Large Dovetail Cutter woes!

[TimB]

Hi,

I am trying to cut some 1 1/2" deep, large dovetails into the end grain of a 3" sq. table leg - in hard european oak. Simple enough I thought, so I hogged out the majority of the waste with a straight cutter, on the router table - no problems there...

Swapped the straight cutter for the dovetail cutter, set the hight and off I went....horrible jarring sounds, motor not happy, really lousy finished cut. I have tried, different speeds, cutting the whole cut with the dovetail bit and finally swapping timbers. Anything softer works like a charm - fir / pine etc.

I have come to the inescapable conclusion that it is operator error ! (But fail to see what is going wrong...)

Can anyone help?[/i]

 

[Chems]

What sort of bit? 1/2 1/4 8mm?

What your getting is chatter, big shank really helps.

 

[TimB]

Hi Chems, thanks for getting back - it's a 12mm shank, 14 degree, 22mm width - at widest point

 

[9fingers]

Might be a silly question on my part but do you have a 12mm collet in your router?

You are generally giving dimensions in inches so I assume you are in UK (?) where 12mm router capacity is pretty unusual.

Bob

 

[Chems]

Did you just measure it now? As 12mm roughly converted is half inch. Is it sharp?

Slow feedrate? The workpiece held down well as it passes over?

 

[TimB]

Hi Bob / Chem, sorry for the cock-up - my mistake, been working in loads of metric and imperial measurements all day.... :-(

It's a 1/2" shank on the bit (not a 12mm as I said previously) and 1/2" collet on the router.

I did wonder whether to use my 'slotting jig' to guide the cut - it just seems that this cutter is a bit large to hand hold - even though my jig controls the router in a 'trapped' cutting motion. So I naturally used the table instead.

I am using featherboards - but they are old and need replacing, so the presure they propduce isn't so hot - possibly the issue here?

The bit is brand new and therefore, I assume, sharp.

 

[9fingers]

Well if the cutter is good and the collet firm, then either the workpiece is vibrating or just maybe the router bearings are complaining about the load.

Not sure what more that you can do other than sneak up on it slowly but then there is a risk of burning.

Ooh! have you tried reducing the router speed if yours can do that??

Bob

 

[TimB]

I have tried reducing the router speed, but I'm now wondering if it could be the router mounting in the table. I have two table setups, the current one (in daily use) - which does leave a lot to be desired and a Festool version.

If my technique is ok (hog out the waste with a straight cutter first), then maybe I'll swap tables and try with the Festool router, running at a slow speed. (It has more torque than the other and the mountings are made of rock ).

 

[jasonB]

If you are trying to reach 1 1/2" deep plus the thickness of your router table with a bit thats got a 22mm cutting length then you must have too much bit sticking out of the collet. Get your chisel out :wink:

Is this for a top stretcher rail with draw opening or are you making a feature out of large dovetails?

Jason

 

[TimB]

Hi Jason, sorry I made another mistake in my original post: the dovetail cut is just over 3/4" deep, with virtually the whole cutter shaft in the collet. The cut is 1 1/2" long, into the end of a leg - to receive a top stretcher rail.

Another way of doing this would be to use the traditional haunched mortice and tenon joint, it's just annoying me that this relatively simple dovetail joint is this hard, to get a clean socket in oak.

(I really shouldn't post questions when I've been up since 4:30am - I should follow the mantra, 'sleep first post later' in future ).

 

[jasonB]

When I do top stretcher rails I clamp a couple of bits of wood to the top of the leg so the router has something to sit on then freehand most of teh waste away with the router then clean it up with a chisel. Though I seldom have top rails over 1" thick and they are also wider so the DT is bigger on plan but not so deep.

Jason

 

[TimB]

Thanks for all your help folks, I'll have another go and see If I can beat it!