I read it a few times. States that it will display the units you select in config, but doesnt explain that you can run metric gcode while set to inches which is where I got turned around. My only gripe turns out to not be a gripe at all. Thanks for clearing that up, everyone.
I will be deep diving grblhal because definitely, at the moment itâs just a cluster of letters that I pick in my post processor. It has worked well for me so far though LOL
Your problem is solved but I thought Iâd try to provide a little more context.
Its just a matter of decimal places right?
To get the most performance out of hardware things like firmware and operating systems are generally programmed in a fairly low level language. In these lower level languages each number will be represented by a certain number of bits. No matter what size the developer chooses for each floating point value, millimeters will be 25.4 times as accurate as inches due to the smaller base unit. While you could technically use more bits for inches it would be inconvenient and waste memory in an environment that typically doesnât have much to spare.
Grbl started as a firmware designed to be run on a specific 8bit microcontroller and grbl used every bit of it. As the cost of more powerful hardware decreased, there was a desire to run grbl on better hardware. The problem, as I understand it, was the code wasnât designed in a way that made porting to other chips easy. The chip specific code was scattered all over the code base. Thatâs where grblHAL came in. Itâs a rewrite of grbl that uses a âHardware Abtraction Layerâ to separate the general purpose code from the hardware specific parts so itâs easier to port to new platforms as they become available.
Happy carving!
Maybe this is more of a philosophical question and for USA users but I have to ask why do people use imperial units in a CNC environment? The Altmill is my first time ever using a CNC and it just seems it is easier to deal with metric. I do have to deal with imperial units of some of the bits I have but I try to use metric in all other cases.
@DavidB Iâm with you. Iâve used metric from the beginning with CAD programs. Now I never measure anything in imperial lengths. Especially in CAD I find base ten far superior to base two fractions.
Which is bigger 27/64âs or 7/16âs? Well 64/16 = 4 and 4x7 = 28 so the latter is bigger. Itâs not like thatâs hard but in metric the answer is immediately obvious.
All my bits are imperial but I delete the imperial section of my tool databases and just enter their metric equivalent.
The only countries that donât use metric are the USA, Myanmar, and Liberia. And the last two use both and are headed to full metric. The switch to metric is too hard for us, I guess weâll just have to bomb the rest of the world until they see things our way.
Rant over. Are their any Canadians that want to adopt a disgruntled American? No? Canât say I blame ya!
@_Michael Maybe if every American household had a CNC, youâd all make the switch to metric.
@_Michael I would argue that Canada is not completely metric and likely never will be.
As an older Canadian, I still buy framing lumber as 2 x 4 x 8. I buy 4 x 8 sheets of plywood and drywall. My end mills are 1/4, 1/8, 1/16. The shaft sizes are 1/4 and 1/8. The bolts that I used for my hold-down clamps are 1/4 x 20. The ducting and flex hose that I use on my dust collector is 4".
I design in VCarve in inches, but write the toolpaths out using a grbl mm post processor.
My latest purchase from Sienci was the 30 x 30 Mk3. Their Altmill sizes are 24 x 48, 48 x 48 and 48 x 96.
All that said, I buy gas in litres, think of temperatures in celsius degrees, and wind speed in kph.
I donât know how big a hectare is, and I canât seem to get my head around using kilopascals for the tire pressure in my car and motorcycle. PSI to the rescue.
Maybe itâs simply that I am old. Maybe the next generation will buy framing lumber as 50.8 mm x 101.6 mm x 2438.4 mm.
@gwilki Same here. The construction industry will likely be the hardest to change. That said, I draw everything in metric for the design and permits and then convert to ft-in for construction drawings.
As for the lumber, a switch to metric would hopefully bring on actual dimensions (38x90 for a 2x4). No more nominal designations. Itâs funny when you look at reviews for masonry and lumber on the HD web site. A lot of the bad reviews are from people who complain that their 2x4 was not actually 2"x4"
@Chucky_ott What makes it worse, I think, is that most sheet goods are no longer 3/4" thick. They are 19 mm. For many applications, the small difference may not matter. However, with many CNC uses quibbling over .0001" variations in dimensions, that .002" thickness variation can really set them off. 
In acylics, I have found that what used to be 1/8" is now 3 mm, which can make for sloppy dado constuction using 1/8" o-flute bits.
Back in the mid 60âs in Engineering School in Iowa, everything was taught in both Metric and Imperial because the world was going to establish English as the âAviation Languageâ and Metric as the âMeasurement Standardâ. Everyone agreed, but then the US did not change to Metric, perhaps because of the cost to manufacturing companies. Now, 60 years later, we have a lot of stuff with both Metric and Imperial parts. What a messâŠ
Oh my chael,
I must confess that I am tiptoeing around the metric/imp issue when posting on this forum. Itâs one of the holy houses I am not willing to be blunt about because I know how sensitive the topic can be and how trivial a reason to trigger a war over. So when my mind tells me to type, âjust use metric and the problem goes awayâ I will sit on my hands and click on back to leave the tread.
On other platforms I do not have this self restricting power and.. lets say.. am enjoying rage baiting waaaay to much to be healthy. But hey, universal healthcare! (Redacted away some other examples to keep the peace. Words these days seem to hurt more than they did in the good old days, where you could burn someone down to their shoe laces and have a beer and laughs afterwards.)
Btw, metric construction lumber comes with a minimum length of 1500 mm and goes up with increments of 300mm. The width/height measurements is the only thing that I wish was like american measurements. You wouldnât believe the variation in lumber size you can get here. Itâs wild. (And stupid.)
See, itâs not all bad! And in a weird way.. I feel ya!
I am a Canadianwannabee too.
Error 33 is due to imprecise arc parameters, could be due to rounding errors from the CAM - at least Freecad did (still do?) produce invalid output sometimes. It can also be due to the limited precison of single precision floats that grblHAL uses internally, but normally that should only show up for extremely small or large radius arcs. I have seen error 33 pop up for very short arcs with kilometer sized radius - IMO where a straight line should be output instead by the CAM post.
Note the conversion from string to the internal float representation does not limit the number of decimal digits to the conventional 4 for imperial or 3 for metric but rather to the total number of digits, currently 9.
BTW grblHAL, like Grbl and LinuxCNC, implements the same radius check for center format arcs - if it is off by more than 0.5 mm or 0.005 mm and 0.1% of the calculated radius an error should be raised. This is in fact a bit more lax than the NIST RS274/NGC spec which requires the error to be less than 0.002 mm.
If the gcode that caused this error is posted I am more than happy to look into the reason behind it.
I knew this was one of those âholy housesâ like tabs vs spaces for programmers but the phrase âMaybe this is more of a philosophical questionâ was too good to resist.
I know some people in other countries use imperial and I think you should use whatever your comfortable with. Iâm not totally metric either because Iâm used to gallons, quarts, Fahrenheit and pounds.
My first CAD experience was making 3D models in Blender for game assets and the units really donât matter in that context. It was when I got my first 3D printer and the units mattered that I started using metric for short distances, I still think in miles for long distance.
I also think itâs great that the tools we have access to let us do things how we want. Designing in inches with metric PP and gSender displaying inches while using metric behind the scenes is awesome.
I know that politics is off limits limits here so I hope my second to last paragraph wasnât too far over the line but sometimes I canât hold myself back.
It doesnât seem like any responses so far have taken offense but just in case Iâll say that was not my intent.
EDIT: Iâll add that the more I think of it itâs not really inches vs mm for me itâs base2 vs base10 thatâs cumbersome for me. I know you can use decimal fractions with inches, dial calipers for example, but itâs less common and below eighths of any unit I find those fractions tedious.
Luckily, I was quickly educated and now am posting in metric and displaying imperial in gsender. 
Maybe because every other tool in the shop uses U.S. Customary Units including scales, raw material, bits, bolts, nuts, ceil height, door size, sausage weights, bread loaf sizeâŠ
Metric parts cost 50% to 100% more, also.
This thread has gotten way off topic. Iâm a part of that.
As the original question has been answered, I am closing this topic.