milling radii

i am trying to locate an OLD formula for milling a radius. this method allows, for example, a 2.5" radius to be milled using a 3" diameter milling cutter by tilting the vertical head to a prescribed angle and utilizing the milling cutter like a fly cutter.
this same technique is sometimes used on radial arm saws to cut a radius for making molding.
i had this written down many years ago and have misplaced it. i know this isn't a very accurate or precise method but it eliminates the need for a variety of cutters to mill shallow radius using a toolromm type milling machine. such a radius is needed for a bronze shaft rest pad on long leadscrews.
thanks in advance for the help,
bcreely

 

I believe the rule of thumb you're looking for can be found at this site. You'll have to do some browsing down a long list to find it. It's good to know there are still people out there who have some imagination and can think outside of conventional thought. Hope it helps.

http://www.geocities.com/mklotz.geo/index.html

 

I just took a look for you, and the the formula program is about two-thirds down the page in a file called radius.zip. Good luck.

 

thank you, this will do nicely. bet all the guys under 50 years old are wondering where my head is.....

 

[knobhead]

Yup....you use a milling cutter like a fly cutter? Wha..?

 

Knobhead old buddy. You just hang around some old manual machinists for awhile. What do you think was done before the almighty CNC came along. There are still a few of us with the know-how to make whiz-bangs for the suits without first consulting a computer to do it. Miller time is especially satisfying when nobody knows "how you dunnit".

 

attaboy ornery, you told him, i knew it would gnaw at the young guys brains. bet none of them ever used an old canned ham can for a belt pulley guard either.
i came out of an old us steel facility that still made their own gear cutters and hobs from scratch in the late 50's, never bought anything.

 

[wawa]

Help!
I am try to mill , 1/2 cylinder concave shape. 8" X 1.6" and the Radius is 1.62".
I don't have CNC nor I know how to use CNC ( newbie here ), only have sherline milling machine.

any tip would be greatly appreciate.

 

[knobhead]

Ah. You can always spot the old manual machinists, cos they've all got fingers missing.

 

if you're doing anything more than a shallow groove, you'll have to tip your head over just about as far as you can can get by with, and use a cutter or flycutter of close to the same radius as what you're milling. Not familiar with a sherline, is it a horizontal or vertical. If it's a horizontal, you've got it made. Just make up a toolbit holder you can run on the arbor. You could also do this in a lathe, make up a mandrel with a bit holder, and clamp your work to the carriage, but with that kind of depth, you're going to have to keep shimming up and taking successive cuts. Good luck, and don't pay any attention to knobhead. Old manual machinists and aerospace engineers usually don't along well to begin with, coz they usually don't know the first thing about ACTUALLY MAKING ANYTHING! They can draw it up real pretty, but ask'em to make it, and you'll just get a blank look. Ain't that the truth, knobhead ?!? HAHA just kidding. Everyone has their place in manufacturing.

 

[knobhead]

Actually, I was a time-served apprentice first, and now I MAKE jet engine components. Yup, machining and everything. (All CNC admittedly, no manual stuff).
But (I hope) I'm not too proud to know my limits, and those chaps with the fingers missing are the guys I turn to first when I get stuck. And they help out a lot, once they've finished trying to get me to go and get a sky hook....

 

[wawa]

thx Ornery Norsk
ok.. how and what do u mean by "shimming up"??
as for Sherline Milling machine, the arbor are about 1 3/4" long , and i can not find exact 1.6" radius cutter.

 

If you are going to use a lathe as a "horizontal mill", Your carriage needs to become the workholder. Because you have no depth control, other than changing toolbit protrusion from the mandrel (which will also change your radius, you need to add spacer shims for each new cut that is taken. You should have a stop of sorts clamped to the carriage also so that you don't lose position and alignment every time that the work is unclamped to elevate the workpiece for each new cut. Because a lathe carriage is usually not as adaptable as a mill table (multiple t-slots) you might find that making a plate fixture to bolt onto your lathe carriage is a good way to go. Granted, this is not a quick and easy method, but it works well when nothing else will. It just depends how accurate and how pretty your radius groove needs to be. You also could ink the side of your work, scribe a radius, and take multiple cuts with the biggest ball end mill you've got, gradually forming your radius. Then a good cleaning up with about a 2 inch sanding disk would get you close. Anyway, hope all of this helps you out.