Forstner bit question
Afternoon everyone! I have a question that maybe a seasoned pro could help a novice wood worker with. I am using a 1-1/4" forstner bit to bore an 11/16 inch hole into 3/4 inch thick pine leaving only 1/16" of material. When I do this, the thin wood that is left has a circular impression in the form of a 1-1/4" circle on the un-bored side that I am finishing. When I look at the hole I can see where one of the outside cutting teeth is going deeper by about 1/32". To bore this hole, I actually use 2 different bits. The first bit is the starting bit that has the centering point tip on the end. I go about 1/2 inch deep with this one and then I use a 1-1/4" finishing forstner bit that I grinded the centering tip off of as so it does not punch through the wood. I have verified that the table is perfectly level along the X & Y planes. I don't know why this is happening. Any help would be appreciated. Thanks in advance.
Forgot to attach pics
It looks like the pressure of the final bore is too much for the 1/16" you have left from the first bore.
Have you used a backer board under your project piece...? This might help to relieve the downward pressure.
Also...the 1 1/4" bit has cutting teeth on the outside edge...this is to make sure the walls are nice and clean when you enter the wood. May also help if those teeth weren't there but then you wouldn't have a clean entry.
Try a backer board first...maybe also clamped to the project piece...
Since you are using 2 bits you might try taking the one you ground the tip off and also grind the rim down. Since you are already down 1/2” they won’t be as important as when starting the cut. I would try doing it by slowly lowering it onto a file while chucked in a drill press. That would also give a chance to see if any are longer than others. But keep in mind that those teeth are supposed to cut before the chippers do so if the bottom of the hole is 1/16” thick the rim of the hole won’t be because of those teeth.
that's a compression mark..
your bit is dull and you are excreting more pressure to bore than you would w/ a sharp bit..
and stop using a bit w/ teeth...
use this style instead...
In woodworking 1/16" is not a lot. I'd just do it the lazy man's way, drill all the way thru, then glue some 1/16" veneer on one side.
Drill down so there's 3/16ths then use a mortising bit (shown) in a plunge router to finish it off. The edge of the hole will guide the bearing. This is a very common bit. You might wish to add a layer on top and drill through that so you have a little more depth as a template to guide the bit.
I think Stick is right about the type of bit, and some kind of board underneath the piece. And 1/16th is a pretty close tolerance for depth of a hole in wood
For perfect stopped holes I use the router, as shown. The material is veneered MDF.
There can also be some flex in the drill press table when you are really pressing down with the bit. You have a lot more mechanical advantage when you think pulling down on that handle, which is why a perfectly aligned table and press can have an error. You can try a lighter cut, let the bit do the work.
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