Inspired by John

[Alex Zeller]

The main reason for using a stepper is so I can control it and possibly make rope patterns and increment the project by a set number of degrees. For example, if I wanted to add fluting to the surface I could carve a flute, rotate 30 degrees, and carve the next flute. A DC motor can't operate stalled where as a stepper can.

I'm using Fusion 360. I created two tool paths, the first was a pocket operation with multiple depths (.1" step down). The second was a parallel tool path using the rest remaining option to clean it up. The wood is red cedar and is prone to tear out plus the 1/4" upcut bit is a pretty old bit. If I broke it I wouldn't care. I'm sure with such a shallow depth of cut and lots of places for the chips to evacuate a down cut endmill would work better.

If you look closely at the video you can see my spindle nut actually hit the square part at the bottom of the leg (that get's cut off). That would be easy to add to the tool path to remove the wood to prevent it. It was a learning experience. I'm thinking either a jam nut or a set screw on the drive side should prevent the faceplate from unscrewing. So there are some improvements I want to add but I think it shows lots of promise.

I'm also going to look into a programable controller vs the signal generator I'm currently using. I think I could easily make a way of adding a way to home the rotary for the controller. It's just not going to be able to communicate with the CNC's computer.

[Carl Beckett]

If you want to 'index' at some point, yep, stick with the stepper. (else you get into encoders and feedback loops which complicate the design).

Pretty successful learning experience, you will tune this in in no time...

Changing direction of cut might be the same as reversing rotation as John says. Mine flips rotation direction easily so am able to do that. It does seem to leave a smoother finish in one direction (I am using full round cutters on centerline). I wonder if there is any advantage to cutting on the 'side' as John needed to, since cutting velocity might be greater and more uniform than a full round cutter...

[Alex Zeller]

I made a second leg out of some scrap read oak (newel posts). I'm still trying to decide on what the final pulley ratio should be. But I found the set screw on the stepper either wasn't tight (I knew there was a wobble in the driven gear that would cause issues) and started to spin. I've got the 48v power supply and the only issue I had was the faceplate wanted to loosen up no matter which way the rotary turned. So I added a jam nut to eliminate that. I'm still learning the correct speeds but the second attempt was much better. The rotary didn't have any issues stalling so I think I could take a bigger step down bite.

This attempt I used a pocket operation with the same worn out 1/4" endmill. I did a .1" step down with a feed rate of 7 ipm. I think I can go faster but was more concerned with getting a good baseline speed. I then did a parallel cut with a 1/4" ball nose bit. I tried at 10 imp because I wasn't taking much off but that was too fast and it created what looked like a screw. So I set it to 1 imp and it created a result that almost doesn't need sanding. I would say it took almost 2 hours total to machine 26" (the total leg length is 30" with the square top). I haven't done any sanding yet on this leg.

rotary 1.jpgrotary 2.jpg

[John TenEyck]

Good progress, Alex. What's the rpm range of the rotary? Hand lathes run at high speed, which would allow a good turner to turn that leg in just a few minutes. When I implement a 4th axis, I'll look have something that would be able to turn one in well less than an hour. Of course, to do fluting, spirals, or more complicated work, the rpm rate would need to be much slower, even stopping for some things like fluting. I'm not sure there is an ideal system to do both, but I can imagine a gear box or step pulley system might be needed to cover the different optimal speed ranges.

John

[Wes Grass]

Finally watched the videos. I was pretty confused over climb cut vs conventional, and rotating into or with the spiral of the flutes, and what might be the best approach. But I was thinking you were using the side of the bit and not the tip ... poor reading comprehension I guess. I was thinking the first stage should be profile roughing at some indexing angle to get it close for rotary finishing. I also wasn't considering the diameter of the stock and usable LOC for the bit.

Somewhere in a distant memory I saw a machine for profiling large columns. It used a large disc cutter with inserts, axis of rotation parallel to the work. Inserts were adjustable so they could be sharpened and reset. Maybe an old book in a box somewhere.

I don't think it was for debarking, but maybe. 55'ish years ago we toured a Weyerhaeuser mill where they were using water jets for that. Cooler were the automatic indexing grinders for sharpening bandsaw blades. HUGE bandsaw blades. And the feedrate thru the logs was amazing.

[Alex Zeller]

It was a real guess at RPM. The link you posted to the Chinese one on Amazon was a 6 to 1 ratio. I made this one 4 to 1. The stepper can go so slow it almost looks like it's stopped with the signal generator I'm using. The fastest it can go is 88 RPM. I was worried about stalling the stepper but I don't know if it's possible while cutting. I'm sure if something got jammed either the motor would stall or the belt would break. But 88 RPM is too slow. I'm thinking of trying 2 to 1 to double the speed. The odd thing about steppers is they like going slower. When they do they put out mor torque. If 2 to 1 is still too slow then I'll directly couple the motor. Trying to incorporate the stepper into this does limit the speed at which I can produce things. But the benefits I think will outweigh not being able to produce parts as quick.