Forstner bit question

2975 Views 20 Replies 10 Participants Last post by Stick486, Apr 26, 2019

fmakrancy

Discussion Starter · Apr 19, 2019

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.
-Fred

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fmakrancy

Discussion Starter · #2 · Apr 19, 2019

3

Forgot to attach pics

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Nickp

· #3 · Apr 19, 2019

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...

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Cherryville Chuck

· #4 · Apr 19, 2019

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.

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Stick486

· #5 · Apr 19, 2019

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...

.

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JOAT

· #6 · Apr 19, 2019

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.

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ger21

· #7 · Apr 19, 2019

In woodworking 1/16" is not a lot.

Depends on who you ask. It's a lot to me....

Reactions: 4

DesertRatTom

· #8 · Apr 20, 2019

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

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harrysin

· #9 · Apr 20, 2019 (Edited)

8

For perfect stopped holes I use the router, as shown. The material is veneered MDF.

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kp91

· #10 · Apr 20, 2019

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.

Reactions: 1

fmakrancy

Discussion Starter · #11 · Apr 23, 2019

Thanks to all that replied

Welp. Common sense got me this time. What I failed to mention was that I made a new vacuum jig from scrap wood to keep the shavings at bay and from going all over the place for this particular application. I disassembled it yesterday and wouldn't you know there is a hole bored right through the jig directly under where I am boring out the new wood. I am going to replace it this evening and I expect this problem will just go away. I guess I'll file this one under D for DUUUUUUUUUUUH!!!!:surprise:

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DesertRatTom

· #12 · Apr 23, 2019

I'd still use a backer board, and I'd clamp the target piece and backer down securely so they behave as one solid piece

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OBG65

· #13 · Apr 24, 2019

Stick486 said:
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...

.

Stick, who makes that bit?

Stick486

· #14 · Apr 24, 2019

OBG65 said:
Stick, who makes that bit?

CMT
Freud
Irwin
Colt
Famag
Bormax
Bosch
Vermont American
DWT
LeeValley

OBG65

· #15 · Apr 25, 2019

Thanks Stick. Looked at some of those brands and most are scalloped. Only one without any scallops or are saw toothed are the W. L. Fuller series 909 and 060. The 909 series has a center point while the 060 don't since according to Fuller it's guided by its circular rim. But the 060 are $60+ each.

Stick486

· #16 · Apr 25, 2019

try this...
https://duckduckgo.com/?q=forstner+drill+bits+images&t=ffsb&ia=web

Stick486

· #17 · Apr 25, 2019

BTW...
W.L. Fuller is a squared away company...

OBG65

· #18 · Apr 25, 2019

Stick486 said:
BTW...
W.L. Fuller is a squared away company...

You are right on that Stick. Top notch stuff. I have their tapered bits, brad point, and plexipoint bits, Type B CB, Type C & H CS, collars, drill bushings, & stops. I have some PC forsteners that I may change out incrementally to the Fullers as need arise since I have had great success with Fuller products. But the Bosch and Diablo/Freud look good also.

Stick486

· #19 · Apr 25, 2019

OBG65 said:
You are right on that Stick. Top notch stuff. I have their tapered bits, brad point, and plexipoint bits, Type B CB, Type C & H CS, collars, drill bushings, & stops. I have some PC forstners that I may change out incrementally to the Fullers as need arise since I have had great success with Fuller products. But the Bosch and Diablo/Freud look good also.

I've been very pleased w/ the Bosch and Freuds... more so w/ the Freud...
the German made Colts, Bormaxs and Famags are a tough act to follow...

OBG65

· #20 · Apr 25, 2019

Who is your source for the German made ones?

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