Spindle Swap to Light Work Steel

[verhoevc]

I’ve done a lot of reading on shopbots (especially the desktop) and working with steel. I’d like to get some vise style hold downs and tackle some light stainless (think 416 and 17-4) work. Think full cutter width passes 0.080” deep taking as many passes as needed to get there.

Best I can tell from this reading, the limiting factor may be the spindle, not the gantry and drive train?

Thoughts on swapping to a low-RPM/high-torque spindle to tackle jobs like this without resorting to buying a mini Tormach or similar?

[coryatjohn]

I think you'll find three problems inherent in the standard ShopBot when it comes to machining steel.

1. The gantry and entire structure is just too weak and wobbly. To machine steel, you need a solid machine made from heavy steel, not aluminum extrusions.
2. The motors that come with the standard SB, even an Alpha, have steps too large to work with a material like steel.
3. A spindle or router spins too fast and a spindle has too low torque at the lowest RPM's to do anything but make a mess.

It's very likely that you'll twist your machine with each step and the results will be just terrible. You'd be better off getting a mill or farming out the work.

[verhoevc]

Yeah, I thought it might be the case that the spindle wasn’t the only constraint. Sigh… looks like I have to buy more tools. OH NO! Lol

[Rob Gunn]

Yeah, wood, foam and even alumaboard is doable. I would never think to try steel. Look on your local craigslist or market place and you can probably find a used cnc mill that would work for what you want to do. I picked up a older cnc Bridgeport a few years ago for $1000.

[coryatjohn]

Wood, plastic, brass, aluminum, copper, non-ferrous only. That's what your SB is capable of machining successfully.

[verhoevc]

Yup, done all of those quite successfully!
Thanks for the replies folks.

[bill.young]

https://youtu.be/i61cy7aAi8A?si=SFDuJqFnKw5UDFqb

[coryatjohn]

Specialized tool path. Most likely the softest steel imaginable. No plunges are shown. That's where the problems would likely be exaggerated. Sure, going round and round like that seems possible but the reality is that this is a specialized application with a specialized tool path probablys started by drilling a hole manually. The video doesn't show how dimensionally accurate the results are either. And this from the official SB poster. Where in the literature does it state that the SB can machine mild steel?

Good luck with that.

[EricSchimel]

You absolutely can cut steel with machines like this. Is a large aluminum framed gantry the best tool for this job? Perhaps not. But it is something you can do. The real magic is in the tool pathing. I don't know for sure on this video, bit it very much looks like these are Fusion generated tool paths, specifically adaptive clearing. It's the accessibility of tool paths like this that make cuts on machines like this even possible.

You can see in the very beginning of the video there is a plunge. The trick is to get into the metal as fast as you reasonably can by doing a helical plunge. From there you so side cuts. This is where Fusions adaptive clearing really shines: It can very precisely control the loading of the chips on the tool, which for a flexible framed router is absolutely key.

There's a pretty fine line for this working and not working. Cut to aggressively and it's game over for your bit.

To make this all work you need something like Fusion to create these paths, and then you need to figure out feeds, speeds and lubrication that all work together. I think the reason we don't see more people doing this is that it's not a well documented process. The cost of routers and the related CAM software to be able to handle steel (and other harder metals) have never really lined up until recently.

To say another way: If you want to machine metal on a traditional mill (Think HAAS or a Tormach) there's always been lots of CAM software and supported machining recipes that will help you be successful the first time around. For routers there's not been this CAM software until only the last few years, and the associated machining recipes are essentially non existent. Obviously this person in the video posted has figured out a very specific recipe that works for their machine, bit and metal and tolerance goals.

Breaking Taps uses a very similarly built machine and does a deep dive into his journey into cutting steel. It's hard and takes a lot of trial and error: https://youtu.be/rTFn84UwFCM

So if this is something someone wants to do with a router it's really possible.

[coryatjohn]

It's also possible to send people to the moon. It's just very practical.

Fusion 360 is going up from $490 to $680 a year. Not cheap!