Tenoning and consistency of measurements

[RogerS]

This is aimed at power tool methods and not hand tools.

I've been thinking about consistency and accuracy of making tenons using power tools (primarily my router table). The question vexing me has been how to maintain consistency of the distance between the shoulders.

For simplicity, imagine making a ladder. What is the best way of making sure that all the rungs are of the same length (assuming they tenon into the main runs of the ladder)?

The best method that I can think of is to prepare the rungs including tenons to be all exactly (and I mean exactly) the same length. Then I can use a 90degree mitre to fix the rung to and slide it over the router cutter to make the tenons. The end of the rung is hard against the fence and so that fixes my reference point (if you see what I mean).

If I have the luxury ( :wink: ) of an Incra fence then that will give me an accurate distance to the shoulder as I cut away the tenon.

Flip the workpiece over (and because they are all the same length) rout again and make the other tenon.

But and this is a big but.....this all assumes that the rungs are the same length.

I can't help thinking that I'm missing something and that there is an easier way to do this...and one that doesn't rely on the rungs all being exactly the same length to begin with.

 

[Steve Maskery]

Roger
You need a jig (but that's not a surprise is it?)

1 Cut your first tenons as you suggest.

2 Make a false fence for your mitre fence, so that you register the first shoulder, rather than the end, on it.

3 Cut the second tenon.

Even if the rungs are slightly different lengths (although I don't really see why that should be too difficult to arrange, IIH), they will be the same length between shoulders.

Personally I wouldn't do it on a router table, but if that's what you have, then the above would work.

HTH
Steve

 

[tim]

Personally I wouldn't do it on a router table, but if that's what you have, then the above would work.

or just buy a ladder....


getting me coat.


In seriousness, this is why i use my FMT jig all the time for this process - the shoulder length is governed by the depth of the cutter. Surely as a ratter, this facility is available on the machine?

Cheers

Tim

 

[engineer one]

how about an "L" shaped block that fits into the first mortice, and is long enough to touch the cutter for the setting the next one.

can't claim it is my idea, saw it in Popular Woodworking, but it
seems to answer all your questions roger. :lol:

paul :wink:

 

[Tony Spear]

Get a Woodrat and it's a piece of cake. (Though I'd get in before Alf!).

 

[RogerS]

Get a Woodrat and it's a piece of cake. (Though I'd get in before Alf!).

Ummm...I have a Woodrat and I can see how to cut the tenon (clamping the wood vertically) but how do you get the consistency of the distance between the shoulders?

 

[jasonB]

Depends what you use to cut your runs to length. I use the sliding carrage on my table saw which has a flip down stop so all bits are cut the same length.

If you have a chop saw or radial arm then a simple stop on the fence will ensure all lengths are the same, if its just a handsaw then lots of practice :lol:

Jason

 

[RogerS]

Hi Jason

I also cut runs to length as you suggest. Keeping the distance between the shoulders then becomes a doddle.

My question was what other techniques are available if you don't cut the runs to length initially. Some good suggestions so far.....

 

[RogerS]

how about an "L" shaped block that fits into the first mortice, and is long enough to touch the cutter for the setting the next one.
paul :wink:

I'm being obtuse a bit here as I can't picture how this would work, Paul. I can see how your suggestion would work for maintaining the spacing between the mortices.

 

[woodbloke]

jasonB wrote:

Depends what you use to cut your runs to length. I use the sliding carrage on my table saw which has a flip down stop so all bits are cut the same length.

That's how I would do it as well. I would also remove the riving knife, lower the blade and cut the shoulders on the saw bench using the sliding table, then use the router table to remove waste, all pieces would then have identical distances between the shoulders - Rob

 

[Anonymous]

Hi Roger

Only way I get the consistency you are after is by making the pieces exactly the same length first. This is not too hard, I simply use my shooting board after cutting them to approx. length and it only takes a few minutes.

Without them being the same length, then some kind of jig or cutting to pencil lines (not accurate enough I'll wager)

Since getting the Rat, my tenons have improved considerably - and they were pretty good before :wink:

 

[ike]

Rog,

Mark 1 Eyeball and a scratch does it for me.

My setup is a pre-Ryobi/Record type CI table/sliding table (badged from Woodcut Trading) with M12V.

I use a planer bit (or might be called a dado bit I'm not sure) 'bout 1-1/4" dia I think for tenoning. My router is permanently fixed to the table and located in a recess. I know even if I remove the router and replace it that the cutter edge will always be in exactly the same Y position. So I scribed a permanent reference line from the circumference of the cutter, along the fixed table parallel to the sliding table.

Shoulder markings are my datum so I ensure shoulder to shoulder scribes are cock-on. I don't worry so much about the overall length
I then simply line up the shoulder scribe to this reference line and clamp the piece. Repeatable withing a couple of tenths of a mill, (only as accurate as the marking out on the timber of course). I set the parallel fence back a couple of mil away from the end of the tenon.

PS. I have a wooden sub-fence on the mitre guage to act as a spelch block.

Ike

 

[engineer one]

roger you are not being obtuse i was being dumb, i thought you
were talking about indexing the mortises.

surely as long as you gang cut the initial shoulder on your ladder,
then all the tenons will be the same length.

same for working on the rat surely, you set the height by having a top datum, that's easy. as for the shoulder width that's where the
infamous masking tape and pencil trick, or you could use the
famous block of wood trick too. since you index the tenon at
the same place in the rat every time, then the wood block spacer
puts in the offset, and allows constancy just as tony suggested.

paul :wink:

 

[dedee]

jasonB wrote:

Depends what you use to cut your runs to length. I use the sliding carrage on my table saw which has a flip down stop so all bits are cut the same length.

That's how I would do it as well. I would also remove the riving knife, lower the blade and cut the shoulders on the saw bench using the sliding table, then use the router table to remove waste, all pieces would then have identical distances between the shoulders - Rob

That's how I did mine except as I do not have a router table I cut numerous kerfs in the waste on the TS then cleaned up with a chisel.

Andy

 

[SketchUp Guru]

Roger, I think Steve has hit on the solution that you need. Since the distance between shoulders is the critical dimension, you need to reference the second cut (shoulder) off the first.

If you use a sled or even a long fence with the miter gauge on your router table or on your tablesaw, you can add a stop block made thin enough to fit under the cheek of the first tenon when you rotate the work for the second cut. This method would basically eliminate the requirement of making all the rungs exactly the same length because you don't really care where the second end is. Of course to put the rungs into the sides of the ladder, you would care but as long as the mortises are slightly deeper than the tenons, that won't be a big deal.

 

[Anonymous]

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[RogerS]

Make a rod and take all the marks from it. Foolproof (almost) trad way.

cheers
Jacob

That smacks a bit of 'hand tool' to me :wink: Seriously, seems to me that places too much emphasis on aligning each piece of wood extremely carefully with concomittant potential for error?

On the 'rat suggestions, I'm still not clear whether people are cutting them vertically or horizontally...either way it seems to me that the starting point has to be equal length stock.

I still reckon Steve's way makes most sense to me at the moment but I'm really enjoying reading all the suggestions and learning all the time.

Roger

 

[ike]

Seriously, seems to me that places too much emphasis on aligning each piece of wood extremely carefully with concomittant potential for error?

Ahh, but there is also the satisfaction of getting it right with an ounce of hand skill chucked in. :wink:

cheers,

Ike

 

[Anonymous]

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[engineer one]

roger finally splashed down to where you want to be. sorry for the
delay, must be a senior moment. :lol: :twisted:

you are not worried about the length of the tenons, rather the distance
between the tenons on either end of a piece of wood.

let's use your ladder analogy again.

10 rungs all different in overall length by up to say 10mm.
the gap is 100mm between each rail, and that is what you want to ensure
is constant.

seems to me the simple solution is to use a scms as follows.
now have to say have not yet tried it, but the logic works.

find the centre of the longest piece of wood. now using some kind
of fixed measuring device which you can guarantee will give you a 50mm
swing on either side of the middle. strike the point at each end, and then square up.

let's say that you are cutting 25mm square tenons in a 50mm square piece
of wood. the offset is 12.5mm. so you need a stop block to ensure that as
the blade moves out and cuts, it does not go any lower than 37.5mm
checking with my 708, i would i think block up the leg from the bottom, and with the blade locked at its upmost height, with it all clamped up.
i am sure it is pretty stable and safe, then cut the top piece of the
tenon. the rear end of the wood would be blocked against a stop block.

assuming scrit thinks this is reasonably safe, then i would go all the way round on this first piece.

now cut another piece of wood the same depth. then make an l shaped
end stop out of this block. now just fix this piece against the fence
at the distance you want the second tenon. since you have chopped out
a complete tenon you end up with your length.

i think :?

i think this is generally safer than working on a table saw or a router,
but a similar system could certainly be fitter to a router table, or
indeed a table saw.

on a table saw, i would create a cross cutting sled as standard, then
cut the first tenon at the height of sled thickness plus height of half tenon,
then you can have a length stop on the the sled fence.

has any of this made sense??

paul :wink: