Making a slitting saw arbor

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Chucketn

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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
 
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IMHO, you can make a far better arbor than you can buy for any reasonable price. Most of my saws are 2.5" diameter, so I use a fairly small arbor. These should be done entirely between centers so they run perfectly true. Hey, how often do you get to turn between centers anyway? I use a 1/2" shank about 2" long. The stock is maybe 3/4", so the saw flange is cleanup under that. I want no more than .001" clearance on the saw, and I typically make a female cap so all common thickness blades can be accommodated. It's very important that the arbor doesn't bow the saw even slightly, so cut the faces carefully. The fastening bolt should be a fine thread- I use 1/4" x 28 cap screws. 1/4" x 20 is far less satisfactory. Make sure everything is the way you want it before doing the threaded hole, since you'll lose the center feature at that point.

Some people don't like my arbors because there's too much cap. If you need to get a saw very close to some interfering surface, you can make a hollow arbor where the "cap" is a piece with a rod that fits up the arbor and fastens with a nut on the far end. The step that locates the saw must still be on the arbor itself, but can be just under the thickness of your thinnest saw. The thickness of the fastening cap/rod depends on what you can live with. Thinner means less clamping force.

IMO, if the saw doesn't cut all or most of the way 'round, you need a better arbor or a better machine/collet to hold it in!
 
Blame582, I did find the Projects in Metal link this morning, but the page was down or had problems as I couldn't connect to it. It is the best discussion I've found yet, and I have added it to my notes.
Conrad and Knudson, thanks for your replies, too. All points to be considered.
I have made several M2 Tapers, so now I think I'll try an R8. Got to get some stock though, I don't have anything that big in Dia. at hand. Is there a car or truck part, like an axil, or strut rod that would be a good source of material? There's a shop down the road that works on big trucks and heavy equipment.

Chuck in E. TN
 
A couple more points- I've made these out of brass, bronze and aluminum in a pinch. You'll never wear it out in the home shop. I never use a key as they're self tightening and I'd rather it slip and wreck the arbor than shatter the saw or rip the work out of the vise. Always use oil (or spray WD-40 for aluminum) and be sure to get both the top and bottom of the saw!

The reason I use a 1/2" shank is something I learned from the real machinist at work. If you want to save time and fooling around, put your drill chuck on a 1/2" stub shank (cut off a standard one). Put your slitting saws on a 1/2" shank. Use a 1/2" edge finder. Make your favorite end mill a 1/2" shank. Now you can do an awful lot without ever removing the 1/2" collet from the machine! Sure, it's nice to have everything on its own R8 mount, but in practice it rarely makes much difference, and time is money.
 
All my saws being 1" I just used a grade 8 bolt works good abd was free.

Paul
 
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