Aluminum work - Spindle vs Router vs AMB or Mafell milling motor

ER collets should be added to this list, for their wide variety and low price compared to router collets.

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Wouldn’t it be more useful to have the software adjust the feed rate (to control cutting power/force), and have the operator adjust the spindle speed based on how things sound (i.e. avoid resonances and such)?

When I first heard of G-Wizard, that was my assumption — that it imported a G-Code file, parsed the physics of it, and dynamically adjusted the feeds and speeds for the best possible cut.

Yes, and you should have electronic speed control for this, either in the communication/control program (are there plans to add a spindle speed rate override to match the feed rate override in Grbl?) or in an external unit — no one should reach into the machine’s working envelope while it is running to adjust a dial.

Power down (and unplug if you have that option — I place the plug for my trim router on top of the holder for the collet wrenches so that I never forget to plug it back in, and so that I have a habit of unplugging it before an endmill change) and be absolutely safe about reaching into the machine’s working area.

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CNCjs does implement RPM override


Assuming that the spindle isn’t exciting some kind of machine resonance, I think that the last thing to do to optimize the cut would be to adjust spindle speed.

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Dynamically was the wrong word to use there — my erroneous assumption would be that the spindle speed would be adjusted as necessary during the cut to adjust for different aspects:

  • climb vs. conventional — when climb milling, adding the current feed rate to the SFM speed to adjust for the spindle movement/cutting, but conventional would subtract it
  • when accelerating / decelerating — apparently the machines adjust speed quickly enough that this isn’t an issue, but doing this might eliminate the need for a dwell command as is used by some processes

At some point I’ll get back to experimenting with TPL, or some other tool for making G-Code directly, and will have to experiment with these ideas.

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Feed rate (IPM) and direction do not affect cutting speed (SFM) unless the spindle bogs down.

In normal usage, no.

But, consider the extreme case — if feed rate == SFM, then when climb milling the endmill edges wouldn’t move relative to the surface, and when conventional milling it would be twice the effective movement — I’m willing to accept that the speed difference is negligible and inconsequential, but I’m curious if one could reap a slight improvement in feeds and speeds.

I also wonder if varying the spindle speeds would better distribute wear on the motor and so forth.

In my experience, having gcode controlled spindle rpm has proven very useful and allows you to achieve consistent chip load from one job to the next. Combined with the bitsetter(which I don’t have yet) it would make for a really seamless job.

It also means you need to remember less… If your tools are configured correctly in the cam software then you never need to set spindle speed, at all.


How about a speed controller with feeback loop from tachometer for the router? The power would be adjusted to maintain proper RPM or feed speed adjusted if the router cannot maintain set RPM.

This is what SuperPID does, you install an optical sensor that can see if the router is beginning to bog and increase power. I’m sure there are others that work this way as well, I’m only familiar with the SuperPID.



I think, getting back to the original question, a Makita is the best bet. Even a converted brushless cuts aluminum quite nicely.

All sorts of trade offs, side benefits, personal preferences that only experience will mold.

Go with a Makita. Move on from there if you like.


That’s what the stock Makita, Dewalt, and CC (reportedly) routers already do (even without “Super PID”). That’s one of the main disadvantages of routers - they’ll provide as much torque (exert as much force) as they can to try to maintain speed. HF Spindle VFDs limit torque (hence machine forces) to whatever level they’re set to. Higher speed = less machine force = good, unless the spindle, tools, workholding, machine operator, or machine resonanances can’t handle it.

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Is that important? Why?

It means that my speeds and feeds are the same from one job to the next, once I’ve got a good combo for a material I want to stick with that… Having it already dialled in the software is time saving and more accurate…

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Do your speeds vary much from one job to the next? If so, is that to maintain optimal chiploads that you’ve established for the jobs?

They sure do, for example I may do a job in timber that uses a 1" surfacing but, a 1/4“ flat endmill, and a 0.5mm tapered ball nose. Each of these tools requires a different rpm and feed rate. Then if my next job is aluminium and I’m using A single flute 1/4" bit, and a 1" surfacing bit, the feeds and rpms are different again.
being able to change spindle rpm through gcode is definitely a useful feature for me.

I think I’m missing something here. Are you saying that maintaining a constant spindle speed is = bad? I don’t see where NOT holding constant speed (bogging down) = good? It’s late, been a long day in the shop, I must be reading that wrong, if so please disregard.


Attempting to maintain a constant spindle speed is bad (and potentially dangerous) if a spindle increases torque (hence machine forces) up to 10 times its maximum rated operating level trying to do so. This can happen when routers can’t maintain speed because something (mishap, hitting a knot in wood, etc.) prevents it.

VFDs for HF spindles limit the torque/force to user programmed levels. They can also show spindle RPM and are typically quiet enough that the operator should hear when they start bogging down so he/she can reduce feed rates as required.

Haven’t run the 60k for a minute because its 220v. The 24k 1.5kw has been running the show because it rides in the back of my truck from Houston to Austin every week.

Aluminum work - Makita rocks with 30k, needs single fluted to run hard. Easy and 3/8s compatible