Default speeds with Aluminum

I’ve been happily using Carbide Create with our Shapeoko Xl for over a year now and it’s great.

The one major issue I have is the default speed for Aluminum being way too fast. There’s no way it is correct, you can’t hold down a part when it’s going that fast…

But, what is the actual correct speed? There are feeds and speeds charts out there, but they don’t match up at all with want is in Carbide Create. Also, seems machinists may be challenged with units and most people don’t show any units and others show what has to be wrong units…
For example, Carbide Create shows feeds in units of “in”. But, I’m thinking it has to be inches per some unit of time. I’m thinking it should be “inches/minute”.

Anyway, I really wish there were a table somewhere of feeds and speeds that matched up with what is in the software so I could make sure it was correct…

Take a minute, check around the forum, you may find a few posts re aluminum feeds and speeds.

I’ll check back when I have more time, point you to a few posts if still needed.

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Start off by reading the Feeds & Speeds section of @Julien 's excellent eBook here:

The defaults in Carbide Create are not correct for a Shapeoko3–maybe they are closer for a Nomad, I don’t know. The feed rate units are inch/minute unless you are using metric units.


To reduce the guesswork, you can also use @gmack speeds and feeds calculator or @Julien a bit simpler calculator found in the Shapeoko e-book thread.


To add to that, if you prefer videos to written content, check out Winston’s video on cutting Aluminium with the Shapeoko : first vid on this page.


The ebook looks great and the spreadsheet looks really good too.

But, I’m terribly lazy and don’t really want to invest the time to understand all that…
There are a lot of variables there that I don’t want to deal with…
First, I’m only using the Dewalt spindle that came with the machine, so I don’t need that to be variable.
Also, I’m only using the cutters that come from Carbide.
As for width and depth of cut, I’d like to trust Carbide Create to do all this for me.

The ebook and spreadsheet do give me a much larger appreciation for Carbide Create!

Anyway, Carbide Create seems to work perfectly well for plastics. It’s just aluminum that is messed up.
I don’t understand why more people are not complaining about this and why it hasn’t been fixed yet…

Good question…it has been reported numerous times here on the forum (at least the part about the RPM recommendations often being wrong for Shapeoko users since they are Nomad values), but it is unclear if the comment ever reached the ears of CC developers. There is now a dedicated thread for CC improvments, and I think I did raise that concern again in that thread, but it was probably lost in the 200+ messages. There are also some hints from Winston that Carbide3D may be cooking up something related to determining feeds and speeds, so we’ll see.

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As a new user, I just stumbled across this post. Thanks a ton!

For aluminum, I override the speed in carbide motion to somewhere between 30 and 50%.

I’ve done some plastics too and those speed settings seem just fine.

I should check that there haven’t been any updates to Carbide Create that have fixed this…

So, my version was old (316). I’ve updated to the latest version (431) but the speeds are the same. Also, there is no mention of fixing this in the version releases…

Changing the machine and material on a simple file with 0.125" end mill, I see these speeds:

Aluminum + Nomad --> 36
Aluminum +Shapeoko 3, XL, XXL --> 60
Acrylic+ Shapeoko XL --> 19.5

Should the speed for Shapeoko be ~2X that of Nomad? I don’t know…

Should the speed with aluminum be ~3X that of acrylic? I think not.
Looking at “feeds and speeds” chart in the wiki, I see speeds for aluminum that are about half of that for plastics.

GWizard uses a K Factor of 18.8, both HSMAdvisor and NYCCNC use 10 and, based on measurements, the SFPF Workbook uses 20 cubic inches per minute per horsepower (cu-in/min/HP) for acrylic.

GWizard uses 4.7, HSMAdvisor uses 3.77 and the SFPF Workbook currently uses 3.34 cu-in/min/HP based on NYCCNC’s K Factor for 6061 T6 Aluminum. The other speeds and feeds calculators I’ve tried use values within this range for 6061-T6 aluminum.

Although K Factors for metals seem to be fairly well established for metals (which is the primary purpose/focus of almost all speeds and feeds calculators), that doesn’t appear to be the case for other materials. IMO and experience, a K Factor of about 20 cu-in/min/HP is reasonable for acrylic. So it likely takes from 4-6 times more power to cut 6061-T6 aluminum than acrylic at the same material removal rates (MRRs). If both the MRR and endmill diameters are the same, milling aluminum would require 4-6 times more cutting force than acrylic. :slightly_smiling_face:

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