I ve just come across the same thing Andrew except I m making deep cuts/cutting off in cast iron and gunmetal..Having spent a long time looking up tpi for a 4″ blade .Coarse starts at 6 it seems..A bit too coarse?
Jonathon

Eric

Selection of slitting saws I have pictured in my album and 2 below show the .025" thick 72T cutting cooling fins on a 6082T6 aluminium cylinder head. Like Andrew says make sure the gullets are kept clear or jamming will occur, I use mist and air immediately after the blade exits the cut, this keeps swarf clear and lubricates the blade. Tooth pitch for the blade shown is 0,120"

Adjust your DOC and spindle speed to suit the job and remember thin blades can easily run off-line if pushed too hard.

Edited By Emgee on 18/05/2016 10:30:14

.

Pardon my intrusion but it's 72 teeth [total count], not 72 tpi

MichaelG.

Yes Michael, for the blade pictured above tooth pitch is calculated as 0,120" which is a shade over 8TPI (8.3).

That depends on how you measure it? If one stretches it out as if it were linear, the tpi would be around 9. Not a lot of difference, just depending on whether one uses the tip diameter or the root diameter. Is there a standard way to calculate it?

Richard, using PiD to calculate the tip spacing on the OD stated gives a tooth tip spacing of 0,11999", seemed sensible to me to round that figure off to the 0,120" stated. 1000/120 provides the TPI of 8(8.3) stated. This is of course the arc measurement but if the chordal length between teeth is calculated the difference is negligible in this case because of the small angle between teeth. This is no doubt the reason for slitting saws to be sold by diameter and number of teeth but not always stating the TPI.

Emgee

Richard, TPI is relevant as the question was course or fine, I note you still insist the pitch is not the 8(8.3) , you must be using the wrong figures in your calculation. Saw diameter is 2.75" and number of teeth is 72, root diameter is not used.

Emgee

Here Again, if you are doing a lot of cut off work with a slitting saw in non ferrous then think about using one of the small diameter carbide tipped blades that are made for cordless circular saws. These are typically 18 to 24 teeth on a 3-4" dia blade and being tipped the main plate of the blade is thinner than the kerf so less chance of binding in the cut.

J

PS I'll let the other guys fight over work out the tpi for you

Too many variables there Jason to come up with a single answer !!!!!!

Emgee

Emgee,

I have nothing more to add but I would ask you to check your formula 72/(Pi*d) as it calculates a very fine pitch saw !!!!!!!

l am very glad that you have nothing more to add! Your maths is amazingly poor..

Just look at the units of that formula.

It is number of teeth divided by a length. In Imperial units that means TPI! Using 2.75'' as d, the result is 8 tpi. Using 2.5 (estimate) the pitch is estimated as 9 tpi. There is nothing difficult in that simple equation for you to calculate ''a very fine pitch''!

As you did not even address my query I am considering your replies as totally inappropriate.

The matter is now closed to you. Anyone else may have some pertinent information as to the normal convention for calculating pitch for a circular saw. I most certainly know that for a linear calculation the answer would be the same whether using measurments from tip or root of the teeth and can be different for a non-linear surface.

Bye

Richard, may I suggest you look at your formula closely, it's clearly wrong as is your description of TPI. When the penny drops you will see your mistake and then may agree my maths are not so poor after all.

As most people on this forum already know the correct formula to calculate the spacing of teeth is length divided by number of teeth, so in the case of the slitting saw: (Pi*d)/Number of teeth.

Using your formula 72/(Pi*d) (teeth/length) results in a tooth spacing of 0,0038" for the 2.750" saw.

Emgee

He is a regular poster that does not do that sort of thing.

Emgee does seem to have a problem seeing your point that if working out the tpi from the base of the gullet which would be approx 2.5" dia you would get 9tpi rather than 8.3 at the tips using the same formula.

Though maybe Emgee is being criptic as you could say the blade has 9gpi (Gullets per inch) and 8.3 tpi (tips per inch). Now as a "tooth" consists of a leading edge, gullet and trailing edge then maybe the Teeth per inch should be taken as a mean of the two lengths?

J

Edited By JasonB on 20/05/2016 07:42:58