Sharpening Fine tooth slitting Saws

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 18/05/2020 18:59:08:

Not sure I exactly agree with Michael's suggestion it's poor quality control, I suspect it's more value engineering because some teeth being a bit longer than others doesn't matter much in practice. […]

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That’s fine, Dave

When the Supplier is capable of providing whichever standard the Customer wants.

Indications from previous posts are that “our” Suppliers cannot.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 18/05/2020 18:59:08:

[…]

Martindale Saws quote a standard diameter tolerance of ±0.005" whatever the size of saw, which isn't exactly super-accurate. However, the more important thickness tolerance is ten times better at ±0.0005".

[…]

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Serious question :

Is a diameter tolerance of ±0.005" actually relevant, when the problem is eccentricity ?

MichaelG.

[WorkshopPeteParticipant @workshoppete]

Thanks everyone it looks like I need an 11V9 which gives a 70Deg included angle of the tooth unfortunately I checked the german supplier on eBay but they are currently out of stock I am waiting a reply as to when and if they are getting tham back.

Once again thank you everyone

Keep Safe

Peter

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Rutzen on 18/05/2020 17:45:00:

The question is why are they eccentric, even new ones? Do other people find that they run true? They are not visibly eccentric , but they don't cut evenly.

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That’s the question that I had already attempted to answer, John … Which is why I asked you to clarify.

Dave [S.O.D.] appears to disagree, so I guess the question remains open.

MichaelG.

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Edit: The fact that these ‘ultra precision’ arbors claim a T.I.R. of less than 0.0001” suggests to me that the target eccentricity for a slitting saw should be zero.

https://www.genswiss.com/sawarbors.htm

Affordable reality will, of course differ … My point was that good QA would make the tolerance known.

Edited By Michael Gilligan on 18/05/2020 23:17:53

[Michael GilliganParticipant @michaelgilligan61133]

I’m still trying to ‘get my head around’ this concentricity requirement …

My instinct tells me that manufacturers should be striving for perfection [simply because any eccentricity turns a circular saw into a single-tooth cutter] … but we need to understand ‘real-world’ acceptability standards.

This is the most helpful document that I have found so far: **LINK**

https://www.researchgate.net/publication/257337051_Automated_optical_inspection_for_the_runout_tolerance_of_circular_saw_blades

… and I think S.O.D. might find inspiration there, for a project.

[ Sorry to lead you into temptation, Dave ]

Note: It discusses inserted-tooth blades rather than solid, but the fundamentals are there.

MichaelG.

[David George 1Participant @davidgeorge1]

You can try here https://www.abtec4abrasives.com/standard-shapes-for-diamond–cbn-wheels-961-c.asp not connected but remember using them at work for grinding carbide for jigs.

David

[John RutzenParticipant @johnrutzen76569]

That's my point Michael, they work as a single tooth [ or maybe 4 or 5 tooth] cutter. The rest of the teeth don't do anything. I use circular saws on wood as well and the difference is I guess that the feed rates are so much higher cutting wood.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Rutzen on 19/05/2020 08:27:13:

That's my point Michael, they work as a single tooth [ or maybe 4 or 5 tooth] cutter. The rest of the teeth don't do anything. I use circular saws on wood as well and the difference is I guess that the feed rates are so much higher cutting wood.

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Then we are in total accord, John

… and my “answer” to Why? remains as stated.

MichaelG.

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P.S. ___ The paper that I referenced earlier is the only place that I have found a suggested tolerance for radial runout

In 5.1 it states: For each sample, the radial runout tolerance was specified as 0.03 % of the nominal diameter,

___ and the tabulated test results are impressive !

Q.E.D. ?

Edited By Michael Gilligan on 19/05/2020 08:49:19

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Gilligan on 18/05/2020 23:03:43:

Posted by John Rutzen on 18/05/2020 17:45:00:

The question is why are they eccentric, even new ones? …

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Which is why I asked you to clarify.

Dave [S.O.D.] appears to disagree, so I guess the question remains open.

MichaelG.

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Edit: The fact that these ‘ultra precision’ arbors claim a T.I.R. of less than 0.0001” suggests to me that the target eccentricity for a slitting saw should be zero.

**LINK**

Affordable reality will, of course differ … My point was that good QA would make the tolerance known.

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Not disagreeing, more a suggestion that the reason is practical. Circular saws could be an example where it's cheap and easy to make them moderately accurately, and much more expensive to meet high tolerances.

Another question: is the run-out due to the mounting hole being off-centre, or is it due to the teeth being cut to different depths? As turning discs accurately to a diameter is painless, I suggest run-out is caused by errors introduced by cutting the teeth.

I don't know but imagine the teeth are ground one at a time with a form grinding wheel that's redressed or replaced when it wears badly, and the machine re-set. Likely more than one form tool is used to finish teeth. Easy to imagine a fine form wheel wearing as it goes so the last tooth is cut smaller than the first. It's a hypothesis, but the evidence is weak. Nonetheless, it suggests a maker of cheap saws might leave form wheels running for as long as possible provided teeth came off reasonably sharp, and not worry much about their sizes!

Tolerances could be lifted by frequent redressing, maybe using a coarse wheel to remove bulk and a fine lightly loaded wheel to finish, perhaps a wear detector on the machine, and inspection.

Michael's 'This is the most helpful document that I have found so far: **LINK** ' made this morning's coffee delicious.

'Automated optical inspection for the runout tolerance of circular saw blades' describes a computerised optical jig for measuring radial and axial run out, repeatable to 2µm. The 2012 paper says the jig is innovative in that existing saw inspections are point contact methods, unreliable because the point wears out!

Despite the shortcomings of point contact methods, the authors found the radial and axial run-outs of their sample saws (inserts, not HSS) made by Yih Troun (Taiwan), were close to 45µm (radial) and 75µm (axial). Pretty good! The maker specification claims radial run-out of 0.03% of nominal diameter, about 30µm on the 100mm test blade (fail), and 60µm on a 100mm blade (pass). This is about 4 times better than the Martindale saws mentioned earlier, and I guess it's because the academics tested their rig on the most highly specified blades they could buy.

I guess saw-blades follow the usual law: high-specification tools cost more than low-specification tools!

But I wonder how much radial run out matters? The noise is annoying, but I don't think one tooth does all the work. Whilst the first tooth cuts deeper than the next, I reckon all the teeth cut because the saw blade is traversing as well as rotating? It's analogous to what happens when two locomotives pull a heavy train. If the first loco travels at 10mph and the second is doing 9.9mph, then the first loco must be pulling the train and the second loco, right? No, it's the sum of both engines that pulls the train.

I guess uneven tooth wear is the main ill-effect of runout. High teeth go blunt first, eventually leaving the saw half-sharp and half-blunt.

Run-out matters when blades are spun at high-speed but we don't do that. Nor do we care much about wear; as tool-changing is an expensive time-waster on production machines it probably pays to buy saws that wear evenly for maximum life between tool-changes. Very little value paying monster money for saws in my now and again workshop.

Maybe tool-abuse is more problematic in home workshops than saw run-out? I misuse mine! The small ones don't have any relief and I guess they're for very shallow slots or slicing sheet metal or thin-walled pipe. Likewise, although most of my bigger saws have relieved big teeth, the disc is flat and I doubt they're intended to cut deep – they're slotting saws. One saw, picked up last year in ignorance at an exhibition, has big teeth and side relief: this I think is the real McCoy, designed to chop metal. Naturally enough, I've been chopping metal with slotting saws for a good few years, certainly bad for the saw and explains why caught swarf was such a problem.

In my workshop, the Operator has much to answer for!

Dave

[egaParticipant @ega]

If my slightly-eccentric slitting saws really are, effectively, single point cutters then re-sharpening would be simple and could be done by hand: identify the high tooth and take a hand hone to it.

Far from a fine-tooth saw, but Quorn owners may be interested in this photo of one half of a TC-tipped 8" dado being sharpened with a diamond wheel:

[Andrew JohnstonParticipant @andrewjohnston13878]

All cutters run eccentric to some degree. Slitting saws probably just highlight the effect due to diameter and shallow cuts. Eccentricity will be due to tolerance build up from grinding spindle runout, accuracy of the centre hole diameter, grinding errors and runout on the teeth, and spindle runout and cutter fit when using the slitting saw. I'd be surprised if a grinding wheel wore significantly while grinding the teeth on one saw. Modern CNC grinders have means of detecting wear and dressing as required anyway.

Here's a picture of a coarse tooth slitting saw:

The gullets are quite rough, almost certainly milled rather than ground. When grinding the teeth only a short (~20thou) primary clearance on the tip of the tooth is formed. The OP specifies a fine pitch slitting saw. These are intended for shallow cutting only, such as slotting screw heads. The shallow cut and reduced feedrate will make any eccentricity more obvious. For the coarse slitting saw shown I'd be happy taking a 0.5" depth of cut and 4 thou/tooth chip load. That reduces the effect of any eccentricity. Incidentally the slitting saw is hollow ground. About half an inch from the periphery the width is 10 thou smaller.

Andrew

[ANDY CAWLEYParticipant @andycawley24921]

Nobody seems to have suggested kissing the periphery of the blade with a rotary grind stone whilst the saw is mounted in its working position. If the eccentricity is so small would it blunt the proud cutting tooth(teeth) that much?

It would surely only reduce the clearance on the offending teeth.

Would that matter so much.

It should eliminate that annoying drring, drring, drring noise that you get when using a slitting saw. I've not tried it as I only just thought of the ideas.

Debate?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by ANDY CAWLEY on 22/05/2020 10:34:37:

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Nobody seems to have suggested kissing the periphery of the blade with a rotary grind stone whilst the saw is mounted in its working position. […]

Debate?

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Have a look at my post of 17/06/2019 23:1807 on the previous thread : **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=142966

[ which I referenced on page_1 of this ]

MichaelG.

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Note: Topping is a term commonly used in horology, but is hopefully self-explanatory

Edited By Michael Gilligan on 22/05/2020 11:02:56

[ANDY CAWLEYParticipant @andycawley24921]

Aha

[Michael GilliganParticipant @michaelgilligan61133]

The important thing, Andy, is that you worked it out from first principles

… it really doesn’t matter that it’s a known process.

MichaelG.

[egaParticipant @ega]

Posted by Michael Gilligan on 22/05/2020 11:01:03:

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Note: Topping is a term commonly used in horology, but is hopefully self-explanatory

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I believe that "jointing" has a somewhat similar meaning.

[John HinkleyParticipant @johnhinkley26699]

And Stefan Gotteswinter does exactly that at the beginning of the video that I referenced earlier, to make the cutter concentric with the arbor, then attended to the gullet.

John

 

Edited By John Hinkley on 22/05/2020 15:38:28

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