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Extending router shanks

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John Haine13/11/2019 19:45:06
3080 forum posts
162 photos

I've had a router gathering dust under my bench for years, bought for grooving MDF for making shelves. Now I want to use it in making a door for the case for my clock. However I've found that once I fit the dust shoe on the router I can't get the tool to extend enough beyond the sole to cut the depth I need. i could buy a longer cutter but they seem to be even more expensive than proper milling cutters!

So, seems to me it should be easy enough to turn up an 8mm shank with a blind hole for the 1/4" router cutter shank, which will fit in the 8 mm collet they supplied with the router, holding it in with loctite.

Does anyone here have any experience with doing this please, will it work? I assume that I should use a high temperature loctite because the cutters must get quite hot

Joseph Noci 113/11/2019 20:18:24
671 forum posts
890 photos

Just be VERY careful! A 6mm cutter in a 8mm adapter leaves only 1mm wall. Those cutters spin upward of 20K RPM, even up to 35K+ RPM. Any TIR in the bored 1/4 inch hole, or the quality of fit will result in notable forces at those RPM's. The type of steel you would use for the adapter also bears consideration. There are considerable side forces on the cutter when pushing through the wood, and at those RPM's, with that supporting wall thickness...

Maybe make the adapter with an 8mm stub into the router, and a 10 or 12mm extension to take the cutter..All with little or no TIR.


Edited By Joseph Noci 1 on 13/11/2019 20:20:27

John Reese13/11/2019 20:22:27
842 forum posts

Please don't try to extend the spindle. At the 20000 or so rpms there is not much tolerance for imbalance in the extended cutter. I chucked a fairly long mounted stone in my Makita die grinder (20000 to 24000 rpm) Dur to the overall length of the stone and the imbalance as soon as I hit the switch the shank of the stone made a sudden right angle bend just outside the collet. It became really exciting. I needed both hands to control the grinder and could not reach the toggle switch on the back of the grinder. All I could do was kick at the cord to knock the plug out of the socket. Eliminate the dust shoe and use standard tool stickout. Tolerate the extra cleanup to prevent the potential damage and injury if the extended becomes unstable.

JasonB13/11/2019 20:28:09
18098 forum posts
1993 photos
1 articles

John did say "turn up an 8mm shank" so I assume he will be starting with larger dia stock, 12mm would be about right.

There are plenty of extensions available that usually have a collet on the end rather than a socket, provided the loctite holds it should be no different to using one of those. Though I'd look at what can be done with teh dust collector first.

HOWARDT13/11/2019 20:54:08
556 forum posts
15 photos

Have a look at the Trend web site, extensions with their speed and diameter limitations. I have both 1/2” and a 1/4” routers and the difference in capability is more than the difference in collet size. If using an extension I would only use in a fixed router table fully guarded.

SteveW13/11/2019 21:13:24
121 forum posts
11 photos

Leave the dust shoe off. Work outside. Wear a reasonable face mask. If you only have a clock case to do it will only take a tick. Sorry not an engineering solution... But safer than a flying router bit!

ega14/11/2019 11:24:44
1709 forum posts
150 photos

This is perfectly possible:


My photo shows a standard 20mm 1/4" shank bit extended by boring out a length of 1/2" PGMS or silver steel and fixing with high strength Loctite. Apart from the extra length, this gives greater rigidity.

In deference to safety concerns, I would not do this if a suitable bit were readily available. Thus far, the extended bit has only been used to enlarge holes in 36mm thick MDF ie drilling.

Peter Sansom14/11/2019 13:28:28
68 forum posts
2 photos

If you look around the specialist woodworking stores sell router extensions with collets to hold the router bits, can be found with Google.

Derek Lane14/11/2019 14:12:49
324 forum posts
73 photos

Is it just a straight bit that is needed and how long does it need to be as there are long router bits available which are used in a set they can be brought as individual bits so no need to buy the set as I have linked to.

See THIS set with a list of the individual part numbers for the bits in the discription

Edited By Derek Lane on 14/11/2019 14:14:18

John Haine14/11/2019 18:43:25
3080 forum posts
162 photos

Thanks for the suggestions folks. After a bit more thought I realised that actually I could make a stronger extension by making it to fit in the spindle instead of a collet. The standard Trend collet is 10mm dia opening out to 12.7 mm at the taper, while the hole in the closer nut is 10mm. I could therefore make an extension 10 mm diameter with a tapered collar to engage with the taper in the spindle. So that leads on to another question:

Does anyone know what the taper angle is on the Trend collets please??

Phil super714/11/2019 19:20:09
11 forum posts

Consider how you would eject the taper from the router spindle. The collet nut not only close's the collet but also ejects the split collet.

John Haine14/11/2019 21:42:40
3080 forum posts
162 photos

Not on these collets it doesn't. The taper is quite steep so it doesn't lock, there's a spring behind the collet and tool to push them out.

John Haine15/11/2019 10:11:11
3080 forum posts
162 photos

This is what it looks like...


John Haine15/11/2019 18:31:09
3080 forum posts
162 photos

And this is the adaptor I just turned up from 1/2" silver steel rod.


Cutter not yet loctited in.

John Haine16/11/2019 10:14:20
3080 forum posts
162 photos

Loctited in the cutter last night. Mounted extension+cutter in router this morning and spun up to max speed, no perceptible increase in vibration. We'll see how it performs for cutting.

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