Our robot army is growing
As our saying goes, “Made in Austin, TX by humans, with the help of a few Robots”. Livid was founded with the use of a ShopBot PRT96 CNC machine that has served us well all these years cutting all of our plastic parts and milling our instrument bodies. As our business grows, it became time to move on to not just a ShopBot brand upgrade, but to an entirely new bot.
Building on the success of our shop built “metalbot” which cuts all of our faceplates and was designed and fabricated from scratch, I began construction of a new CNC machine to replace our ShopBot that has served us quite well.
By building another custom bot I was able to build to our specs and needs.
60″ X 96″ Extra wide cutting area – With the ShopBot, we always had to remove our body milling jig to cut a full sheet of plastic. A wider table lets us leave the table setup and saves a lot of time.
Better Z-axis precision – The ShopBot always seemed to have a dip in the middle and didn’t have the necessary support it needed along the X-axis (length). This meant the Z-axis (height) always varied from point-to-point and we had to adjust a lot to compensate.
Transfer/jog speed – After building the metal bot with a transfer speed of 400 in/min. I realized how much production time is saved in moving much faster between cuts. My goal for the new bot was 400 in/min or better.
Cutting speed – Since we are no longer a “garage” operation, we need to worry about things like “production per minute.” Cutting speed is greatly affected by the machine’s rigidity. If the machine flexes, then the bit vibrates, which creates more friction and heat at the cut, and cutting has to go slower.
For the sake of others who are into building bots so I documented fabrication as I went along:
Step 1: CAD out the bot so we have plans and my crew knows what they are building!
With the intent of building a very heavy, rigid machine, I chose steel for this project. While steel works well when bolted, there is always a chance of vibration loosening the fasteners during use. We always had to re-adjust ShopBots bolts, sort of like how you have to tune a guitar. We’re not playing guitar here, so we welded: welded steel isn’t going anywhere.
Step 2: Buy a truckload of steel. It’s heavy, rusty/dirty, and full of awesomness. I used mostly 1/4″ wall tubing and angle.
Step 3: Weld up the main table. I have cross supports every 18″ that are 2″ angle and the outside frame is 2″ square tubing. While welding the table makes a very rigid construction, you can’t “undo.” Everything must be clamped and measured and adjusted and measured and clamped and adjusted and…… The table must be perfectly square, flat and straight. “Measure twice, cut once?”: it’s more like “measure at least six times before commiting to welding, and still worry about it while you are.”
Step 4: Weld the table legs and end supports. I designed the machine to be welded into three main parts that bolt together. This gives me the advantages of welded strength but allows the bot to be disassembled into manageable pieces for the glorious day we get to move to a bigger shop. The legs and end supports are 8″ C-channel and super heavy duty.
Step 5: Mount the table ends to the main table. I use 1/2″ bolts. The drilling begins. It takes a lot of sweat and cutting fluid to drill through 1/2″ of steel over and over. By the way, “sweat” and “cutting fluid” are not the same thing.
Step 6: Bolt on center leg and cross bracing. The cross braces are welded to the cross supports. This really helped take the flex out of the middle of the table and keeps the Z-axis consistent and precise.
Step 7: Build and mount the X-axis rails. This bot uses a rack-and-pinion drive system that glides with bearings on 1/4″ cold rolled steel plate. I wanted to avoid warping the rails with welding, so the steel plate is bolted every 6″ to 2″ x 3″ rectangular tubing. Then the rails are bolted to the table every 12″. That is A LOT of drilling and tapping!
Step 8: Weld the Y-axis carriage and mount to the X-axis rails. The Y-axis carriage carries the Z-axis with the mill head across the X-axis rails. I used 3″ square tubing for the rail piece and 3″ x 2″ rectangular tubing with 1/4″ steel plate to make the triangle ends of the carriage. The Y-axis carriage has two sets of roller carriages on each, spread out to prevent the whole axis from racking.
Step 9: Paint or powder coat the entire machine. I used a bare metal prep and a gallon of blue metal enamel to completely coat anything and everything for rust prevention and to make it pretty (and, yes, it is “pretty”). I masked the cold rolled steel where the bearings roll over them to keep them bare and clean of paint.
Step 10: Build and attach the Z-axis. The Z assembly rolls over the Y-axis rail with a rack-and-pinion system and the same roller bearing assembly. I oversized the steel body of the Z-axis so that I can some day add a much larger CNC spindle with tool changer (hopefully!).
Step 11: Mount the router carriage. The router slides up and down with a stepper motor and an acme screw. It is not designed for speed, but for accuracy and holding strength. The last thing you want is the router dropping as it cuts!
Step 12: Mount the stepper motors with rack-and-pinion system. I am pretty impressed with this system. It uses a timing belt 2:1 ratio and is built to add speed. These nema 34 stepper motors have plenty of slow speed accuracy and power and the belt system adds speed for jogging.
Step 13: Install the bed and “spoiler” board. This is the cutting surface and the machine is programmed to surface itself and make it perfectly flat.
Step 14: Build the control box. The control box consists of 4 motor drivers, a large power supply, computer power supply for low voltage, a breakout board for communication with the computer, and a relay board to turn on the router. My control box is built into an empty computer case. It is from a gaming computer and has all the extra fans to keep it cool. Plus it looks like megatron so that adds to the coolness.
Step 15: Connect to a pc and run this mofo. I use mach3 cnc software to run my machines. We have movement! The bot lives!!!!
I am so proud of this machine and how well it turned out. It is very fast for our shop and glides smooth up to 700 in/min! I tried to keep this post short but could have written a book on building these machines. I love to talk about building bots so feel free to chat with me and pick my brain.
Video to come soon.