Inspired by John

[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.

[Wes Grass]

'Something' I worked on some years back... steppers.... 'stall torque' ... ???

Open loop ... missed steps from overloading the system ... ugly parts ..

'Book Search' system was open loop. Worked ok. But more or less no real load. And on to 'Street View' and aerial...

Good times, good people ...

[John TenEyck]

'Something' I worked on some years back... steppers.... 'stall torque' ... ???

Open loop ... missed steps from overloading the system ... ugly parts ..

'Book Search' system was open loop. Worked ok. But more or less no real load. And on to 'Street View' and aerial...

Good times, good people ...

Yes, that will happen with open loop steppers if the load gets too high. On my machine, it could if you try to run production rates on it; I don't really know, I've never tried to do that. At "reasonable" rates the loads are well within the capabilities of the steppers.

There are closed loop steppers now available on hobby level CNC's. OneFinity launched one several months ago.

John

[Ronald Blue]

Following your project closely. So at this time you don't have the ability to "index" if you were wanting to do some sort of fluting? Basically at the moment the 4th axis is just a rotary spindle on your CNC without any positioning capabilities yet? Still very intriguing and makes one realize the possibilities within our reach. Have you looked to see what most 4th axis units use for a drive ratio? Whether they are one to one or something different?