Dados with the router

[wizer]

Just a quicky.

I am about to cut a large amount of dados using a router and guide.

Questions is, should I try to find a bit that matches the board thickness (18mm) OR use a smaller bit and reposition the guide on each cut to achieve the exact width?

Reason I ask is that I believe 18mm ply is not always exactly 18mm

 

[Andy Pullen]

The chances of adjusting your router exactly each time is remote and a lot of faffing about, get an 18mm cutter, IMO.
Now someone will come along with a method of adjusting your router precisely, just to be difficult :roll:

 

[mailee]

I don't know if this is of any help Wizer, but I made this jig for Dados and it works great for me. I always use a 1/2" cutter with it and after setting the side guides to the thickness of the shelf it is perfect.

 

[Tom K]

WiZer, how about making a template and and using a bush? A test piece is best if you are uncertain on sizing you know like Uncle Norm does :lol:


Regards Tom

 

[BradNaylor]

I'd use an 18mm cutter.

I think you'll find that the ply is pretty consistant - certainly to within a quarter of a millimetre.

If it's a bit too snug - take a bit off with a block-plane or ROS

If its a bit loose - it'll be so little so as not to matter.

To start routing all your trenches twice with a smaller cutter would be a right pain in the jacksy!

 

[Rich]

Hi Andy, not wishing to disappoint you, but when I bought my Axminster router I also purchased a fine height adjuster and a fine fence adjuster, I added to the fine fence adjuster a couple of nuts which I lock together when I am happy with the width of cut and then proceed with multiple cuts knowing that when ever I move the fence it can only move as far back as the stop nut.
Regards, Rich.

 

[Andy Pullen]

Hi Andy, not wishing to disappoint you, but when I bought my Axminster router I also purchased a fine height adjuster and a fine fence adjuster, I added to the fine fence adjuster a couple of nuts which I lock together when I am happy with the width of cut and then proceed with multiple cuts knowing that when ever I move the fence it can only move as far back as the stop nut.
Regards, Rich.

All my routers have fine adjusters on the fence, problem is that I can never remember which way to screw the knob :shock: . An 18mm cutter will be close enough IMO 8)

 

[DavidE]

I made a load of 18mm slots for the Router Table I am making. The plywood was up to 0.5mm bigger than 18mm. However, the method Dan mentioned works a treat. I just put a lead on with a block plane and it all went together very snug. I bought the 18mm cutter for the job as I couldn't be bothered keep adjusting (especially as I had to do them by hand). It will be very useful for this type of construction time and time again.

Cheers
David

 

[Tom K]

WiZer, Or you could buy the router sled for your Triton. Now take your pick.

Regards Tom

 

[wizer]

Thanks all, I think i'll go with the 18mm bit.

So the next question is, what bit? Just a normal straight cutter? or some new fangled option which I am unaware of?

 

[Andy Pullen]

Thanks all, I think i'll go with the 18mm bit.

So the next question is, what bit? Just a normal straight cutter? or some new fangled option which I am unaware of?

I thought the downcutting type were best to stop the edges spelching but usually I just grab whatever I have and have to clean them up afterwards. Could you score the cutline ?

 

[Shadowfax]

Guys
Stop going on about 18mm bits, bushes and stuff. Mailee has given you the best answer. This is by far the best method. I made the same type of jig ages ago. You use the piece you want to set into the groove to fix the size and just route away. No measuring and no worries.
A half inch bit is all you need. Twenty minutes to make the jig and you are off and running! As long as you use the same router and bit size each time you use the jig you will have no problems.
Trust me. (!)

SF

 

[Steve Maskery]

I have to say that I think that Mailee's approach here is the right way to attack this. It's true that 18mm MDF is an approximation to its actual size, and a quarter of a mm can matter in some cases. If you are making housing joints, for example, a tight one can make the female board bend from flat.

I've been cutting dadoes myself, today, with just such a jig, but it wasn't quite long enough, so I removed the upper connector. I though I had it all right, I nice big clamp, but no. The forces exerted by the router are huge, and my dado opened up before I could say "Norm Abrams" causing me grief and a lot of wasted time. If you use that kind of jig (which works brill), get it clamped fore and aft on both sides. I didn't and have paid the price.

On the whole this has been a productive week. A MkII short fence, a great new guard for my TS (it works even better than I had hoped, and a new tenon jig to boot, but the dado jig was a slip too far. I should heed my own advice now and again!

S

Edit - The other advantage of this kind of jig (coming shortly to a mag near you) is that each side of the groove is cut separaqtely, in the correct direction, so you don't get one good side and one furry side.

 

[Newbie_Neil]

Hi WiZer

Tony's jig is a variation on Mailee's. The big difference is that the router sits in the jig.

Firstly, you put your ply into the jig and then tighten. All you then do is run the router up and down. Perfect trenches/dadoes everytime.

You must use the same cutter so that you have an equal distance everytime.

When making the jig you let the router/cutter combination make the cut in the base board so that your allowance for the cutter is exact.

The photos are of Tony's jig.

Cheers
Neil

 

[BradNaylor]

Old dog, new tricks, and all that...

Please ignore my advice above to use an 18mm cutter. A jig like Mailiee suggests is the answer.

The daft thing is that this is exactly the method I use when routing dovetailed dadoes - which I use on the odd occasion when a client insists on solid wood carcass sides instead of the normal veneered MDF.

I never thought of it for this job.

I must be getting old...

Cheers
Dan

 

[Woody Alan]

You use the piece you want to set into the groove to fix the size and just route away. No measuring and no worries

I have obviously been a bit dense on this, I have seen Mailess jig a few times but have only just realised it doesn't require a guide bush which does clearly make set up very fast. I hadn't looked too closely because I use a jig with a bush. Just one question. Does it rely on the base of the router being perfectly concentric around the bit or just that you hold it the same every time. I am not sure my Freud is that accurate, could always make a sub base for the job with square sides though I suppose.

Alan

 

[Chris Knight]

Alan,

Any router operation of this type requires the router be held in the same orientation. No router I have ever used has been perfectly symmetrical around the bit, although some are better than others. The same applies to guide bushes in spades although they can often be centred with a mandrel held in the router chuck before any operation requiring concentricity.

In practice, it's no great restriction on the use of a jig like Mailee's.

 

[mailee]

That's correct Alan, the router must be held in the same orientation each time as there is no guide bush used. It becomes second nature once you get the hang of it and as has been stated there is no measuring. It is very quick indeed. :wink:

 

[chippy1970]

I have a similar jig to Mailee's one but I use a 1/2" cutter and 30mm guide bush, same set up as I use for worktop joints.

I used to make a rough jig up everytime but now I have an adjustable one where you put the shelf in the jig to set up the dado and it fits perfectly everytime.

With a 1/2" cutter its usually only two swipes, forwards and back and its done, also use dust extract to keep it all clear as you go.

 

[motownmartin]

Wizer, I was lucky when I done this, I found the ply that I used was very evenly sized, I used an 18mm cutter and a straight edge and if the dado needed to be any wider i'd just move the straight edge a fraction for a second pass.
Just an option if you don't want to make a jig.