The best way to approach this issue (IMO) is to start with the recommended chipload (CL) for your bit and your material. Then calculate the feedrate (FR) and router speed (RPM) from there.
If the end mill vendor/manufacturer didn’t supply a recommended CL (some do, most don’t), there are lots of charts on the Internet that can give you “typical” values. Most are in Inches/tooth (IPT), so you may need to convert to mm/min (IPT * 25.4 = mm/tooth) to get metric FR.
CL = FR/(RPM * # of flutes)
FR = CL * RPM * # of flutes
RPM = FR/(CL * # of flutes)
Here’s an example:
Chart from Chip Load: Guide for Beginners - MellowPine
| Material | 1/8″ tool | 1/4″ tool | 3/8″ tool | 1/2″ tool |
|---|---|---|---|---|
| Hardwood | .003”–.005” | .009”–.011” | .015”–.018” | .019”–.021” |
| Softwood/ | ||||
| Plywood | .004”–.006” | .011”–.013” | .017”–.020” | .021”–.023” |
| MDF/Particle | ||||
| board | .004”–.007” | .013”–.016” | .020”–.023” | .025”–.027” |
| Hard plastic | .002”–.004” | .006”–.009” | .008”–.010” | .010”–.012” |
| Soft plastic | .003”–.006” | .007”–.010” | .010”–.012” | .012”–.016” |
| Acrylic | .003”–.005” | .008”–.010” | .010”–.012” | .012”–.015” |
| High-pressure | ||||
| laminate | .003”–.005” | .009”–.012” | .015”–.018” | .023”–.025” |
| Aluminum | .003”–.004” | .005”–.007” | .006”–.008” | .008”–.010” |
Note that these recommendations are for Depth of Cut (DOC) = tool diameter. If DOC + 2x dia., reduce by 25%, and if DOC = 3 * dia., then reduce by 50%
If you wanted to use your 1/4" 2 Flute bit at the slowest RPM for your router (10,000 RPM) at 6mm DOC (1x dia), and assuming you select the middle of the Plywood CL range (0.012 IPT), then the formula for FR would be:
FR = CL * RPM * # of flutes
= 0.012 * 10,000 * 2
= 240 IPM (*25.4)
= 6096 mm/min (101.6 mm/s)
That is probably too fast for the LR3 (or LR4) to achieve without skipping steps, Although theoretically if you increased DOC to 18mm, then the value decreases by 50%, so you would be in the 3000 mm/min range that @Tokoloshe mentioned (Edit - as @Tokoloshe mentions below, 18mm DOC may not be physically practical).
If instead you use a 1/8" single flute bit at mid RPM (20000) the formula for 1x dia. works out to
FR = CL * RPM * # of flutes
= 0.005 * 20000 * 1
= 100 IPM (*25.4)
= 2540 mm/min (42 mm/s)
Hope this helps!