Thread: Smallest diameter round head bit

What size (dam and depth) are you after?

If these dimensions are small enough something from a Dremel might suit.

I should also be possible for someone with a tool and cutter grinder (metal working gear) to grind a half circle "D" bit from some tool steel.

Make a scratch stock out of scrap wood and a hacksaw blade.

You can get pretty much any size you want, they're very commonly used in the engineering world for 3D contouring. Look for "ball nose endmills"

Down to 3mm here TiN HSS 2 Flute Ball Nose End Mills
Down to 0.2mm here (there's a side bar on the left of the page to easily pick your diameter): Ball Nose End mill for Sale | Ball Nose Slot Drill Online | AIMS

Just be aware of the shank size and get something your router can actually hold.

Those really small bits can't really be used in a standard router situation as they usually require precision slow feeding on metal mill of some kind.
Routers have too much weight (inertia) and the slightest jerk can snap the bit.
A CNC would be ideal for this.

You should get more fine control than a router with a smaller tool like a Dremel with a mini router attachment.
A pre-cut with a V shaped tool first might be worth cdoing.

I reckon you could get away with 3 or 4 mm in a router, probably stick to HSS over carbide though (and 2-flute ONLY); they're a bit more flexible so less likely to snap.

Am I missing the point or can you cut the block in half, clamp it back together and drill the required hole. I may be too far into a bottle of red to have understood the problem �� cheers

If you're going to cut a dado (groove) half the depth of the diameter of a ball nose carbide bit I can't see any problem going as small as 3mm or 1/8". That would be a depth of cut of 1.5 to 1.6mm, and you think the bit might snap. Forget the HSS bits.

Yeah...wasn't really thinking there

I'm sticking with 2 flute only though; 4 flutes at router rpm = burn city.

Originally Posted by Adrian Marshall

Hi, what's the smallest diameter I can rout a semi-circular cross-section groove? It seems to be limited to 1/4", maybe because anything smaller may break (with dangerous consequences)?
What I want to make is a small diameter circular hole 15 cm long in a piece of timber in such a way that the timber block can be opened up to reveal the two half grooves, if that makes sense.
It's for an experimental bee hotel.

Lee Valley (yes, I'm in Canada so LV is my go-to store) have 1/4" shank core box bits in 1/8" and 3/16" -- both smaller than 1/4"


but if what I think you are trying to do is correct, "wrongwayfirst" has the answer.
cut the block in half
clamp it back together
drill a 15 cm (6") long hole with a drill -- you'll need a long series drill bit




BTW
how big are the bees?
1/4" would appear to be more than a bit on the small size for a bee including its legs

Happiness is knowing the right search term, thank you! And those links are great, appreciated.
The router table I've borrowed uses a 12mm shank. I'm guessing it's not recommended finding some adaptor to let it take 6mm shanks?

Originally Posted by elanjacobs

You can get pretty much any size you want, they're very commonly used in the engineering world for 3D contouring. Look for "ball nose endmills"

Down to 3mm here TiN HSS 2 Flute Ball Nose End Mills
Down to 0.2mm here (there's a side bar on the left of the page to easily pick your diameter): Ball Nose End mill for Sale | Ball Nose Slot Drill Online | AIMS

Just be aware of the shank size and get something your router can actually hold.

You're right, I could. But I'm planning on making many of these and thought clamping individual pieces and drilling would be slower than routing one long groove and cutting it down to length. Also. perhaps more importantly, I want to try routing wiggly (technical term! What were you saying about a bottle of red?) grooves in a future version of this bee hotel, which I won't be able to do with a drill.

Originally Posted by Wrongwayfirst

Am I missing the point or can you cut the block in half, clamp it back together and drill the required hole. I may be too far into a bottle of red to have understood the problem �� cheers

The native bees in my patch of Australia like holes up to 8mm in diameter, depending on the species. Researchers have typically used holes 4mm or greater, but there are a lot of really small bees (e.g. "cellophane bees" that have bodeies only a couple of mm long, which haven't really been studied (I think).

Originally Posted by ian

BTW
how big are the bees?
1/4" would appear to be more than a bit on the small size for a bee including its legs

Originally Posted by Adrian Marshall

Happiness is knowing the right search term, thank you! And those links are great, appreciated.
The router table I've borrowed uses a 12mm shank. I'm guessing it's not recommended finding some adaptor to let it take 6mm shanks?

Some people don't like using adaptor sleeves, I have used them with no issues; just make sure you get the right one (12mm is close to 1/2", but they are NOT interchangeable)
COLLET SLEEVES AND ADAPTORS | JPM Tools

I have 1/2" to 1/8" and 1/2" to 4mm collet adaptors in stock. If you want either of these sizes send me a PM and I'll send you one for free. $30 for a collet adaptor is totally ridiculous.