Thread: Saw for sliding dovetails (pt 1)

Well, the proof of the pudding, as they say…..

I cut a short sliding D/T to see how it all worked. The first thing I noted was that my marking-out procedures need a bit of smartening up. I am too used to doing these with the router and a simple jig, so it took a few heavy head-scratches to lay out my joints, but eventually I worked it out. I set up my simple fence to cut the sides of the trench, which has 1mm taper across the 120mm wide bit of scrap on the angled side, which would normally be the ‘down’ side of a shelf or carcase component.. (pic 1)

A bit of serendipity is that the bevel on the saw cheeks (which is matched to the bevelled side of the trench), means that the vertical cut and the angled cut end up as close to the same depth as you could wish for. So a bit of chiselling out of waste, cut the matching D/T and Bob’s your relly!

Pics 2 & 3 show the pieces after a couple of trial fittings. It’s sitting proud by a few mm after being slid firmly together – a couple of firm taps drove it solidly home.

All good on that quick test-run – it will be a another story when I try a couple of full shelf-width D/Ts! But this has shown me I need two things – a bit of practice at laying out, and a router plane. I did have one for a while, but never used it, so sold it off. Now I’m thinking of getting a couple of LV blades & making myself one. Darn it – I thought I had all the tools I ever needed…….


Cheers,

Ian- You do very nice work! -Howard

Hi Ian

Nice saw, especially as there is a developmental process involved.

I would still call this a stair saw, especially as it is breasted and capable of starting the cut in the centre of a board.

I am not sure that I have the skills to use one to saw accurately for either a dado or a dovetail, and prefer a guide (which I use with a mitre saw - you've seen this before so I shall not post a picture of it, but the link is here). The question is, can you design a guide for this saw?

Regards from Perth

Derek

Originally Posted by derekcohen

I am not sure that I have the skills to use one to saw accurately for either a dado or a dovetail, and prefer a guide ..... The question is, can you design a guide for this saw?

Hi Derek yes, the principle is the same as a stair saw. The crowning is slight, just enough to make it easy for initial kerfing along the cutting line. I just guessed the amount, thinking I'd keep it minimal to begin with, because of the aforesaid problem with having a slightly shallower cut when doing stopped trenches. But the amount I gave it is adequate, and it's very easy to start anywhere along the line.

It does have a guide, albeit a very simple one (see first pic in 2nd post) P'raps I should have referred to it as a 'fence'? I simply ripped a piece of wood with a right angle one side, and the dovetail angle on the other. I was prepared to experiment a bit with fence heights, but the 20mm piece I started out with felt right, so that's what I'll stick with for now. You just hold the saw firmly against it with your left hand as you saw. The narrow, stiff blade makes it very easy to feel when it is against the fence. The almost zero set prevents the saw from chewing up the bottom of the fence, but I imagine it will scuff it up a bit over tme - no worries, it takes about 2 minutes to make another.

The cheeks of the saw are planed to the complementary angle, so that they meet the fence at full depth on the angld cut. When sawing the vertical side of the trench, the side of the fence is a little shorter than the angled side, but the inside of the cheeks hits the fence sooner, so the cuts end up as close to the same depth as my eyes can discern. After it happened, I did a bit of mental trigonometry, and realised that that is how it should be, of course, if the angles are complementary. But I won't claim I thought of it in advance!

You under-rate your skills, my lad - if you can cut accurately with that great weapon you used (I would make a right mess with something like that!), you would find this saw a breeze. It's very easy to position, everything is in line & close to the action, and as I said, you can easily feel when that short blade is snugged up against the fence. I produced two near-perfect cuts on the first try, and I certainly don't think I am any more skillled with a saw than you are.

Looks like I will have to send you one for evaluation & further development, before we sell the patent rights to Veritas or LN???

Cheers,

I would still call this a stair saw

Surely the inventor can call it whatever he wants

A couple of questions:

1. Could you make the handle in two pieces to make it easier to construct, and either laminate two halves together to arrive at what you have there, or just have one side of the spine as a separate piece and have it all held together with the bolts?

2. What's the reasoning behind the half-dovetail? Is it just because it's easier to only have to cut one sloping side?

Originally Posted by silentC

2. What's the reasoning behind the half-dovetail? Is it just because it's easier to only have to cut one sloping side?

in a way you could say that, but really in many applications (shelves for instance) thats all that is needed to do the job, to stop the sides from bowing or cupping outward, so the theory is if thats all thats needed then why do more. the dovetail housing joint in its most basic form would not have the added shoulder (or rebate) to the top of the shelf as in the pic above (its laying on its side if representing a shelf), it would be left square and the housing in the side trenched a little wider to fit, adding the shoulder to the top can help hide a (finished) gap if the taper on the dovetailed shelf or housing are somewhat mismatched (loose if you like).


cheers
chippy

As usual, you've produced a lovely looking saw Ian, but I don't understand why a dedicated saw is required for cutting sliding dovetails. I may be missing something vital: I'm a self-taught 'cabinetmaker', so it's not beyond the realms of possibility.

I begin the angled cut on the edge of the board with an ordinary back saw and saw it full depth to start with so my eye 'learns' the necessary lean angle. After that it's just a case of keeping sawing until the cut is done.

How does your crowned blade design help? Why start sawing in the middle of the cut? Surely if you begin sawing on the edge it would be straightforward and wouldn't require a bevelled wooden guide.

thats all that is needed to do the job

Good enough reason in my book

Originally Posted by silentC

Surely the inventor can call it whatever he wants

Maker, silent, not inventor - it is indeed based on "stair saws".

Originally Posted by silentC

A couple of questions:

1. Could you make the handle in two pieces to make it easier to construct, and either laminate two halves together to arrive at what you have there, or just have one side of the spine as a separate piece and have it all held together with the bolts?

2. What's the reasoning behind the half-dovetail? Is it just because it's easier to only have to cut one sloping side?

Answer to 1, "Any of the above". I don't see why any of those methods would not work just as satisfactorily. I did it in one piece because that seemed like the best option for me, but if you don't happen to have a haandy slitting saw set up like mine, a two-piece construction might be the btter way to go.

Chippy has already answere Q2 as well as I could. When making S/Ds with router, you of course end up with angles on both sides. That's a theoretically stronger joint in terms of resisting tensile forces, but whether the difference matters in practice is a moot point. It doesn't complicate things overly to do angles both sides if you really want, & if I were doing this joint for say, the bottom of a cabinet, I would probably make both sides angled.

But of course, having to deal with only one angled side is easier. I would always rebate the 'top' side, myself, simply because it is easier to make a clean shoulder on the shelf piece and get a close-mating joint than to rely on getting the top side of the trench perfect, given that you are guddling away in there with a router plane or whatever......

All fair questions, & I hope that addresses them...
Cheers,

Originally Posted by Woodwould

As usual, you've produced a lovely looking saw Ian, but I don't understand why a dedicated saw is required for cutting sliding dovetails. I may be missing something vital: I'm a self-taught 'cabinetmaker', so it's not beyond the realms of possibility.

I begin the angled cut on the edge of the board with an ordinary back saw and saw it full depth to start with so my eye 'learns' the necessary lean angle. After that it's just a case of keeping sawing until the cut is done.

How does your crowned blade design help? Why start sawing in the middle of the cut? Surely if you begin sawing on the edge it would be straightforward and wouldn't require a bevelled wooden guide.

WW - all fair comment, & reasonable questions.

No, I don't need a dedicated saw, but I wanted one, and becaause I can, I did.....

True, you can make a long straight cut across a board with a backsaw. However, if you look at the pics in the link Derek posted, you will see that he had a bit of trouble cutting to his scribe line. I have at least as much trouble getting a long saw with teeth in a straight line to follow a long cut from such a shallow attack angle. The method you describe is pretty much how I have done it previously, when trenching for shorter S/Ds such as for drawer dividers & so forth.

You can also make a legitimate argument that the cut needn't be absolutely perfect - anyone who has done a few S/Ds will know that they can be a bit rough in places, but the joint can still snug up nicely enough, and any ragged bits should be well hidden by the over-riding shelf edges.

However, it just seemed to me that a saw with a shorter, narrower blade, a low centre of gravity, and slight crowning would make the task a whole lot easier, and in my short test, that is exactly what it did. I was able to start the saw at the right angle anywhere along the line, & having an automatic depth stop, & not being forced to guess when I am at depth is worth the effort alone. The shorter, crowned blade allows me to cut a stopped trench closer to the blind end, meaning less chiselling & mucking about at the stopped end.

I would probably still use my regular D/T saw to cut the sides for a 50-60mm long drawer-runner trench, for e.g., because I couldn't be bothered having to muck about & clamp on a fence for such short cuts, and the S/Ds for table legs mating into a round pillar can only be done by eye, since there's no practical way of using a fence in that situation. But this saw makes doing 400-500mm long cuts much more accurate, & easier than any method I've tried, apart from a router & jig.

So, I don't think everyone need rush out & make themselves such a saw - if you only plan to make few S/Ds in your life, it's not worth thinking about. But if you just happen to like making saws...........

Cheers,

Fair enough. It's something else I should try some day.

How does your crowned blade design help? Why start sawing in the middle of the cut? Surely if you begin sawing on the edge it would be straightforward and wouldn't require a bevelled wooden guide.

WW, I think that there the crowned blade is a throwback to forming a housing joint in the middle of a board. Of course we are talking about a dado and not a sliding dovetail (you cannot have a dado in the middle of anything). The stair saw is crowned for this purpose, and the design is common to both Western and Eastern saw users.

With a sliding dovetail the trench needs to be entered from one edge (at least). There is no need for a crowned tooth line. I have also used a dovetail saw for stopped dovetails. If, however, the dovetail extends the full width of a board, then I use a long mitre saw. This follows the line more easily.

You also make an interesting point about sawing from the edge - I assume you mean that you create a saw line (which becomes a guide for itself) from the marks on the edge of the board. I've not thought to do that before.

Regards from Perth

Derek

Originally Posted by derekcohen

.....
You also make an interesting point about sawing from the edge - I assume you mean that you create a saw line (which becomes a guide for itself) from the marks on the edge of the board. I've not thought to do that before.

Derek, when doing something like this table pillar, I could not think of any other way of doing the trench sides. Even if you chisel out some of the waste at the end, it's still not possible to get the cut to full depth at the end. You still end up doing a fair bit of paring, but at least you have established the right angle....

Cheers,

Originally Posted by derekcohen

You also make an interesting point about sawing from the edge - I assume you mean that you create a saw line (which becomes a guide for itself) from the marks on the edge of the board. I've not thought to do that before.

Regards from Perth

Derek

Until someone else recently mentioned using an angled guide, I knew no other way of doing it. It's how I begin the majority of saw cuts. How else do you saw half-blind dovetail sockets?