Forstner bits

**Mobyturns** · 10th September 2020, 09:22 AM

Originally Posted by BobL

My saw toothed Forstener set is from CT and have had it for almost 15 years. The main thing I drill with them is Al and have not touched them up yet although the 19 and 25 mm sizes could probably do with it.

To more easily drill larger sizes (>32) I sometimes drill relieving holes inside the area being removed as shown below.
This makes a big difference in sawdust removal, and if your DP is underpowered or you are using a hand held drill.
I do the same with hole saws - in this case the relief holes have to just touch the side of the circle being cut by the saw.

Attachment 480464
A is for holes withe either a Forstner or hole saw , B is for hole saws when you want to keep the inside circle as one piece .
Even a single 1/4" relief hole makes a big difference with hole saws.
I find 2 x 1/4" relief holes results in not needing to withdraw the saw from the hole to clear sawdust.

Another tip if you are using a hole saw to cut wheels set the hole, saw center so that it exits the side of the board but still cuts a circular wheel - similar idea to Bob's example B. This allows the sawdust to exit the slot which means it cuts cleaner, cooler and requires less clearing. Most users do not clear a holesaw often enough which leads to overheating / burning.

**Brenton Stein** · 10th September 2020, 02:16 PM

One thing that has been overlooked so far in this thread is the ease of sharpening any drill bit including Forstners. I have TC Forstners, HSS and then the generic, cheap, carbon steel, Carbatec style set, which I use the most. All drill bits lose their edge eventually including TC, especially when drilling hardwoods and even more so when drilling into end grain of hardwoods. The ability to sharpen them myself is a huge advantage, which I can do with the cheap carbon steel bits with a file. It's a lot simpler to do than you might think and once done they perform just as well as the more expensive TC and HSS bits, if not better. The HSS and TC bits tend to gather dust once they are blunt until I have enough to take in to get sharpened by the professionals. So, for most hobby woodworkers I would recommend the cheaper carbon steel bits as a good starting point.

**aarggh** · 10th September 2020, 03:59 PM

I've never understood the misconception that carbide can't be sharpened held by a lot of people, carbide sharpens and grinds as easily as HSS with the right wheel\abrasive. Nothing at all difficult about it.

cheers, Ian

**markharrison** · 10th September 2020, 05:23 PM

I recently bought a set of the Chinese carbide Forstner bits from a local Ebay seller. Sizes are 15 through 65 in 1mm increments in the lower sizes. I paid less than $60 delivered.

I hemmed and hawed about keeping them as a significant number of them have an eccentric centre point. However, with the drill press dialled down in the low hundreds in speed, it is controllable. You just can't clamp down the work piece. The seller was willing to take them back so I don't have any problems with the transaction or the seller. I was the one that bailed on returning them.

Still; for the money paid, they are acceptable. I will replace individual items if I need to down the track.

The good part is that they cut beautifully even in quite hard woods I've tried.

**Woodturnerjosh** · 12th September 2020, 11:13 AM

I use the tungsten tipped ones from Timbecon both in my own workshop and at the University workshop where I work.
My own ones have done a heap of work in hard timbers and when they start to dull they can be easily sharpened with a diamond hone.
They work best at much higher speeds than you would use a regular forstner bit.

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