Which slitting saw

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

Poster reported for trolling.

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

Richard, I fail to understand why you can't see and admit to an error in the order of your formula and description for calculating TPI ?

Emgee

I can't see how you get 0,0083" and whats the comma doing there?

Taking Richard's formula

72 / (pi x d)

72 / (3.142 x 2.750)

72 / 8.6405

8.33tpi whats wrong with that?

Edit. Maybe you used 2750 as the dia rather than 2.750, should be using inches as we are trying to work out teeth per INCH

J

Edited By JasonB on 20/05/2016 14:57:00

Andrew thanks for posting the photo, like you I would class the one on the right and Emgee's as fine blades, OK for the shallow fins shown being cut but not ideal for cutting through thick stock.

J

Edited By Emgee on 20/05/2016 19:38:06

RIchard's formula was correct for TPI.

To work out the tooth spacing you need to take the reciprocal of Richard's formula (i.e. turn it upside down).

Neil

I have been following this thread hoping to find the answer to the question posed in the thread title. I am still not any the wiser. I suppose it is important to know the TPI to calculate feed speed and RPM.

But.....

What Slitting saw(s) should I buy? I work with mainly ali and mild steel with a bit of CI thrown in when I can afford it.

Bruce

Neil, exactly the point I was making but it seems Richard and I were on different topics.

Emgee

To try to get away from sums, whenever I try to cut a slot with my thinnest slitting saw it wanders off and gives worse results than I could have achieved using a hand saw. Anyone got any tips as to what I'm doing wrong, or is it just poorly sharpened?

Hi Duncan

I have experienced exactly the same result, put it down to me pushing the feed rate too high, another possibility was the blade had a lot of overhang to the OD from the arbor and clamping washer. I also found it important to have an accurately faced arbor and turned heavy duty clamping washer so the blade is not distorted.

Emgee

On my vertical mill I find that, for deep cuts, slitting saws go walkies irrespective of saw thickness. On the horizontal mill they cut straight, presumably because the horizontal arbor is stiffer and supported at both ends.

Andrew

Duncan, here are a few homemade arbors for slitting saws, 2 ISO 30 and 1 for an ER collet. I also made a selection of thick washers of various Ø's . I prefer to have the minimum amount of blade showing [ hence the various Ø's ] Also you must make sure that the mill is perfectly in tram in the x and y, or else wander and binding WILL occur. Any RADIAL run out is not to critical, in fact, even though these arbors show less than 0.005mm RADIAL runout even the best slitting saws like these Wolferal ones usually show radial runout. It's the AXIAL runout [wobble ] that can, and will also cause the saw to wander. These arbors have just under 0.004mm axial runout. with a 100mm Ø blade. They are made from En 24t .

I recently bought a 0.8mm x 50mm x 22mm bore slitting saw from a well known West Yorkshire based company but on fitting it onto a true running one piece mandrel I found the bade was running out of true eccentrically by 0.5mm which might be OK on a big casting but I was cutting a slot into a small, delicate and difficult to hold brass item so the eccentricity made the depth of cut a hit and miss affair and I was also worried that the eccentricity might dislodge the item from it's tenuous hold in a small chuck.

So I returned the saw and I am now on the lookout for a true running one if someone can suggest a supplier of good quality saws?

Sadly, thicker saws will also wander off, as i know to my cost!

Possibly, you could calculate the feed on the basis of Feed per Tooth. My traing notes, from 1958 suggest: soft materials, such as Plastics, Aluminium, Brass 0.003 to 0.005 Ferrous materials 0.003, Stainless steel 0.002 inch.

Obviously, I have been over anxious in my feeds. At least, remembering my Instructor's advice, by not using a key, the saw merely jammed rather than shattering.

Howard