Slitting saw arbor design

[mikey553]

I have acquired quite a few slitting saws in several bore sizes, but still do not have arbors to put them on (except for two very small ones). There are several projects with the need of a slitting saw, so I cannot wait any longer.

I have a basic design done. All of the arbors will have a 3/4" shank to be held in a collet. A slitting saw will mount on a cap, which will be guided by a bore in an arbor. A single socket head screw will provide the needed clamping force. My question is about torquing this screw. Do I need to make a provision in the arbor for wrench flats? My vertical mill has a spindle brake and I use it all the time for torquing ER32 and ER25 chucks. Do you think I can use this brake to hold the arbor in a collet when installing and removing slitting saws? Or do I need to have wrench flats on an arbor? I would rather not use the flats, if my brake and collet force are sufficient. What's your experience with this issue?

[Tim Clarke]

Based on my limited experience, you'll be fine with the brake and collet. I built one very similar, and I used a socket flat head screw. Herein lived my troubles. I've had to drill 2 of the screws out because I rounded out the hex socket. I need to put wrench flats on the cap but seem to forget about it until it's time to use it.

[Doozer]

2 wrench flats is just 2 swipes with the end mill.
Why question doing something so easy?

-D

[mikey553]

Based on my limited experience, you'll be fine with the brake and collet. I built one very similar, and I used a socket flat head screw. Herein lived my troubles. I've had to drill 2 of the screws out because I rounded out the hex socket. I need to put wrench flats on the cap but seem to forget about it until it's time to use it.

Flat head screws have very small sockets. That is enough reason not to use them for a slitting saw arbor.
Why do you need to put wrench flats on the cap? Is it because your screw socket is stripped?

I am basically afraid that saw may catch on something and tighten the screw to the point of "impossible to remove". Do you think it may still happen with the good socket head screw?

[mikey553]

2 wrench flats is just 2 swipes with the end mill.
Why question doing something so easy?

-D

I think the wrench flats would make the arbor longer that it would be otherwise.

[J Tiers]

Doozer has it. It is easy to put wrench flats on, and when you do it you will never need to kick yourself for not doing it. There is no downside.

I have had saws tighten the screw to nearly the point of "welding". Anything you can do to make it easier to remove the saw in such a case would be an excellent idea.

It is fractionally more trouble, but you always have the option of using TWO screws. Then it is impossible for the screws to be tightened by the saw jamming.

There is no need for it to make the arbor any longer. Even if you put flats on the cap.

[BCRider]

I've only used slitting saw blades a handful of times over the years. My previous large size arbor used a 5/16 cap head screw set in a counterbore in the "cap". It was never an issue to loosen the center screw. But then I never had the arbor grab and lock up in the cut either.

For the bigger sizes you will have a section of the arbor below the 3/4" stub that will be 1.25" in diameter. You need that to give yourself a nice 1/8 ledge for the 1" ID saw blades. So there's simply no reduction in stiffness by also milling a couple of flats in the 1.25 portion to take a suitable wrench. A quick CAD check shows that 1" across the flats would give flats that are 3/4" wide. 15/16 across the flats would give you 0.82" wide flats. But mostly I suspect that in any sort of harsh lock up to remove the shards of the blade you would remove the arbor and hold it on the flats in a vise so you could get a nice grip on the screw. So 1" across the flats and 3/4" wide is fine.

There will be some flex at the 3/4 inch shank and depending on how long you want the arbor things might become a little wobbly. I know for mine I wanted to reach as far as reasonable. So I went with the direct R8 shank idea to maintain the most stiffness from a 2" reach. I suspect I might have gotten away with more but the slug of metal I had wasn't long enough.

I did mine a little along the lines of how Brandon on Inheritance Machining did his. But it was a PITA overall and I still ended up with more runout than I think is possible even using his "vertical lathe" trick of his for turning the final bore for the blade plug in the mill. If I were doing it over ( I might) I think I'd go with the chuck end for the 1" size saws that is like this sketch.



1.25" OD and the bolt shown is a 5/16 x 1.5" hex socket cap screw. The ONLY critical parts, outside of nailing the R8 shank dimensions, are the two blade registration shoulders on the tan portion. And for those I'd be using a center support off the tail stock and only drill and bore the center out for the retainer cap afterwards since non of the cap or cap recess dimensions are super critical. So I could just hold it up close in the chuck. The only downside is the need to make up a small trepanning tool for the face groove.

The wall around the bolt head counterbore is still 0.13 across in this sketch. So I think that's more than enough for the loads involved. And in fact perhaps less might be better if it acted as a sort of "fuse"?

[old mart]

Wrench flats are a boon when making the arbor. Both the mills at the museum have had wrench flats milled in the spindle as close as possible to the bottom bearing seal to make the spindles lockable, and I also put flats on an early er25 collet arbor, the later ones already have flats, and by pure luck are the same size.
There are arbors available with a stepped spring loaded centre which have steps to fit about 4 different bores. I have never used one, so cannot comment on their value.

[BCRider]

.....There are arbors available with a stepped spring loaded centre which have steps to fit about 4 different bores. I have never used one, so cannot comment on their value.

Somewhere at some time someone might have made one of those that actually was workable. The ones I've seen in the import tool stores were all horrid. Lots of play and no assurance of even keeping the blades in a flat plane.

[J Tiers]

Somewhere at some time someone might have made one of those that actually was workable. The ones I've seen in the import tool stores were all horrid. Lots of play and no assurance of even keeping the blades in a flat plane.

I have one that was quite nice, until the screw locked up solidly once. I got it apart, but I have not used it since. I forget just what the issue was. I have pics of it somewhere, and may have posted them here even.

[mikey553]

Thank you guys for the ideas. You have convinced me to put wrench flats on every arbor. Most of my saws are in metric sizes. Right now I am going to make arbors for 16, 22 and 27 mm saw bores. I was planning to use 5/16, M10 and M12 socket head cap screws correspondingly just because I have them on hand and the screw head is still small enough to fit it in the cap counterbore.. Metric M10 and M12 screws have finer pitch than 3/8 and 1/2" coarse threads, which I think is a plus in this case. However I see BCRider used a 5/16 screw for a 1" slitting saw. Is it sufficient? Do I need the big screws I was planning to use?

There is one more question. A few of the bigger saws have a keyway slot. Whoever designed them could see a lockup as a potential problem. It is too much trouble for me to use a key in the arbor, I am not going to do that. Have you guys ever used a key with a slitting saw?

[J Tiers]

....................................Have you guys ever used a key with a slitting saw?

I pretty much always do. Nearly always no issue, I try not to get it jammed......

One time one did jam. It almost cut through the key, but I got it all apart OK. Odd thing is that the jammed one was not a thin one, but one around 0.090 thick (about 2mm or a bit more). It still cut into the key.

[mikey553]

I pretty much always do. Nearly always no issue, I try not to get it jammed......

One time one did jam. It almost cut through the key, but I got it all apart OK. Odd thing is that the jammed one was not a thin one, but one around 0.090 thick (about 2mm or a bit more). It still cut into the key.

Thanks. What bore size are you talking about? Can you show a picture of such arbor to see how a key is installed?

[BCRider]

....However I see BCRider used a 5/16 screw for a 1" slitting saw. Is it sufficient?

It was good enough to cut through a scrap that was 1/2 x 3/4 as a first trial with a 0.032" blade. No idea what'll happen with thicker blades. But it does take a LOT to break a 5/16 bolt.

[J Tiers]

Thanks. What bore size are you talking about? Can you show a picture of such arbor to see how a key is installed?

It was a horizontal mill arbor. The key was probably 3/16" or larger. The bore was probably 1 inch.

You can see a key in the keyway of one of the arbors in this picture....


I also have some short arbors with keys made in various ways. Some have keyways in which short keys are put, at least one from some toolbox or another has a piece of round rod in a drilled hole to function as a key. I have never used that one.