Rotational Adapter

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Rotational Adapter

Postby bdring » Sat Apr 30, 2011 3:51 am

It did a blog post on the Rotational adapter.

http://www.buildlog.net/blog/2011/04/op ... er-part-1/

It took me a while to get the right belt, but it is now fully assembled and functioning. My laser is in Pololu driver testing mode, so I think I will send it off to twehr for testing.
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Re: Rotational Adapter

Postby trwalters001 » Sun May 01, 2011 11:16 am

I'm definitely interested in a kit.
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Re: Rotational Adapter

Postby tylerv » Sun May 01, 2011 3:08 pm

I'm interested in a kit as well, though it would be a while for me before I could use one. I used to etch wine glasses and glass pitchers and things with sandblasting and acid cream, but this could produce much finer results.
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Re: Rotational Adapter

Postby twehr » Fri May 06, 2011 8:35 pm

I noticed something in a pic of another rotary adapter. This one has an idler wheel inside the glass. We should keep this in mind, if it turns out that Bart's initial design has any slippage issues.

BTW - UPS just notified me that the test unit Bart built was delivered at my home today. I have a packed weekend, but will try to make some initial tests before Monday and let everyone know how it goes.

[photo - notice the extra idler wheel INSIDE the glass at the left end]
Rotary Adapter.png
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Re: Rotational Adapter

Postby whmeade10 » Wed May 11, 2011 3:57 pm

How is the testing going Tim? This will be my first accessory for the 2.x laser.

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Re: Rotational Adapter

Postby twehr » Wed May 11, 2011 4:27 pm

I got to play with it a bit on the weekend (Mother's day took up most of my time). Last night I started some real testing with pics, etc. I hope to work on it again tonight for a couple of hours, at least. Since this is also going to be used on Bart's blog, I want to put it together as a full report, rather than piecing the experience out over a number of posts. If all goes well, I will have a write up by the weekend.
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The Test Drive

Postby twehr » Mon May 16, 2011 1:23 am

OK, took a bit more time to put this together than usual, my system's Emergency Deadline Detector kicked in and put lots of stuff in my way (see post on shattered lens), but test results are in and here they are.

Mechanical Setup: I got the unit already assembled by Bart - it was his prototype so I did not have to do too much. From what I could see, actual constructions should be a breeze - just small handful of 2020 and corner brackets, along with the custom plates and pulleys. I assume full assembly should take less than 20 minutes.

I adjusted the belt tension (by rotating the motor body which has one fixed corner and the opposite corner with a screw that slides through a curved slot. Work nicely, but had a little trouble getting the screw (that goes through the slot) tight enough to hold. The screw head faces up against the plastic mounting plate which is pretty soft. Adding a larger flat washer to get a little more surface contact with the plastic helped. Once secure, the belt tension remained constant.

The two idler pulleys at the tail stock (non-driven end) tend to bind when you try to tighten the wing nuts enough to take any wiggle out of them. I had to back it off just a hair and it worked fine. Bart knew about this before he sent it to me and I believe he has modified the design slightly to take care of it. I will have to do a small mod on this one, but I was able to get by with just doing really careful adjustment.

Installation: After a few quick tests to ensure the motor was working and everything "moved" OK, I mounted the two under-z-table-frame mounting brackets. This was the first dilemma - where exactly (along the y axis) should I put the center line of the adapter? I considered putting at y 0.0, but decided against that. At this point I am not sure of the diameter of the largest usable object, so I decided to simply put it out a known distance from y 0.0 - I choose y 100.0. It is easy to remember and easy to get to - go to zero and move exactly 100mm in the +y direction.

With that decision made, I had to figure out how to set the center line of the adapter at that point. I put a mark, with permanent market, at the center point on the tail (non-driven) end plate. Then I put a piece of tape over it so I could see the line showing through and I could zap the tape with the laser without zapping the adapter itself (see photo below). I simply moved the mounting place until I get the tail end aligned. Then I just locked that mounting plate down.

On the head stock (driven) end, I did something similar, only I added the tape on top of the driving pulley and motor shaft. (Think about it now, that would not be the perfect place, since the motor axis is not guaranteed to be exactly on line with the engraved object - remember the rotation of the motor to tighten the belt. But, I I doubt it would ever be so far off that it would actually show up in the finished product as being off.)

Once the head stock was aligned, I locked its mounting plate down as well. Now, I can simply set the adapter in, move to Y 100.0, swap the connectors in the Y drive, and I am ready to go. Afterwords, swap connectors again and pull the adapter out. My z table was originally set up with a removal top, so this is all a snap to do. Takes about 1 minute to do the compete setup or tear down. Really great mounting plate design - thanks Bart!

[Photo - center line adjustment]
Tail stock alignment.png


Electrical Setup: Nothing to this - Wire up the four wires from the motor to your y drive, just like any other motor. I had to swap the wires on one pair to get the rotation the direction I wanted for my machine setup, but otherwise I just had to plug it in.

Software Setup: Again, not much to do here. I am using the DSP from LightObject. It has a custom mode for using a rotational adapter. Using that mode does a couple of things. First, it no longer expects a y-axis limit switch single for homing on reset. Second, it allows you to input the diameter of the object you are working with AND a diameter that corresponds to the actual output your are getting. This allows for for minor adjustments so that your output looks as you expected it. I did not really need the later, as the design of this adapter moves at the same constant speed/distance that a normal y axis would. I suspect a different design (where the piece is "chucked" and rotated by its long axis rather that turned by its circumference) would really need this feature of the DSP.

If you are using Mach3, you should need to do anything in software, since Mach3 is going to simply look at it as a flat y axis. You MAY need to deal with the lack of a home limit switch when using the adapter, but since Mach3 always starts from the current location and follows the GCode commands for movement, it probably won't be an issue for you.

Now that we are ready to go, let's look at the numbers (which assume use of the under-z-table-frame mounting brackets):

Max length object: 354mm
Max diameter object: ~ 95mm (I did not measure exactly, but this is pretty close.)

I ran several test that I will describe here briefly. You can also look at the video that is probably more interesting than just reading about it.

[Photo - checking focus]
checking focus.png


Test one was a 25mm diameter pine dowel at 354mm length. I simply engraved a photo of one of my granddaughters. It was a fast, easy graphic to through at it. It worked rather well, but the video makes it a bit hard to see as it was turning away from the camera - so you don't see anything on the dowel till near the end. I cut out most of that really boring stuff, just showing it start and then moving on to the end. Below is a photo of the finished engraving.

[Photo - engraved photo]
Dowel Engraved.png


I found a spot where the engraving came out much darker than anyplace else. Turned out to be where there was a bad spot at the end of the work piece, causing a "flat" on the circumference where it temporarily stopped turning. See the photo below, and keep this in mind when you select your objects to engrave.

[Photo - bad end of work piece]
Dowel flat end.png


Test two was on the same workpiece, but an engraving of a vector object instead of a photo. It was a Celtic design. I chose this because I could ramp up the power a bit and go for deeper engraving. It worked quite well, as you can see in the video.

Test three was, again, the 25 mm dowel, only this time doing the Celtic design in vector mode. In vector mode you really have to keep the y axis speed down, as the adapter relies solely on the friction between the object's circumference and the rubber o-rings on the driving pulleys. In my case, the 25mm dowel is very light, which means there was not much friction. As you will see in the video, too fast it can through the workpiece right out of the adapter. The first try was at 10mm/sec and it flew out, just as I expected it to. Doing it again at 5mm/sec seemed to be pretty good. I would still want to play with the vector cutting a lot more before I would rely upon it being successful.

The final test (shown in the video) was on a very short glass votive candle holder. I wanted to test both the shortness and the material. Overall, it was pretty successful. The extra weight of the glass (compared to the wood dowel), helped out.

[Photo - finished votive candle holder]
Votive candle Holder.png


OK - here is the video.


I did not show it in the video, but I ran tests on a couple of different votive candle holder. The one in the video did well, the other presented some real challenges. specifically, the angle of the glass coming up from the base was so great that it made it very difficult for the maintain contact between the base of the glass and the rubber o-rings on the drive wheels. Look at the angles of the base-area glass on the two pieces in the photo below. I added red lines to make it easy to see the angles. The more rounded candle holder has too much angle for stable placement on the drive wheels. Keep this in mind, as well, when selecting your work pieces.

[Photo - two different votive candle holders]
Base Angle.png


General observations:

Overall - it did really well. Everything works just like you would expect.

Tail stock idler wheels: They work. I would probably opt for larger diameter idlers, and maybe add some rubber o-rings here, just like the head stock. I think it would be a bit better "idler" performance.

Adjusting the position of the idlers is easy. Due to the fixed hole locations, I can imagine one could find a workpiece for which it just doesn't match up the way you might want it to. I have a couple of ideas in mind that, if I can get some free time, may try to give more flexibility in the idler positioning. If it works out, I certainly share it with everyone.

Adjusting for different lengths of workpiece is really easy - just loosen a couple of thumb screws and slide the whole tail towards or away from the head stock. I had a little trouble ensuring that tail stock plate was parallel with the head stock plate. If you don't get them pretty close to parallel, it put the center line of the idler pulleys off the center line of the pulleys on the head stock. you don't have to be exact, but being too far off will definitely cause problems - just be careful.

Let's cut to the chase - this adapter is a keeper! For the price, easy of use, and general capabilities, I don't see how you could do any better. Certainly, there is nothing out there short of 3-4 times the money, so it is a clear winner.
tim
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Re: Rotational Adapter

Postby bdring » Mon May 16, 2011 1:55 am

Thanks for the great write up and video.

A couple of the issues I have already addressed.
The rear idler binding was an oops on the design where both the inner race and the outer race can contact the plastic
The access to the motor screws have been moved slightly.

Note: The position of the motor should have no bearing on the center on the rotation. It just tensions the belt. All the rollers stay in the same location.

I think the piece is jumping off due to the momentum. If the wheels stop suddenly the parts wants to keep going. A custom low accel profile in Mach3 might prevent that.

I never really considered vector work when I designed it, but now I can imagine some cool ideas like a cutting a pattern in an acrylic cylinder. If you spread the idlers wider and adjust the height accordingly it might have a bigger hill to climb, but that does not address the drive end. One of the overall design goals was to keep it as short as possible and that fights putting in bigger wheels. I was also aggressive on how small diameter an item you can use. Maybe requiring it to be 1/2" or larger would allow the drive wheels to spread a little and help the jumping.
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Rotational Adapter Demo

Postby twehr » Mon May 30, 2011 12:45 pm

Thought I should do a quick video that shows how quickly and easily you can run a rotary engraving job, once you have the initial setup completed. In this video, I show the process:
    1. Remove the normal engraving table top
    2. Install the rotational adapter into the adapter mounting plates
    3. Connect the electronics
    4. Run the job
    5. Disconnect and remove the adapter
    6. Replace the normal engraving table top
I found that the whole process really takes no longer and is just as easy as running about any other type of job. The design of the adapter mounting plates and having everything set up correctly the first time makes future jobs a breeze.

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Re: Rotational Adapter

Postby dirktheeng » Mon May 30, 2011 7:28 pm

Tim,

That looks really cool! I can't wait to get mine running! I'm really excited!

One quick question:

Were you pulling out the motor wires with the power on? Doesn't that potentially ruin the driver or do you have a special setup that will allow for this?

Just curious.
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