4th axis rotary

@dannym I’ve made a bit of progress learning how to use vcarve to program rotary projects. What all is involved in getting our 4th axis rotary attached to the cnc? And should we group this idea in with the other thread about making space for vertical stock?


Just adding a cross-ref link to the other thread: CNC Modification for end of long stock?

Regardless, I love the idea of giving our CNC machines a few more super powers. :slight_smile:

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Hey @dannym I know you’re busy with lots of stuff. Just wanted to bump this up to see what you think. For now I’ve hired a company to do my 4th axis cnc stuff but I’d love to bring this in house at some point if it’s do-able with our machine.

Hello @Mollie
I’ve been wondering quite a lot about where that axis is! I’m pretty sure I got one early on and stored it in the CNC router’s kiosk initially. That was a while ago, it’s not there, and I haven’t been able to uncover it. Searched there and at home and I can’t find it. I found the drive for it, but not the hardware.

Someone mentioned a 4th axis being in the Tormach cabinet, I’ve been meaning to check but I think I saw one in there but it’s a different type.

I’m still wondering where else it could be?


It is probably the same 4th axis.

Ah, that’s it!! Well, the head, at least. Have you seen the tailstock? I went through the cabinet a couple of times but didn’t find the tailstock or the chuck key.

The box needs another motor drive installed and the LinuxCNC installation will need to be reconfigured, and it needs a cable to go from the drive to the motor. I have another AM882 drive for it.

@Mollie could you share your job’s requirements here? How big is the stock, is it an internal or external grip (almost certainly external), and does it require a tailstock?

The rotary is 2" from the axis to its base. It’s got “U” cutouts for bolt-down from there. Once the jaws are opened, though, they may extend far enough outside the chuck to contact the level of the base. So, these things do sometimes need riser blocks on the headstock and a matching one for the tailstock (if used). There is a bit under 8" of clearance from the spoilboard to the nut on the spindle, and the total clearance needed would also include the length of the bit in the spindle too.

It is fitted with a 100mm 3 jaw scroll chuck. I think I do have a 4-jaw independent and a 3 jaw independent at home that will fit that.

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So awesome you found it! I’ll be using 11 inch long, 1.5 inch diameter stock. I can probably run it without a tailstock. I’m not sure about internal or external grip. The finished piece will have a threaded bolt at one end. I could install that first and possibly use it as a mount?

Most operations are external grip, where the jaws compress. Some jaws are reversible, like if you’ve already turned the inside of a bowl and need to turn the outside, you can make it apply pressure from inside-out. It’s uncommon.

As a 3-jaw, it grips round things, so that chuck is perfect for your app. 4 jaw would grip square or round stock. It’s possible to use a lathe to turn a round end on a square piece to make it grip in a 3-jaw as an option, but you’ve already got round.

Hey @danny! Thanks for showing me the 4th axis the other day! I’ve started brainstorming a fixturing base for this new feature. When you have a minute please send over a link to the live center tailstock and I’ll get it ordered.

I’m hoping to have cnc table leg manufacturing tested and my assistant trained up before I go on maternity leave in nov/dec.

Hey @dannym! I wanted to follow up on adding the 4th axis rotary to the CNC machine. I have a plan for the mounting but want to purchase the tailstock before building.

Would something like this work?

OR, would it be helpful to get a kit like this. Does this look like it includes some of the electronic pieces you needed to integrate the 4th axis with the CNC? @dannym @JoeN


That looks like the correct tailstock. I do have all the electronic components needed but they got lumped together with a lot of other stuff after the Tarkin build. I’ll go dig them out


It looks like the center of the tailstock is about 0.5 inch taller than the jaws. What do you think is the best way to mount the two so that they are level? A wood base with T track or a rigid aluminum frame?

Then maybe I’m mistaken, that wouldn’t be the matching tailstock. The heights should match.

I would say a T-track. Note that Z clearances can be an issue, so thick tracks are less desirable. There are two types of interference limits here- one, while mounted on a track, there’s clearly a radius limit for the raw, uncut stock before it would interfere with the track. That can be improved by adding spacers to raise the stocks further over the track.

But there’s also a total Z limit of course, which factors in track thickness, height of the headstock (with or without a spacer), the height of the raw material above the centerline of the headstock axis, and the length of the bit being used.

There’s a case for mounting a track facing sideways and the base of the headstock and tailstock could be mounted on the side instead. This does take the thickness of the track out of that calculation, but not the other factors.

Hey we found the missing tailstock!

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It was taken to the machining area at some point, although I looked for it there like 10 times over. Eric found it.

I’ll get it plugged in this weekend. Also have new 15x30 drag chain for the side that started folding.

Wooooo!! Thats fantastic news! I have a sample program ready in vcarve to test it out. I’m not sure when I’ll be in the shop next. My baby is due tomorrow, though who knows when she’ll arrive. I will give @Tanner the file to help test out the 4th axis.

There are so many cool things folks will be able to make with the 4th axis!


Fingers crossed she doesn’t wait too long to arrive!

Yay!! 4th axis!

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Go @Mollie go! I’m rooting for you.


Where is the 4th axis going to be mounted? Or is it going to be a plug-in and use kind of thing? I frequently cut over-sized sheets, and have it hanging off the end of the bed.