Anyone know if there is a way to pause an operation and retract the spindle for a tool change? I'm using the "blackbox" controller and " openbuilds control ....179 to run a desktop cnc router. Everything works great but I'd like to be able to replace the bit without restarting the entire job. This isn't a pre planned tool change. Just wanted to be able to replace a bit that breaks or gets dull. The control software does allow a "pause" and "resume" but you cannot retract the Z axis when it' s paused. FYI.. I'm using an old lead screw, early Chinese, desktop CNC that I got used on e-bay, a "blackbox" controller and open builds control software. I've got everything working the way I want but if I need to replace a bit I have to start the whole operation over again and some of these take hours to run since I'm using a very slow feed rate. Just curious if it's possible to pause, retract, return to previous cutting point and restart. Thanks
Hi Fran, can't help you with blackbox or OB control I'm afraid - you'll have to wait for one of the experts on those. Just a thought though - you're going to need a bit more than just retract Z because you will need to re-zero the Z after a tool change. Alex.
Of course BlackBox isnt locked to CONTROL (Control is for beginners) Try bCNC, CnCjs, UGS or any other Grbl hosts till you find one that does the advanced things you need
Thanks that's kind of what I was trying to avoid. I thought that if I used the zero value at the time I paused the progress of the GCode I could pull the Z axis up and after I replaced the bit return the Z to the value at the time of the pause. I don' t need to adjust the X or Y just the Z enough to remove and replace the bit. I have an Idea to try using a terminal since it looks like some of the Grbl commands can be executed at any time but I don't know if it will allow two different applications to send commands to the USB port. The motor I'm using as a spindle is manual on/off so stopping that is easy. Going to try it shortly, I have a job running and the bit has many hours on it and is starting to show signs of wear out (the cut is wandering off the trace line). FYI .. I'm engraving flat pieces of limestone using a high torque low rpm motor. I have the feed and plunge rate set just right so I'm not breaking bits but after about 20 hrs the bits start wearing out. I like the way it works now. It's quiet and doesn't make a mess throwing stuff all over.. only drawback is it can take 30+ hrs to engrave a 12x12in pattern with some text , 10mm deep on a slap of rock. One that I finished looks pretty neat. Thanks again
Break your job into multiple sections. I cant speak for anything but Fusion 360, but its easy to do with tool path containment.
The point I was making @fran jackovich is that the new bit you put in will not be at exactly the same Z height as the old one and you will need to re-set Z zero. Alex.
if you break a bit the correct thing to do is EmregencySTop the machine. reset, replace the bit, reset Z zero for the new bit, and resume the job. If you want to stay with OBControl then you will have to edit the gcode in notepad to remove the stuff before the bit break. This is tricky but can be done. Much easier is to turn off blocks in bCNC. You can see what you are doing and then you can saveas the file so it only cuts the active blocks. even if you dont use bCNC for actual machien control I think it is worth installign just for this job.
I'll post a few pics later today. I did try using GTKTerm (linux hyperterminal) to send Grbl commands to the USB port (with the BlackBox) and it did hang the port to the OpenBox control app. So I downloaded one of the recommended CNC controllers and will play with that later today if I have time. All in all I very satisfied with both the BlackBox and OpenBuilds software. This was something I wanted to get around to for some time. Now that I see what I can do with this resurrected CNC I can get to playing with various control methods. Thanks
Hi... I figured there would be some variation in the height that's why I wanted to control Z while the operation was paused. Thought I could eye-ball Z on the material make no change the the next step in OBC ,then restart. Unfortunately if I "STOP" the operation when restarted it goes to the beginning of the GCode and starts over again at the first past depth of cut , when in fact it may have already cut to say 5mm . If I use "Pause" I can't manually adjust Z (it's locked). I tried using a hyperterminal to send command to the USB port ,$J= Z20.0, to try and manually lift the Z while OBC was "paused" but it caused OBC to hang. I downloaded another control program to try out later so I can move on from OBC. There's really no way to predict when a bit is going to break or need to be replaced. I'm milling limestone and there's inconsistencies in both the surface and density. I'm using cheap bits, a $50.00 12VDC spindle motor, a desktop CNC the came off e-bay for cheap and the BackBox with OBC control.For me this is more of an arts/crafts poke and hope plaything. Definitely not a real engineering project ... but it does have potential. Thanks again
As a random thought (which may or may not work) measure your bit extension from the collet and drill a hole in a small block of wood to the same depth. Each time you mount the bit, drop the bit into the hole in the block and push the block up flush to the collet before tightening the bit in place. As I noted, it may or may not work but if it does it'll provide depth continuity between bits.
I do something similar and use a torque wrench since the length can vary depending how tight the collet nut is.
Another trick - often used in pcb drilling - is to use a tight fitting collar on the bit. If you set several tools before starting a job you could replace the bit with some degree of accuracy. Not much help to you if you are on a tight budget @fran jackovich, but the Duet controller that came with my workbee from Ooznest in the UK, and their version of the rep-rap firmware allows me to jog the machine after pausing a job and reset Z zero before resuming. Alex. EDIT - the pause and resume on the Duet are macros and easy to customize - see Workbee with Duet controller macro changes
I uploaded some pics of the first experimental rock It didn't amount to much but I can tell that with some time I'll improve the results. I stuck a drill bit chuck on my spindle/motor but even with that I still need to retract the Z axis to get an old bit out. I'm pretty sure that using a different control software I should be able to do what I want. Using a block of wood to get the exposed bit consistent is a very good idea. Thanks
You have to set your feedrate to correctly work in the hard parts of the material. Then the bit will survive the hard spots, mostly. You really should be running flood coolant on that rock. This will keep the tool cool and also flush the chips away which is very important, recutting chips puts enormous strain on the bit. Yes, there is a way to predict when a bit will need replacing. It is called 'time in the cut' and is a measure of how long the bit has actually spent cutting. Expensive controllers like Fanuc, Siemens, Haas and so on will keep track of this for you and allow you to program a change to a new bit when some milestone it reached. This is used a lot by people who cut titanium and stainless steel. There are many GUI's for GRBL (which is the software the Blackbox runs internally) and there may be one that allows jog and zeroing during a pause. However, this is generally not the case since doing so is a major safety issue. The correct way to do it is to stop the job, replace the bit, reset zeros properly and then restart the job. As I said before, bCNC makes this easy and safe since you can just untick blocks of code that precede the one you want to restart on (and you can see which block is selected in the 3D display). Just make sure never to untick the first block which contains the basic setup codes. Without that block you will break a lot of new bits.
I was speaking of the material and hardware I am working with . Since I'm working with a low RPM I don't need any cooling hardware. The temperature of the motor and bit rises to a certain level then stabilizes since it's dissipating as fast as it's created. The bits I've broken happened when the GCode led to a soft spot or ridge in the stone and the feed rates pushed it a bit hard laterally. Otherwise the bits don't get dull till they've been turning for 30+ hrs. Then they tend to ride on the stone without cutting much. Since they only cost about $2.00 each I don't see the need to make other changes. At least for this current endeavor. All I wanted to do was be able to raise the Z axis so I could get at and replace the bit. Then put it back on the surface as close as possible to where it was so I could restart the GCode from that specific point. Just got CNCjs running a minute ago. Machine is working on the job I started yesterday and seems to be following the GCode evenly. I'll know when I have to make Z axis adjustments if this takes care of my issue. Had to use the CNCjs app instead of the standalone desktop version. The desktop would connect to the blackbox but wouldn't communicate. There were no response messages from any command , just a click and a "connected to..." message.
Can you increase safe Z height? I think that there's not enough safe Z height if the rock/stone isn't flat. I think that the wiper motor doesn't spin the bit fast enough. Are you using the right kind of bits for cutting rock/stone?
The bits are part of the problem right now. The first batch i got worked better so i ordered some more today. The current bits seem to be taking off less on each pass. i wanted a low rpm motor. This one does about 60 rpm and im using about a 20mm feed rate taking off .25 mm each pass. its quiet and doesnt throw stuff off the work area. I just look at it every couple of hours to see if its on track. More like hand carving than milling. They sell these motors as garage door openers too. High torque and slow. Think i found a CNC macro that will let me adjust the z axis while the operation is paused then return to work coordinates and resume. going to try tomorrow.
If that macro works @fran jackovich, you may be able to modify it to allow re-zeroing your Z axis. Alex.
The existance of a macro or which commands to send in other words, is not the main reason most hosts don't offer this, its because pausing a job at a random spot, then letting a user perform commands (whether via console, macro, or buttons) can take the machine off path by accident, and then when you resume, result in a crash (which may lead to damage, or worse, injury) Therefore most host applications do not allow for moves during Pause. The correct-er way is to split up your gcode into known chunks that can be run before tool wears out. Then as each part of the job is a self contained Gcode file, you are sure all Modals are setup correctly, and you can doublecheck things like Zero position before running again.
I think here? Sorry @sharmstr! But yes, good to confirm more than one person thinks thats the best option overall
