Yes you will need an arbor and overarm with arbor support. And eventually an overarm support to really make it rigid.
First up, assess your milling attachment.
Are whatever it has for bearings good and not sloppy?
Do the toolholders fit tight and without slop?
What is the SLOWEST rpm you can get with the attachment? I think I remember it being all belts for the drive, which is not as nice as some gears, but will work. (I have 5:1 back gears and belt reduction before that).
OK To work regular cold rolled mild steel/machine steel/boiler plate/1018/etc, you want the cutter to be at about 100 SFM. That's about 100 RPM with a 4" dia cutter. For tool steels, and some others, you want more like 40-50 SFM, so 40-50 rpm with 4" cutter. For aluminum multiply by 3, so you may want to have 300 rpm with 4" cutters for aluminum.
4" cutters are a good plan, because they give you good clearance under the arbor. You need to have room for the arbor and spacers to go over the work, over the hold-downs, studs and nuts, etc. 4" cutters are by no means perfect for that, but better than smaller ones.
Arbors are not too hard to make. The taper is the only troublesome part.
You will have an arbor the diameter of the cutter bore. That will be 7/8" for many gear cutters, 1" for some cutters, and 1 1/4" for other cutters. The arbor will also require spacers, to go between the cutter and the ends of the arbor, to hold it steady. The nut on the outer end of the arbor clamps them against the cutter
The arbor will need at least one keyway (refer to machinerey's handbook to find sizes for the arbor diameters) on each arbor. Some sizes may need two to cover all possiblities, in which case put them opposite each other.
For an end bearing, you can use either a rediuced size journal (I did that), OR bearing sleeves that go over the arbor in place of some of the spacers. Sleeves are handy, but they take up room on the arbor. Make the arbor longer if you use them. I;d advise against the plan of running the arbor against a center cone on the end. I just don't like that plan.
Arbors are rarely straight, so as you cut you will hear a pulsating "rrrrrrrrrrRRRRRRRRRrrrrrrrrrrrrrRRRRRRRRRrrrr rr" as the areas where the cutter duts deeper and shallower go thru the work. If you hear that everything is happy and working.
There will usually be some banging as the cutter gets into the work, Once you have a couple teeth in the work at all times, it should settle down to a happy cutting noise as above. If NOT, you have something wrong. Check it out before it messes up your part.
DO NOT TRY "CLIMB MILLING" IT WILL NOT WORK AND YOUR PART WILL BE MESSED UP. You will not be able to control climb milling, it WILL take off on you with any serious depth of cut. Feed the work into the cutter as it rotates against the feed (conventional milling)
Always clamp down twice as much as you think you need to. Horizontal mills will push the part off the table if it is pushable. Almost as bad as a shaper, but not quite.
Arbors I made
7/8" made of CRS years ago, still fine.
1 1/4", made of 4140, no better than the CRS for the 7/8", really.
Chomping through steel with a 2" high helix cutter on a 1" arbor. Note the bolt-down vise and extra support from overarm to knee . Backgear is "in", note the lever is UP on the backgear bracket at right.
Cutting a gear. Looks like I just finished the last pass. Note that the dog driver actually clamps the dog to avoid any movement during a cut.
Last edited by J Tiers; 04-20-2017 at 11:53 PM.
Keep eye on ball.