I just had the pleasure of using a 1/8th in. single flute upcut O bit you linked. WoW! This thing is well worth the cash and it is a night and day difference from my previous bit. I will try and post some pics of how everything turned out tomorrow for all to see. The acrylic is being cut beautifully with very clean edges. Thanks again @kram242 for the link on the bit.

The RPM meter hasn't arrived yet but couldn't wait to get started. I used @The Dude 's settings for acrylic which is probably too conservative with the new bit I'm using. On my next cuts I will get some readings and do the math (use speed/feed tool) to really dial in the parameters for acrylic. I think I can probably go a lot faster with this new bit.

 

Here are some photos of the results with the bit in case any want to see. The circle didn't come out too well because I was having troubles with the Y axis again. Should be good again now though, I kept having strange issues with one of the motors on the Y not wanting to work while moving -Y but was ok moving +Y.

Going to try and recut the circle in hopes I can salvage the part. I will use one of the plunges I drilled earlier to line this up again for another attempt. Just curious but does anyone else drill a hole in their material right from the start to use that for alignment if they have to stop a cut? Or is it just me? I find it useful to do that so I can line everything back up again in case something goes wrong. Is there a better way to do this sort of thing? I saw http://openbuilds.com/builds/tool-position-setting-part-iii.490/ and would like to do that but I'm afraid I'm using GrblController so unless I add the code myself it may be hard to do. Would anyone out there like to have this capability added to GrblController?

 

Excellent tip @Rick 2.0

Tweakie.

 

This doesn't work when the machine slips during a cut. You have to manually touch off the workpiece again to resume. A tool-mark helps make this possible and an automatic tool positioner is even better. I suppose you could write down the offset of the workpiece from the home position when starting a job and then if it slips just rehome it and set the offset.

 

The photos show what looks like a timing issue. I had the same kinds of cuts on acrylic. Try slowing down the timing when changing directions. On LinuxCNC it's called "Direction Hold". There is also a rising edge and falling edge to each signal and getting them wrong can produce a missed step "only on -Y". If you're board is using rising edge then maybe changing the "Direction Setup" timing would fix it. read all about it here http://cockrum.net/cnc.html

 

I agree and thanks for the info. I saw a technique for doing 2-sided PCBs which uses the same principle. With PCBs it's even more critical to get a square piece and flip it over perfectly. Actually this technique can apply to any material giving the possibility of machining 2 sides.

 

I tried to re-cut tonight I aligned the part spot on and it worked great for a while but when it got close to the end after the 30th pass or so things started going south west. Literally started going that direction, then it cut a large chunk into the side on the very last cut. Maybe the motor's are overheating? If it were a timing issue I would expect it to be consistent. I'm wondering if I will have the same troubles with something a little more tried and true like Mach3. Can I use Mach3 with a grbl shield? Will it still work?

 

I don't use a grbl shield. I don't use Mach3. You can measure the temperature of your motors and see if it exceeds the specs.

 

This needs to be said for the benefit of others that follow;

A properly built / constructed machine when used correctly will not slip during a cut.

Tweakie.

 

Below I will give some percentages. For reference 0% is no current, resistor turned all the way counter clockwise (full resistance). 100% is full on (no resistance) all the way clockwise.

I have noticed that my Z motor gets really hot on the back side. So much so that I don't want to touch it. I have the current limited to a little under half on the Z about 45%. The Y axis motors are both cool to the touch even after cutting for a while. There is not near as much current running through them since the current gets split at the driver for the Y anyway they want double the amount of power. The Y I can almost drive wide open with the grbl shield but I have it limited to about 60% currently. On the X axis current limited to about 50%.

I will try knocking down the current limits on the X Y and Z to about 30% and slowing down the machine as a starting point for tuning/troubleshooting. How long would you guys recommend running the machine testing before you are confident that your motors are not over-heating.

Currently I do not have a fan blowing on the board but I will see about getting some heat sinks and a fan. We may have some where I work that I can beg or buy. @kram242 does your routy build use heat sinks on the driver chips or just a fan? Or both? My electronics are not mounted onto the back of the machine as suggested but rather in the front of the machine. Cable drag chains carry the wires to their respective destinations.

 

@Ceiling Cat - from my experience I would suggest that the stepper motors current should be adjusted so that they run hot to the touch but not so hot that you cannot hold your hand on them (even after hour of use). Now not everybody will agree with me on this but as a principle it has served me well for many years now.

Tweakie.

 

Thank you guys, I will try again tonight sometime. I have a little fan here and I will run it directly over the boards to push the heat away. Hopefully that will take care of it and it starts cutting true again for long periods of time. I'll also tune the current and let ya know. I'll shoot for warm to the touch but nothing you can fry and egg on. Thanks again for the suggestions and help.

 

Thanks for all the help guys, I think I found the problem last night when I was going over the machine. I put a 12V fan on my 24V supply. You can run it at that voltage by the way... granted I don't know for how long but it will put out a lot of air, more than enough to keep the board cool. I actually don't think over heating was the problem anymore. Last night I found that one of the set screws on my Y axis motors was completely gone. After closer inspection I found that the last set screw had almost worked its way completely out and was off the flat part of the motor shaft. Once corrected the machine is a lot more stable.

 

Another question on a different topic for anyone using LinuxCNC. I'm starting to realize the limitations of grbl controller software. I also don't like the fact that if I tell it to stop it just keeps on going its marry way until it empties out a buffer (bad design imo). I'm looking into LinuxCNC but it seems to go that route I would need a parallel port which I do not have on my host computer. I see they sell these USB to parallel port adapters:

http://www.newegg.com/Product/Produ...04004&ef_id=UsLpjwAABDjZxO83:20140401122923:s ​

has anyone used one of these successfully with LinuxCNC or Mach3? I was thinking of purchasing one to play around with LinuxCNC. It seems like a more feature complete CNC software than grbl controller.

 

Those adapters are only intended for use with printers and do not work with Mach3 (not tried it but I assume they will not work with LinuxCNC either).

Tweakie.

 

By host computer, I have a mini http://www.newegg.com/Product/Product.aspx?Item=N82E16856173029 driving my machine currently. I like it because it fits in the palm of my hand and can mount directly to the machine in a little tiny control box I'm building to contain all electronics + power supply. I just remote into it from wireless network and do whatever I want. I can use my phone as a control interface with RDP, but this box does not have a parallel port or serial port, nor does it have room for an expansion card. USB is my only option so it looks like I could be stuck here unless I create a driver for LinuxCNC using HAL and a new controller board to match it. Mach4 looks to be supporting some sort of Motion Device Driver model so looks like we could possibly get a plugin for grbl shield + Mach4 with a little work.

My other option would be to take out my mini and put it on the back of a TV for xbmc somewhere and use either my RaspberryPI or BeagleBone Black for the brains of my Routy machine. Anyone done anything with the PI or BeagleBone married to either LinuxCNC or Mach3?

 

If you wish to use Mach3 with USB connection you could use an external motion controller such as the UC100 or Smooth Stepper etc.
Mach4 still has some way to go before it will be ready for release so it could be a long wait.

Tweakie.

 

That's too bad about mach4. Which is better smooth stepper or UC100? I didn't think it was possible to use USB connection with Mach3. How do you set that up?

 

The UC100 and USS are just different approaches towards the same end but I could not say which one is better.
I use the USS with one of my machines and have no complaints.
Setting up data etc. for the USS is here http://warp9td.com/index.php/documentation

Tweakie.