-
Welcome back Guest! Did you know you can mentor other members here at H-M? If not, please check out our Relaunch of Hobby Machinist Mentoring Program!
What is "chip load" and why is it important in milling?
- Thread starter Nelson
- Start date
- Joined
- Jan 28, 2011
- Messages
- 3,614
Chip load is important to good parts and tool life. Too small of chip load and you tend to rub which causes the tool to wear down without getting all one can get from the tool. Too fast and the chip may not clear which causes the chip to rub on the part (bad finish) and the flutes tend to load up and tool breakage is high. Also you could be running too hot for the tool or material that you are milling, could cause hardening on some steels for example. You tend to get bad finish and larger burr when the loading is wrong.
Machinery's Handbook has the formulas that allow one to calculate the best rpm and feed rates for your machine and tool combo. The results should not be taken as cut in stone, there is wiggle room depending on circumstances.
Example I have 2 high speed milling machines. The first one that the shop bought had a 24000 rpm and when using SMALL end mills like a .020" I could go about 15" per minute without breaking the tool. Tool life was pretty good but could be better. 2flute end mill. 15"/(2x24000)=.00031"/tooth
The new machine the spindle has a max rpm of 60000. Now I can feed at 30-40" per minute and get the same or better tool life. The tools I use in this example are solid carbide and the millings is done dry due to the type of metals being used. 40"/120000=.00033 Not much difference between the two but big difference in tool life and speed of the operation.
Others likely can explain it better than I can.
Pierre
Machinery's Handbook has the formulas that allow one to calculate the best rpm and feed rates for your machine and tool combo. The results should not be taken as cut in stone, there is wiggle room depending on circumstances.
Example I have 2 high speed milling machines. The first one that the shop bought had a 24000 rpm and when using SMALL end mills like a .020" I could go about 15" per minute without breaking the tool. Tool life was pretty good but could be better. 2flute end mill. 15"/(2x24000)=.00031"/tooth
The new machine the spindle has a max rpm of 60000. Now I can feed at 30-40" per minute and get the same or better tool life. The tools I use in this example are solid carbide and the millings is done dry due to the type of metals being used. 40"/120000=.00033 Not much difference between the two but big difference in tool life and speed of the operation.
Others likely can explain it better than I can.
Pierre
- Joined
- Jul 30, 2011
- Messages
- 348
chip load= chip thickness per tooth of the cutter...
for instance using a four flute endmill: if you figure it to have .004 chip load, its .004 per tooth which would be .016 total chip load... If your running 2000 rpm multiply 2000rpm by .016 (total chipload) = feed rate of 32 inches per minute..
for instance using a four flute endmill: if you figure it to have .004 chip load, its .004 per tooth which would be .016 total chip load... If your running 2000 rpm multiply 2000rpm by .016 (total chipload) = feed rate of 32 inches per minute..
- Joined
- Mar 10, 2012
- Messages
- 1,382
I still haven't had my darn coffee yet so go easy now.... :biggrin: It sounds like chip load is somewhat akin to feed rate.....? How would you know what your chip load is unless you know exactly what your feed rate is, the size of the cutter and # of flutes, the depth of cut, and spindle RPM....right?
Last edited:
- Joined
- Jul 30, 2011
- Messages
- 348
chip load is directly related to your feed rate..
On a mill you use rpm and chip load as your base to figure feed rates... I figure my rpm first, then figure feed rates, and yes, depth of cut, radial depth of cut if your side milling plays a part..
Chip load comes from mills using inches per minute as opposed to lathes that use feed per revolution..
If your not familiar with figuring feed rates in mills, you will find out most books are not exactly correct on feed rates, My teacher back in trade school told us that these feed rates in books were figured using pretty much perfect setups in a production environment such as automotive manufacturing, so you have to account for that. I always cut my feed rate in half or more to start with, then gradually bring the feed rate up with the feed rate override to a level i'm comfortable with.
Carbide is a bit different as its more forgiving than highspeed steel tooling when it comes to speeds and feeds, with carbide you have a wider envelope of speeds and feeds..