Forstner Bit Cutting Rate

[jackellis]

I'm drilling some 2" x 13/32 deep holes with a HF forstner bit. DP speed is 350, though I may increase that to 600. I haven't used a stopwatch but it seems to take about 10-15 minutes to cut each hole. I apply pressure just short of the point where the bit graps and stop periodically to let the bit cool and vacuum up shavings.

It seems like this it taking way too long, but then again this is the first time I've cut holes this size with a forstner bit. Should I suspect a dull bit or will a faster DP speed help?

[pelligrini]

I can't really comment on the time. I just wanted to show you some tests Sarge did on large bits.

http://www.bt3central.com/showthread.php?t=42949

[LarryG]

You don't mention the wood species, but I'd definitely suspect a dull bit. The last 2" holes I drilled with a Forstner bit were in 3/4" Baltic birch plywood. I used a Freud brand bit and doubt that it took more than a minute per hole, going all the way through.

I have two sets of the HF Forstners, one with the TiN coating and one without. They're okay for the few dollars they cost, but they're not even remotely in the same league as my Freuds.

[jackellis]

You don't mention the wood species,

Construction lumber (2x4), probably fir. I guess the HF bits are fine for what they are but I need to look into a better set. Apparently the Grizzly bits are also decent, especially for the price.

[SARGE..g-47]

I'm on coffee bread and just finished two holes with a forstner bit about 1" deep and 1 1/2" radius in SYP for a blade rack while waiting on glue to dry on a furniture project. It took about 30 seconds to drill both.. Look at the chart Pelligrini posted as I did a somewhat extensive test with Forstners as I was puzzled about them myself.

First.. bump your speed up to 650 or 700 as you mentioned as I found that to be the best speed with my "el cheapo" Old Hickory (made by Oldham) bits. It should not take you that long unless those bits are just utterly poor design.. dull or the wood is extemely wet.

Try that and see what happens. A light plunge and release as you mentioned is correct. But.. if you have a shop vac handy.. hold the hose or attach to grap chips. And clamp that stock good.. if the bit graps at that width... it will definitely take the stock for a ride and you just may be in the path.

Gotta run and good luck....

[LCHIEN]

one thing i will say is that changing the speed of the drill press faster proportionally reduces the torque available before it stalls out, or graps (grabs?) as you say.

That said, 15 minutes for less than a half- inch deep hole sounds awfully long to me.
Either the wood is hard or real fibrous or your bit is dull. You don't say how much its been used but there are ways to easily sharpen a forstner with a diamond hone, look on the internet - here's a couple that pop up:

http://www.highlandwoodworking.com/i...=Custom&ID=101

http://www.ehow.com/how_2293304_shar...drill-bit.html

[cabinetman]

Large forstners are recommended to run slow. I seem to have better luck with them running about 1000 RPM IIRC. I bore boss holes for euro hinge cups at that speed. If they need sharpening, diamond hones like these work good.

For the length of time your holes are taking, a hand brace with an expansive bit might be faster.
.

[jackellis]

...and the answer is...contamination.

The bit is plenty sharp, but dust had attached itself to the cutting surface, causing a lot of friction while keeping the blade from contacting wood. Cleaning was as simple as wiping the cutters with a rag.

Works fine now. Thanks for all the suggestions. Loring's post that shows how a Forstner bit works was particularly helpful.

[LCHIEN]

i keep an old toothbrush by the DP to clean off forstners and other bits.
Raise it up and clear or clean it often.
All that rubbing on the chips can really heat up and de-temper your bit.

[jackellis]

Interesting follow-up. Yesterday I chucked a brand new 35 mm forstner into the DP to install some concealed hinges in cabinet doors (pics soon). Raised the DP speed to 800 RPM. That bit cut like a hot knife through butter. It might have been the speed and it might have been the bit but cup holes took about 30 seconds apiece.

I think I've been running my DP way too slow.

Thanks for all of the advice, folks.