What depth of cut is safe to take with a HSS end mill of 1/8" dia, and how fast can you feed in mild stee without breaking or quickly dulling the end milll? The ROT of that I'd read in a book years ago was 1/8th of the end mill diameter as the depth of cut (0.015 for an 1/8" mill)
I don't have power feed, and have never had coolant, except flood coolant (what a mess) the few times I ran the horizontal part of the mill. [1940s vintage Hardinge Universal horizontal mill with a Bridgeport C head in the overarm hole for vertical milling - not very rigid, but it's what I have] Any technique to use to do hand feeding of the table?
Without some sort of auto feed the task you have at hand is near imposable.
You might control the feed speed steady enough for some short period but being human sooner or later your hand will involuntarily "jerk" and while it might not seem like much, the "jerk" could easily quadruple the feed speed for an instant and in tough material that's enough to hear the fat lady sing.
A thought did occur to me while writing the above and that is if you geared down your feed enough, manual hand feed irregularities would not translate into such violent
(violent for a 1/8 th end mill)
bed movements. Thing is, if you go to all that trouble you might as well have a motor of some kind drive it.
I can get away with 0.050 depth but prefer 0.025 for such a fragile tool. The manual feed on my well-worn Clausing 8525 is sensitive enough to feel the cutting resistance and I control it with light finger pressure rather than trying to hold a speed. The inertia of the dial evens out the impulses from each flute cutting.
Once I have the feel for the cut, I speed up the mill and use the same pressure.
Speed for mild steel no faster than 120 ft/min, but since you will probably be using a squirt of cutting oil, maybe 60 ft/min. A 1/8" endmill is .033 of a foot in circumfrance. 60/.033 = ~1800 RPM.
DOC 1/4 of diam = .032"
Feed .0005" per tooth, two flute cutter = .001"/rev. At 1800 rpm =
1.5" per minute, that works out to one turn every eight seconds.
When I hand feed, I use a two handed motion, (grabbing on the dial), one hand rotates about 20 degrees, then other hand 20 degrees, repeat. By making the changes often, it seems to even out the motion for me Easier if you have round wheels instead of a crank.
If you're making a full-width slot with the cutter, use coolant to remove chips. You need to remove those chips. If you don't get the chips away from the cutter, you'll likely break the tool from the chips jaming in the flutes of the cutter. Use a 2-flute endmill!
Make sure the machine is pretty tight (this is *always* important!). If you can't tell, use an indicator on the table, and give the table a good tug. If you can see more than perhaps a thou or two of play, you should consider adjusting your gibs. If the machine isn't tight and you change your grip or something, you run significant risk of breaking the cutter. I typically snug the table lock until just before the table won't move.
Always make sure to lock all the axes which aren't moving! You must
*always* do this! If you don't lock your axes, the cutting forces can drag the axes enough to break the cutter (or at least start cutting where you don't want to cut).
What you're attempting is pretty standard stuff and you really shouldn't have trouble. Machining isn't magic, but it's also not very tolerant of sloppiness either. If you don't follow standard proceedures (like outlined above), you're never going to get consistantly good results.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.