Thread: Slitting Saw Runout

I measured the runout in the arbor with the setup shown below. Not perfect due to the entry angle of the DI, but good enough to eliminate the arbor as the source of the problem. I measured less than 0.01mm of runout in the arbor bore. The DI needle barely flickered as I rotated the chuck. I got the same result with a piece of 16mm drill rod in the arbor as per pipeclay's suggestion.

I remounted the blade and the runout is still horrendous. There is no perceptible side-to-side wobble in the blade. I took a short video and as soon as I work out how to upload it to YouTube I'll post a link.

Chris

Seems like you may of just got a badly ground tool.
Perhaps get it resharpened?

Originally Posted by pipeclay

Once you have established the amount of run out on the 16mm diameter divide 100 by 16 and then multiply this by the runout of the 16mm drill,this will then tell you pretty close what the od of the slitting saw is running out.

Would be good if you could measure the 16mm od at the same spot where the slitting saw would be sitting out from the collet chuck.

If the drill was running .048mm out of true 100/16= 6.25, 6.25x.048=.3mm

Hi Pipeclay,
I struggle somehow to visualize this. Why should the runout increase with the diameter? Or do you mean the wobble, yes the wobble will increase with diameter. Runout measured radially (like measured on the pic in the 260) is independant of the diameter. But wobble (=runout measured axially on the face of the arbor) will increase with diameter. Chris

Why not put the saw blade in the three jaw chuck external jaws and measure the centre hole run out with a test gauge ?

That's assuming the scroll chuck is reasonably accurate.

Rob

Originally Posted by cba_melbourne

Why should the runout increase with the diameter?

I'm having problems with that also. Radial run out doesn't increase / decrease due to diameter. Axial - side to side - lenght wise, wobble would. Like you would get with a bent arbor, second rate spacers. But not if the arbour hole is off true to the teeth.

Originally Posted by Machtool

I'm having problems with that also. Radial run out doesn't increase / decrease due to diameter.

That's right, but the degree of effect ie. the percentage of runout relative to the diameter does.

ie. - 0.03 mm runnout on a 5 mm diameter shaft will be more noticeable than on a 400 mm shaft.

So as the blade diameter increases, the noticable effect of the runnout becomes less apparent when cutting. It's still there, but it's hidden more by the longer cutting circumference.

Rob

Originally Posted by Clubman7

Seems like you may of just got a badly ground tool.
Perhaps get it resharpened?

Yeah, but that would only increase the cost of an already expensive (overpriced?) saw blade. I don't see what is so difficult about making a slitting saw blade with very small runout. None of my wood saw blades suffer from this. Are these things stamped or ground?

Here's a short video of my saw in action. I reckon the runout is completely unacceptable, but I'm keen to hear from others with more experience. My first YouTube upload, so go easy on me!

slitting saw runout - YouTube

Chris

Originally Posted by nearnexus

That's right, but the degree of effect ie. the percentage of runout relative to the diameter does.

ie. - 0.03 mm runnout on a 5 mm diameter shaft will be more noticeable than on a 400 mm shaft.

So as the blade diameter increases, the noticable effect of the runnout becomes less apparent when cutting. It's still there, but it's hidden more by the longer cutting circumference.

Rob

I'm struggling to understand this as well Rob, TIR is TIR isn't it?

Originally Posted by Techo1

I'm struggling to understand this as well Rob, TIR is TIR isn't it?

If you cut with a 30 mm slitting saw with 0.03 mm runout, it will be more noticable than cutting with a giant sawmill blade with the same run out.

The runout is still the same amount. It's a bit like comparing 0.03 mm runout in a watch component compared to a giant ships propellor shaft.

The watch wont run, but the propellor shaft will.

Nice going with the YouTube video.

That's pretty awful runout.

I suppose you could say there's merit in having a loose fit on the mandrel - you can move the disc around to negate the runout

Rob

Well, this "book machinist" struggles to find a scientific explanation for the mathematics offered by Pipeclay as well.

Sounds more like "reverse engineered" pseudo-science to me.

Maybe the reason that slitting saws are more sensitive to runout is this:

The typical slitting saw does only cut radially, and not like a regular saw at the two sides (faces). Slitting saws have no setting to the teeth, meaning they cut a slit exactly the thickness of the saw disc. Whereas normal saws cut a slit larger than the saw disc, because of the setting of the teeth creating a side relief.

And this means that a slitting saw has some pain clearing chips away, it has to be used at slow speed and with a slow feed rate, much slower feed rate than possible with a saw that has set teeth.

Now, a very slow feed rate means that the slightest TIR causes only a few teeth to do the whole cutting job - that is the few teeth that because of the runout travel the futhest away from the center line. This can be very clearly heard. And it is this hearing it, that sensitises the user to notice and worry about, even if the same runout on a normal circular saw would be perfectly normal and undetectable. With a normal saw the feed rate is typically many times larger and ensures that always all teeth are cutting. Chris

I found a similar amount of runout in 2 slitting saws from CTC. They cut on about 1/4 of the teeth.After thinking my home made saw arbour could be the culprit I embarked on the usual testing and self doubt .The runout in my parts was basically un-measureable as I had taken a fair amount of care in manufacture.
The cure was to mount the slitting saws in the tool and cutter grinder and top all the teeth back to a circular pattern. After this the runout is gone but it is clear where it was by the longer bevels on top of each tooth.They now cut on almost every tooth and obviously cut a very nice slot.
I asked an engineering friend about the problem and he educated me on a phenomenom in manufacturing these days called the "Give a F$%K Factor". This is measured by agonising over your own work but in the end realising that you "Care" more about your results.
It is staggering to think of how worn their gear must be to make a saw blade from scratch and get that amount of runout in it .This is where the "GaFF" comes into play.

Chris,
What you say makes sense, but I still don't understand what's so hard about making a saw blade with negligible runout.

localele,
If it's true that SOBA blades are made in India, I'd say the GAFF factor would be very high.

Anyway, I'm calling this blade a dud and will send it back. If it was a $10 eBay job I could accept it, but not for $38.50 plus postage.

Chris

Postscript- the seller has asked me to send it back Reply Paid and will replace it. Hopefully the replacement doesn't have as much GAFF in it.

I had been thinking of this saw in the shed and was going to recommend sending it back. Good to hear he is working with you on the return.

A bit OT but about some Aussie sellers
My son bought a pair of motocross boots for my grandson earlier in the week and they turned up yesterday from SA. The seller had a note that said if the boots where the wrong size to send them back then email the consignment number and they would post off the new size back strait away (before receiving the others). The boots are fine but thats great service.

I hope your new blade is better, as you say it's not like a $10 blade.
I always keep my eye out for bundle deals. A few years back I bought 180 odd slitting saws for around $120 from ebay and they where new old stock. There where only a couple of larger ones like yours, but buying them this way makes them really cheap, just keep your eye out even when you don't need them.

Dave

Thanks Dave,
I think in future I will only buy quality brand name blades. I will keep an eye out on eBay for NOS.