# Sheet Metal + Plate Steel **URL:** \ **Category:** šŸƒšŸ¼ Tools & Speeds\ **Created:** [July 19, 2026, 8:50pm UTC](https://forum.sienci.com/t/sheet-metal-plate-steel/26746 "2026-07-19T20:50:43Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Spindle\_Shogun](https://forum.sienci.com/letter_avatar_proxy/v4/letter/s/d26b3c/32.png) [@Spindle\_Shogun](https://forum.sienci.com/u/Spindle_Shogun)\ **Post date:** [July 19, 2026, 8:50pm UTC](https://forum.sienci.com/t/sheet-metal-plate-steel/26746/1 "2026-07-19T20:50:43Z")
Hello - Iā€™m considering an AltMill with the 2.2 KW spindle. I would mostly work with wood and an occasional aluminum project. That being said, I also have a steel project where Iā€™d like to be able to cut some parts out of plate steel (say 1/4"). I read that the AltMill is not appropriate for this kind of work but I also see videos like the ā€œMetal Outdoor Wall Artā€ where steel is being cut: [https://www.youtube.com/watch?v=HV\_5VjVdxc0](https://www.youtube.com/watch?v=HV_5VjVdxc0). I watch a lot of Stefan Gotteswinter and this video in particular catches my attention: [https://www.youtube.com/watch?v=WzT4HJalwAs](https://www.youtube.com/watch?v=WzT4HJalwAs). Is it not possible to leverage this technique on an AltMill? Even with some form of coolant? ---
**Author:** ![gwilki](https://forum.sienci.com/user_avatar/forum.sienci.com/gwilki/32/366_2.png) [@gwilki](https://forum.sienci.com/u/gwilki)\ **Post date:** [July 19, 2026, 11:25pm UTC](https://forum.sienci.com/t/sheet-metal-plate-steel/26746/2 "2026-07-19T23:25:38Z")
@Spindle_Shogun Welcome to the group. The steel being cut in the Sienci video is 16 gauge = less than 1/16". I didnā€™t watch all of the other video, but I did see that he was cutting 2mm stainless and using a depth of cut of .1mm.You want to cut 1/4" or 6mm. So, using his specs, you will need to take 60 passes. You are a much more patient man than me. šŸ˜€ ---
**Author:** ![Jens](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/d2c977/32.png) [@Jens](https://forum.sienci.com/u/Jens)\ **Post date:** [July 19, 2026, 11:45pm UTC](https://forum.sienci.com/t/sheet-metal-plate-steel/26746/3 "2026-07-19T23:45:54Z")
I donā€™t know about RPMā€™s for cutting steel - I know my knee millā€™s highest speed is way less than the Altmillā€™s lowest spindle speed. Is seems that this (in addition to rigidity) could also be an issue. ---
**Author:** ![Chucky\_ott](https://forum.sienci.com/user_avatar/forum.sienci.com/chucky_ott/32/8692_2.png) [@Chucky\_ott](https://forum.sienci.com/u/Chucky_ott)\ **Post date:** [July 20, 2026, 12:32am UTC](https://forum.sienci.com/t/sheet-metal-plate-steel/26746/4 "2026-07-20T00:32:40Z")
@Spindle_Shogun yeah, the spindle speed will be a problem for steel. The minimum speed is still too fast. ---
**Author:** ![mick\_s](https://forum.sienci.com/user_avatar/forum.sienci.com/mick_s/32/9655_2.png) [@mick\_s](https://forum.sienci.com/u/mick_s)\ **Post date:** [July 20, 2026, 12:33am UTC](https://forum.sienci.com/t/sheet-metal-plate-steel/26746/5 "2026-07-20T00:33:51Z")
I would never try cutting steel on my AltMill. The machine is plenty stout to handle it given conservative depths and feeds. However, cutting steel generates a LOT of heat (without adequate flood coolant) which transfers up the tool to the spindle bearings and evaporates the grease out. Wrong application for this machine, IMO. ---
**Author:** ![Spindle\_Shogun](https://forum.sienci.com/letter_avatar_proxy/v4/letter/s/d26b3c/32.png) [@Spindle\_Shogun](https://forum.sienci.com/u/Spindle_Shogun)\ **Post date:** [July 20, 2026, 12:50am UTC](https://forum.sienci.com/t/sheet-metal-plate-steel/26746/6 "2026-07-20T00:50:59Z")
Any idea why the spindle speed only goes down to 7500 rpm? Given the VFD setup Iā€™d think it could go lower? There is no hope of faster travel to keep the chip load in the same ballpark? Stephan has some other videos where he uses Isopropyl alcohol in air as coolant (and I have such a mist setup). I really wouldnā€™t cut steel often, and recognize it could take quite some time, but itā€™s a tough pill to swallow to have an expensive CNC and then have to send out parts. BTW I think he was doing 0.2mm DOC so only 32 passesā€¦ ---
**Author:** ![mick\_s](https://forum.sienci.com/user_avatar/forum.sienci.com/mick_s/32/9655_2.png) [@mick\_s](https://forum.sienci.com/u/mick_s)\ **Post date:** [July 20, 2026, 1:05am UTC](https://forum.sienci.com/t/sheet-metal-plate-steel/26746/7 "2026-07-20T01:05:31Z")
Because the available torque falls off below that causing the spindle to overheat. ---
**Author:** ![Jens](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/d2c977/32.png) [@Jens](https://forum.sienci.com/u/Jens)\ **Post date:** [July 20, 2026, 1:12am UTC](https://forum.sienci.com/t/sheet-metal-plate-steel/26746/8 "2026-07-20T01:12:52Z")
While torque does fall off, I would think that reduced cooling air flow from the slower spindle fan is also a big factor. ---
**Author:** ![DavidB](https://forum.sienci.com/letter_avatar_proxy/v4/letter/d/76d3ee/32.png) [@DavidB](https://forum.sienci.com/u/DavidB)\ **Post date:** [July 20, 2026, 3:57am UTC](https://forum.sienci.com/t/sheet-metal-plate-steel/26746/9 "2026-07-20T03:57:48Z")
It is possible to lower the minimum spindle speed for the AltMill/VFD (and is required to do so for the RapidChange ATC to work). I do believe however the air flow is the issue as @Jens mentioned. For the RapidChange ATC it isnā€™t an issue since you are running it at the lower speed for only a very short amount of time. ---
**Author:** ![DavidB](https://forum.sienci.com/letter_avatar_proxy/v4/letter/d/76d3ee/32.png) [@DavidB](https://forum.sienci.com/u/DavidB)\ **Post date:** [July 20, 2026, 4:11am UTC](https://forum.sienci.com/t/sheet-metal-plate-steel/26746/10 "2026-07-20T04:11:04Z")
That does make me wonder if swapping out for a different spindle that runs without cooling issues below 7500 rpm would work. It wonā€™t be as ā€œplug and playā€ as using a Sienci spindle but the SLB-EXT supports many different spindle models. ---
**Author:** ![DavidB](https://forum.sienci.com/letter_avatar_proxy/v4/letter/d/76d3ee/32.png) [@DavidB](https://forum.sienci.com/u/DavidB)\ **Post date:** [July 20, 2026, 4:23am UTC](https://forum.sienci.com/t/sheet-metal-plate-steel/26746/11 "2026-07-20T04:23:07Z")
PwnCNC has a water cooled 800MHz 2.2kW 80mm metal-working spindle for sale but it is special order.