# Thread: Calculating feeds and speeds using FPM and IPR

1. ## Calculating feeds and speeds using FPM and IPR

I need to drill holes in carbon laminate using the Onsrud solid carbon drills for composites.

The datasheet indicates the following two formulae:

RPM = (3.82 x SFM)/tool dia
Feedrate (IPM) = RPM x IPR (inches per rev)

For a #16 drill at .177" diameter, RPM calculates out at about 4963rpm with a quoted 230 SFM

Can anyone advise how IPR is calculated? My assumption is that the IPR is the circumference around the drill bit or pi x D but this yields huge feed rates.

Thanks,Tony

2. IPR is the amount of feed for each rev of the spindle.

RPM = SFPM/((TOOLSIZE/12)*PI)
IPM = DRILL_RPM * IPR

An IPR of 0.002 for the drill would result in a feed of 9.93 at 4963rpm.

3. Thanks - want to make sure I am correct before I start drilling,

I also calculated feedrate from Chipload using RPMxCLx#of flutes

6837x0.002x2 - yiedling 27.4 IPM

The result was an IPR of 0.004

So if I run the drill at the calculated speed, I assume that my vertical (z)plunge feed rate must be 27.4 IPM - is that correct?

4. >>>>>>>>>>>>>>>>>>>>>>>>>>>>
RPM = (3.82 x SFM)/tool dia
>>>>>>>>>>>>>>>>>>>

RPM=(4 x sfm)/dia is easier to remember, not as precise, but the error is on the side of caution............

your IPM feed looks right to me

Bill