[OP]
Contributor
Well sort of. It was something I was planning and I did buy a few parts to make it happen. But when John posted his tapered leg idea that motivated me to get-r-done.
Here's a short video of my rotary. I have the signal generator set in the middle speed range controlling the stepper. In the video I first speed it up and then slow it down.
Contributor
I will be very interested in any details you can offer:
Motor specs and pulley ratio
Any torque issues, like missing steps during a heavy cut
I'm going to make one myself, and people seem to use the largest stepper they can get their hands on. It would be nice to have some experimental limits on that. Thanks!
Steve
Contributor
You have my attention, Alex. Can't wait to see how it works.
John
Contributor
This is great!
How are you holding the workpiece at the ends?
[OP]
Contributor
It's a 4 to 1 ratio but I'm using a rather small timing belt. Not sure if it'll handle the forces. But it was in my junk drawer so I used it. I know the one John asked about in a different thread is a 6 to 1 ratio but I think that one is for doing metal. This is more of a proof of concept and if it works I'm going to put two bearings on each end. The only machining I did was aluminum on the cnc router. Other than that I did everything else on a drill press. I was trying to keep it simple so others could copy, and possibly improve it.
Right now both sides use a 1/2" shoulder bolt but on the drive side I'm going to up it to 20mm standard bolt(since metric bearings are easy to get). I used a die to thread each side of the 1/2" portion of the shoulder bolts. I don't have a metal lathe set up so I threaded them by hand and it's much harder than tapping threads. The next version I'll just drill a hole into the end of the bolt and tap it for a 3/8-16" stud. I'm also thinking of buying a new driven timing pulley with a 20mm bore. If I do I can change the ratio to 6 to 1.
I used a 3/8-16 thread on each end. My plan was to just use a wood insert but I felt it would be easier to make a faceplate like a wood lathe uses. They are just 1/2" aluminum scraps I had. Here's a picture of the wood side of each end plate.
rotary 1.jpg
Here's the timing belt side before I cut the aluminum plate down.
rotary 2.jpg
Contributor
Thanks for the details, I will definitely keep reading.
[OP]
Contributor
The test went sort of ok. Right off the bat I was having issues with my VFD for the spindle (low voltage) before actually cutting anything. I recently did some upgrades so I need to look into what's not happy. I did a complete guess at what speed to run the X axis at. I decided to try 10 imp and that required the signal generator to be set to the high speed jumper and dialed up as fast as it could go. I just made a simple profile of the shape I wanted and started the cut. I'll post a video in a day or two. To do about 22" of wood it was going to take 52 minutes.
When it got to the smaller tapered end the spindle acted up. The bit slowed down and stalled the rotary. I'm using a 24v power supply for the stepper driver. It's in the range listed for it but it really should be 48v. That'll make it much harder to stall the rotary. I'll order a 48v power supply and get the spindle sorted out. My first impressions are that this is going to work good.
I also want to look into modifying the signal generator so I can supply holding current to the stepper. Right now when the run/stop button to stop it rotating the stepper can be easily turned. I'm sure it's not hard to do.
The wood I'm testing this out on is red cedar. It's easy to cut but it also splinters pretty easily. I suspect that if it was hard maple the speed the X axis moves at would have to be cut in half.
Contributor
Looking forward to the video.
[OP]
Contributor
So it's been a bit of learning but this is where I ended up. The first is after it finished but before I sanded it. I probably spent 5 to 10 minutes smoothing it out with a RO sander. The second is with a quick coat of clear. I did make a mistake of turning the wrong direction. The faceplate was unscrewing from the arbor that was causing issues. The second is the stepper is kind of weak. I've ordered a 48 volt power supply that should fix that problem. I'm uploading a video right now that I'll post shortly. The proportions of the leg are a bit off but I was working with spare wood and kind of wanted to try a few things.
leg 2 (2).jpgleg 1.jpg
[OP]
Contributor
Here's a video
Contributor
Looks like a great first try to me Alex. You already have some ideas on improvements.
One thing to try if possible is the direction of rotation. The finished surface is smoother in one direction than the other (dont ask me which).
This is a pretty large dia which impacts what size motor you need. As you go smaller in dia you may need less torque. Also, stepper motors are not necessarily the best at delivering torque for continuously rotating duty. They are designed for 'incremental positioning'. In your application a simple DC motor and variable voltage power supply may serve you better.
Keep at it!
Contributor
Wouldn't switching to a "dumb" DC motor eliminate the possibility of doing fluting and other types of embellishment where Z and X need to communicate? That's a feature I want to make sure I have if install a 4th axis.
John
Contributor
Excellent progress, Alex. What kind of toolpath did you use and did you control the DOC with the depth per pass feature in the tool database? Also, were you using the rotary job type in VCarve?
About Carl's comment on rotation direction effecting smoothness, I don't think it matters. I think you'll get the same effect if you either reverse the direction of cut or switch from conventional to climb cutting with the direction you used.
John
Contributor
'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 ...
Contributor
Originally Posted by Wes Grass
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
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