Speeds and Feeds question

CF:

Your Machinery's Handbook should have what you need. But below are some speed/feed data sites. 2 HP isn't a lot to play with, and could be an indication of a very light duty machine, so I'd tend to take multiple light cuts rather than try honking hogging cuts. At least until you get a feel for what the machine and setup can take.

I fix that problem by tossing the steel into the woodstove. Next morning it machines a lot better on a 3/4 HP Clausing at 600 RPM, manual feed, 1/2" 4 flute HSS endmill with the corners slightly beveled.

Or finish the part on the surface grinder.

jsw

Just off the top of my head, and after about a zillion hours of cutting steel on Bridgeports (long ago, though), I'd start with 90 SFM and .002 chip load per tooth. That may not be perfect; but for mild hot-roll, it's guaranteed close enough that speeds and feeds aren't messing up your job.

Is your vise really holding the work securely? Or is the rough surface maybe just gripping at a couple points, leaving the rest of the workpiece to squirm and dance around?

If you're really got a good grip on the work (it's not hanging off the end of the vise or anything, right?), then something else is wrong. The tool holder or collet? Climb cutting with too much backlash? Servo problem that's causing vibration or "loping" under load? Can you lock the saddle and quill while you cut, or were the locks removed when it became a CNC? Something's loose or wiggling, I suspect.

One way to find out if it's machine or workpiece is to use the same cutter, same speeds and feeds, same DOC, etc., on a piece of something that you KNOW you can clamp securely and hold like it's welded. Maybe a nice thick piece of 1018 left over from another job. If that works better, then your grip on the hot roll is in question. If the problems stay the same with a different workpiece and better grip, then something's wrong with your machine.

HTH.

KG

Or maybe you just got hold of a cheap-assed endmills that's not relieved right.

Or maybe your mild hot-roll isn't so mild after all. Hard to tell just by looking or tasting.

Or... Well... You get the idea. Could be lots of things. Change or test them one at a time. The culprit will show itself if you make sure it can't hide amid the complexity and confusion.

KG

I'm surprised no one has said that it's often difficult to get good finishes when machining hot-rolled mild steel. I haven't milled it for a long time but turning it can produce really ragged surfaces. It's kind of gummy and it doesn't shear cleanly. Turning, I usually get the best results by finishing with a relatively deep cut, with the highest speed I can use. If I have to take a skim cut, I can count on it tearing. I use lard oil, which does help somewhat.

But as I've said here before, I rarely machine mild steel at all, and I've always realized there are tricks out there that I don't know about.

As mentioned by others, a host of issues could be at work here, and it would be difficult to tell without looking at the details more closely. Feeds and speeds sound unlikely to be the problem. I would just mention that if you haven't run steel for awhile, the issue of chatter is something to consider, and all the tricks involved in reducing it. Chatter is rarely ever a problem in plastic, in my experience, but an often considerable problem in steel. If the poor surface finish you describe is characterized by a wavy, repetitious tool marks and you get end mill noise simultaneously, it's chatter. Apologies if this is all simple stuff to you, but I think chatter is one of the hardest phenomenon to understand and correct.

How do you know it is "hot rolled mild steel"? Do you mean A36? Take a file to a piece of it for reference. Heat it to a meduium red and quench in water. See how it files now. If its much harder to cut, it wasn't mild steel. Even then, mild steel isn't necessarily all that mild anymore. See:

Pete Stanaitis

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Carla F>