Those are pretty cool. I am going to give this turntable idea a rest for now as I have some other things to work on.

 

Someone on the V1engineering forum mentioned using springs and then that made me think about using rubber bands. They are a perfect simple solution with no other electronics needed. I will have to adjust the sliders a little to give a little lip under the pegs & make the pegs probably a little longer. Here are a couple of photos to show proof of concept. Just when I am ready to put this project aside, I get pulled back in to finish it.

 

I had to try the straight slots to see what the problems were with them versus the curved slots. During the design, one problem that is quite apparent is the end of the slots are a lot closer to the sides of the other slot next to it. They also don't move well along the straight lines as they do along the curve. I am printing the new design today & maybe try it tomorrow.

 

Here is the 1st test of the self centering rotary axis. Seems like this painters tape core has a coating that does not burn well in some spots. It also seems like the rotary axis is moving faster than the linear axis. I posted a message to lightburn forum about it, but maybe someone here also knows what the problem might be.

In the rotary section of Lightburn, I have 32 mm per rotation (DRV8825 drivers) and Chuck rotary type set. Y-axis is the rotary axis & X-axis is the vertical linear axis in my current configuration.
You can see this problem in the 1st part of the linked video below when it is drawing a rectangle around the object.


Below are the GRBL settings I am currently using in this configuration.
Grbl 1.1h [’$’ for help]
$0=10 ;Step pulse time, microseconds
$1=255 ;Step idle delay, milliseconds
$2=0 ;Step pulse invert, mask
$3=3 ;Step direction invert, mask (invert x & y)
$4=0 ;Invert step enable pin, boolean
$5=0 ;Invert limit pins, boolean
$6=0 ;Invert probe pin, boolean
$10=1 ;Status report options, mask
$11=0.010 ;Junction deviation, millimeters
$12=0.002 ;Arc tolerance, millimeters
$13=0 ;Report in inches, boolean
$20=0 ;Soft limits enable, boolean
$21=0 ;Hard limits enable, boolean
$22=0 ;Homing cycle enable, boolean
$23=0 ;Homing direction invert, mask
$24=25.000 ;Homing locate feed rate, mm/min
$25=500.000 ;Homing search seek rate, mm/min
$26=250 ;Homing switch debounce delay, milliseconds
$27=1.000 ;Homing switch pull-off distance, millimeters
$30=1000 ;Maximum spindle speed, RPM
$31=0 ;Minimum spindle speed, RPM
$32=1 ;Laser-mode enable, boolean
$100=160.000 ;X-axis steps per millimeter
$101=200.000 ;Y-axis steps per millimeter (200 * 32 = 6,400 rotates 1 revolution with 1.8 nema17)
$102=200.000 ;Z-axis steps per millimeter
$110=500.000 ;X-axis maximum rate, mm/min
$111=500.000 ;Y-axis maximum rate, mm/min
$112=500.000 ;Z-axis maximum rate, mm/min
$120=100.000 ;X-axis acceleration, mm/sec^2
$121=100.000 ;Y-axis acceleration, mm/sec^2
$122=10.000 ;Z-axis acceleration, mm/sec^2
$130=435.000 ;X-axis maximum travel, millimeters
$131=435.000 ;Y-axis maximum travel, millimeters
$132=0.000 ;Z-axis maximum travel, millimeters

 

There is a setting for that & it was set to the diameter of the object I had.

After some trial and error today, I have it pretty darn close by watching the video test I shot & checked frame by frame near the end of each movement to get the time it took to run a 100mm square in both directions. I switched to using Z-axis since I got that to work, so less firmware settings to change. Since rotational axis was 7.296x faster than linear, I used 200/7.296 = 27.412. Since I am using DRV8825 (200*32=6400) 6400/27.412 = 233.47mm.

I set:
$102=27.412.000 ;Z-axis steps per millimeter
and 233.47mm = mm per rotation in Lightburn rotary setup

It was a little off, but speed difference between linear & rotation seemed close. I wanted to see if I could use whole numbers, so I changed the $102=27 and starting adjusting the mm per rotation until it made one full rotation correctly. It came out to a nice whole number for that also.
$102 =27 and 245 =mm per rotation in Lightburn rotary setup. With those settings, it does one rotation right on the money & speed difference between linear & rotational movements seems correct. I am seeing a little stuttering in the rotary axis, so am thinking that is the DRV8825 doing that.

I tried the LV8729 drivers (1/128 microstepping) but they did not seem to work properly. Either the Eleksmaker board does not support them or they are bad drivers. I did check the vrefs on them before putting them on and from my previous notes I have the correct voltages. I will just stick with the DRV8825s. After putting the DRV8825s back in I rechecked the rotatary setup & had to change that 245 to243 as it overshot the 360 by a little bit.

So my final numbers for DRV8825 drivers are $102=27 & 243 for lightburn rotary setup. I don't see a rhyme or reason for how those numbers came out that way, but seems to work. I was expecting those numbers would be a multiple of 6400 (200*32), but it is 6561. I might do another video test to verify the speeds are still exact.

 

The other day while looking at the grabcad terms of service, it was not clear to me whether I could release a derivative of that cam & follower design. The next morning I realized that design was very much like the Trammel of Archimedes design & I had remixed a version of that 3 years ago: Remix of Trammel of Archimedes by GeoDave - Thingiverse Rather than concern myself with grabcad, I redrew that portion of the design and cut out some volume of plastic in the process.

I am getting very close to releasing this turntable design to thingiverse, probably tomorrow. One problem I was running into was smaller objects less than about 1" in diameter, which probably is not used much. Dowels are a good example of that small a diameter & would be a good test burn. The bracket attaching the top to the motor would interfere with making those pegs get closer to the center. So what did I need, Spacers inserted over the pegs. Another simple solution. Here is what the final design will probably look like. I estimate $15-$20 in parts and almost no cost if you have the motor & bearings.

 

I have a plethora of 3/8" dowels I could test this on. Might have to make the spacers a little taller to make sure it stays vertical. With the spacers, I can get it down to holding about 5mm diameter objects. This turntable portion of this build is turning into quite a useful & inexpensive project that @Mark Carew inspired me to work on.

 

That was good to know about the pens before releasing this. I had 5.6mm diameter hole in the center & changed it to a 3mm hole so a small object won't accidentally go thru it. Of course you could put a piece of tape over the hole also. Here is what it looks like with at 5mm cylinder in the center.

 

Here is what a 3/8" dowel looks like attached to this turntable.

 

Here is a 3/8" dowel burn running at 3000 mm/Min & 90% power. 1st image is what the design looks like. I wanted it to wrap all the way around to see how close it came to meeting other side. I did a video of this burn also, but probably won't get to that for a few days.

Came out good for a 1st test, but is not quite aligned with length of dowel. This dowel was quite straight, so probably dowel was not quite parallel with the cantilever arm.

You can see a slight overlap here. Measuring with digital caliper, it is about .65mm overlap.

 

I have the self-centering turntable design published on thingiverse now using the Creative Commons, Non-commercial license. I also downloaded the zip file from thingiverse & put it in the files tab here.
Self-Centering Turntable for use with Vertical Laser Engraver by GeoDave - Thingiverse

 

Here is a video of engraving that 3/8" dowel. Think I see some flames in part of that video.

 

This uses a diode laser which is not capable of cutting or engraving metal. You can probably engrave the anodizing on metal.

 

Someone on V1engineering forum asked if I could do a toothpick, so I have to try it. Reprinting to drop it down 4 more mm to keep it straighter. Not much room for not being perpendicular here. Definitely need to start at lowest power & work up from there. Toothpicks are about 2mm in diameter with just a hair less than 1/4" in circumference. Laser is about .5mm width, so should work.

 

Not sure I would attempt that, but toothpicks do work.

I had it at 30% power for the 1st one running at 1200mm/min & acceleration is at 100. I was waiting for it to burn in half, but never did. You can see the patterns. I had the laser probably 3 inches or so away on the 1st couple of burns since the holding cylinders around the part would get hit by the laser. I changed the cylinders to my smaller ones & moved it quite a bit closer & ran the last couple at 5% power & same other speed settings. You can read part of the 2mm high text. I shot a video of some of this, but might have to reshoot it before uploading.

 

Here is a video of it engraving text on the toothpick.

 

I would be happy to do that, but do not currently have a wooden pen. Where is a source for a reasonably priced wooden pen? I made another video today that should be better than my 1st video. I am still editing it though.

 

I am not sure that logo will look good on a toothpick. I do have some 3mm diameter bamboo skewers that are about 4" long that it might show up on. That gives me about 3/8" circumference.

 

I spent more time editing the video this time & should be a lot better than previous video. I also speeded it up during the longest burn so it is not so boring.

 

I wonder what it would be like to use this for marking stringers to cut. I have cut 4 soon. I cut 8 last summer & they were a pain to mark accurately because of the rounds on edge of the wood, at least they were for me. Standard stringers you buy are a little too off for me to use. I would have to get some longer V-Slot to be useful for me.

 

[Edit 9/18/2021] I put together assemblies of each alternative of this design that looks reasonable. I changed these options & didn't want to confuse folks with different info here.