I’ve had a S3 with a 611 for several years and just upgraded to the HDM with 2.2KW spindle. Researching feeds and speeds and just wanted to make sure I’m understanding those correctly.
I mainly use .25 2-flute downcut bits. The manufacturer recommends 20k RPM and 160ipm. That is a chipload of .004. I’ve done a few small pockets in MDF using that and it seems OK. I’m wanting to verify that I’m using the correct speed/feed/chipload. The ideal chipload for MDF looks to be .013-.016. The max speed on the HDM looks to be 196ipm and slowest spindle speed is 8k. Based on all the calculators I’ve found, I’d either need to go much lower than 8K rpm of much faster than 196ipm.
I would probably start by questioning that 0.013-0.016" chipload recommendation. It seems too high to me for a 1/4" tool. The second question would be, do you need that hefty chipload? I would suppose that you are more after a high material removal rate, not necessarily a large chipload ? The HDM being much more rigid than the S3 (and the Pro), there is scope to use much more aggressive depth per pass / width of cut settings, to end up with a much larger MRR than you were able to achieve on the S3. Then comes the side effect of large MRR: the need for very efficient chip evacuation (or rather dust evacuation, in the case of MDF). Plus the fact downcut endmills tend to pack the chip down the cut, making good dust collection even more important.
I see the HDM primarily as a workhorse for machining metals, and it was therefore not designed for lightning fast feedrates in the high hundreds of ipm (but @Luke would be in a much better position to comment, obviously).You should be able to leverage its oompf to machine MDF faster than ever, if you adapt your other cutting parameters
That said, if you still want to maximize chipload, and you have already hit the min RPM and max feedrate limit, the remaining option is to decrease flute count, since chipload = feedrate / (RPM x flute count)
Not that using a single flute to machine MDF sounds very natural to me, though.
I often find that my feedrates and depth of cuts are constrained by my work holding, especially for larger bits. I only push my feeds and doc if my patience is being tested forcing me to experiment. So it often depends and i would rely on your own experimentation after researching a good starting place.
Thanks for the thorough answers! The MDF chipload may be hefty and I’d definitely say I’m after a higher MRR than chipload. I do have a large JET Cyclone connected to the machine. I really only need to mill a few work holdings out of the MDF.
Though my main use of the HDM will be milling woods, they will be extremely hardwoods 2K+Janka. The hardest wood I normally cut is Katalox, which is closer to 3.6K Janka and maybe close to Aluminum in hardness if the scales are comparable. I plan to keep a wide piece of MDF bolted to the back of the wasteboard and mill several three sided holding jigs in the front edge. I can then cam clamp my precut wood blanks into the holding jigs for milling. I think once I start cutting these hardwoods, the numbers will all fall in place. I think MDF may be an outlier for now and I’ll just do some experimenting.
The CNC Cookbook folks have a bit on this:
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