Cutting Load Calculations

[kolokithas]

Greetings,

I recently finished a Bronze sign for a friend of mine.Because im not familiar with rpms, cutter diameter and feed,i usually use my ear to see if the cutting process is going Ok(if the tool chaters etc.)
I come up with an idea and i would like to see if other people made calculations about cutting forces etc.or know anything about that matter.

Let me show you the calculations that i've made.

I used a 2 flute 4mm HSS endmill to cut the sign.
My feed rate was 100mm/min and my depth of cut was 1mm into bronze
The spindle RPM was 1680.

So i tried to do some math to see if i get something...

I divided the rpm by 60sec
1680/60sec=28 revs per second

I divided the Feed by 60 sec
100/60=1.66mm/sec

And i divided the feed to the rpm(i also tried to multiply the two numbers)
1.66/28=0.059 was the result

Now the questions are:
The result: 0.059 is the thickness of material being removed by each revolution or is a random number?
Should i take into consideration the number of flutes of the endmill?
Or the number 0.059 doesn't represent anything and the calculations are

I would like to discuss this issue with other members here because i think that something good will come up from these calculations.

[CarbideBob]

You're on the right path.
Note that you can skip the conversion to seconds since both RPM and feed are in minutes.
Feed Speed/Spindle Speed = Feed per Rev (FPR)
100/1680 = 0.059 Feed per Rev
The machine is moving 0.059 forward for each revolution of the cutter.
Now that you know how much material is removed in one revolution you divide by the number of teeth in your cutter.
0.059/2 = .0295
This is the amount of material removed by each tooth as it swipes through the material. This is feed per tooth (FPT) also know as chip load.
So if you have 4 teeth you can feed twice as fast and have the same load per tooth.
200 Feed / 1680 RPM = 0.119 Feed per Rev
0.119 Feed per Rev / 4 Teeth = .029 Feed per Tooth
Bob

[kolokithas]

So...

I reinvented the wheel!!!!
Lol.Some times is better to discover something by yourself rather to have it served to your table.
I think that the FPT is the most important factor when you cut a material,right?
Because if your tool can't stand the forces,feed rate and RPM are useless once your tool is broken!!!
Another (known) factor comes to make it more complex the depth of cut.
But i have read that you should cut by 50% of the cutter diameter.I think trial and error is good,but to make some formulas according to calculations is also good!

(I discovered later that there was another similar post about cutting etc
so i could enter this post there instead starting a new thread.My bad)

CarbideBob thanks for your remarks!

Panos Labrakis
Greece

[mrk]

I cut aluminum and only have 3500 rpm at the spindle so for me almost everything is at max rpm. The factors I can play with are feed per tooth, axial depth, and step over amount.

I don't know much about brass. Lately I am cutting 7075 alloy and I am finding some slight differences between it and 6061.

For my machine and the type of part I can slot at around .003 inch per tooth. If I am doing a profile cut I can go up to .010 inches or some times even faster if the amount of tool engagement is small. Axial depth for slotting is around 50% of the tool diameter or sometimes less depending on my mood. For profile cuts with light tool engagement my axial dept is often the full flute length for the tool so at times I am cutting with the entire tool depth but only when it is a profile cut.