View Full Version : Question regarding "chip load" on vert mill

Your Old Dog
03-04-2007, 06:44 AM
Once again Grasshopper comes to the well in search of knowledge.

I'm aware of the term "chip load". I know it means how big a bite of the stock the cutters individual flutes take in one pass. But what I don't know is what is normal?

What should I be looking for in a properly sized chip? I assume if I get hair like slivers I'm not doing much cutting but dulling the cutter faster. I suppose if the chip is large and blue I'm taking too big of a cut. It would really be helpful if someone could explain what needs to be taken into consideration before saying I have a good or adequate chip load for a given operation.

All my work is done in mild steels and aluminum, nothing exotic. Work is done on Rung Foo mill with it's limitations as to tooling sizes. It is equiped with power feed.

Thanks for any light anyone can shed on this topic.

03-04-2007, 07:57 AM

The chip load is going to vary with the material, obviously. It will also vary with the type of end mill you are using. I usually go by the charts from the manufacturer for CNC work; but for manual machines, it's more "seat of the pants".

In steel, I would get your spindle speed set up first, then you can vary your feed to suit the cut. For Hss cutters, when the chip starts to turn brown, you are starting to push the limit.

Aluminum; you can't go by chip discoloration. You are going to have to watch for chip evacuation, chip welding, etc. You can try doubling what you would run in steel to start with.

For guidelines in general in steel, for end mills I figure about .001 Per tooth for 1/4", .001-.002 Per tooth for 1/2, .004 Per tooth for 1", and so on. So for 1/8 , it would be about .0005 Per tooth.

These numbers should get you started; but the condition of your end mills, and your machine capabilities are going to need consideration also.


03-04-2007, 11:15 AM
YOD, you might find a program called "ME Consultant Pro" to be helpful. It's a feeds and speeds calculator, but it does a lot more than that and is a handy shop program to have around. Many of the PM board pros swear by it.

To use it, you enter your operation (end milling, drilling, turning, etc), the material, cutter diameter, and flutes. It gives you back the best spindle rpm and feedrate for that combination.

I also find it is helpful when looking at feedrates, which are inches per minute, to do the conversion on my mill to "handwheel turns per second". The latter is not hard to estimate by counting and lets you dial in the power feed or your armstrong feed pretty closely.



Your Old Dog
03-04-2007, 01:32 PM
Thanks Kevin, that's very helpful. I'll copy it off and hang it on the wall till I get it sunk in !!

when you say "For guidelines in general in steel, for end mills I figure about .001 Per tooth for 1/4", .001-.002 Per tooth for 1/2, .004 Per tooth for 1", and so on. So for 1/8 , it would be about .0005 Per tooth." Can I assume you mean thickness and not width of the chip?

Bob, I have that site and in fact just left it a little while ago. http://www.jonathansaada.com/speeds_feeds.php I was wondering though what you looked for in a chip to determine that you were infact cutting properly and max'ing out the tooling. It sounds like you read the metal chips pretty much like wood chips on a chain saw. If you get power for wood chips you know the saw is dull. In this case, if I get super fine swarf then I'll assume the feed rate is too slow. I've only busted two bits but I'm so darn cheap on somethings I hate it when that happens !!

If these answers don't work for me I'll go over to www.HomeShopSeptic.com in search of more knowledge. They tell me those guys over there are pretty sharp !! Well, maybe tapered would be a better choice of wording :D

03-04-2007, 01:59 PM
Since you aren't running CNC or a mechanical power feed driven off the spindle gears you really don't have any way of knowing or setting a chipload.Your only real method would be using the powerfeed starting at the lowest setting and ramping the feed up until it starts to chatter and then backing off a bit.It really is a matter of feel on a manual mill.

03-04-2007, 01:59 PM
Those numbers would be chip thickness. If you're just rubbing around, you'll dull your cutting edge.
I usually figure what my spindle speed needs to be, then adjust the feed to suit . Pull a chip; but when steel chips start to discolor, back off a little. Aluminum will start clogging up your flute at high feeds.
Your mill may determine the max feedrate you can use.
Ball end mills are going to be different; because your cutting speed drops off as you get toward the center, and you don't have as much chip clearance on the ball end.


Your Old Dog
03-04-2007, 09:43 PM
Thanks Weird, thats about the way I've been doing it now but not sure if it was correct.

Joeby I went back out again this evening and got some better looking chips. I think if I just set spindle speed first I'll be okay if I watch for smoke!!