Thread: Slitting Saw Runout

Gents,
I bought a "SOBA" brand 100mm slitting saw blade from a supplier in QLD. I mounted it on my shop-made arbor this morning and gave it a test run. Sadly it has a huge amount of runout. I don't know how you are supposed to measure the runout of a slitting saw (the teeth are very sharp), but using feeler gauges against a steel bar I estimate the runout to be about 0.3mm. In use this means the blade only contacts the work briefly each rotation and makes a very distinct "chomp, chomp, chomp" sound. Not pretty.

I don't have a DTI to measure the runout in the bore of my arbor. Given that I bored it in the same ER40 collet that I mount it in when I'm using it, it should be fairly true. Any runout here should be due to the collet, not the boring. The 75mm blade I had before cut nicely on the same arbor.

The blade was $38, so I reckon it should be more true than this. Any tips on reducing the runout, or should I just send it back?

Chris

You can hardly send it back until you're sure its the blade.
0.3mm run out you'll be able to check with a vernier from the bore of the blade to the tip of the teeth.

Stuart

I did measure the bore-to-tooth distance with my dial vernier, but it seemed a bit of a dodgy way to do it. I was getting figures between 37.2 and 37.8, but I figured some of that 0.6mm difference had to be measuring error. I didn't feel it was a valid way to do it. If it IS a valid way to measure runout I'll have another go at it and strive for more accuracy.

Try measuring your arbor spacers, because unless they are parallel, it will cause runout on your cutter.

Hi Chris,

I'm curious, what difference does it make to the cut? Is it just one tooth that's high, or is the hole in the middle off center?

I can't think of a good way to measure it, other than spin the arbor, backwards ( so the teeth don't cut too much ) with a shim to protect the indicator tip?

Regards
Ray

I have bought several different slitting saws, some cheap (ozmestore), some not so cheap (CTC) and all of them show runout to various degrees.

I at first put it down to the el cheapo multi-arbor I was using, so I made my own arbors. This did improve things, but there was still some runout.

Did some searching on a few of the metalworking forums and the general consensus seemed to be that virtually all slitting saws exhibited runout, whether cheap or expensive, so I just live with it.

Bit disconcerting though.

I must admit I haven't paid as much as $38 for a slitting saw, but if I had and it had appreciable runout I would be returning it.

Well its a pretty doggy test and a little tricky to do, but if you can get a repeatable reading on one tooth then it should be ok. I'm sure there are better ways but it depends what gear you have.

Stuart

I tried again with the dial vernier. I was a bit more careful this time and I'm getting about 0.3mm difference.

Clubman, there are no spacers on my arbor (see pic below).

Ray,
To the naked eye it definitely seems to be the hole that is off centre while the saw is rotating. It try your suggestion of the dial indicator and a shim.

Fred,
I baulked at $38 too, but I couldn't source a 4" saw with a 1" bore, so I just bit the bullet. All the 4"/100mm saws I found on eBay had a 27mm bore.

One upshot of this is that I'm finally going to buy a lever DTI for measuring inside bores.

Chris

Chris, is that a homemade arbor? Never seen one like that before. Not sure how you would check that particular make for runout, you would have to mount sort of a test disc to check with a DTI.

Anyway, I think all slitting saws have some runout. For me its the hearing test, as you carefully and slowly approach a workpiece, you can clearly hear that only a few teeth contact at first. And from the sound you can guess the runout - not in absolute microns, but in terms of "excellent" / "acceptable and normal" / "below average" / or "something is wrong". I often found that cleaning the arbor and remounting the saw can make a difference. Sometimes remounting the saw several times whilst changing the saw alignment lets you find a "sweet spot" where runout errors of chuck and arbor and saw cancel each other out.

Arbors that mount directly to the spindle are the best choice. If you mount a not so well made arbor through a low cost collet chuck using a dirty or worn collet, you will get enough runout to clearly hear it through the hearing test.

If the arbor spacers are not exactly parallel, you get another type of runout. Not a radial runout at all. You get the circumference of the saw wobbling in the axial plane. That causes the slit you are cutting to become wider. (Indeed, there is a special type of slitting saw arbor that uses two spacers that are cut on purpose out of parallel - by rotating these two spacers with the saw blade in between, you can control how much the saw wobbles, and thus have stepless variable control over the slit width you are cutting, whilst having to own only one thickness of slitting saw - the two spacers have graduation to dial in how much wobble, wobble plus saw thickness = slit thickness).

In both cases, axial runout or wobbling, you have only some teeth do the bulk of the cutting work. So what, they will wear out first and then the others will begin to "carry" - as long as we are talking only small runouts.

"SOBA" products are as far as I know made in India, and are aimed at the hobby market, not at industry. You cannot expect them to be as well made as say, "Fraisa" slitting saws made in Switzerland and costing 2-3 times more. I have a couple of the latter though, and they do show some runout too (the hearing test is very sensitive to the very slightest runout). I guess it all depends what the slit you are cutting is used for, and how long you expect the saw to last. For most hobby use, I would have thought SOBA would be a reasonable choice. Chris

Here is a commercial saw runout fixture.

DSCN2726.jpgDSCN2725.jpg

Hi Chris,
The test indicators sold by CTC etc are not a bad little unit, I bought mine years back and they where branded Mititoyo, but where definitely copies.
There are also rocker attachments for a dial indicator, I have a few here and are good for deep bores.

I have a lot of slitting saws here (all quality ones) and they pretty much all the have run out like you speaking about, but not as much.

Thats a nice arbour you made, with out it being a press fit you are going to get a little run out from it, not saying thats your problem in this thread but something to think about.
See if you can find the run out of your abour/collet at it's worst, then put it on the opposite side of the saw run out, this will help reduce it.

Dave

Hi Chris,
yes it is home made. It is a design recommended by one of the blokes on this forum (Big Shed I think?). Advantage is it allows you to get up close to the workpiece. The top-hat part is a snug fit in the saw blade and in the bore of the arbor, so I figured I could measure the runout with a DTI inside the bore. Not perfect, but pretty close.

I don't think there is any wobble in the saw, but I will check the faces of the arbour and top-hat part.

Dave,
I am looking at buying this DTI, but not from this mob. A friend can get me one cheaper from the Mitty agent O/S:

Mitutoyo Metric 0.8mm Dial Test Indicator. #513-404T

I will try to set the blade such that its runout partially cancels the arbor/collet runout and see if I can reduce the overall runout to an acceptable amount.

Are you using a M/T4 collet chuck,if so when you place a drill or other ground piece of material in the collet chuck how much runout do you get.
If you get minimal less than .001/.002" or less runout divide the diameter of your test piece into the diameter of the cutter and multiply this by the runout measured,this will give you a pretty close size for how far the saw is running out.

Yes Peter, it's a MT4 collet chuck. I will do as you suggest and measure the runout of the collet+chuck using a 16mm drill bit in the collet (since I'm using the 16mm collet for the slitting saw arbor).

I'm not sure I follow your last sentence though. Can you please elaborate?

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