8mm router bits.

[Honest John]

I’m curious if an 8mm shafted router bit offers any/much advantages over a 1/4 inch shafted version. There must be some rigidity or strength advantage, but is it significant? Clearly a half inch shaft would offer a much greater strength advantage, but is not a desirable option for me for the task I have in mind. I am of a mind that a 1/4 inch router cutter could complete most of the activities of a half inch cutter but more gently, unless someone can give a convincing argument ?

 

[sunnybob]

The router determines the bit size. I have a 3/4 size powerplus router ( DO NOT BUY ONE!) that uses 8 mm and 6 mm, but will not take 1/2".

I see no other reason to have 8 mm, but there are lots made. I can even buy 8 mm bits easier than 1/2" here.

My Makita 1/2 router will take all sizes with the appropriate sleeve, I even have a few 3/8" bits and sleeve that I can use.
My advice would always be to buy a 1/2" router, because then you can use any damn size bits you want.

 

[Rorschach]

Seems to me that it's too small for serious stock removal, but too big for easy trimming work.

 

[Phil Pascoe]

From what I've read you should buy 8mm where possible as they are significantly stronger than 6mm ones, mainly because there is more material on the joint between the shank and the actual cutter. As they are often the same money that makes sense to me.

 

[Droogs]

Generally the thicker the shaft, the more stable and less vibration at the cutting edge. Resulting in a much smoother and more refined finish. A larger shaft also allows you to push more power through it meaning that you can take a larger bite with each cut and so can remove waste much more quickly.
When routers first came about the most common sizing system in use in their largest market was imperial and so this was used. Since then most of the world has moved to metric but tradition and all that. 8mm is a more stable size to use but has a much smaller range of available cutter shapes and types. Resulting in manufacturers making what will sell rather than trying to move the market to a more useful size with regards to both machines and cutters. Catch 22 type of thing.

So in general terms you can do probably 80% of work done by most users with 1/4" shafted bit but there are many occassion when you need the ability to put cut a much large sized profile than you can posssibly do with the smaller bit or have a need for speed to remove waste quickly. So having machines that can use differing sized collets is useful but at the same time, you really would be better off having both a small machine (Trim/Palm router) as well as a larger (2000W 1/2" collet) machine, giving both flexibility in type of profile and speed of work. Still if you need to go to production levels then get the behomoth of routers, which is not a hand machine at all but a dedicated stationery machine - the spindle moulder.

 

[Phil Pascoe]

A quick calculation - the 8mm is about 75% larger than the 6mm (by surface area of the shank), so there's more difference than first apparent.

I was comparing an 8mm to a 6mm, but it's still about 60% compared to a 1/4" one.

 

[AES]

Gents, there is a potential danger in what you're doing! Please do NOT talk about Imperial and Metric router bits - AND router collets - in the same breath. I found out the hard way when I first moved here bringing a 1/4 inch router with me and subsequently tried to buy router bits, and a new, bigger router here. Here is the text I posted back in 2016 when I was first struggling with this problem,

Being in Switzerland I learnt some info re router bits and collet diameters the hard way. Router bit shanks are "commonly" available (somewhere or other - see below) in the following diameters:

6mm; 1/4 inch (i.e. 6.35 mm); 8mm; 12mm; 1/2 inch (i.e. 12.7mm).

And you MUST have a collet/s which is the exact size for each of the above diameter shanks that you want to use.

My problem was that I bought a cheapo router over here which was fitted with a 12mm collet but then bought a router bit by post from the UK with a half inch shank because I thought they are the same. They aren't, and only after a lot of hassle was I able to get a half inch collet to fit my router.

Thank goodness it wasn't the other way round (i.e. in my ignorance, me trying to use a 12mm shank bit in a half inch collet) as that could have been really nasty - it would have "fitted" but not gripped properly.

To sort all this out I did some "research" by visiting a very good tool store locally who stock Bosch, DeWalt, and Festool routers. Comparing those on the shelf with the published specs for "the same" models available in UK, I found out that, for example, the same Festool machine supplied with a 12mm collet in Switzerland would be supplied with a half inch collet in UK. Similarly the other brands mentioned above.

The same applies with router bits - over here bits with 6mm dia shanks are freely available; bits with 1/4 inch shanks are as rare as rocking horse manure; bits with 8 mm shanks are becoming more and more common; bits with 12 mm shanks are freely available; bits with 1/2 inch shanks are similarly very, very rare here.

I'm not of course aware of what the exact situation is in UK, but from the websites of people like Wealden, it seems that in the main, bits with 1/4 inch; 8 mm; and 1/2 inch diameters are the most common in UK.

So if you're a "hybrid" bloke like me, with a mixture of UK and "continental" gear, then you need a collet to fit each router and router bit you have (or will have).

Of course there are collet adaptors (which some people seem not to like) but obviously, while you can step down diameters (e.g. 12 mm or 1/2 inch collet to 8 mm shank) you can't step up.

The main thing is safety, as I learnt from the very helpful people here. So do NOT even consider putting a "too small" shank into a "too big" collet - e.g. a 6mm shank into a 1/4 collet. It'll fit but won't close properly, leaving you with a potential bomb in your hand, as mentioned above.

Sorry the above is lengthy, I found out it's a complicated subject.

Quite why the manufacturers have made it so complicated I have no idea - trap for the unwary.

I agree that a 8mm router bit has much more meat on the shaft than a 6mm, but in order to fit an 8mm bit, as above, you really MUST have an 8mm collet - or if you're OK with them (some people are not it seems) then the appropriate adaptor/s.

Not trying to teach granny to suck eggs, hope the above helps.

 

[Eric The Viking]

A blob of primary-coloured paint or bright nail varnish on the end of the shaft ought to minimise mistakes. I can only imagine 6mm cutters to be problematic, as the shaft is getting too small to give clean results.

My small stuff is all 1/4" at the moment, but I have 8mm collets for my Bosch POF series routers and intend to move that way instead because of the quality improvement. Also, if the cutter does loosen (it happens occasionally), the wider collet is likely to be less damaged. I have worn out 1/4" collets from damage - I can't really see or measure it, but they simply don't grip properly.

AND cheap Chinese cutters may be out of spec (supposed to be 1/4" but actually not). I have had a few of these. Keep the collet scrupulously clean, and if something feels loose (or too tight) when you first try it, consider just chucking it out - probably not worth the risk of collet damage (Bosch and Trend/DW collets are very expensive, considering).

I know for certain there are variations: I have my 1/4" cutters stored in hardwood blocks: some are tight in the holes some are not, and if you swap around, the fit goes with the cutter more than with the drilled holes to take them! Rust on the shanks will cause similar problems - All my cutters are stored indoors in the winter, as I can't take the risk.

 

[sunnybob]

I have 1/4, 8 mm, 3/8", and 1/2" bits.

I have sleeves for each size to use them all in my makita 1/2" router.

The bits are friction fit in the sleeves, before you put them into the router. If the bits have to be forced, theyre wrong. If they slop around, theyre wrong.
The smaller router which takes 8 mm and (presumably) 6mm also uses friction fit collets.

The 8 mm bits are red painted from new. I dont know if thats a colour code or just that manufacturer.
The 3/8" bits (which are at least 20 years old but some still have protective wax on them) are also red but theres no chance of a crossover there. #-o

 

[Honest John]

Thanks for all the replies and info. I’m surprised at the suggested strength difference between 8mm and 1/4 inch. What prompted my thoughts on this subject was the purchase of a Leigh jig to quickly cut box joints. This requires the use of an American style screw attached adjustable guide bush. This will easily fit (with an adapter) to my Trend T5 and much less easily to my Axminster white series and or my b and q power pro half inch beasts. I have a Trend T3 that will also fit easilily, but that’s a lower power and less suitable jobbie. My T5 will be my device of choice as it is much lighter and pleasant to use and has good fine adjustment. ..... it also has both 1/4 inch and 8mm collets! I refuse to buy yet another router, they’re starting to take over from hand planes as acquisitions that tend to stick to you :roll: I’ve got a big Triton TRA001 in a table as well come to think of it that would work well but would need a different adapter, and require removing from the table every time I wanted to use it, so that’s not going to happen. I’ve just taken delivery of an 8mm shafted CMT 1/2 inch long series bit that looks like it will do the job, and I’ve ordered a similar one from Trend. These are the first 8mm bits I’ve ever owned and this is what prompted my interest in how different will they be. Leigh supply a nice looking 1/2 inch bit with the jig. Irritatingly I couldn’t find a suitable equivalent from Wealden in 8 mm. Thanks again for the replies.

 

[AES]

+1 for everything sunnybob says (except the 3/8 inch router shafts - I never came across those in my "research" a couple of years ago): But just as he says, the "feel of the fit" tells you all but at the time I was so ignorant on the subject I just didn't really appreciate that a "1/2 inch" collet (example) was NOT the same as a "12mm" collet (example again). Of course I knew that the measurement wasn't the same but just thought that here, being metric, a 12mm collet (or shaft) was the same as a 1/2 inch collet or shaft in UK (being still largely imperial). Actually the fits and tolerances on router collets seems to be just as tight as those on "engineering" collets (for metal working).

Just don't ever mix metric router bit shafts into imperial collets (and vice-versa) and you'll be OK.

Good luck honest john - just don't make the same (nearly nasty) mistake that I nearly did, simply due to my lack of knowledge and mixture of "continental" and UK gear.

 

[johnnyb]

Leigh themselves are champions of the 8mm bit. Suggesting a massive increase in strength over 1/4. I've got an elu 97 that's great with 8mm bits as it's also pretty powerful. Unfortunately router manufacturers love to "bend us over" with the collets. I paid £100 for a Bosch trim router kit i paid 36 just for a 1/4 collet that had snapped!

 

[MikeJhn]

The Draper Expert router takes the Leigh bush without any adaptor, 1/2" collet so takes all the adaptors to take different router bits, the handles are low down so very stable for jig work, it has a see through base with three LED lights built in, I was impressed enough to buy another and use both in my Leigh Dovetail jig in preference to any of my other six routers, highly recommended.

Mike

 

[user22161]

I frequently use roundover and edge trimming 8mm bits in my Katsu with a collet from Makita.

 

[Honest John]

Thanks again to all for your replies.
Mikejohn thanks for the heads up on Draper Routers. I was not aware that there was a uk supplier of routers that worked directly with the American style Porter Cable bushes. However as an owner of 5 little used routers as I much prefer hand working these days, I’m not about to add another to the collection. What I have discovered though is that amongst the pieces that comes with the Triton bush accessory plates, is a ring that is designed to fit PC bushes to a different Triton router that I don’t own, and is therefore of no use to me..........or is it? With a little filing, drilling M5 tapping and use of a cantering cone, I can now perfectly fit my Leigh E11 bush to my Axminster 1/2 inch router. Soft start, fine height adjuster, reasonable weight and balance. Just what was required. As regards my initial enquiry, I have found that the 8mm bits are very much more stronger if that’s the right word, than the 6mm ones. The 8mm bit works perfectly in my Trend T5 ( with an 8mm collet) and so is also a good option for jig work.