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Tips/Techniques Intermixing metric and imperial on a CNC machine

Tips/Techniques
jcdammeyer

jcdammeyer

John
Premium Member
I would like to say I've gone totally metric but in fact I still have the the CAM program generate imperial movement commands. If I type in the MDI window G1 X2 F3 I know it goes 3 inches per minute and I have a feel for that speed. If I was running the machine in metric mode then the feed is 76.2 mm per minute which is a value I can't get my head around. Plus I have to remember that the machine would be in metric mode especially since an F76.3 in imperial mode is quite fast.

The problem is so many of the drawings for say the robot arm are in mm not inches or dual dimensions from the drawing. So if I've done a project using say a 1/4" two flute cutter as Tool #3 the dimensions in the dialog are in inches.

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But the software hasn't got a parameter in the tool table definitions to flag it as metric or imperial so if I bring in a drawing which is done in metric dimensions the G-Code generation now assumes that the tool diameter is 0.25mm not 0.25".

If I say well just change the global parameter for the document to be imperial rather than metric no problem. Except all the work done to set up tool path programss for each tool etc. vanish.
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With the list above wiped out I have to start over again for example all the center drill points first.
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And so on. So what I thought might be the easiest solution is to create two tool tables and load the appropriate one depending on metric or imperial drawings.

The table would still have a Tool#3 but instead of 0.25 diameter the value would be 6.35 and feeds and speeds would change from 11 IPM to 280 mm/min.

None of this would be needed if the MECSOFT AlibreCAM was able to switch units without destroying all the tool path programs.

And just as an aside, when MECSOFT stopped supporting Alibre they offered the identical MECSOFT VISUAL CAM software except now it imports a STEP file where often a circle is two half circles. Again more tedious to work with.

Want to make one tiny change to make machining easier, change the drawing, export the new STEP file and import back into MECSOFT CAM with the total loss of all the pre-programmed motions. In other words start over.

Sorry for the ramble.
 
I can see that is a pain in the ass. I've just recently been playing on the controller side with PathPilot and noticed that it displays the tool information in whatever system is selected by the current G code (G20 or G21). So easy and intuitive. Even if I'm using a mix of metric and imperial tools, all I need to do is MDI G20 and I can enter a 0.093" drill without conversion, and then switch to G21 and put in a 3mm end mill.
Still learning fusion, didn't notice how it picks mm or inch when setting up tools as I have just been using tool definitions I can find from vendors for now.
 
I only have G-code on the plasma table, and can chose which system at the start.
John, you put it very well, having a feel for it. When the father of Blackface brought metric to Canada, I was already out in the real world and worked as a machinist and a sawyer, and all in inches. I noted then that people who lived in the abstract world, teachers and bureaucrats had little to no problems, because they had no concept in their minds of a inch, a foot, or mile. It was only a number to them.
I understand metric in principle, but when machining a metric part, I convert to inch and do it, rather that screw up a part due to a miscalculation. Some day when time is not an issue, I will experiment with machining some junk in metric to build skill.
 
Ironman said:
I only have G-code on the plasma table, and can chose which system at the start.
John, you put it very well, having a feel for it. When the father of Blackface brought metric to Canada, I was already out in the real world and worked as a machinist and a sawyer, and all in inches. I noted then that people who lived in the abstract world, teachers and bureaucrats had little to no problems, because they had no concept in their minds of a inch, a foot, or mile. It was only a number to them.
I understand metric in principle, but when machining a metric part, I convert to inch and do it, rather that screw up a part due to a miscalculation. Some day when time is not an issue, I will experiment with machining some junk in metric to build skill.
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In truth unless you use furlongs per fortnight you already use the metric system in a fashion. When you specify a distance with a G-Code you may type in:
G1 X21.351 Y32.776 F250

Now as you are on a plasma table (or full size CNC router) likely those size moves might well be normal as inches and decimal inches. For my mill they aren't. Unless I have G21 enabled. So if the drawing I'm following is in metric and I want that slot from 21.351 to 32.776 and if the drawing is in imperial units the move might be:
G1 X0.854 Y1.290 F10 (should be F9.843 for direct conversion but F10 is close enough)

In the machine shop we use decimals and follow drawings or sketches and rarely does CAD produce 7 5/16 although it can.

Now in the wood working shop it can be a bit more difficult if the tape measure is only imperial or the drawing of that night stand has a width of 14 5/32".
But there my table saw fence is marked off in both units. I have a tape measure with both units so I use the scale that matches the drawing. And again I'm following a drawing.

But you are right. I have to think harder to envision metric distances for 2x4's which aren't 2x4 so that imperial stuff is kind of crap anyway. I still have to measure the board to find out what it's dried and planed size is. And as likely metric would work just as easily. I switch back and forth on the Mitutoya when I'm checking something to see if what I picked up is metric or imperial.

I'll leave it at that.
 
I still think in inches etc. I no longer think about temperatures in deg F, only C. Things would be easier if Everyone would simply get on the metric bandwagon.

I love the simplicity of Altium "Q" toggles between inches and metric and many of the dialogs show both units.
 
slow-poke said:
I still think in inches etc. I no longer think about temperatures in deg F, only C. Things would be easier if Everyone would simply get on the metric bandwagon.

I love the simplicity of Altium "Q" toggles between inches and metric and many of the dialogs show both units.
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Hmmm. Didn't know that Altium does that. Have to try that on the next board design.
The only reason stores have the larger text for prices in pounds is for the same reason items are priced at $2.99 (but without all tax in). Conn the buyer into thinking something is cheap.

Here in BC the private liquor stores started posting their prices without any of the taxes making it look like their stuff was cheaper than the BCLB. That's because at the time other than PST/GST the BCLB included the other taxes. So they moved backwards and now also show the price w/o taxes and sure enough the private stores are more expensive.

On our trip to the UK two interesting observations. Like most of Europe the price you see is the price you pay all inclusive. The receipt shows the taxes at the bottom so you do know what the taxes were but there's no surprise at the till.

Even more interesting was the number of places that no longer accept cash at all. That was a surprise. I think here in Canada it's still a law that Canadian currency must be accepted.
 
I agree it would be "simple" to switch over to metric but, for example, teaching in a mechanical engineering college course, we have enormous amounts of tooling and measuring tools in imperial and simply don't have the budget to purchase everything in metric. Although we have started certain designs in metric, 90% of the hardware on hand is all imperial (nuts, bolts, SHCS, washers, dowel pins, etc ...). Even in my home garage, it's a financial challenge to work in metric when all my tooling acquired over the years has been imperial. Just my 2% (imperial units :))
 
lucsimoneau said:
I agree it would be "simple" to switch over to metric but, for example, teaching in a mechanical engineering college course, we have enormous amounts of tooling and measuring tools in imperial and simply don't have the budget to purchase everything in metric. Although we have started certain designs in metric, 90% of the hardware on hand is all imperial (nuts, bolts, SHCS, washers, dowel pins, etc ...). Even in my home garage, it's a financial challenge to work in metric when all my tooling acquired over the years has been imperial. Just my 2% (imperial units :))
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I've slowly started moving to metric. Buying packages of screws and nuts when I need only a couple. Over time my inventory will be up where I can do everything in metric. Like it or not much of what needs repair now uses metric anyway.

My Robot Arm project has drawings in metric and sometimes with dual dimensions. My mill still has imperial ACME lead screws but once I change to ball screws I'll change the mill HAL and INI files so the machine becomes metric by default.

One of the reasons we ballroom dance is that sort of dancing addresses a large number of different areas of the brain and body. Physical exercise, music, memory, rapid decision making, learning new things, social interaction both with partner and other dancers. All are important to warding off dementia.

Learning how to do new things differently as in metric verses imperial is just another thing that stimulates parts of the brain building new pathways or reinforcing less used ones. So grumble as I might about metric sometimes I like the challenge.
 
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It’s all fun and games until you have to explain to a new engineer that a metric drawing showing a 9.525 x 1.5875 UNC bolt is not proper terminology, and sending that drawing out to the fab shop might be a lifelong source of hazing.
 
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