Making a slitting saw arbor

[Chuck in E. TN]

I recently acquired a few HSS slitting saws with 1” keyed bore, in thicknesses from .040 to .125”  (Thanks again AdeV). Now I need to make an arbor for them, for my X2 mill which has an R8 spindle.
I have Googled, and Googled, gathering drawings, articles, and tips.
Here’s what I think I know:
Arbors for slitting saws are available commercially, of varying quality, shank type, clamping method (internal or external cap, multi sized bore), and of course varying price.
Slitting saws, as opposed to wood working saws are hollow ground for clearance, like a parting tool, so they are thinner at the bore.
For the hobby machinist, it is not necessary to include the key, so if the saw jams, it will spin on the arbor, rather than shatter. (I also have the X2 belt drive  Mod, so not an issue)
Though I have found some I consider affordable, I would rather make one.
What I would like to do is start a discussion on the general attributes of a good, serviceable, shop made saw arbor. Would you use an internal cap, or external cap, and why?  Would you make it on a R8 blank stub, or straight shank to be used in a collet, and why?  The biggest R8 blank stub I can find is 1 1/8”. Is that big enough? Does the arbor need to be hardened/tempered or not, and why?
How much bigger than the 1” bore, does the clamping part need to be? 1 1/8”? 1 ¼”? 1 ½” (diameters) ?
I hope I’m making sense.  I have enough confidence in my abilities to make the arbor, but have been confused by the many design variations. Plus, I’m not an engineer.
Thanks in advance to all who contribute to my education.

Chuck in E. TN

[Lew_Merrick_PE]

Chuck,

The advantage of a combined R8-shank is minimizing accumulated eccentricity in the tool.  Getting "near zero" there has advantages that will probably not accrue given the machine you are running -- a couple of thou eccentricity only means that (say) 75% of the cutting happens on 1-4 teeth.  There is probably enough "flex" in your head support and spindle to create those conditions anyway (especially if you run at anywhere near commercial feeds).  An arbor that fits in an R8 collet is likely to be sufficient.

A heat treated saw arbor is going to last longer and require less detailed care than a non-heat treated saw arbor.  Unless you have something like a toolpost grinder, getting the best fit (say .002/.0005 clearance) between your saw and your heat treated arbor is going to be a pain.  If you have something like a (good) toolpost grinder, then hardened is the way to go.  A hardened arbor is going to last longer, be more resistant to wear, and less susceptible to dings.  It will also be (about 15%) more rigid.  That said, I have dozens of non-hardened tool holders made for specific tasks with many dozens of hours of use on them.  I generally keep them in their own wooden box and inspect them carefully (making minor repairs as required) before use.

Make sure you have sufficient clearance between your spindle nose and the cut you need to make.  You want to minimize this for the greatest rigidity (flex being relative to the cube of the distance between the nose of your spindle and the mounting point for your saw).  I prefer to use a closely fit tubular spacer to clamp the saw.  Also, I prefer to use a screw (left-hand thread) to clamp rather than a nut as that lets me have a lower profile at the end of the arbor.

Does that help?

[Chuck in E. TN]

You bet that helps, Lew. Never thought about a left hand screw. Nothing I've found so far suggested that!
 Chuck in E. TN

[picclock]

Hi Chuck
FWIW I made mine out of some 2" steel bar and incorporated an MT2 taper on one end. The reason is that I wanted to ensure really low runout and 'wobble', as any wobble makes the slot wider. The adapter is 58mm long excluding the taper, with a body of 33mm ending with a 3mmx46mm shoulder to support the blade as near to the cutting edge as possible.
The 'wobble' clocks at under 1 thou next to the cutting blade but the runout, or eccentricity is not so good at around 3 thou. I made the adapter long to enable me to cut slots in the centre of the work by overhanging the adapter.

I should have been using it today but found that the metal I had delivered was incorrectly sized at 1/16th inch instead of 1mm. It was an old order so no chance of replacement or refund .

Not sure what you mean by internal / external cap. On mine the adapter ends in a male piece turned exactly to the size of the saw inside diameter. There is a central threaded hole which combined with the an end piece clamps the saw to a diameter of 46mm. I have used a conventional right hand thread as this will tighten in event of slippage, although I have cut and plan to use a keyway.

This will be my first use of a slitting saw so it may well be that some of my assumptions are incorrect 

Good luck with your project Chuck.

Best Regards

picclock


 

[Bogstandard]

Chuck,

I have several slitting saw arbors, all commercially made and all have the same basic faults.

1) Their OD is much too large, and when using say a 2.5" saw or end and face cutters (yes you can use those as well) very little of the saw remains protruding to get a decent cut depth.

2) The holding block underneath is just too deep, and this restricts your cutting close to the vice jaws.  With some thin or small components, you can't get your saw anywhere near close.

3) The saw is held too close to the spindle nose, not allowing you to do cuts on parts that need to be cut close to the vice jaws when the part is sticking up a fair amount from the vice.

4) Left hand threads should NOT be used, the arbor screw will be trying to slacken itself off all the time. Invariably on commercial units, they use countersunk cap head screws, and after tightening up by the use of a saw, the hex in the head very easily strips out as they are too shallow to take the undoing strain. That has happened on all of mine, so I actually use a normal cap bolt with a chamfer cut under the head on the thread side, it gives a much deeper head, but does protrude at the bottom a little.

I have had a bit of a think about this and have come up with the C-o-C below which combats all those faults.

It should easily be able to hold a 3/8" thick saw or end and face cutter.

BTW, none of my commercial units are actually hardened, but they are made of some sort of tough steel.

I personally would just use a straight arbor held in a collet. If you wanted to do it with a blank end R8, they don't do them long enough, but you could easily bond a lump of long stuff onto it with loctite and pins, then turn the fitting shown onto the end, that will ensure things stay concentric.

I hope this helps in getting your design correct.


Bogs

[Chuck in E. TN]

Thanks for your input, Bogs. Aways enlightning.

Chuck in E. TN

[lordedmond]

I too have a couple of slitting saw holders and a few shop made

whilst the body runs true as does the did that goes ing to saw "Bogs 0.998 on his CoC " all my saws run eccentric , the side face is ok , is it an inherent fault with these saw or what ( its the same from el cheapo to the better ones )?


Stuart

[Bogstandard]

Stuart,

I think that eccentricity is caused by the grinding wheel, so the first tooth ground will be perfectly on size, then the further it gets around the saw blade, the teeth get minutely longer because the grinding stone has worn away a little, so doesn't grind as much off.

I get it when I resharpen my saw blades.


John

[spuddevans]

I too have a couple of slitting saw holders and a few shop made

whilst the body runs true as does the did that goes ing to saw "Bogs 0.998 on his CoC " all my saws run eccentric , the side face is ok , is it an inherent fault with these saw or what ( its the same from el cheapo to the better ones )?


Stuart

My mandrel also seemed to run out of true, then I discovered that there is a little play in the fit between the blade and the mandrel. The solution I came up with was to just nip up the tightening screw, run the mill at a very slow speed and very gently touch the rotating blade off a piece of scrap ( our in my case the workpiece, which often becomes scrap at some point ) this then centers the blade on the mandrel. Then just stop the mill and tighten up the holding screw.


Tim

[lordedmond]

Thanks for the answers John and Tim

John looks like I need to fire up my Dekel clone and sort out a jig for the blades.


Tim tried that no improvement the shop made one was spot on and sized for a particular blade ( a good one ) and it still ran out


So I am coming to the conclusion confirmed by John that the blades are eccentric

Stuart

[AdeV]

Nice design that John, I reckon I might make one or two of those... I have the problem you describe with my commercial unit - the countersunk screw won't release, and to add insult to injury I may have accidentally bumped that over-sized bottom into my vice, so now the blade wobbles by several thou (obviously, the bigger the blade, the bigger the wobble)...

[Stilldrillin]

I've used many slitting saws. But most of my working life I used side n face cutters, for milling splines and such.

ALL of them were eccentric, to a greater or lesser degree...... 

I agree with Boggy. It must be the tool grinding! 

David D

[Bogstandard]

Running eccentric shouldn't really make any difference, as I found it is normally only a couple of thou anyway, but even so, that should help slightly in the cutting, as it is gently being fed into the material by the amount of eccentricity as it goes along.

Just make sure you allow for it if cutting to a critical depth.


Bogs

[Chuck in E. TN]

Does it matter if the shank is 1/2" or 3/4" stock, locktited in? I'd hate to have to turn  1 3/8" or 1 1/2" stock down to fit the collet.

Chuck

[arnoldb]

Hi Chuck

You can make the shank separate for a push or light press fit - and loctite it in.  I would however recommend pinning it as well for additional security.

Regards, Arnold

[Chuck in E. TN]

Well here is what I came up with.

http://s571.photobucket.com/albums/ss157/chucketn/Machining/Slitting%20saw%20arbor/

It holds the 2 3/4”saw good and tight, and while still on the lathe I checked runout. Zero!
I did not add a key as I didn’t have the right size stock. If it becomes an issue, I’ll add it later.

Thanks to all who had input, I appreciate your help. I did not make any drawings, just worked from what I had in the possibles box. The shank is drill rod, the body a piece from Dad’s collection that already had the ½” hole. The cap is a slice off of a 1 1/8” mystery metal bar, again inherited from Dad.

I will test it today on my mill, cutting some ¼” ali plate.

Chuck in E. TN