Slitting Saw Arbor

I’m sure someone on here said you shouldn’t use a key on a slitting saw arbor so I took mine out some time back. Slitting saws aren’t something I use too often but I needed to slit the end of a bar today so out came the arbor. Three times the nut holding the saw came undone so I replaced the key and it stayed put and I got the job done. The arbor seems unusable without the key so I won’t be taking it out again. Any thoughts?

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Only surprise

When mine slipped, it tightened the screw [*] so much that I had to drill it out to release the tension.

MichaelG.

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[*] equivalent to your nut, on a small arbor.

On my arbour the nut is on the bottom and it tends to tighten when the cutter is used but I still use a key mostly anyway. You could turn the cutter over and run in reverse if the nut is on the top and that would tend to tighten up in use.

David

I use an MT3 arbor that I bought fom a reputable seller.....not had an issue with any saw blade so far....and it was keyed..and most of all of my blades are keyed...

I guess it comes down to how hard you push the blade..

I guess it depends if you have a left or right hand thread...?

Neil

The nut on the bottom of the arbor has a left hand thread.

**LINK**

The arbor I made years ago had a RH thread so self locking, I bought one recently which had a LH thread so does come undone if you don't use a key. Obviously if you can reverse the spindle rotation there is no problem.

In my experience if a thin slitting saw slips it can easily cut through the key.

Tony

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That would explain it then.

... I am no longer surprised.

MichaelG.

Right and left handed screws apart, isn't this a case of choosing between two evils?

• When the saw is used without a key, there's a risk that it will slip.
• When the saw is used with a key, it might jam and break.

In my limited slitting experience it seems that the saws cut best when used gently. The size of the teeth suggests to me that the saws aren't intended to buzz.

I don't use a key and haven't had a problem. Perhaps my slow feed-rates are girly! How fast should a slitting saw cut?

Dave

Does seem odd that it has a LH especially as most of the others from the same supplier are right hand, wonder if the MT2 one was made with the Myford user in mind where the work is more likely to pass under the saw so reverse running means no climb cutting.

As for speed work it out based on diameter of saw and as they are usually HSS the fpm will be the same as for turning or any other milling with HSS tools. Quick simple rule of thumb is a 4" saw has a 1ft circumference so FPM = rpm

As an example let's take a HSS coarse tooth slitting saw, 1/16" wide and 4" diameter with 36 teeth. In steel the usual 100ft/min surface speed applies, so a spindle speed of about 100rpm. I'd allow a chip load of 3 thou per tooth. That gives a feedrate of 10.8 in/min at 100rpm. I'd be happy taking a 1/2" depth of cut or more at each pass. Essentially the calculations are exactly the same as for any other cutter. For fine tooth slitting saws I'd reduce the chip load to allow for the smaller gullet, but of course the depth of cut should be much less.

Andrew

I have two saw arbors. The smaller one was home made from a purchased blank MT1 arbor and has no key. It does tend to tighten (as Michael suggests) because of the R/H screw used. I use it on my small EW lathe with a purpose made table to cut small brass sections - which it does well and it doesn't slip as far as I can tell.

My Chinese MT2 1" arbor gets mostly used on the Atlas MF instead of the overhead arbor. It has a key (which I use) and a L/H thread. This is also used mainly for cutting brass sheet (where it's length is a factor) using either the edge of my sub-table for support or on a sacrificial plywood platform if I need a deeper reach or some kind of custom hold-down (e.g. strategically placed screws!)

None of my slitting saws are hollow ground (that I'm aware of) and none of them have any kerf. I'm always very cautious when using them and would think very carefully before trying any very deep (long) cuts with them - something for which they are not designed for in my view - at least the thinner ones. I have several other means of making deeper cuts if required - either with milling cutters with proper side clearance - or using saw blades with a kerf (e.g. in either an Armstrong or a power hacksaw).

Call me chicken - but there you are!

Regards,

IanT

Thanks Andrew (and Jason)

I've got the rpm right, but my feed-rate is about half yours and depth of cut much less (only a couple of mm). I shall try being more aggressive!

Dave

I don't think anyone mentioned the phenomenon of the work closing on the saw towards the end of the cut; I understand this is due to the release of stress within the material and in my experience can be strong enough to arrest the saw. On the occasions when this happened I was using a shop-made arbor without a key and with RH nut and RH rotation.

I now have an MT3 arbor with LH nut which casts doubt on the Myford theory.

Set?

I got the link wrong, it should have been the MT3 version.

**LINK**

They both have left hand threads though.

Most of the others just say nut, they don’t say whether it’s left or right hand thread.

"I don't think anyone mentioned the phenomenon of the work closing on the saw towards the end of the cut."

They have done in the past but not here as you observe. I often wonder if the inventor of the caliper brake had ever been inspired by the buttock clenching fright at the end of a cut when"that" occurs. Suitably Halloweenish?

Rik

Hi Vic,

I make my own arbors and all ways use a key otherwise the blade slips (I may be a bit heavy handed). In my opinion if the blades were intended to be used without a key the manufacturers would not have included a keyway.

Peter.

I happened to have some of ARC's slitting saws out for the next part of the Milling for Beginners series and thought I would check the thickness and all are hollow ground and the amount of hollow increases as the thickness goes up. For examle a 0.5mm blade was 0.003" thinner in the middle than at the tool and the 2mm thick one was 0.010" thinner

The remedy when slitting into a bore would be to fit the bore with a temporary, tight-fitting plug.