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Improving runout in a slitting saw

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andrew lyner17/06/2019 20:45:35
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I have read a lot of comments about slitting saws, going back years and years. But I haven't found anything about improving the runout.

As far as I can see, if the saw is eccentric then there will be some teeth that are hardly doing any work at all if the cutting depth is less than the runout. I measured / estimated the runout on my 50mm saw and it's around 0.3mm and that seems to be typical. Ching ching ching. Has anyone tried using an abrasive stone (at an angle, perhaps) to achieve a uniform 'ching' over the whole rotation? I realise that not all teeth would be cutting well but surely there would be more teeth doing work than when it's only the high spot on the wheel that's working. There will be teeth that never get used at all!! That offends my stingy streak.

When you think about all the care that's used in grinding HSS lathe tools and the obsession with the correct angles . . . . . I can't think I'm the only one to have thought about this.

Do saws 'wear down' to circular in the end?

Edited By andrew lyner on 17/06/2019 20:46:28

old mart17/06/2019 21:19:42
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Maybe thinking about an adjustable mandrel would be the better option. All of mine are eccentric too, probably not being British made is the reason.

Andrew Johnston17/06/2019 21:45:05
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Posted by old mart on 17/06/2019 21:19:42:

All of mine are eccentric too, probably not being British made is the reason.

Yep, that'd do it!

With a quality arbor and slitting saw I'd expect the eccentricity to be better than 0.05mm, give or take. A value of 0.3mm is awful. Having said that even with a perfect arbor and quality saw there will still be some eccentricity, and the saw will still go ching ching. If you're taking a reasonable depth of cut and using a good feedrate a small eccentricity doesn't matter.

I've never seen an adjustable slitting saw arbor, or needed to think about it. I guess it comes down to cheap saws probably needing adjustment and better ones not.

Andrew

Michael Gilligan17/06/2019 22:23:40
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I suspect that the only way to 'correct' an eccentric saw would mount it by the teeth and re-bore the hole.

... Could get tedious dont know

MichaelG.

ega17/06/2019 23:05:46
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Posted by Michael Gilligan on 17/06/2019 22:23:40:

I suspect that the only way to 'correct' an eccentric saw would mount it by the teeth and re-bore the hole.

... Could get tedious dont know

MichaelG.

Wouldn't it be better to mount it by the bore and re-grind the teeth?

Michael Gilligan17/06/2019 23:18:07
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Posted by ega on 17/06/2019 23:05:46:

Wouldn't it be better to mount it by the bore and re-grind the teeth?

.

Seems like a lot more work, to me !

... unless you are proposing to just 'top' them

MichaelG.

.

http://www.slitting-saw.com/down_file.php?downfile=tooth-forms.jpg

Edited By Michael Gilligan on 17/06/2019 23:31:25

andrew lyner17/06/2019 23:32:26
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I wonder just why they tend to be so 'bad'. It's another of those mysteries to me how the things are actually made. I could imagine the blanks being stamped out and then the teeth sharpened and set as the blank is rotated past a die of some kind. Where do the errors come in?

I have the same question about drills which can be made in three ways (according to the adverts) at various costs.

In the end, does it matter except that cutting with a bad blade could take longer.

Edited By andrew lyner on 17/06/2019 23:33:31

Michael Gilligan17/06/2019 23:43:49
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Feast your eyes on this, Andrew : **LINK**

https://youtu.be/FAs-f_9IJK4

[ rough approximations are available elsewhere ]

MichaelG.

fizzy18/06/2019 07:07:55
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love the final set up in the video link

- hit it wit ommer till its straight!

JasonB18/06/2019 07:35:53
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The only problem with regrinding your own would be by the time you get all the way round your stone would have worn so you will have taken more off the first tooth than the last particularly with the tendency to use high tooth count saws when less will do for 90% of cutting. May fair a bit better with diamond.

Michael Gilligan18/06/2019 07:47:53
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Posted by andrew lyner on 17/06/2019 23:32:26:

I wonder just why they tend to be so 'bad'. It's another of those mysteries to me how the things are actually made. I could imagine the blanks being stamped out and then the teeth sharpened and set as the blank is rotated past a die of some kind. Where do the errors come in?

...

In the end, does it matter except that cutting with a bad blade could take longer.

.

I posted the video link before I saw your edit, Andrew

Regarding that closing comment/question :Taken to its logical conclusion; a single-tooth cutter would work, if you have appropriate speeds and feeds.

MichaelG.

David George 118/06/2019 07:57:34
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As part of my apprenticeship I had to learn how to reground cutters and part of this was regrinding slitting saws and you would dress the wheel quite a few times when grinding the actual cutting faces the throat and clearance to make cutting edge. You would put a cut on and go round the whole saw and then put a couple of thou cut on and repeat the cut round again till you got no disernable difference then put a slight tenths cut on and repeat till you were sure it was round, the wear on the grinding wheel at the amount you took of was zero. This was repeated for the cutting edge clearance and so you could be sure if the arbour on the machine was correct it would run true.

David

andrew lyner18/06/2019 10:43:16
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Posted by Michael Gilligan on 17/06/2019 23:43:49:

Feast your eyes on this, Andrew : **LINK**

https://youtu.be/FAs-f_9IJK4

[ rough approximations are available elsewhere ]

MichaelG.

Cheers for that, Michael. That is all pretty top-end I would think. Very interesting to note the actual time taken on each individual blade. Cost a lot more than a fiver!! so out of my spending league. If I bought one of those, I'd mount it on a mahogany plinth and stick it on the mantlepiece.

andrew lyner18/06/2019 10:48:41
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Posted by Michael Gilligan on 18/06/2019 07:47:53:

Regarding that closing comment/question :Taken to its logical conclusion; a single-tooth cutter would work, if you have appropriate speeds and feeds.

MichaelG.

If they are not actually in contact with the work, all those other teeth are only there to make the tool 'look' symmetrical. I guess they help to locate the actual cutting portion laterally but they can't be cutting unless there is a lot of vibration.

Makes you think . . . .

Ian S C18/06/2019 14:15:43
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I was watching U tube the other day, the chap was using a slitting saw, he mentioned that all the saws tend to ching ching, but once he got cutting he upped the feed until he got continuous cutting sound.

Ian S C

Edited By Ian S C on 18/06/2019 14:16:22

andrew lyner18/06/2019 16:12:05
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Posted by David George 1 on 18/06/2019 07:57:34:

As part of my apprenticeship I had to learn how to reground cutters and part of this was regrinding slitting saws and you would dress the wheel quite a few times when grinding the actual cutting faces the throat and clearance to make cutting edge. You would put a cut on and go round the whole saw and then put a couple of thou cut on and repeat the cut round again till you got no disernable difference then put a slight tenths cut on and repeat till you were sure it was round, the wear on the grinding wheel at the amount you took of was zero. This was repeated for the cutting edge clearance and so you could be sure if the arbour on the machine was correct it would run true.

David

Didn't that method produce rounded off teeth on the high side of the wheel? But I guess that the shape of the teeth would still produce a cutting edge if the slope on the teeth were perpendicular. Otoh, a small portion of the trailing edge would be curved and that could cause more friction (no relief).

Lesser of two evils I suppose.

Engineering is full of little wrinkles.

On the quoted video, the actual tooth cutting seemed to be done with a tool that moved in and out to the depth of the teeth.

Neil Wyatt18/06/2019 16:43:44
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IME cheap holders are less accurate than the saws. I must get around to making an accurate one.

Neil

Howard Lewis18/06/2019 17:23:51
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Even with a 3 MT arbor turned to 1" in the lathe, slitting saws still run out (and I am using Sherwood cutters from Cromwell Tools, so they should be of reasonable quality )

The problem will be that every time that a cutter is remounted on the arbor it is likely to be in a different angular position, so making the register on the arbor eccentric, to compensate for the saw, will not provide a cure.

One way of using every tooth would be to feed at. a rate per tooth greater than the eccentricity, which may may be too much for a bad run out.

Me? I just moan, and live with it!

Howard

Nick Clarke 318/06/2019 17:34:07
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Apropos of nothing it is all part of the richness of the English language that 'Improving runout in a slitting saw' can mean both decreasing it and making it more concentric or increasing it and making it more eccentric.

I know what you mean, but isn't language wonderful!

SillyOldDuffer18/06/2019 17:41:50
4713 forum posts
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Posted by Ian S C on 18/06/2019 14:15:43:

I was watching U tube the other day, the chap was using a slitting saw, he mentioned that all the saws tend to ching ching, but once he got cutting he upped the feed until he got continuous cutting sound.

Ian S C

Edited By Ian S C on 18/06/2019 14:16:22

That's my feeling; if a saw is chiming, I assume it's not cutting deeply enough and up the feed-rate slightly until it stops ringing.

When a circular saw is being pushed steadily into metal surely all the teeth will be cutting? Feed-rate and depth of cut should never be so low that only one tooth does all the work. (Going too fast seems to cause saws to wander, bad for another reason.)

Once a saw is cutting steadily I've not noticed some teeth cutting slightly deeper than the others makes any difference. Maybe I've just been lucky and my selection of slitting saws all have lower run-out than average. How far out can they be?

Dave

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