Re: How fast is your homemade CNC?
I do not currently have a completely ground up home built CNC.
I had a MaxNC 5 that except for the frame and dovetails was home built. My own screws, bearings, bearing keepers, spindle, after market control etc. It did 80ipm rapids and cut a 65ipm when I retired it.
My Taig never was able to reliably run faster than about 65ipm if adjusted to have low backlash, table slop, and head nod. That was with aftermarket controls and motors.
My X4 Speedmaster cuts at 80-110ipm 90% of the time and all axis rapid at 150.
I haven't powered up my new X5 Speedmasters yet, but with the reduced friction and stiction of going from dovetails to linear rails I expect they will be faster.
The Hurco KMB1 will cut at rapid speed if the speeds and feed and cutter will support it. I have a completely retrofit control system on it currently using DuGong 160 servo controllers. I have all axis set to 200IPM, but with only a 3600 RPM spindle it will rarely support that much feed.
All of that being said: For the type of machining I do acceleration is more important than feed rate. I do a lot of very short move 3D sculpting in aluminum. Who cares if the calculators says you can make the cut at 80ipm if the machine never reaches that feed rate anyway. This is where you start to get trade offs. High acceleration will cause your machine to fault almost before it starts. With stepper systems you may see the machine stall or chatter. With servo systems your servo driver throws a fault output to the control. On a stepper driven system (except some closed lop systems which act more like servos) you just lose position and your part is quality suffers from not quite right to totally destroyed. On a properly setup servo system the machine just stops when the following error is exceeded.
What can you do? Reduce the acceleration rate is one thing. On a servo system you can increase the allowed following error. If your controls can handle it you can increase voltage to the servos too. On a stepper system you might be able to increase voltage or current to your steppers, but most small steppers systems are already setup at their max. From my experience usually higher than their max for longevity. You are back to reducing acceleration. Sometimes acceleration also affects the top feed rates. It winds up being a balancing act in those cases.
What do my machines do?
The MaxNC accelerated (after I fixed it from its abominable initial setup) at a solid 20iss.
The Taig when adjusted to cut good tolerances was about 15iss.
My little Chinese router (forgot that one) seems like it will accelerate at 30iss, but on long jobs its position drifts on all axis with Z expectedly being the worst.
The X4 Speedmaster does a solid 25iss all day long on all axis (if the Z weight is balanced) and it just has big steppers. Currently its doing 90% of my paying work. Even so I'll often program 80-110 IPM and not see the display reach half that. I actually tested upto 45iss on X&Y and and 40 on Z after changing gas springs and adding weight to the head. I figure 25iss rock solid is good enough for now. 25iss is the setting in the stock config file.
The X5s remain to be seen, but I am hoping for 30-35 out of them since they also have more powerful spindles. It would be nice to produce at feed rates the 24K spindles can support.
My Hurco again is the odd machine out. Back when I ran GeckoDrives I had to keep turning the acceleration rate down as they were used. Over the course of a year they would drop from 25iss rock solid to 12iss and flakey. I'd replace the drives and it would be great again. I went to the DuGongs and it was like a whole different machine. The initial following error was huge so I did all kinds of crazy tests. Acceleration at 100iss. Rapids at 450ipm (X&Y) and higher. It was stupid. Scary too. When you see over a 1000 pounds of table being slung around like that its pretty wild. I cranked down the following error (I think I have it set at 50 with 10K pulse per inch) and I get a solid 30iss and 200ipm on all axis after much testing at higher accelerations and feed rates. I could run it faster, but there really is no need with just 3600 RPM out of that spindle. I keep playing with the idea of putting a high speed companion on it.
Anyway, my point is that while feed rate is important to material removal rates, so is acceleration. In some types of work a machine with good acceleration and modest top feed rate can outproduce a machine with wild feed rates and more modest acceleration.
Bob La Londe
http://www.YumaBassMan.com