Rip or cross cut blade?

[promhandicam]

Can anyone tell me if this is a rip blade or a cross cutting blade.

Thanks









;D ;D

Steve

[Sgian Dubh]

Probably rip. It's got an aggresive hook and fairly large gullets. To be sure look to see if it's got a flat top (FT) grind. If it's an FT grind it's definitely a rip pattern. If it has an ATB (alternate top bevel) grind, it's a bit of a compromise, but to be effective as a rip pattern the bevel will be less than 10º.

Also look at the number of teeth per inch. A rip pattern has a tooth spaced roughly 1.25" to 1.4" apart, so a 24" diameter sawblade will have somewhere between roughly 50 and 60 teeth on the rim. A 24" diameter blade has a circumference of 75.384", (pi x d) or 24" X 3.141 = 75.384". To give you a comparison a 10" diameter FT grind rip blade typically has something like 20-24 teeth on the rim, and a 10" diameter blade has a 31.41" circumference. Slainte.

[promhandicam]

Thanks for the reply. I count 56 teeth and the dia is about 32" so that gives a tooth spacing of about 1.8". So from that I think we can safely assume that it is a rip blade. With regards to the tooth profile this is a bit more tricky. Several of the carbide tips were missing and some of those that were there looked as if they had been sharpened using an angle grinder. The owner was telling me that to get carbide tips replaced he has to go to neighboring Cotonou, capital of Benin as there isn't anyone in Lomé that can do the work.

Cheers, Steve

[engineerone]

at that size, steve do you really think the wood is going to complain ;D

not sure who looks more scared the blade or the bloke

paul

[promhandicam]

Jun 14, 2008 21:06:22 GMT engineerone said:

. . . not sure who looks more scared the blade or the bloke paul

You can see what the blade came out of here and I can assure you having been near it when it was running, you would have every right to look scared when that thing gets going, particularly as the operator - it was bad enough being a spectator!

Steve

[Sgian Dubh]

Jun 14, 2008 21:05:15 GMT promhandicam said:

I count 56 teeth and the dia is about 32"; so that gives a tooth spacing of about 1.8".

Cheers, Steve

Good point, Steve and something I'd forgotten to account for in my original response. Larger diameter sawblades are for cutting thicker stock of course, so they need suitably large gullets to carry away the waste: each tooth is engaged with the wood for a greater distance than the teeth on a 10" or 12" diameter blade could ever be. Slainte.

[promhandicam]

Jun 15, 2008 9:21:56 GMT Sgian Dubh said:

I'd forgotten to account for in my original response. Larger diameter sawblades are for cutting thicker stock of course, so they need suitably large gullets to carry away the waste: each tooth is engaged with the wood for a greater distance than the teeth on a 10" or 12" diameter blade could ever be. Slainte.

Richard, Presumably the smaller gullet size on a crosscut blade due to the closer pitch of the teeth means that the feed rate when cross cutting has to be slower when comparing wood of the same thickness?

Steve

[Sgian Dubh]

Jun 15, 2008 10:22:52 GMT promhandicam said:

Presumably the smaller gullet size on a crosscut blade due to the closer pitch of the teeth means that the feed rate when cross cutting has to be slower when comparing wood of the same thickness?

Steve

I haven't thought about that too much, but I suppose I do generally cut slower on cross cuts. They're quite often precise cuts, such as cutting to length and it helps prevent spelch and splintering, plus shoving the wood too fast through the saw often stalls a small saw anyway.

The gullets are smaller, but that's because cross cut blades are ATB tooth pattern. Blades designed for a very smooth chip free cross cut use a HATB (High Alternate Top Bevel) pattern, usually something like a 40º bevel, although I've seen some blades advertised with up to, I think, a 60º bevel. I saw these blades mostly in the US when I lived there, and I see them advertised in the US magazines I subscribe to, but I'm not sure I've seen any with exactly this kind of configuration in the UK.

ATB and HATB tooth patterns are more like shark teeth or needles really and designed to slice, so lots of teeth equals more slicing. They create mostly dust and very small chips. The small gullets aren't especially efficient at carrying away the chips and dust compared to large gullets, but I don't think they need to efficient in the same way as a rip blade tooth pattern-- see next paragraph.

There is however another consideration. FT grind teeth, designed for ripping, have more of a shaving or scraping action. They create long curly shavings that take up a lot of space, so here's where a large gullet really helps. If you've ever cut up a load of wood with a FT grind tooth pattern blade you'll see a mass of these long curly shavings in your dust collector at the end of the day. I've even seen some extraction pipes choked with these shavings because the extraction system wasn't powerful enough to handle the volume of shavings. Slainte.

[promhandicam]

Thanks for that considered reply. I'd never really thought about the fact that chips or shavings formed by a FT pattern blade would take up more room than the dust produced by an ATB pattern blade. I suppose as well although the gullets are smaller there are more of them and so for each revolution they can possibly clear a similar amount of waste. I've not come across HATB pattern blades - they sound like the CS equivalent of a japanese pull saw blade. I guess however that it would be unwise to try the equivalent to cutting on the pull stroke by feeding the timber from the rear

Steve

[Sgian Dubh]

Jun 16, 2008 23:23:19 GMT promhandicam said:

I guess however that it would be unwise to try the equivalent to cutting on the pull stroke by feeding the timber from the rear

Steve

Er, yeah, probably, ha, ha. Slainte.