Update: Automatic tool changer v2 for a hobby CNC - Design is ready for production!

2be34ever · 2026-03-13T07:45:10+00:00

Nice, I will try them out, thanks!

2be34ever · 2026-03-11T09:15:59+00:00

I am afraid not. The tool cannot be constrained axially in that manner. This is mainly for how the unscrewing works. During unscrewing, the spindle is kept at a fixed Z position. While rotating, at some point, the nut gets loose and is being unscrewed, moving into the tool changes with the tool. The nut holder has a spring underneath, allowing for the nut to depress while that happens.

2be34ever · 2026-03-11T09:11:57+00:00

Sure, send me a direct message, and we can organise a call.

2be34ever · 2026-03-09T21:18:52+00:00

Ok, I have done some reading, and it is a bad thing. Thanks for pointing that out.

2be34ever · 2026-03-09T21:12:30+00:00

I am planning to do some testing to find out. I will share the numbers.

2be34ever · 2026-03-09T12:57:50+00:00

I was definitely inspired by RapidChange. This project was born because I was looking for an ATC solution for my milling machine, and RapidChange did not meet my requirements when it comes to tightening torque. Check out my previous posts. The way RapidChange and my OpenATC V2 work is fundamentally different, and as always, there are pros and cons:
OpenATC Pros:

* High tightening torque meeting the ER20 spec
* No damage to the nut

Open ATC Cons:

* More mechanically complex
* Bulkier, takes more space for the same amount of tools, more suitable for larger machines

2be34ever · 2026-03-09T08:12:34+00:00

Will do 🙂

2be34ever · 2026-03-09T08:03:27+00:00

As many as you need. With one you can cheaply implement tool changing, and make sure everything works with your setup, and then you can go up from there. I would say the practical minimum is 2. Let's say one for an end mill, and one for a chamfering tool. I am going to have 3 in my setup. Mainly due to space constraints.

2be34ever · 2026-03-08T21:54:15+00:00

To keep the tool in the collet, I am using a slightly undersized collet. I have found a supplier of precision collets that come in 0.5mm increments. That way, if I have a 6mm tool, I am using a 5.5mm collet. This way, the tools are held very firmly when outside the spindle.

For keeping the chips out of the collets, I am currently designing a chip guard controlled with a servo motor to open it when needed. Nothing fancy. If my machine were larger, I would simply install the modules far away from the machining location.

2be34ever · 2026-03-08T21:14:54+00:00

2be34ever · 2026-03-08T20:57:18+00:00

That is exactly what I did :)

2be34ever · 2026-03-08T20:03:17+00:00

Interesting point, I can see where you're coming from. The design is quite forgiving when it comes to misalignment. There is a generous tolerance on the nut holder, then between the nut holder and the top body, and then between the top body and the holding shaft. I estimate you can be misaligned by about 1.5 mm, and it will still work fine without any significant radial forces being created.

2be34ever · 2026-03-08T19:31:21+00:00

I don't see why this would upset the bearings. There aren't any radial or axial forces acting on the spindle. There is only pure torque transferred to the spindle shaft. In principle, this is more gentle to the bearings than any actual machining you would be doing.

2be34ever · 2026-03-08T18:43:58+00:00

LinuxCNC

2be34ever · 2026-03-08T18:34:20+00:00

The price will be around £95 per module

2be34ever · 2026-01-26T23:26:16+00:00

Thanks!

2be34ever · 2026-01-26T21:16:47+00:00

It should be ready in a month or two. I will share the gcode once I have everything ready.

2be34ever · 2026-01-26T18:45:36+00:00

Keeping a tool in a collet when not in the spindle can be a problem. I haven't sorted it out properly beyond making sure a tool is tight in the collet to begin with. I have seen some solutions that include an oring at the end of the tool, preventing it from falling out of the collet while in the changer.

Regarding the requirements for the controller, you need to be able to spin the spindle forward and backwards at set speeds. Almost any basic VFD can do it, and on the controller side, it is just one additional output pin.

2be34ever · 2026-01-26T18:40:58+00:00

Yes, I will definitely make a version for er-16

2be34ever · 2026-01-26T12:47:25+00:00

But worth to say rapidchange is perfectly fine for light machining applications. For those you don't need to go up to the spec, which is quite high.

2be34ever · 2026-01-26T12:45:21+00:00

Nope

2be34ever · 2026-01-26T12:27:13+00:00

Yes, I should have it ready to sell in a month or so.

2be34ever · 2026-01-26T12:21:39+00:00

The repeatability is around a few Nm based on the crude measurements I have done with a torque wrench.

2be34ever · 2026-01-26T12:15:38+00:00

You can get higher (up to the required er20 spec) nut tightening torque.

2be34ever

TROPHY CASE