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Advice on milling depth/width/feed of cut for novice!

Hi All,

Had my first real go on the Marlow yesterday making up some T-nuts for it (awkward 7/16" width). I got there in the end but I really doubt I was doing it in the most efficient manner. I've done various searches to find the spindle speed (1/2" 4 flute HSS endmill cutting mild steel) and ended up at 800rpm. But I'm unsure about the depth of cut. One place I found said for roughing it should be 1/2 the cutter diameter, so that's 1/4". I was cutting a width of 0.175" off the side of a 20mm sq steel bar but was getting absolutely nowhere with such a large depth of cut. Could well be that because I was hand feeding I was pushing too hard, I couldn't get a feel for it like I can on a lathe. The machine is pretty damn solid but even so I was getting vibrations. In the end I just had to reduce the depth and slog though the metal on multiple passes. The cutter didn't look too happy at the end of it.

I also found out that the coolant drain hole on the table is too small to cope with a decent flow from the pump, bit of a flooding issue there ;)

Regarding feed rates, I've found 0.002-0.008 in./rev for steel giving

6.4-25.6 in./min, presumably the deeper the cut the slower the feed rate? I need to get the feed motor rewired to delta so I can get the power feed up and running!

I suspect I'm just taking these theoretical values too seriously and just need to adjust to suit what the machine will cope with, but for such a solid lump of a thing I was hoping for slightly better results.

Cheers, Rob

Reply to
Robbus
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IIRC one should think in terms of half the width of the cutter wide by the width of the cutter deep if cutting on the side and half the width of the cutter deep if cutting over the full width of the cutter. So if you were actually taking the full 20mm off the side of the bar, you were pushing it a bit, even with less width of cut, the endmill would have been bending more than it wanted to.

On the other hand I'm pretty iggerant, since all my milling at the moment is on a Myford lathe and they really aren't solid lumps!

Mark Rand RTFM

Reply to
Mark Rand

Sorry, should've said, I was only cutting 2-3mm deep each time, any deeper and I felt I was pushing it. If I could've done 12mm deep in one pass, that would've been fantastic as the job would've been done in two passes. Hopefully it's just me being clueless, maybe I should also invest in some carbide cutters rather than HSS, and/or indexable jobbies. I must admit I like my indexable lathe tools.

Cheers, Rob

Reply to
Robbus

I cut 12mm deep in one pass, slow hand feed, using a 1 dia inch ripper cutter at 250 rpm on Saturday, using plenty of soluble oil on mild steel 13 inches long, on a Bridgeport, if its any guide for you. Not sure if the smoke was the cutter or the Old Holborn !!!

Reply to
Emimec

I can't get anywhere near the full width and depth cut on my little mill (a Centec). But I find I get better results on light cuts if I keep the depth and width in proportion (more depth than width). I also find that I get a feel for the feed rate after a while, and that as with turning, I need to have enough feed to take a positive cut. The chips coming off are also a guide to cutting performance.

Wilfrid Underwood

Robbus wrote:

Reply to
Wilfrid Underwood

I need to make everything out of plastic it seems, metal is sooo last week! I've just made up a cap to cover the hole left on my Warco headstock where I took the milling head off, ploughed through the stuff like it was butter, with a pretty blunt cutter, most satisfying ;)

Cheers, Rob

Reply to
Robbus

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