Why does circular saw blade scorch the timber?

[Nick]

Recently acquired a 3ph saw bench (Norsaw 1603) with 16" Trend tct blade, 40 tooth I think. Saw needed a little fettling. After a trial run I removed blade and delivered to sawdoctor for sharpening. Whilst this was being done I set the saw up to my satisfaction. Replaced the blade and tried it. Blade runs true as far as I can tell. Cuts well enough but 2 immediate problems.

1) Sawn edge of timber is scorched on both sides. Have tried this with various timbers from 10 to 125mm. 2) On pushing timber through the blade the far end tends to lift from the bench. Not a good thing. Both these problems were evident when I first got the saw and tried it.

A riving knife is fitted and all timber is well seasoned/dry. I can only think that the blade has a bump or something but there is nothing visible.

Any thoughts please?

Nick.

[Tim Lamb]

In message , Nick writes

Riving knife not thick enough to match kerf?

I folded a thin piece of sheet steel to widen mine.

The other question is... are you sawing high sap timber? This quickly builds on the clearance space behind the teeth and loads the cutting action.

[Mr Fuxit]

I can't see how you could set-up a saw with no blade fitted!

[Tricky Dicky]

Got to agree with Tim the riving knife is probably too thin. The last bench saw they bought where I worked came with a pair of knives one for a standa rd blade and one for tipped blades. Has your saw doctor done a good job can you see a set to the blade tips, we had a few bad experiences with some th at we used in the past before we found a good one.

Richard

[Bob Minchin]

The blade must be exactly parallel to the table slot otherwise the teeth on the exit side of the blade will rub on on side or other of the cut made by the front (cutting) teeth

Usually this is set by loosening the table and tapping until a dti registers the same from front to back of the blade body.

Final test can be done by cutting a narrow strip of wood clamped to the mitre gauge and listing to the blade it passes the back of the blade. You should hear a very slight noise. No noise almost certainly means it tilted away from the cut and would burn on that side if you were rip cutting. Lots of noise and it will be burning the end of the test piece. Note that is the arbour bearing is worn, any attempt at setting will fail. Fix this first.

[Bob Minchin]

This might be of relevance

[John Rumm]

Scorching sounds like one of two things...

Either the feed rate is too low - you need to feed the stock through faster. (note also some wood scorch more easily than others - cherry and maple are particularly easy to scorch IME)

Or, and this is the one I suspect given your comment about the back of the wood lifting. you have not got the saw setup correctly, and the wood is being pinched between blade and fence. If so this needs fixing PDQ because not only will lit trap and scorch the wood, its also a kickback waiting to happen.

You need to do the setup in two stages. Stage one, alight the table surface to the blade, and then stage two, align the fence to the blade.

The first is usually done by slackening off the bolts that hold the table, and moving it about until its mitre slots are exactly parallel to the blade. (long straight metal rule against the blade - missing the teeth, then use a dial indicator in a travelling sled in a mitre slot.

[Thomas Prufer]

I'd also set up the saw with melamine-faced chipboard. Real wood sometimes will bind fiercely on properly set up saw...

And the melamine facing will chip off where the saw comes "up" through the wood if the saw is off true.

Thomas Prufer

[fred]

Or he may have a blunt blade though I'm also more inclined to go with the misaligned theory.

Leave off the fence and push the timber through free hand.(CAREFULLY using at least one push stick) If it doesn't scorch then the fence is the problem

[stuart noble]

IME most hardwood scorches because of the resin content. I've got various bits and bobs lying around, some of which are at least 150 years old, and they still bleed resin when cut. I would test the blade on sheet materials or decent quality softwood.

[John Rumm]

Rather than pushing by hand, use the mitre slot guide or a sledge instead of the fence.

[tabbypurr]

Sometimes you just need to reduce blade speed.

NT

[fred]

Not my experience. I'm using some oak obtained when an old teacher training college closed. Judging by the style of the construction the general fini sh and the age of the school this furniture is at least 70 years old. Cutti ng it on a table saw gave no burning. It mostly cane out of a lab.

There was also some pine among the items and it had the most beautiful scen t when re-cut.

Nearly all gone now into Versailles planters.

Similar story with some native oak we re-cut out of an 8ft log some 15 year s ago and air dried. Bugger to cut but no burning and the appearance of the quarter sawn boards is beautiful. The reason we re-cut it ourselves was to get the best of it quarter sawn

Good sharp blade and right speed of cut should give good resukts.

What hardwood were you using with a high resin content ?

[stuart noble]

The one I remember specifically was beech. The blade was well gummed up after cutting. Some unspecified fruitwoods, although soft in texture, also gave problems. I think maybe the blade hits a resin "pocket" now and then. Actually, oak has never given me problems.

[fred]

Not that I doubt you for a second but I've never had a problem with resin i n beech. The worst problems I have found were with Pine and its sisters. Tr ouble is I'm a miserable bastard and invariably use re-cycled wood as I get it free. But then I have to re-design things around available sections and keep a sharp eye out for buried metals and watch that buried dowels don't suddenly appear in the wrong place.

[tabbypurr]

in beech. The worst problems I have found were with Pine and its sisters. Trouble is I'm a miserable bastard and invariably use re-cycled wood as I g et it free. But then I have to re-design things around available sections a nd keep a sharp eye out for buried metals and watch that buried dowels don' t suddenly appear in the wrong place.

I find a tct blade eats nails happily enough. I wouldn't want to cut an eas ily rotatable metal fixing though, if it turns in mid cut you'd have a prob lem.

NT

[fred]

in in beech. The worst problems I have found were with Pine and its sisters . Trouble is I'm a miserable bastard and invariably use re-cycled wood as I get it free. But then I have to re-design things around available sections and keep a sharp eye out for buried metals and watch that buried dowels do n't suddenly appear in the wrong place.

asily rotatable metal fixing though, if it turns in mid cut you'd have a pr oblem.

Well with 300mm blades costing upwards of £150 for good ones I wouldn't b e risking it. Lots of present day chipboard is made from re-cycled material s so seeing the odd spark isn't unusual but I've had a whole tooth knocked out when cutting fresh 25mm sheets.

In theory we can pay extra for virgin sheets but in reality they're like he n's teeth

[DerbyBorn]

[e-mail] wrote in news: [e-mail]:

Has the blade got body clearance? I would expect the teeth to be wider - or staggered - to give the body of the blade clearance.

[tabbypurr]

I can't imagine a 40 tooth tct blade not having

NT