Feed Rates
Overview
The feed rate is the speed at which the spindle travels through the material
To slow and the milling process can take hours to complete, too fast and it can lead to the spindle over heating or bending with excessive load.
Speeds tend to be measured in mm/min.
A speed which is too fast is really bad, as it can lead to:
- The milling bit becoming too stressed / breaking / bending
- The machine skipping steps leading to all sorts of problems with miss-alignments
To get the best speeds, it’s best to do a pass with a larger mill bit first, then a smaller bit afterwards Also try to set the speeds in the Cam software instead of using the multiplier in Chillipepr
Feed Rate recommendations
300W Spindle - MDF
For MDF I’d recommend we only do 2mm at a time on a given pass for the depth of cut
Commerical software such as hsmworks tends to default to about 1000mm/min and 333.3 mm/min but this is way too fast
| Material | Bit Type | Cutting Speed | Plunge Speed | Depth Pass | Description |
|---|---|---|---|---|---|
| MDF | 3mm Flat End Mill | 250mm/min | 83.325mm/min | 1 mm - 2 mm | This seems a safe setting for general use |
| MDF | 6mm Flat End Mill | 250mm/min | 83.325mm/min | 1 mm - 2 mm | Not sure with this spindle, needs to be tested |
I’ve noticed that when setting the max depth of cut to 2mm instead of 1mm when going around the outside of a part can result in the part becoming too loose early on during the final pass / cut around the outside. So if you are going to do that try to hold the part down a bit with something heavy.
TODO
We could do with experimenting with different speeds / spindles / materials etc.
So far I’ve not tested a 6mm bit with the spindle, but we need to use one where an area needs to be leveled out
as trying to do this with a 3mm bit will take a long time.
Considerations
Heat
The first consideration is the amount of heat generated by milling through the material. With a really small mill bit it’s going to get hotter more quickly than a larger mill bit. This is due to the larger mill bit having more metal to store / get rid of the heat.
A dremmel typically isn’t cooled, but the 300W spindle has air flow over the bit and the spindle, this which allows us to mill more. As one example, while milling mdf with a dremmel and too high a feed rate I managed to cause the mdf to turn black and start to burn. With an air cooled spindle such as the one currently on the shapeoko this doesn’t seem to have this problem.
Skipped Steps
The shapeoko2 we have in the hackspace only uses Nema 17 Motors so we can’t apply a lot of pressure quickly. Therefore, running too quickly or too deeply can lead to uneven cuts. One way around this is to do a rough cut initially if possible to clear out most of the material except for about 0.5mm or so. Then afterwards a 2nd fine pass afterwards to remove the remaining material.
Depth of Cut
The deeper we cut on a pass the more heat will be generated, and the more force the shapeoko will need to provide. This in turn can affect the heat generated by the stepper motors.