"Teeth per inch" question

[Lazy-Ferret]

OK, so I under stand that if you have 15TPI, on a saw blade, you have 15 teeth over an inch of blade....

But what does 5/8TPI mean? I had a go at googleing it, and it just wants to tell me about "Threads per inch", which is not much help on a saw blade.

[rustic]

Originally Posted by Lazy-Ferret

OK, so I under stand that if you have 15TPI, on a saw blade, you have 15 teeth over an inch of blade....

But what does 5/8TPI mean? I had a go at googleing it, and it just wants to tell me about "Threads per inch", which is not much help on a saw blade.

Logic says... if say 1/2 tpi, would mean two inches between each tooth, so 5/8 tpi would be 8/5 or 1.6 inches between teeth.

What have you got with tooth spacing like that... a dinosaur...lol

I have not heard about this before... so I might be wrong... but using logic...

[Lazy-Ferret]

Originally Posted by rustic

Logic says... if say 1/2 tpi, would mean two inches between each tooth, so 5/8 tpi would be 8/5 or 1.6 inches between teeth.

What have you got with tooth spacing like that... a dinosaur...lol

I have not heard about this before... so I might be wrong... but using logic...

Well, like you, that was what I thought and is totally logical, but it's not the case.

I can only think it is something to do with the blade having a variable TPI, this picture shows it a lot clearer than my blade does, where it is hardly noticeable.

http://www.ebay.co.uk/itm/Bosch-RDN9...item4d25f868d5

What I still don't understand though, is how that would work, e.g, are there 6x5TPI, followed by 6x8TPI? It does not look like that in the picture though.

[rustic]

Originally Posted by Lazy-Ferret

Well, like you, that was what I thought and is totally logical, but it's not the case.

I can only think it is something to do with the blade having a variable TPI, this picture shows it a lot clearer than my blade does, where it is hardly noticeable.

http://www.ebay.co.uk/itm/Bosch-RDN9...item4d25f868d5

What I still don't understand though, is how that would work, e.g, are there 6x5TPI, followed by 6x8TPI? It does not look like that in the picture though.

So some teeth are spaced at 5 teeth per inch, and some of the teeth at 8 teeth.
per inch.

[Lazy-Ferret]

Originally Posted by rustic

So some teeth are spaced at 5 teeth per inch, and some of the teeth at 8 teeth.
per inch.

I guess so.

Like I said though, that does not really tell you anything, I mean it could be half the blade is 8, the other half, 5, or it could be every other tooth. \not really sure what the benefit is either.

[johnb5177]

I deal with saw chain all the time, and we use `pitch` on a chain which is the distance between 3 rivets. The same as a bike chain. On the rack benches I have used the teeth are about 1 every 1.5 inches, for ripping down timber.
5/8 tpi and variable tpi sounds very odd and would produce a very unbalanced disc, if it is a round saw, or is this a band saw?
Even so I imagine cutting would be very prone to vibration and catching, even set up some very strange ocillations and waveforms in the band?

[Lazy-Ferret]

Originally Posted by johnb5177

I deal with saw chain all the time, and we use `pitch` on a chain which is the distance between 3 rivets. The same as a bike chain. On the rack benches I have used the teeth are about 1 every 1.5 inches, for ripping down timber.
5/8 tpi and variable tpi sounds very odd and would produce a very unbalanced disc, if it is a round saw, or is this a band saw?
Even so I imagine cutting would be very prone to vibration and catching, even set up some very strange ocillations and waveforms in the band?

This is only a reciprocating saw, so not such a problem, just like an over sized jigsaw.

The main reason I asked was, I purchased some "General purpose" blades for it, and some Wood/plasterboards ones. The wood/plasterboard are 15tpi, but the general purpose ones have this weird 5/8TPI, which got me thinking and wondering.

The blades are similar to the ones I showed in the picture, where the actual teeth look about 7TPI, which I guess it's an average of the 5 and 8, give or take a bit.

[johnb5177]

So sorry for being a complete dumbo....

I did not look at the fleabay link! It would have been self evident.....prat, sorry!

[solarman216]

5 teeth followed by 8 teeth etc, sales/marketing crapp, have tried them all, what makes the difference is how sharp they are and the set of the teeth, ie how far they are bent from the flat blade each side, or the kerf, there is more but this will do for now, Rick

[kitchenman]

I prefer variable pitch on hole saws starret type, with fixed pitch they set up a vibration, much smoother with variable, most likely the same with straight blades

[solarman216]

they have been trying for years to come up with a one blade saw that will do rip and cross cut, all have failed, hole saws are a bit different, Rick

[Lazy-Ferret]

Originally Posted by kitchenman

I prefer variable pitch on hole saws starret type, with fixed pitch they set up a vibration, much smoother with variable, most likely the same with straight blades

Good point, it is definitely noticeable on the hole saws, but I just thought it was because they tend to be the better quality ones in my tool arsenal.

I will have to try a couple of cuts with the different blades and see what they do.