Slitting Saws?

[KEITH BEAUMONTParticipant @keithbeaumont45476]

My experience with slitting saws is similar to Rods, I have at least 20, 10 of which are Dormer and they all are eccentric on the teeth diameter. I have one that is perfect that I re-ground the bore and made a mandrel to fit. I did this because I was muti slitting some thin tube and the eccentricity was making a mess of it.

I find the reason for this a mystery. Wood working saws, sent for re-sharpen, have the outside diameter trued up first, before re-shapening. Cutting on all teeth is important in wood to avoid overheating, so where is the reason for metal cutting being different? The fact that it is throughout the quality range must have a some theory behind it.

Keith.

[Bo’sunParticipant @bosun58570]

A comment in MG’s previous link eludes to a possible cause being grinding wheel wear, as the grinding process progresses around the saw from tooth to tooth.  Especially in this case, as there are 130 teeth to grind.

This seems entirely plausible.  So maybe the manufacturing process is flawed.

[JasonBModerator @jasonb]

You should be able to spot that with your measurements.

If it is wear in the grinder then you would expect a sudden step in the reading. if it is simply eccentric then the needle should swing one way and then back.

 

Modern CNC saw sharpening for TCT saw blades has compensation for grinder wear but as it is diamond or CBN there won’t be as much wear as ther would on a more traditional stone.

[Michael GilliganParticipant @michaelgilligan61133]

My own unproven hypothesis is simple:

For the sake of manufacturing convenience, the saw blanks get mounted on undersize arbors, and the eccentricity is thereby built-in.

MichaelG.

[Bo’sun]

On Bo’sun Said:

A comment in MG’s previous link eludes to a possible cause being grinding wheel wear, as the grinding process progresses around the saw from tooth to tooth.  Especially in this case, as there are 130 teeth to grind.

This seems entirely plausible.  So maybe the manufacturing process is flawed.

Possibly the eccentricity is an accidental feature of the manufacturing process, but grinding teeth is usually a precision operation.  I have a Chinese made set of steak knives that are ground identically with a similar single knife in a Sheffield made kitchen set.   The only detectable difference is the Chinese blades are stamped ‘Stainless’.      My guess is both manufacturers have the same grinding machine, both buying in grinding wheels pre-shaped to form steak knives.  The wheels come with a steel template, which the grinding machine uses to periodically reshape the wheel with a diamond disc.   The resulting knives are identical.

I’d expect the same technology to be available for grinding slitting saws.   If so, maybe the eccentricity is deliberate, perhaps to start the blade into an initial contact cut rather as twist-drills align into a centre-pop.   I agree 0.55mm seems excessive though!

How well, or badly, does the blade cut?

Dave

 

[Bo’sunParticipant @bosun58570]

Hello Dave,

Both slitting saws seem to cut OK (to me anyway), apart from the ching, ching, ching………..

I’m cutting a 2mm wide slot, 6.6mm deep in 1/4″ dia brass bar stock to form a small clevis.

Whatever the reason for the seemingly excessive runout, it just seems wrong for something you expect to be relatively precision ground.

I tried Neil’s suggestion of measuring from the centre, and within the limits of a digital caliper, the results are comparable.

Jason,

Full marks for your sleuthing.  Yes, the saw blades did come from RDG.

[Bo’sun]

On Bo’sun Said:

…the saw blades did come from RDG.

There’s the answer to your question.

I would expect slitting saw teeth to be ground to the same sort of accuracy as S&F milling cutters. On a Clarkson T&C grinder I would expect eccentricity to be no more than a thou or two. The effect is more noticable when cutting with a slitting saw as the feedrates tend to be lower than for a S&F cutter.

Andrew

[bernard towersParticipant @bernardtowers37738]

Surely not Michael thats backyard engineering, they most probably are mounted on a air operated expanding chuck similar to circ wood saw sharpening

[Michael GilliganParticipant @michaelgilligan61133]

If you say so, Bernard

MichaelG.

.

Do you have a better explanation ?

[Michael GilliganParticipant @michaelgilligan61133]

Now here’s an encouraging find:https://crtoolsuk.com/product-category/slitting-saws/

MichaelG.

[JasonBModerator @jasonb]

But at 5 times the price and no mention of run out who will take a chance?

[Russell EberhardtParticipant @russelleberhardt48058]

If anyone is worried by the runout of slitting saws they can easily be sharpened and run out corrected using the simple fixture described in Howard Hall’s book “Milling a complete course” no 35 in the workshop practice series.  I made one about 15 years ago and found it very easy to use.  Not needed it since though.

Russell

[samuel heywoodParticipant @samuelheywood23031]

I made my ownclose fit arbor , i only use 50mm saws as i doubt the X1 would cope very well with anything bigger.

I have noticed radial runnout, not quantified it,& not been a problem thus far.

I think lateral runnout would be more of a concern.

Now you could i think make your own arbor with an undersized central boss & “bump true” like some people do with lathe chuck?~ Though personally i couldn’t be bothered with the faff.

[Bo’sunParticipant @bosun58570]

Good afternoon,

Perhaps I’m expecting too much.  I had assumed the teeth were ground.

I noticed with these slitting saws, that the tooth gullets were a blackish colour, the sort of colour you would expect after hardening.  The side faces having been ground.  Closer inspection with an 8x loupe, shows the teeth haven’t been ground and several have rounded cutting tips.

If progressive grinding wheel wear is some of the problem, I might expect milled teeth to have a chance of maintaining respectable concentricity.

[Bo’sun]

On Bo’sun Said:

Good afternoon,

Perhaps I’m expecting too much.  […]

Referring back to Jason’s comment about pricing …

Perhaps we do get what we pay for [?]

MichaelG.

[Bo’sunParticipant @bosun58570]

Hello Michael,

I suspect that’s partly true, but perhaps we’re also to blame for putting up with it.  We do that with plenty of other merchandise too.

Maybe they could make them even cheaper by not cutting the teeth that don’t do anything?

Has anyone any experience with ARC’s slitting saws?  Judging by the quality level of tooling I’ve bought from them over the years, I suspect they may be better.  I didn’t buy from ARC this time because they didn’t have the size I wanted.

[JasonBModerator @jasonb]

They are about all Ihave used for the last few years as my imperial ones don’t get much of a look in these days.

2mm saw cutting 1/4″ brass. Two different power feed rates than a one handed hand feed. Not easy to turn the spindle one handed and I just did random teeth but I would say it runs to 0.0002″ or 0.005mm and that is on the end of a fairly long arbor.

[Bo’sun]

On Bo’sun Said:

I had assumed the teeth were ground.

They should be ground, if not then the cutter is not fit for purpose. There are two rules for buying cutters:

1. Don’t waste time and money on cheap cutting tools

2. See rule 1

Andrew

[Kiwi BlokeParticipant @kiwibloke62605]

OK, I’ll stick my neck out…

The evidence suggests that a little eccentricity is (almost?) universal. Since I’m sure the reputable manufacturers are capable of grinding to better concentricity than the saws typically exhibit, one has to conclude that the eccentricity is deliberate. Why might this be?

Most of us will be familiar with a slitting saw wandering off the straight and narrow, even when we’ve done our best to get its alignment spot on: for some reason, it gets deflected sideways. It’s clearly vital that a saw starts its cut correctly, and without deviation or sideways deflection. My suggestion is that the eccentricity serves to relieve periodically the cut on the saw, allowing any sideways deflection to relax, and the saw to straighten its kerf, as the saw starts its cut, perhaps analogous to pecking with a fragile drill bit, if there’s no centring dimple. Once the saw has got properly going, I can’t think that it serves any useful purpose, except, perhaps, to allow coolant to get to the action.

[Edit. Wow, that Bold font really is bold, isn’t it (at least on my system)? Didn’t mean to shout…]

If this hypothesis is correct, the saw should be allowed to cut intermittently, at least until it’s established in a guiding kerf, rather than cranking it into cut, at the start, with a too-high feed rate.

[Kiwi BlokeParticipant @kiwibloke62605]

Agree wholeheartedly with Andrew Johnston’s post, above. I’d also suggest removing ‘cutting’ from Rule 1.

[Neil LickfoldParticipant @neillickfold44316]

If anyone is really concerned about the sharpness or the concentricity of the saw, they can be sharpened with a dremel and a diamond file. Mount the dremel in a holder so the grinding wheel can true the od of the saw teeth running in reverse slowly and very slowly advancing the saw till it cleans up all the marker pen witness of the teeth OD. Mark up the outer of the teeth, and then using a diamond file, rub on the back of the tooth until you see a very faint line left of the effective ground diameter of the blade. Even with a 0.1mm of the diameter of  the blade still at the edge, it will still cut well in softer materials. For iron or steel cutting, get the land to a faint line, or about 0.05mm wide and it will cut just fine also.

It is how I have sharpened saws in the past or when I make a single edge cutter.    You can also use the desic diamond wheels instead of a stone. If you can mount the dremel vertically and  the body over the edge of the bed, it is easy to use the diameter of the stone. This method can also allow you to create a shape on the end of the saws, like a radius or a chamfer instead of just the sharp square corner that may create a stress raiser in the part. It could also be done in the lathe instead of the mill, if it is easier to protect the workings and slides etc.

[Michael GilliganParticipant @michaelgilligan61133]

Enjoy this over breakfast, folks

Stefan Gotteswinter sharpening a slitting-saw:

https://youtu.be/MBG26a2UB6g?feature=shared

MichaelG.

.

Ref.

https://gtwr.de/stefan-gotteswinter-prototyping-tools-and-machines/

[Alan CharlestonParticipant @alancharleston78882]

Hi,

There is a bright side to an off centre slitting saw. When it becomes blunt, all you have to do to get it sharp again is to identify the half dozen or so teeth which have blunt tips and grind them down so they don’t contact the work. The saw will then cut as well as it did when new. A lot easier than grinding all the teeth.

Regards,

Alan C.

[Michael GilliganParticipant @michaelgilligan61133]

Which of the hobbyist suppliers will be the first to advertise that as a feature, I wonder ?

🙂

MichaelG.

[JasonBModerator @jasonb]

The problem of “not buying cheap” is not easy for many.

Can you define cheap? Is it pot luck from Ali etc, is it from Uk ebay, is it from an know ME supplier or is it from an industrial supplier.

The OP’s saw is only a pound or two cheaper than a similar dia saw from ARC yet both are maybe 25% the cost of the saws Michael linked to. Or the last time the subject came up I linked to some that were £4-500 a pop which makes Michaels link look cheap.

With the amount of tooling anyone new or even the long in the tooth hobby engineer may need they have to justify what they spend. Who would be happy paying a couple of hundred pounds for say 4 saw blades which should cover most needs?

Like the Drill arbor thread there is a point where the “cheaper” end of the market is just as good as the top end . It is just a case of finding that point and sticking to it or accept that taking a punt of that bargain may not always pay off.

[Author]

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