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Drawing Robot - Arduino Uno + CNC Shield + GRBL

by henryarnold, published

Drawing Robot - Arduino Uno + CNC Shield + GRBL by henryarnold May 27, 2017
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Summary

This drawing robot is similar to the commercially available AxiDraw. It is powered by an Arduino Uno controller and a CNC Shield and uses GRBL firmware. Aproximate cost to build this drawing robot is $100.

The drawing robot receives G Code commands that are created by a drawing program called Inkscape. The robot was put together using two other people's designs. I added the improved pen slider and the controller enclosure. This drawing robot allows you to draw things in Inkscape and then plot them out. Below are the links to the software I used. Avanhanegem's design has a great tutorial on how to generate G Code within Inkscape and then send it to the drawing robot using Source Rabbit G Code Sender.

When setting up your hardware:

  1. Be sure to install 3 jumpers on the CNC Shield for each stepper driver. I have added a photo showing the jumpers.
  2. Replace the "config.h" file with the one I provide which has the correct features enabled before you compile and download from the Arduino IDE.
  3. Set the GRBL parameters to the settings that I provide in one of the photos.

I have posted all needed parts from the two source designs. There are only 15 parts to print and none of them are very large. I added a stronger pen slider and a controller enclosure. I also clarified the names that were in Spanish. I have posted all needed files so that there isn't confusion regarding which parts are needed from each of the original designs.

My drawing robot is modified version of this one
https://www.thingiverse.com/thing:2058866

GRBL Firmware for the Arduino
https://github.com/robottini/grbl-servo

Here's how to upload GRBL to your Arduino Uno
https://github.com/grbl/grbl/wiki/Compiling-Grbl (Ignore references to GRBL V1.1)
Copy the config.h which I supply to the directory where GRBL resides and then do the upload. The new config.h will be used for the compile of the GRBL code.

Inkscape Drawing Software
https://inkscape.org/en/

Source Rabbit G Code Sender
https://www.sourcerabbit.com/GCode-Sender/]

Tutorial on how to generate G Code in Inkscape
https://www.thingiverse.com/thing:2058866

HARDWARE
2x Nema 17
2x Linear rod M8 x 450mm, X Axis
2x Linear rod M8 x 350mm, Y axis
2x Linear rod 3.0mm of CDROM, Z Axis
(You can find them in any old CDROM or purchase on EBay)
1x M8x470mm threaded rod
8x LM8UU or printed
1x Servo sg90
2x GT2 Pulley 16 teeth
5x Bearing 624zz
1x 2000mm GT2 belt

misc M3 and M4 screws and nuts
M8 nuts

Electronics
Arduino Uno
CNC Shield
12V 2A Wall Transformer
2-4 limit switches ( optional. Suggest to leave them off and add later if you want them)

Software
Inkscape which is the graphics design software (Includes G Code Extension)
Source Rabbit which is the G Code Sender (sends the machine commands from a file)
GRBL which is the Arduino firmware (programmed into the Arduino Uno)

I have supplied a few G Code files that work with this drawing robot. If yours is identical to this design, the G Code files should also work with yours.

Here's a video
https://youtu.be/kpTIFBDcTaY

Update 6-15-2017: I added the limit switches about 10 days ago and they don't add much to the functionality. When GRBL sees a limit switch hit, it just stops with an alarm condition. You must soft reset the robot and your drawing cannot be continued. The homing feature doesn't seem to work. I read in another persons post that they could not get home to work in GRBL 0.9. At this point I suggest building the drawing robot without the limit switches. As long as your drawing does not exceed the envelope of the robot, you won't need the limit switches.

Update 6-19-2017: My friend found a better Inkscape Extension for generating G Code.
I think it is easier to use and generates better G Code:
http://www.mediafire.com/file/ae0wquqornzc3o2/MI+Inkscape+Extension.zip

Update 6-26-2017: I added the config.h file from GRBL for this machine. With this file and the parameter settings in the screen shot, you should be able to easily get your machine up and running. Don't forget to install the stepper driver jumpers.

Update 7-4-2017:
The top and bottom clam shells did not fit without pushing the LM8UU bearings slightly out of alignment. I removed a small amount of material from the top clamshell to allow clearance for the bottom clamshell posts. The old Top_XY_clamshell.stl file has been removed and replaced with the Top_XY_clamshell_V4.stl file. Thanks to rocketmannate who caught this problem.

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Hello, I want to do this project but I have a question.
I am using universal gcode sender, what parameters do I need to change? the parameters would be $$ (As an example $ 100 = 250)
Thank you so much.
Sorry for my bad English, I'm using the translator!

There is a photo showing the value of each of the parameters. Enter them using the Universal GCode Sender by selecting "Settings", "Firmware Settings", "GRBL".

Hi. firstly Thanks for sharing. How can I find to arduino cod ? please send me...
[email protected]
THANK YOU..

Thanks for sharing this proect. I almost done all assebly and printing. Can you show how to connect the servo to CNC shield?

The wiring is shown in the 22nd photo. Plug the servos in one way and if the movement is reverse of what you want, reverse the direction of the connectors. Reversing the direction a servo is plugged in reverses the direction of the servo.

Hello, I like this revised version very much, but do you have a step by step instruction of assembling?

Carlos

No I have not created step by step instructions. The original Drawing Robot also did not have step by step instructions.

Do you know if the wire connecting the input power to the arduino vin pin is necessary? I can see other people dont have that wire soldered on here: https://www.thingiverse.com/thing:1517211/#made

Project: DrawingBot
by MakerC

No it is not required. If you don't add it, you will have to supply power to both the CNC board and the Arduino. Many people do that. If you add it, you only have to supply power to the Arduino which then powers the CNC Shield.

Hallo there. Its a very nice designe, but the top shall and bottom shall do not work when I import the STL file into Slic3r.

Check the other comments. Someone else had the same problem with Slic3r. You might try a repair. The design does work on most slicers.

Hi, firstly thanks for sharing edited version of yours

I've done my draw machine just two days ago. However mine works really slowly comparing with yours. Could you share your g-code that you used in the video. I think that the output of g-code I prepared makes my draw machine slower, even though I changed the speed of x and y motors with using $110=1000, $111=1000 commands.

Thanks!

I already posted 3 example files. Here's and example line of G Code:
G02 X92.350578 Y77.988298 Z-1.000000 I-1.815724 J0.869674 F3000.000000

The F3000.00 sets the speed at a fairly good clip. You probably are using F1000.00 which would be much slower. I think that is mm per second.

Hi again,
After following the settings you shared, it has reached the speed that I wish, thank you again!
Although it works great I have another situation which you can see in the picture. it gives some spaces when it's drawing picture,
what do u think what might cause this problem?

https://ibb.co/bCwDOa

It looks like one of your belts is slipping across a drive pulley. Make sure the belts are very tight. Try drawing something simple like a circle. I suspect it will work fine because that doesn't put much stress on the belt and pulleys. That geometric pattern has a lot of directions changes and tight turns.

After streghtening the belts it got better, but I still have another issue: it draws the picture's reverse and with 45 degrees.
Even though i tried writing with a basic letter "a", you can see the results in the pictures.

https://ibb.co/nepAEQ
https://ibb.co/gTsmok
https://ibb.co/ghUXTk

I am using Minebea Nema 17 stepper motors which are kind of old ones comparing with others on internet however I am not sure that's the problem. Thank you for your help!

It sounds like your stepper directions are reversed. You should be able to fix it in the GRBL parameter settings. There's a screen shot showing how to change the parameters.

I have changed the grbl parameter settings according to the settings here ( https://github.com/grbl/grbl/wiki/Configuring-Grbl-v0.9 ) and i found solution to reverse problem but still have issue with 45 degrees I mean it still draws picture in cross position :/

Please post a make of this Thing with a photo showing your problem. It sounds like you are getting a slanted drawing. Did you turn on the CoreXY option in the config file?

Sorry for not clarifying the problem, the problem is that I get a slanted drawing as you said and here it is the photo:
https://ibb.co/dRqSW5

I guess you mean I needed to do this part to turn on CoreXY option which I did exactly the same as mentioned here:
Arduino code: (compiled and uploaded using the Arduino IDE; make sure to update config.h in your /Arduino/libraries/grbl folder to enable CoreXY !!!)

I don't know why your Drawing Robot is acting strange. All I can tell you is to be sure to replace the "config.h" file with the one I provide which has the correct features enabled. You must also set the GRBL parameters to the settings that I provide and last you must be sure to install the stepping jumpers as shown in one of the photos. None of these things explain why you would get 45 degree printing. Its baffling. Please let us know what you did if you can fix it. If you can't fix it, ask the original designer if he has any ideas. I just built the design with a few mechanical changes and it worked fine.

Hi Henry,
It worked finally! I was not aware of that I needed to change "config.h", I must have missed it :(
Sorry for frustrating progress to figure out what caused this, but at least we know why that happened.

Thank you so much again for your time and share!

Glad you got it working. Be sure to post it as you made one.

So, I've used your config.h, and I'm testing the X and Y motors. My stepper motors move mm's but not full inches. Any distance greater than 4 mm and the motors just squeel. I've uploaded the geometric code, and the motors just squeel. I'm at a loss with how to debug here. Thoughts?

Did you install the jumpers on your CNC Shield? This is my fault. I think I need to create a document that gives all the steps of setting this machine up. For my stepper drivers, all three jumpers need to be installed.

Hey there! Thanks for replying! You've really done a fantastic job of helping all of us out. The stepper drivers. Those are the simple chips placed in each of the slots for the X, Y, and Z areas? I actually put all four of the drivers(those chip things) on the board. I didn't think it made a difference. Should I remove the fourth stepper driver? Also, I haven't actually run the Z-axis-wires onto the board yet. I thought that the board would be able to run just the X and Y motions and then I can finalize the Z axis later. I'm not focusing on the Z axis just yet because my Z axis set up(the literal pen holder) is different than yours. Thoughts?

You're welcome. You need two stepper drivers to run this machine. Any extra drivers will not have an effect. Make sure you note the correct orientation when installing them. They can be damaged by a wrong insertion. You should also set the drive currents using the procedure you can find on the web. Your plan to test out the X and Y axis without the Z action is exactly what I did while I was getting my Z axis parts together.

Alright dude... Give me something here. Stepper drivers are installed, the x/y axis works, but only on MM movements. Loading Gcode and hitting run has the motors whine but not move. Is there anything else you think is super valuable in terms of tinkering with? My controller settings match yours perfectly... Help me Help me... I just want a robot to draw a picture of me.

Yes. Did you install the stepper driver jumpers and did you adjust the driver currents on each stepper driver?

ummmm.... adjust the driver currents what now?

So you installed the jumpers and you adjusted the drive currents and your motors still do not work? The next thing is to check that your GRBL parameters are set correctly. There is a screen shot showing how to access the parameters and what the correct settings are.

Also tell me the color order of the wires on your stepper motor connector. There are blue, black. red, and green wires. You may have wires that are in a bad order. This usually doesn't happen but I did receive one motor that was wired incorrectly.

Hahaha... No, I meant, how do I adjust the driver currents? Is this a physical adjustment or a coding adjustment? I didn't see anything like that in the build instructions.

You must do an internet search on your driver type such as "4988 driver current adjust" or "8825 driver current adjust". Each type of driver can be different. You need to se the X and Y axis drivers to deliver 500 MA or 1/2 Amp.

Example Video explaining the setting of the current.
https://www.youtube.com/watch?v=89BHS9hfSUk

Which version of inkscape are you using for adding the extension. I tried the mi extension with the latest but gives some error while converting to gcode. Is any particular version of inkscape only supports the extension? Pls reply...

I'm using Inkscape 0.92. The MI extension works fine. I'm not very expert at using Inkscape or the MI extension. Try testing with the samples I provided and beyond that you'll have to resolve software problems with a Google search.

I have done the same thing but the on board regulator is over heated and now the arduino got fried... Now it is not detecting by the ide

You must have wired it wrong. Vin of the Arduino doesn't come from the regulator. It is a direct connection to the power connector. The jumper I suggested just connects the two power ins of the Arduino and the CNC Shield.

how are you providing the 12volt power. at the uno power socket or the cnc power connecter??

There are two pictures are two photos in this "Thing" showing how to wire power and motors. The second photo shows how to add a jumper that connects Vin to the CNC Shield power. Once you do this a 12V 2A power supply plugged into the Arduino powers everything.

Just checked your hint for the new extension for Inkscape and trapped into a bug. After changing 1 Line in Server.py it works fine now: Check the Bug here : http://www.tylerforsythe.com/2015/02/inkscape-laser-engraver-bug/

There are two pictures in this "Thing" showing how to wire power and motors. The second photo shows how to add a jumper that connects Vin to the CNC Shield power. Once you do this a 12V 2A power supply plugged into the Arduino powers everything.

How specifically did you wire for power? I ave the arduino uno power cord, but I'm not sure how to wire up to the cnc shield. Can you demonstrate with pictures of your actual device?

Comments deleted.

I'm confused, why did you use two motors on the x axis instead of using a pulley on one end?

Check out this article on CoreXY. It uses two motors total to move the pen in both X and Y directions while neither motor is mount on an axis.
http://corexy.com/theory.html

That's awesome! I had no idea that was even possible. Great design!

Thank you for sharing the updated designs.
I am planning to adapt this to the size of a dollartree foam board. 40"x30". I figured that instead of 8mm smooth rod, I should switch the x axis to .5" smooth rod & bushings. This will allow adding the weight of the 2500mw laser module & fan to the head. What changes to the bottom clamshell do you recommend?

I don't have any experience with scaling a machine up that big so I'm not sure what it will take. If you haven't already done so, I suggest you build the Drawing Robot in the stock size so that you can learn where its weaknesses may lie. I think you will be fine with the X axis frame but the carriage reach of 30" may be a problem. My friend and I are working on a different version of a drawing robot that may be better suited to scaling as large as you want to go. You can look at it here:
https://www.thingiverse.com/thing:2374238

The software and controller are the same between the two machines.

2020 DRAWbot

Hi henryarnold,

I had to repair the top & bottom camshells to work in Slic3r. I am building the current version to spec to test with pen & laser module. My ultimate goal is to scale the current design to foam board size. Local availability of 2020 extrusion in the Tampa Bay area is the only reason why I am going with the current design.

Yes but I don't see any reason that other versions wouldn't work.

I have redone the top clam shell to make sure that it planar with the print surface. The only change to the original design is a small amount of additional clearance for the post from the bottom clam shell. The Top Clam Shell is Version 4

Comments deleted.

What specifically sized screws and nuts(hardware) did you use and of what quantity? I couldn't find the specific sizes needed for this project and how many. Thanks in advance.

The original thing didn't have a complete parts list and I didn't put one together either. You'll just have to print the parts and figure out what you need as you build it. Maybe you could put the parts list together and share it with all.

is there any problem for printing the top clamshell v3. i couldnt sucessfully print it. adherence issues any suggestions

Yes there have been problems but I thought I took care of them. I suggest printing the top clam shell from the original Thing. Sorry for the inconvenience.

slicing with s3d is problematic but cura did it well and sucessfully printed, thanks.....

i added now tje 3 bridges unter the driver, but the steppers only make a noise, no rotation!

Check your config.h file and that you set the parameters to those in the screen shot. Both are required to have a functional controller.

i could not find These Settings, i know too Little about it, sorry!
Can you upload a working config.h file?

The config.h file is in the "Thing Files: section of this design. You can download it from there. The parameters are shown on one of the photos with Source Rabbit. Source Rabbit or Universal G-Code sender lets you set the GRBL parameters. If you are not familiar with these files, you should read about how to use GRBL. Try this link for more help:

https://github.com/grbl/grbl/wiki/Compiling-Grbl

Thanks, but i dont know where to set the Parameters from the photo in the config.h file, i think thats the Problem! or maybe my english ;-)

From the Source Rabbit "System" menu pick "GRBL Settings" and the screen shown will pop up. Edit each parameter so it matches the parameter shown on the screen shot. I added a screen shot showing the menu selection.

i made this already, but i could not find these parameters in the config.h file, because you said, both are required for a functional controller!
The Motor is getting something when i click on the X or Y axis, but there is no rotation!

Comments deleted.

I'm not an expert on adding extensions. Apparently you did something wrong when adding it.
One trick I found out is that you add only the files inside the extension to the extension directory. You don't add the whole extension directory. Review the instructions again.

Comments deleted.

Have you already done all of your EEPROM setup? It sounds like it's either trying to home (with an endstop switch) or it's trying to move further than it's supposed to, as if it's not calibrated correctly. Did you add the jumpers to the headers under the stepper drivers to enable microstepping?

I've uploaded the firmware and done the settings as it shown in the screenshot! But i thought the same, its trying to home!? And no, i've done anything unter the stepper drivers? can you send me a picture, because i cant see anything like that!?

Follow this link to find a photo of what I'm talking about. This isn't my photo (credit to 3dpBurner), but shows the jumper configuration to enable microstepping:
http://1.bp.blogspot.com/-R9x3jUTxT64/VR-szVT9fWI/AAAAAAAAJAo/Orf0Byhv820/s1600/kk.png

Ignore the yellow "ground" marking as it's unrelated to our discussion.

Thanks for the info, I overlooked

Thanks for sharing this project...
I'm part way through printing the parts.
Although this old guy knows nothing about GRBL, I'm working through the set up and I think I have the firmware set OK
on my Arduino. I have replaced the config.H file with the one on here.
At least the GcodeSender is "talking" to it....
So far so good, will shout if I get stuck :)

One thing, what is deemed to be the home position for the pen at start of print?
Great fun!
Regards
Phil

Sounds like you are doing fine. There are two things that set the configuration. The config.h file which you have swapped. You also need to set the parameters which the G-Code Sender (Either Source Rabbit or Universal) allow you to set. I provided the screen shot with the parameters. Basically the config.h sets the behavior such as the fact that this is a CoreXY machine and the parameters set things like the number of stepper steps for a millimeter. Also: Be sure to install 3 jumpers on the CNC Shield for each stepper driver.

The G-Code Sender allows you to set the home position. Using the direction arrows, move the pen to where you want home to be and then set home. On Source Rabbit it is "Reset Work Position". For the configuration I have provided, it will be witht he arm extended and in the left position on the carriage.

Thanks for the response :)
Yes, I set the parameters as per your screen shot...
Would have missed the three jumpers so cheers for the heads up on that.
Is that for setting micro stepping?

Nearly done all the printing except for the top XY clamshell which has gone wrong twice by lifting off the bed and
messing up during the first couple of minutes printing...

Will sort it...

Regards
Phil

Also: The printing of the two clamshells is critical because any curvature will lead to incorrect spacing of the bearings. I posted an updated top clam shell with a fix for clearance for bottom clam shell posts. Make sure you have the latest.

Yes, the 3 jumpers are for 16 pulse stepping. I forgot to add them on another build I'm doing so it reminded me to add the note to this thing.

Hmmmm...
Still having trouble with printing the top XY clamshell.
It keeps lifting off the base and fouling up..
Sent the file to a mate of mine to get him to print it for me on his 3D printer..

Similar thing is happening to him.
He says that he thinks in the design, not all of the clamshell is sitting properly on the base..
Could that be right?

Regards
Phil

I"M SO SORRY. YOU WERE RIGHT!!! The top clam shell had a very slight angle to it. It was literally 0.2 degrees. I didn't notice it. I somehow was able to print it with this angle. The original part was standing up and introduced the angle when I rotated it flat. I have posted the new file with the angle corrected. My sincere apologies for this mistake.

No problem...
I printed one this morning from the origonal files and that went OK..
Pleased you spotted it as my mate was sure it was off the bed at one side..
Just wiring the steppers :)
Onwards and upwards

Regards
Phil

Comments deleted.

I printed it on BuildTak with 30 % infill. It stuck so well I had to pry it off. Design is fine.

Good to know, I'll put fresh eyes on it tomorrow :)
Just had a thought that given you modded it slightly to make a better fit for the bearings that something
might have gone wrong then...
Anyhoo, all the other bits have printed so I'm well on the way now and looking forward to running it..

Thanks for your response, much appreciated..

Regards
Phil

The mod I made was minor. You could print the original source version just to make sure.

Will do later today..
Just out of interest, did you print this part flat on the bed or vertical?

Regards
Phil

Definitely flat. With the logo facing down which is how the file is presented and the photo is displayed.

Just to chime in: I had problems printing it on glass/blue tape. There's just so much surface area that the thermal contraction causes lifting in the corners. So I switched to another of my printers that has a GeckoTek HT build plate and it worked beautifully. BuildTak would work well too, as Henryarnold said, but I always have problems removing parts with high bed-adhesion area from BuildTak surfaces so I didn't risk it.

Long-story-short: If you've got access to some kind of specialty build plate surface (I.E. BuildTak, GeckoTek, etc...), try that for better bed adhesion. And, as always, make sure the bed is nice and clean before you start by wiping it down with rubbing alcohol (or acetone if your build surface will handle it).

Also, thanks for mentioning the jumpers; I'd forgotten to put them on. I was wondering why it had calibrated at 5.4 steps/mm :-P

Unfortunately this problem is my fault. I introduced a small angle in the part when I rotated it to the flat position. USE REV 3 of the Top Clam Shell

I'm interested in building this. I was wondering if 20 toothed pulleys would work or if there's an important reason for 16 teeth.

20 tooth pulleys will work. You will have to adjust the X/Y step mm in the configuration. See the GRBL controller settings. Once you get the drawing robot together, direct the X axis to move 100 mm. Measure it and you will probably find that it moves 125 mm because 20 teeth are 25% more than 16 teeth. Entering 160 instead of 200 for the steps per mm should compensate for the difference in pulleys.

Did anyone else have problems with the clamshell parts? The LM8UUs don't really fit in it, and the two halves of the clamshell don't line up. With a bit of force, I was able to get the bearings in, and get the clamshell together, but then the bearings wouldn't line up, and the rods were binding badly. I know that my printer is properly calibrated, as I use it for mechanical parts on a regular basis.

Any ideas?

Yes, I had some minor problems. I took a Dremel tool and opened the area where the posts on the bottom of the clam shell line up with the holes on the top of the clam shell. This keeps the bearings from being pushed out of alignment. I only had to remove a small amount of material.

I have fixed the problem with the top clam shell file by removing a small amount of material that conflicts with the bottom clam shell posts. The new file has been posted and is Top_XY_clamshell_V2.stl

Thank you rocketmannate for catching this problem.

Amazing build had fun building this thanks for this

I just added the config.h file from GRBL for this machine. That and the configuration parameters should making bringing up your machine easier.

Hello !
Congrats for your work. I'm just printing mine and i have a question : Are you using support material to print the slider ?
I'll post when i have finish

Yes I had to use supports and I printed it vertically. This part is a difficult print because it has protrusions on both sides so you can't easily print it flat. My vertical print had supports for the 3 posts. I had to clean up those posts before the pen holder would fit onto the posts. Another possibility is to print it laying down with the 3 posts facing up and supports on the side with the servo tab. Let me know what you end up doing.

I just wanted to say thanks for the design and the thorough explanations! This is great! I'm currently in the process of building mine. I'll post when I'm done.

You're welcome. I enjoyed building mine. It is a fun project. My plans are to experiment with a laser mount and a mount for a swivel blade for cutting materials.

That's a good idea! I have owned several vinyl cutters over the years. For this setup, I'd recommend the Roland style blade and holder, such as the one found here: http://www.uscutter.com/USCutter-SC-TC-Series-Blade-Holder . They're inexpensive, readily available, and designed to be clamped into a machine such as this.

I plan to experiment with using wire wheels on a small rotary/engraving tool to do a patterned brush on sheet metal. I'm also using this as my introduction to GRBL. I've used Marlin quite a bit, so I expect to learn quickly, but this seemed like a fun project :-)

I checked the link and they have no stock on the blade holders. Do you have any suggestions on a design for a mount for the blade holder? I want to design something where the pen holder and the blade holder are easy to swap out. I perceive that the it would be an advantage to have a fine adjustment of the blade depth in addition to the robot lifting the blade. Any other thoughts?

Here's a link to another similar one. It's made of plastic instead of aluminum, but should still be plenty strong:
https://www.amazon.com/holder-Blades-Roland-Cutter-Holder/dp/B01DP2G4KE/ref=sr_1_1?ie=UTF8&qid=1498565454&sr=8-1&keywords=roland+blade+holder

Coincidentally, the features you mentioned are exactly the reasons that I suggested the Roland style blade holders. It's possible that the blade holder will be able to be clamped into the pen holder without any modifications to the pen holder, though the blade holder may need some sort of adapter to make it longer and more pen-shaped. Whether it requires a different pen holder or not will depend on the range of motion of the slider (the Z-depth, if you will), as the blade holder is only about 2-3" in length.

Also, the cutting depth in the blade holder can be adjusted precisely using the threaded barrels on the back of the blade holder. One of the most critical adjustments on a normal vinyl plotter is the cutting force. It's possible that you could just add weight to the pen holder to account for this, but I'm not sure. I don't really have a solution for it at the moment, but it's something to consider.

I'll finish my build in the next day or two (once my LM8UUs arrive) and I'll try it out with one of my blade holders and let you know how it goes.

Thanks for the suggestions and information. I think an adjustable downward force could be useful for both the knife holder and for pens. I'm going to try to come up with something.

Very nice this desing is better than others in my opinion, i like it

Would this work acceptable wall mounted?

Yes as long as you have a spring to keep the pen on the paper. I'm currently using the weight of the pen to keep it on the paper. Some of my photos show springs which I removed. You will need some kind of spring or springs.

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