Thread: 8mm vs 12mm shanks

Your Makita router takes 1/2" (12.7mm) shank bits NOT 12mm. Although 8mm shank bits are reasonably readily available I'm wondering whether you're actually talking about 1/4" (6.35mm) shank bits. Your router most likely came with a 1/4" collet adaptor NOT an 8mm one. Quality 1/4" shank bits in smaller diameters shouldn't present any concerns for you, however if you're using bigger diameter bits that are hogging out a lot of material it would pay to reduce the feed rate and take multiple passes.

I prefer to save the few 1/4" bits I have for when I'm hand routing.

The 1/2" shanks are a bit more robust and, as you've mentioned, there's more of a disconnect when feeding a table so it's easier to knock the bit about without realising it.

It only took a few 'scalloped' cuts when using 1/4" for large, batched jobs to convince me they're not suitable for use in a router table.

They're OK in a hand-held because the moment you start to feel the vibration...

Originally Posted by aldav

Your Makita router takes 1/2" (12.7mm) shank bits NOT 12mm. Although 8mm shank bits are reasonably readily available I'm wondering whether you're actually talking about 1/4" (6.35mm) shank bits. Your router most likely came with a 1/4" collet adaptor NOT an 8mm one. Quality 1/4" shank bits in smaller diameters shouldn't present any concerns for you, however if you're using bigger diameter bits that are hogging out a lot of material it would pay to reduce the feed rate and take multiple passes.

Yes you are quite right, i had a gut feeling that 8mm didn't look right, too big!

Most are either 1/2 inch or 1/4 inch ( though i do have a dovetail machine, 3/8 at a guess - that was a special order - most places give you that blank look ) They will give you " metric " ie 12.5 mm etc. However the basic sizes are still the same. Do you think 16 mm board was a natural choice - surely 15 if anything - Have not checked but 8 mm is probably about 3/8" There are true metric (rare ) like 10 actual mm - rare.
Personally I am very guilty of breaking a few skinny -say 3-5 mm bits by not taking things in many cuts (cheap nasty Chinese things) Probably would have survived if done in say 5 mm bites. OOps

Originally Posted by wood spirit

Most are either 1/2 inch or 1/4 inch ( though i do have a dovetail machine, 3/8 at a guess - that was a special order - most places give you that blank look ) They will give you " metric " ie 12.5 mm etc. However the basic sizes are still the same. Do you think 16 mm board was a natural choice - surely 15 if anything - Have not checked but 8 mm is probably about 3/8" There are true metric (rare ) like 10 actual mm - rare.
Personally I am very guilty of breaking a few skinny -say 3-5 mm bits by not taking things in many cuts (cheap nasty Chinese things) Probably would have survived if done in say 5 mm bites. OOps

In the interests of clarity 8mm is approx. 5/16" (7.9375mm) and 3/8" is 9.525mm. Whilst I've seen quite a few 8mm shank bits I've never seen one 12.5mm. Metric shank bits - 3,4,6,10 - tend to be endmills and are primarily for CNC machines.

16mm thick boards are a re-branding of 5/8" (15.875mm) so not so strange if you have any longer term knowledge. That of course is no guarantee that any board sold as 16mm will be 16mm or even 5/8", just that it will be close to that.

Just to clarify for people following this thread

Metric SHANK router bits are available in 6, 8 and 12 mm sizes.

Imperial SHANK router bits are available in 1/4, 3/8 and 1/2 inch sizes.

End mill cutters are available in additional sizes but are not that common for router users.


The cutting diameter of router bits vary from 1.5 mm (which is the actual size in mm and not an approximation of 1/16") through to sizes approaching 3 inches.
Bits are available as both metric and imperial, though some Australian retailers size imperial bits to the closest metric approximation.
More reputable retailers will size bits to their true size, using metric for metric bits, and imperial for imperial sizes.
Note a full metric bit mounted on an imperial sized shank is the norm.

Originally Posted by ian

Metric SHANK router bits are available in 6, 8 and 12 mm sizes.

For Australia, USA and the UK best to forget about 12mm shank bits. Yes you can buy them, generally not locally except for endmills, but routers that have collets that can take them are as scarce as hens teeth. While it's possible to buy collet adaptors to convert 1/2" to 10mm and smaller shank metric bits you can't buy a 1/2" to 12mm adaptor. Yes some router manufacturers offer 12mm collet cones for their routers, but seriously why would you bother?

Originally Posted by wood spirit

Have not checked but 8 mm is probably about 3/8"

You were obviously born after 1974!

Originally Posted by wood spirit

Have not checked but 8 mm is probably about 3/8"

Just to clarify an 8mm shank bit is exactly 8mm. It is not an approximation for 5/16". and 8mm is certainly not an approximation of 3/8".

As far as I know, standard router shank sizes are:
6 mm
1/4" Remember 6 mm and 1/4" shank bits are not interchangeable
8 mm -- Leigh dovetail jigs are often supplied with 8mm shank bits. Also Woodrat jigs take 8 mm shank bits.
3/8" and 10 mm -- I believe both these sizes exist, but can't easily find references to the size.
12 mm -- Festool and other German manufacturers make bits with replaceable carbide insert cutters in this size shank.
1/2" -- again 12 mm and 1/2" shank bits are not interchangeable.

Originally Posted by aldav

For Australia, USA and the UK best to forget about 12mm shank bits. Yes you can buy them, generally not locally but routers that have collets that can take them are as scarce as hens teeth. Yes some router manufacturers offer 12mm collet cones for their routers, but seriously why would you bother?

not sure about "scarce as hen's teeth"
Ideal Tools stock 12mm collets for Festool 1400 and 2200 routers.

However, I'd only bother with a collet suitable for a 12mm shank bit if I were using a bit that was only available in that shank size.

Ian,
Ah yes Festool! Of course we all aspire to own a router that costs more than twice as much as any other comparable brand so that we can use their brand bits that cost 3 to 5 times the cost of a comparable quality router bit - NOT. Some of us live in the real world. Do Festool routers come with a 12mm collet -no, can you purchase a 12mm collet as an accessory - who cares! There are other manufacturers who offer 12mm collets as an extra cost accessory too, does anybody know anyone who has bought one - NO. I stand by my statement that 12mm collets are as scarce as hens teeth. Your final statement sums it all up - you can effectively forget about 12mm shank bits. Stop nitpicking!

Originally Posted by aldav

Your final statement

Originally Posted by ian

I'd only bother with a collet suitable for a 12mm shank bit if I were using a bit that was only available in that shank size

sums it all up

I totally agree

In Australia despite what may be available as a special order or optional part, the commonly supplied collet sizes are 1/4" and 1/2".

I've never seen or bought an off the shelf router, that wasn't either 1/4" or 1/2" as standard.

If you're using it in the router table and can use 1/2" router bits, this would be the best course for rigidity.

Certain European routers such as Virutek's come with an 8mm or 12mm collet, along with a 1/4' (and sometimes a 6mm collet) adapter most times, but usually supply a 1/2" collet on request.

6mm shank router bits are mostly used for ER11/ER20 cnc router spindles. It's pretty rare you'd ever use one on any standard router.

cheers, Ian

Originally Posted by aarggh

6mm shank router bits are mostly used for ER11/ER20 cnc router spindles. It's pretty rare you'd ever use one on any standard router.

cheers, Ian

Yep, 6mm endmills are pretty handy for cutting mortises for strap type box hinges though.