Wide kerf table saw blades safe for non-through cuts?

[uncleswede]

Hi,

Pretty much novice woodworker here.

Is it safe to use a table blade saw that is wider than the riving knife providing it's never used for through cuts?
Basically, I'd like to use a 6mm kerf blade for my DeWalt table saw (which has a 3mm wide riving knife) for box joints using a custom crosscut sled...

Cheers
CD

 

[Jacob]

Hi,

Pretty much novice woodworker here.

Is it safe to use a table blade saw that is wider than the riving knife providing it's never used for through cuts?
Basically, I'd like to use a 6mm kerf blade for my DeWalt table saw (which has a 3mm wide riving knife) for box joints using a custom crosscut sled...

Cheers
CD

Yes. The riving knife has to be narrower than the sawblade anyway or it'd bind. Ideally just a fraction thinner but anything is better than nothing. You can saw through without a riving knife too, but with caution, in case of timber movement snatching the blade. More likely to happen with thicker material.

 

[deema]

No! The riving knife should be slightly larger than the plate of the saw blade, but narrower than the kerf. Using a 6mm kerf blade is highly likely to have a plate size wider than your riving knife. The riving knife becomes useless. You need a riving knife matched to the blade.

 

[HOJ]

use a 6mm kerf blade for my DeWalt table saw (which has a 3mm wide riving knife) for box joints using a custom crosscut sled...

For your intended purposes a riving knife will play no part, you will only need to make a cut just over the crown of the blade, then pull the sled back.

Make sure you do the diligence on extra measures to cover the exposed blade

 

[Jacob]

No! The riving knife should be slightly larger than the plate of the saw blade, but narrower than the kerf.

OK yes that's what I meant - ideally. But a thinner riving knife would still be effective

Using a 6mm kerf blade is highly likely to have a plate size wider than your riving knife. The riving knife becomes useless.

No it'd still help with wandering bits of wood.

You need a riving knife matched to the blade.

Ideally.

 

[Sideways]

Let me rewrite your question as this is in no way worse and probably better:
Is it safe to use a sawblade without any riving knife provided it isn't a through cut ?

It's not impossible for the wood to twist and pinch a little but it won't close up the way a rip cut all the way through can.

Try to clamp something across to give you a crown guard over the exposed blade if you don't have a proper overhead mounted guard.

I wouldn't be handholding the wood to the fence myself. I'd want it clamped and my fingers far away.

 

[Jacob]

....

I wouldn't be handholding the wood to the fence myself. I'd want it clamped and my fingers far away.

Yes i forgot to say two push sticks every time!

 

[Sideways]

Yes i forgot to say two push sticks every time!

I said it for you and then changed it when I remembered that this is supposed to be box jointing using a sled

 

[Eshmiel]

This is a rather strange procedure. Or is it the sparse description of what's being done that's causing some confusion?

If you're using "a custom crosscut sled" to make 6mm wide fingers/slots in the ends of a plank intended as a box side then you should have the workpiece firmly located in position by means of a tab-for-the-slot that's a fixed part of the crosscut sled ..... is that right? You move the plank sideways as each slot is cut, to cut the next one, leaving a finger of the same width between the slots as you do so ..... ? And you're pushing the workpiece on the sled just past the crown of the blade then pulling it back, by moving the sled forward then back, so it never reaches the riving knife .... ?

If so, the width of the riving knife is irrelevant as the workpiece never reaches it. If the workpiece is thick, it may reach the riving knife - but the knife is made redundant by the workpiece being kept aligned by the crosscut sled and its tab (and perhaps a clamp).

The sled with its tab will keep the workpiece moving aright as you clasp the workpiece against the fence of your crosscut sled - although you could increase safety by clamping the workpiece to the sled-fence as well, for each push through the blade, so it can't come loose from the sled fence and its locating tab then skew into the blade and kick back.

How do push sticks come into it?

Apologies if these guesses are entirely wrong. A more comprehensive description of your process might help, particularly what you mean exactly by "a through cut". This could mean that you don't go right past the blade or it could mean that the workpiece is thicker than the blade height so only cuts a groove in the underside of the workpiece when passed right over the blade. I presume its the former, if you're making finger joints - what you call "box joints" ...... ?

 

[Orraloon]

It is perfectly OK to use a trenching blade for non through cuts without a riving knife. Lets face it it's what those blades are made for. Box joints using a sled is even safer. As Eshmiel pointed out clamp the work to the sled fence for each cut and you have the full belt and braces safety thing happening. Actually clamping the work on a sled makes for better cut as nothing can move out of place during the cut.
Regards
John

 

[hlvd]

Anything you see on YouTube done by US woodworkers using a Circular Saw’s best avoided. Use a router table instead.

 

[Doug71]

This is one of those operations which thanks to Youtube often involves novice woodworkers with homemade jigs removing the blade guard, standing inline with the blade, leaning over the blade, fingers too close to the blade etc............I would suggest it's best avoided.

There is a reason SawStop is so popular in America.

 

[rob1693]

I made this jig for box joints,in operation it's pretty safe blade is covered for full length of cut and both hands are on the fence in use

 

[Eshmiel]

This is one of those operations which thanks to Youtube often involves novice woodworkers with homemade jigs removing the blade guard, standing inline with the blade, leaning over the blade, fingers too close to the blade etc............I would suggest it's best avoided.

There is a reason SawStop is so popular in America.

I tend to agree. All my box joints are made using a router table and a sled running on the fence that's made for the job (by Veritas, not me). The advantages are many, not least the ability to cut box joints with fingers & slots from 3.2mm up. One installs a straight spiral-edged router cutter of the required width and sets two metal indexing tabs to the same width.

Slotting cutters or dado sets are far more expensive. What would it cost to vary the width? Zillions! Home made sleds can, as you mention, be well made or ..... not. Those YouBoob vids showing dangerous table saw operations of every kind, with not a safety device in sight, are also legion.

 

[Agent_zed]

Trying not to get too far off-topic, but the 2 danger areas it would seem to me with sledges are

putting your hand over the sledge where the blade passes through
Solution - but a polycarb cover over the sledge to cover the blade. Add handles to the ends of the sledge and only push on those. Paint all areas close to the blade in red, and never put hands in that area.

Blade passes through the sledge and blade is exposed to the rear
Solution - Build a box with a clear cover where the blade comes out. If it has a tab that is lower than the edge of the saw, the sledge cannot be pushed far enough to expose the blade past this 'safety box'.

Clamp all work pieces and don't use hands to hold them.

Am I missing anything?

 

[brocher]

I tend to agree. All my box joints are made using a router table and a sled running on the fence that's made for the job (by Veritas, not me). The advantages are many, not least the ability to cut box joints with fingers & slots from 3.2mm up. One installs a straight spiral-edged router cutter of the required width and sets two metal indexing tabs to the same width.

Slotting cutters or dado sets are far more expensive. What would it cost to vary the width? Zillions! Home made sleds can, as you mention, be well made or ..... not. Those YouBoob vids showing dangerous table saw operations of every kind, with not a safety device in sight, are also legion.

Eshmiel, I was just wondering what your veritas jig is. Where can I buy it in UK? As I have a hankering making a few smallish boxes for charity shops from my supply of miscellaneous wood! Thanks

 

[Eshmiel]

Eshmiel, I was just wondering what your veritas jig is. Where can I buy it in UK? As I have a hankering making a few smallish boxes for charity shops from my supply of miscellaneous wood! Thanks

Hi Brocher,

Alas, Veritas no longer make and sell their older version of a router table. A pity, as it comprised a whole system of add-ons for doing all sorts, even pin-routing. The core table top is still dead flat after 20-odd years of use; and all of the fence and other parts still operate and adjust perfectly too.

Nor is there a PDF manual showing all it could do. I have the 73-page paper manual that came with it and somewhat grainy videos about how to use all the various add-ons but that's it.

There are probably modern equivalents .... maybe even a cross-cut item for making box joints ..... but if so I don't know what they are.

I can photograph the table, fence and box-joint gubbins on mine, of you like. It wouldn't be impossible to make one to do the same operation on a modern router table. Ideally the sliding arm that pushes the workpiece into and across a cutter to make the box-joint fingers and gaps should slide down some sort of way (e.g. T-track) along the fence, with the fence used with a micro-adjuster to position the sliding arm and hence the fingers/slots.

Give me a day or three and I'll make some photos.

 

[brocher]

Hi Brocher,

Alas, Veritas no longer make and sell their older version of a router table. A pity, as it comprised a whole system of add-ons for doing all sorts, even pin-routing. The core table top is still dead flat after 20-odd years of use; and all of the fence and other parts still operate and adjust perfectly too.

Nor is there a PDF manual showing all it could do. I have the 73-page paper manual that came with it and somewhat grainy videos about how to use all the various add-ons but that's it.

There are probably modern equivalents .... maybe even a cross-cut item for making box joints ..... but if so I don't know what they are.

I can photograph the table, fence and box-joint gubbins on mine, of you like. It wouldn't be impossible to make one to do the same operation on a modern router table. Ideally the sliding arm that pushes the workpiece into and across a cutter to make the box-joint fingers and gaps should slide down some sort of way (e.g. T-track) along the fence, with the fence used with a micro-adjuster to position the sliding arm and hence the fingers/slots.

Give me a day or three and I'll make some photos.

Thanks Eshmiel. That is useful

 

[Eshmiel]

Pics of the old style Veritas router table and cross-cut fence. (I must clean the dust of it).

The table top is held by a birch ply frame and has a Triton 3hp router suspended underneath. The Triton is good for such a role as one can wind its collet up above the table height to change bits, which also prevents the router from starting.

The tabletop is 1/4" sheet steel that has a very slight crown so that hanging a large router from it of typical weight pulls the tabletop dead flat. It's stayed that way for 20 years so far.

The fence has many T-tracks built-in and can be reconfigured in many ways by undoing Allen-head grub screws. Various hold-downs, stops and see-through Perspex protection plates can also be mounted. The fence is movable by use of a micrometer thingy reading in, of course - its from North America, thousands of an inch rather than a sensible metric value.

The fence also has a way along the top on which the cross-cut fence can ride. This cross-cut fence too can be reconfigured in various ways; and it takes hold-downs et all just like the main fence. The small block of wood facing end-grain-out is for use as a spelk-preventer when the cross-cut fence is used to make finger/box joints. The block can be rotated or replaced with a new one as its used up over several sessions. It's held by special T-track sliders with wee teeth, pressed into the block by more grub-screws that force the fence parts together.

To make a box joint, a straight cutter (perhaps with a spiral) of the required finger-width is put in the router at the appropriate height. The plank to be fingered on its ends is then held vertically against the cross-cut fence with hold downs riding then locked in the T-track; and the work piece is positioned for each cut by opening the small metal fingers to the finger width then using them to index the sideways movement per cutting operation, as slots are cut one at a time to leave the fingers.

There's a set-up process for placing the initial cut and getting the finger/slots width exact. Its possible to make softwood slots and fingers that are a tad too tight as softwood squashes so the resulting jointed corners are very hairline-jointed with ne'er a gap. For hardwoods, the gaps and fingers are set to an exact width - a couple of thou change is possible using the main fence micrometer adjuster.

Once the thing has been set up, one may batch process as many box-sides as needed. They'll all match and be gap-free. There's no spelching or other breakout if the backing block is used, a spiral bit is used and the passes of the workpiece over the cutter are made at an appropriate rate. One's own fingers and hands are well out of the cutter path. The hold downs attached to the cross-cut fence will hold the work piece firmly in place during each cut.

 

[Hugh M.]

Eshmiel, I was just wondering what your veritas jig is. Where can I buy it in UK? As I have a hankering making a few smallish boxes for charity shops from my supply of miscellaneous wood! Thanks

You can get the Rockler jig in the UK. Imperial only which is a little 1950s. You only need 3 cutters though. The jig comes with spacers for 1/4, 3/8 and 1/2. You need to find extra spacers for each size.