the benefit if a flat bottom hole is when you are drilling 35mm/1-3/8" diameter holes for Euro hinges. These style hinges require a 1/2" deep hole. If you drill a 1/2" deep hole in a 3/4" thick cabinet door with a spade bit or a huge twist type bit you will certainly drill through the opposite surface of the stile.
Actually I believe Mike mentioned totally flat. And I thought Doug was just wondering about a flat bottom hole, NOT necessarily devoid of a perimeter indention or center point.
My mistake if I misunderstood Doug.
notbob wrote in news: snipped-for-privacy@mid.individual.net:
Unlike other bits, a Forstner can easily be used to drill multiple overlapping holes. If a router won't work for some reason, you can make pockets with a Forstner and a chisel. The little divots left by the Forstner bit would be very unappealing in that case.
Puckdropper
Yes! and why I mentioned doing this on a DP. ;~)
Good Forstner bits are not cheap. Cheap Forstner bits can be cheap.
With out a center spur the bit has to be well made and sharpened to keep it on track. FWIW I would choose a Fuller bit over a Bosch or Freud if I needed to accomplish an excellent result repeatedly hundreds of times.
BUT not even that bit creates a "totally" flat bottom hole, it still creates an indentation around the perimeter of the bottom of the hole, and typically about as deep as the spur center on those that have them.
The Forstner bit requires the perimeter of the hole to be cut first, like a brad point bit and then the flutes cutting edges cut out the center and leave a flat surface.
Ascetics if the hole will not be filled.
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