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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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Dimensions in CAD with fractions.
My company occasionally receives customer CAD files that have all or
most dimensions in inch fractions. What puzzles me is that when I convert the fractions to decimal inches, the actual values turn out to be only approximations of the fractions. On one drawing, there was a line of holes regularly spaced and dimensioned fractionally from one end. Based on the fractions, the spacing seemed to be 6-11/32" hole to hole. After I converted the fractions to decimal, the location of each hole from the end was not an exact decimal equivalent and the hole to hole spacing was from 6.3405 to 6.3445". The distances didn't get progressively longer, just wandered around the decimal equivalent of 6-11/32". In another case on the same drawing, several hole diameters were given as 1/8", yet changing it to decimal showed one line of holes to be .173" and another on the same part .117". Why does this happen? How do you input 1/8" and get something other than ..125"? David |
#2
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Dimensions in CAD with fractions.
"David R. Birch" fired this volley in news:kpbaf301fl7
@news1.newsguy.com: Why does this happen? How do you input 1/8" and get something other than .125"? I've never seen a CAD that screwed up things that badly. Usually, it's a matter of setting the decimal precision for the app. If you call out to two places, and use fraction conversions, they'll never be right. But if you call out to three places, enter 1/8" and get something other than 0.125, then you have a very very defective chunk of junkware. Note that many 'normal' fractional sizes go out to five places right of the decimal (that last place usually is a '5'). LLoyd |
#3
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Dimensions in CAD with fractions.
"David R. Birch" wrote in message ...
My company occasionally receives customer CAD files that have all or most dimensions in inch fractions. What puzzles me is that when I convert the fractions to decimal inches, the actual values turn out to be only approximations of the fractions. On one drawing, there was a line of holes regularly spaced and dimensioned fractionally from one end. Based on the fractions, the spacing seemed to be 6-11/32" hole to hole. After I converted the fractions to decimal, the location of each hole from the end was not an exact decimal equivalent and the hole to hole spacing was from 6.3405 to 6.3445". The distances didn't get progressively longer, just wandered around the decimal equivalent of 6-11/32". In another case on the same drawing, several hole diameters were given as 1/8", yet changing it to decimal showed one line of holes to be .173" and another on the same part .117". Why does this happen? How do you input 1/8" and get something other than ..125"? David If you don't mind my asking, and of course I have no intention of trying to tell you your business, but is the intention for you to use those CAD files to run a CNC machine? Or are you getting a *drawing* that was created on a CAD system. If it's intended to be CNC input, I see that you (and your customer!) have a serious problem with the customer's input. You just won't get a good part. But if it's a drawing, as I understand things isn't it your responsibility to work from the callouts and not try to scale from the drawing? I'm no machinist, but the machinists to whom I give CAD drawings in DXF format for prototyping or one-off production refuse to scale from the drawing, but instead work exclusively from the called-out dimensions. Which is good, because sometimes I purposefully put out-of-scale dimensions on the drawing (and this is a specific answer to your how does it happen question), which I do, in TurboCad anyway, by merely clicking on the dimension on the screen, and just editing the dimension to whatever I've decided to change it to. If I change my mind about a hole size, I might just for instance change a 1/8D typ. to a 3/16D typ., without bothering to redraw the circles to a different size, if I even actually put circles on the drawing instead of just crosses. I use TurboCad myself, most of the time. When you tell the thing how "fractional" you want the dimensions to be displayed at (16ths, 32nds, etc.) the software rounds the displayed dimension to the nearest such fraction even if the actual decimal dimension isn't exact (this behavior is a design flaw in my opinion). I have to set it to snap to the fractional dimension in order for the points or lines or whatever to lie right on the correct decimal equivalent. Tom |
#4
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Dimensions in CAD with fractions.
"David R. Birch" wrote in message
... My company occasionally receives customer CAD files that have all or most dimensions in inch fractions. What puzzles me is that when I convert the fractions to decimal inches, the actual values turn out to be only approximations of the fractions. ... Why does this happen? How do you input 1/8" and get something other than .125"? David It may be an accumulation of rounding errors. I've had to manually reconstruct the intended location of features dimensioned as two-place decimals obviously converted from fractions, 0.62" for instance, and make sure the sum of dimensions equalled the (ref) length of the part. That was trial-and-error detective work. A friend at Saco did that for the 50 cal machine gun that John Browning originally dimensioned to 1/128". It's helped to learn the fractional and metric conversions, so I recognize that the 0.434" I measured on an old South Bend part the other day was 7/16" minus a production tolerance, or 0.that 470" means 12mm. jsw |
#5
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Dimensions in CAD with fractions.
On Wed, 12 Jun 2013 21:23:30 -0500, "David R. Birch"
wrote: My company occasionally receives customer CAD files that have all or most dimensions in inch fractions. What puzzles me is that when I convert the fractions to decimal inches, the actual values turn out to be only approximations of the fractions. On one drawing, there was a line of holes regularly spaced and dimensioned fractionally from one end. Based on the fractions, the spacing seemed to be 6-11/32" hole to hole. After I converted the fractions to decimal, the location of each hole from the end was not an exact decimal equivalent and the hole to hole spacing was from 6.3405 to 6.3445". The distances didn't get progressively longer, just wandered around the decimal equivalent of 6-11/32". In another case on the same drawing, several hole diameters were given as 1/8", yet changing it to decimal showed one line of holes to be .173" and another on the same part .117". Why does this happen? How do you input 1/8" and get something other than .125"? David I can think of any number of ways to get that behavior, depending on the software. The most obvious is that the drafter placed the features by eye and the dims are rounded to the nearest 1/32. Or they were arrayed or placed on a grid and then unintentionally disturbed slightly. Are the drawings 2D cad drawings, or drawing views of a 3D model generated by a parametric modeller like Solidworks or Inventor? -- Ned Simmons |
#6
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Dimensions in CAD with fractions.
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#7
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Dimensions in CAD with fractions.
David R. Birch wrote:
My company occasionally receives customer CAD files that have all or most dimensions in inch fractions. What puzzles me is that when I convert the fractions to decimal inches, the actual values turn out to be only approximations of the fractions. On one drawing, there was a line of holes regularly spaced and dimensioned fractionally from one end. Based on the fractions, the spacing seemed to be 6-11/32" hole to hole. After I converted the fractions to decimal, the location of each hole from the end was not an exact decimal equivalent and the hole to hole spacing was from 6.3405 to 6.3445". The distances didn't get progressively longer, just wandered around the decimal equivalent of 6-11/32". You have to carry the decimal fraction to 5 places to keep roundoff error from accumulating. In another case on the same drawing, several hole diameters were given as 1/8", yet changing it to decimal showed one line of holes to be .173" and another on the same part .117". Why does this happen? How do you input 1/8" and get something other than .125"? I think you need to learn your CAD software better. Someting is just wrong, and I can't believe it is that broken. One possibility is this is a graphical CAD package, and the only data actually stored in the drawing is the LINES. The lines as shown on the screen are only approximations of the true data, smashed to fit onto the pixels of your screen. If it then makes dimensions off the on-screen representation, that would explain everything. This would not be considered a CAD package by most people, but a "DRAWING" package. Trying to use it for precision manufacturing drawings or the production of CAM data would be a big mistake. Jon |
#8
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Dimensions in CAD with fractions.
"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70... Jon Elson fired this volley in news:eP- : This would not be considered a CAD package by most people, but a "DRAWING" package. Hmmm... I never even considered he might be using a graphics package as an ersatz CAD... That would explain a lot. G Lloyd I recently had a friend who owns a similar contracting company to my own ask me if I would cut his logo in a piece of mahogany if he sent me a piece. What he wanted was in the working envelope of my CNC router, and wood cuts really fast so I agreed. (roughing at 200-250 and finishing at 100-150ipm) He's helped me out a few times so I told him if he sent me good drawings to work from I'ld just do it for him. After about the 9th or 10th redraw and the millionth lost line fragment or shape gap I just redid the whole thing for him and never told him. It was painfully obvious he was using something like Coreldraw with snaps turned off and a low precision levels set that would export DXF files of whatever crap it was fed. To be fair, I used Coreldraw as 2D CAD years ago and produced some of the self same crap until I learned how to use it. It look great on a page, but drove you to frustration if you tried to use it as anything other than a computer image. |
#9
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Dimensions in CAD with fractions.
"David R. Birch" on Wed, 12 Jun 2013 21:23:30 -0500
typed in rec.crafts.metalworking the following: My company occasionally receives customer CAD files that have all or most dimensions in inch fractions. What puzzles me is that when I convert the fractions to decimal inches, the actual values turn out to be only approximations of the fractions. On one drawing, there was a line of holes regularly spaced and dimensioned fractionally from one end. Based on the fractions, the spacing seemed to be 6-11/32" hole to hole. After I converted the fractions to decimal, the location of each hole from the end was not an exact decimal equivalent and the hole to hole spacing was from 6.3405 to 6.3445". The distances didn't get progressively longer, just wandered around the decimal equivalent of 6-11/32". In another case on the same drawing, several hole diameters were given as 1/8", yet changing it to decimal showed one line of holes to be .173" and another on the same part .117". Why does this happen? How do you input 1/8" and get something other than .125"? depends on if you have small values of .125 and large values of 1/8" Or more exactly - precision of the actual dimension is enough to generally fit into the 1/8" spec. Alternatively, the drawing may "read" 1/8", but the actual dimension is something else. (I know I can override dimensions in AutoCAD, so that a dimension showing on screen/paper is correct, but the measurement isn't.) Thirdly, you may have a conversion error somewhere along the way, from when they converted the measurement into fractional inches, to how it was stored in the file, to how it is converted into the CAD s/w you use. David -- pyotr filipivich "With Age comes Wisdom. Although more often, Age travels alone." |
#10
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Dimensions in CAD with fractions.
"Jim Wilkins" on Thu, 13 Jun 2013 10:16:31
-0400 typed in rec.crafts.metalworking the following: It may be an accumulation of rounding errors. I've had to manually reconstruct the intended location of features dimensioned as two-place decimals obviously converted from fractions, 0.62" for instance, and make sure the sum of dimensions equalled the (ref) length of the part. That was trial-and-error detective work. We was told that some drawings will have .13 (etc) where it is actually .125 "but everyone knows that" and the dimension precision is held to 0.00 because it is cheaper than 0.000. A friend at Saco did that for the 50 cal machine gun that John Browning originally dimensioned to 1/128". Yikes. It's helped to learn the fractional and metric conversions, so I recognize that the 0.434" I measured on an old South Bend part the other day was 7/16" minus a production tolerance, or 0.that 470" means 12mm. 12mm =.472 - they're cheating, again. -- pyotr filipivich "With Age comes Wisdom. Although more often, Age travels alone." |
#11
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Dimensions in CAD with fractions.
On 6/12/2013 10:23 PM, David R. Birch wrote:
My company occasionally receives customer CAD files that have all or most dimensions in inch fractions. What puzzles me is that when I convert the fractions to decimal inches, the actual values turn out to be only approximations of the fractions. On one drawing, there was a line of holes regularly spaced and dimensioned fractionally from one end. Based on the fractions, the spacing seemed to be 6-11/32" hole to hole. After I converted the fractions to decimal, the location of each hole from the end was not an exact decimal equivalent and the hole to hole spacing was from 6.3405 to 6.3445". The distances didn't get progressively longer, just wandered around the decimal equivalent of 6-11/32". In another case on the same drawing, several hole diameters were given as 1/8", yet changing it to decimal showed one line of holes to be .173" and another on the same part .117". Why does this happen? How do you input 1/8" and get something other than .125"? David As others have said, I think that the displayed dimensions have been added manually, rather than reflect how the objects were put down. The design was probably down by a that-looks-about-right approach and then the dimensions added manually, rather than asking the CAD app to display what it has in its data base/file. So, when you "... [changed] it to decimal ...", the CAD goes to it's data & displays it in decimal. It doesn't convert the manually added dimension. If you now went back and changed it to fractions it would show the fractional value of its data (e.g. 3/16 for .173), _not_ the 1/8. The 1/8 is a "note" that is gone (unless UNDO can bring it back) - I hope you have a copy of the original file. As to the 6-11/32 dimension: what do you mean that it "seemed" to be that? Was it called out/dimensioned that or what? Again, like the 1/8 hole, when you convert to decimal, the program goes back to the design data, which may or may not be 6-11/32 You need to clarify this mode of communication with your customer. It seems as though he is using the CAD file for its display value. I.e., he expects you to print it out & build to the drawing. In which case you would have to convert the fractions to decimal independently of the CAD program and add them to the drawing. Or, if you need a file for CNC, build it from scratch, using the fractions as shown on his original drawing. Bob |
#12
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Dimensions in CAD with fractions.
"pyotr filipivich" wrote in message
... "Jim Wilkins" on Thu, 13 Jun 2013 10:16:31 It's helped to learn the fractional and metric conversions, so I recognize that the 0.434" I measured on an old South Bend part the other day was 7/16" minus a production tolerance, or that 0 470" [typo fixed] means 12mm. 12mm =.472 - they're cheating, again. pyotr filipivich 0.470" as measured. I didn't have to deal with pre-CNC metric drawings, only figure out whether optical bench and electronic equipment had been made inch or metric. 8, 11, 14, 16 and 19mm are very close to commonly used fractional sizes. jsw |
#13
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Dimensions in CAD with fractions.
"Jim Wilkins" on Fri, 14 Jun 2013 10:05:17
-0400 typed in rec.crafts.metalworking the following: "pyotr filipivich" wrote in message .. . "Jim Wilkins" on Thu, 13 Jun 2013 10:16:31 It's helped to learn the fractional and metric conversions, so I recognize that the 0.434" I measured on an old South Bend part the other day was 7/16" minus a production tolerance, or that 0 470" [typo fixed] means 12mm. 12mm =.472 - they're cheating, again. pyotr filipivich 0.470" as measured. I didn't have to deal with pre-CNC metric drawings, only figure out whether optical bench and electronic equipment had been made inch or metric. 8, 11, 14, 16 and 19mm are very close to commonly used fractional sizes. Yep - as a car mechanic who learned on VWs, I am well aware of those B-) jsw -- pyotr filipivich "With Age comes Wisdom. Although more often, Age travels alone." |
#14
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Dimensions in CAD with fractions.
On Thu, 13 Jun 2013 14:10:58 -0500, Jon Elson
wrote: David R. Birch wrote: My company occasionally receives customer CAD files that have all or most dimensions in inch fractions. What puzzles me is that when I convert the fractions to decimal inches, the actual values turn out to be only approximations of the fractions. On one drawing, there was a line of holes regularly spaced and dimensioned fractionally from one end. Based on the fractions, the spacing seemed to be 6-11/32" hole to hole. After I converted the fractions to decimal, the location of each hole from the end was not an exact decimal equivalent and the hole to hole spacing was from 6.3405 to 6.3445". The distances didn't get progressively longer, just wandered around the decimal equivalent of 6-11/32". You have to carry the decimal fraction to 5 places to keep roundoff error from accumulating. In another case on the same drawing, several hole diameters were given as 1/8", yet changing it to decimal showed one line of holes to be .173" and another on the same part .117". Why does this happen? How do you input 1/8" and get something other than .125"? I think you need to learn your CAD software better. Someting is just wrong, and I can't believe it is that broken. One possibility is this is a graphical CAD package, and the only data actually stored in the drawing is the LINES. The lines as shown on the screen are only approximations of the true data, smashed to fit onto the pixels of your screen. If it then makes dimensions off the on-screen representation, that would explain everything. This would not be considered a CAD package by most people, but a "DRAWING" package. Trying to use it for precision manufacturing drawings or the production of CAM data would be a big mistake. Jon True indeed! -- "You guess the truth hurts? Really? "Hurt" aint the word. For Liberals, the truth is like salt to a slug. Sunlight to a vampire. Raid® to a cockroach. Sheriff Brody to a shark Bush to a Liberal The truth doesn't just hurt. It's painful, like a red hot poker shoved up their ass. Like sliding down a hundred foot razor blade using their dick as a brake. They HATE the truth." |
#15
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Dimensions in CAD with fractions.
On 6/13/2013 2:10 PM, Jon Elson wrote:
David R. Birch wrote: My company occasionally receives customer CAD files that have all or most dimensions in inch fractions. What puzzles me is that when I convert the fractions to decimal inches, the actual values turn out to be only approximations of the fractions. On one drawing, there was a line of holes regularly spaced and dimensioned fractionally from one end. Based on the fractions, the spacing seemed to be 6-11/32" hole to hole. After I converted the fractions to decimal, the location of each hole from the end was not an exact decimal equivalent and the hole to hole spacing was from 6.3405 to 6.3445". The distances didn't get progressively longer, just wandered around the decimal equivalent of 6-11/32". You have to carry the decimal fraction to 5 places to keep roundoff error from accumulating. Rounding error isn't going to turn one 6-11/32 length to to 6.3446 and the next to 6.3417. In another case on the same drawing, several hole diameters were given as 1/8", yet changing it to decimal showed one line of holes to be .173" and another on the same part .117". Why does this happen? How do you input 1/8" and get something other than .125"? I think you need to learn your CAD software better. I know my software just fine, the problem is in the drawings we're getting. Someting is just wrong, and I can't believe it is that broken. Exactly, and the reason I'm asking is that I also can't believe it is that broken and I also can't imagine how I could duplicate the distortion. How did he do that and what can I tell him to make him stop? One possibility is this is a graphical CAD package, and the only data actually stored in the drawing is the LINES. The lines as shown on the screen are only approximations of the true data, smashed to fit onto the pixels of your screen. If it then makes dimensions off the on-screen representation, that would explain everything. This would not be considered a CAD package by most people, but a "DRAWING" package. Trying to use it for precision manufacturing drawings or the production of CAM data would be a big mistake. Jon You're talking about the raster output of a graphics package vs. the vector output of CAD software. What we are receiving is a vector AutoCAD DWG drawing with the dimensions all in inches and fractions of inches, but the values of those fractions are not precise decimal equivalents, or even consistently skewed. David |
#16
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Dimensions in CAD with fractions.
On 7/16/2013 12:12 AM, Richard wrote:
On 6/15/2013 10:26 PM, David R. Birch wrote: I think you need to learn your CAD software better. I know my software just fine, the problem is in the drawings we're getting. Someting is just wrong, and I can't believe it is that broken. Exactly, and the reason I'm asking is that I also can't believe it is that broken and I also can't imagine how I could duplicate the distortion. How did he do that and what can I tell him to make him stop? You're talking about the raster output of a graphics package vs. the vector output of CAD software. What we are receiving is a vector AutoCAD DWG drawing with the dimensions all in inches and fractions of inches, but the values of those fractions are not precise decimal equivalents, or even consistently skewed. David The question is, from where are the dimensions referenced? Are they all referenced from a common point? They were all referenced from the same end of the parts. Similar dimensions for each part from one end, but not consistent spacing and the inconsistency wasn't consistent from part to part. Or are they referenced - from each other? Nope. A string of points that reference from a single point should line up just they wan one would expect. In engineering, yes, I think this was done by someone with an architectural background. But what it sounds like is a string of points chained together from one to the next - with rounding errors. Or? They were just located by eye... The annoying thing is that they are close to location, but not close enough for the various parts to actually fit together when assembled. Ask the draftsman to practice saying, "you want fries with that?"... No, if they have a degree, they say " would you like some fresh ground pepper on that?..." David |
#17
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Dimensions in CAD with fractions.
On Sat, 15 Jun 2013 22:26:23 -0500, "David R. Birch"
wrote: Exactly, and the reason I'm asking is that I also can't believe it is that broken and I also can't imagine how I could duplicate the distortion. As I and a couple other folks suggested earlier, the easiest way to explain it is the drafter placed the holes by eye and the dims are set to round to the nearest 1/32. Fractional dims in autocad can be set to round the displayed value anywhere from 1/2 to 1/256. How did he do that and what can I tell him to make him stop? That's a much more difficult question. -- Ned Simmons |
#18
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Dimensions in CAD with fractions.
On 6/15/2013 23:26, David R. Birch wrote:
On 6/13/2013 2:10 PM, Jon Elson wrote: David R. Birch wrote: My company occasionally receives customer CAD files that have all or most dimensions in inch fractions. What puzzles me is that when I convert the fractions to decimal inches, the actual values turn out to be only approximations of the fractions. On one drawing, there was a line of holes regularly spaced and dimensioned fractionally from one end. Based on the fractions, the spacing seemed to be 6-11/32" hole to hole. After I converted the fractions to decimal, the location of each hole from the end was not an exact decimal equivalent and the hole to hole spacing was from 6.3405 to 6.3445". The distances didn't get progressively longer, just wandered around the decimal equivalent of 6-11/32". You have to carry the decimal fraction to 5 places to keep roundoff error from accumulating. Rounding error isn't going to turn one 6-11/32 length to to 6.3446 and the next to 6.3417. In another case on the same drawing, several hole diameters were given as 1/8", yet changing it to decimal showed one line of holes to be .173" and another on the same part .117". Why does this happen? How do you input 1/8" and get something other than .125"? I think you need to learn your CAD software better. I know my software just fine, the problem is in the drawings we're getting. Someting is just wrong, and I can't believe it is that broken. Exactly, and the reason I'm asking is that I also can't believe it is that broken and I also can't imagine how I could duplicate the distortion. How did he do that and what can I tell him to make him stop? Make the part to the dimensions on the drawing, don't use the CAD dimensions, and don't convert. When his stuff doesn't work, and he still has to pay for it, he'll fix it. -- Steve Walker (remove brain when replying) |
#19
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Dimensions in CAD with fractions.
On 6/15/2013 10:26 PM, David R. Birch wrote:
I think you need to learn your CAD software better. I know my software just fine, the problem is in the drawings we're getting. Someting is just wrong, and I can't believe it is that broken. Exactly, and the reason I'm asking is that I also can't believe it is that broken and I also can't imagine how I could duplicate the distortion. How did he do that and what can I tell him to make him stop? You're talking about the raster output of a graphics package vs. the vector output of CAD software. What we are receiving is a vector AutoCAD DWG drawing with the dimensions all in inches and fractions of inches, but the values of those fractions are not precise decimal equivalents, or even consistently skewed. David The question is, from where are the dimensions referenced? Are they all referenced from a common point? Or are they referenced - from each other? A string of points that reference from a single point should line up just they wan one would expect. But what it sounds like is a string of points chained together from one to the next - with rounding errors. Or? They were just located by eye... Ask the draftsman to practice saying, "you want fries with that?"... |
#20
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Dimensions in CAD with fractions.
On Wednesday, June 12, 2013 at 10:23:30 PM UTC-4, David R. Birch wrote:
My company occasionally receives customer CAD files that have all or most dimensions in inch fractions. What puzzles me is that when I convert the fractions to decimal inches, the actual values turn out to be only approximations of the fractions. On one drawing, there was a line of holes regularly spaced and dimensioned fractionally from one end. Based on the fractions, the spacing seemed to be 6-11/32" hole to hole. After I converted the fractions to decimal, the location of each hole from the end was not an exact decimal equivalent and the hole to hole spacing was from 6.3405 to 6.3445". The distances didn't get progressively longer, just wandered around the decimal equivalent of 6-11/32". In another case on the same drawing, several hole diameters were given as 1/8", yet changing it to decimal showed one line of holes to be .173" and another on the same part .117". Why does this happen? How do you input 1/8" and get something other than .125"? David |
#22
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Dimensions in CAD with fractions.
"Martin Eastburn" wrote in message
... How can you tell. Print it out at what scale ? and what precision. Don't guess and measure with a ruler. Use a mouse and the CAD file and have the Cad program measure it. CAD might scale a Tabloid into 11/17 with 3/8 borders or anything. It is relative. When 1:1 you normally use D and E size paper and make sure the CAD is printing at only 1"=1" or 10" or 5 or some even number. Cad fits a drawing into the paper size and the scale of ink vs Tube vs planned is always off. Martin The X and Y scales of a paper print may differ because separate mechanisms control them. |
#23
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Dimensions in CAD with fractions.
On 3/24/2019 11:53 PM, Martin Eastburn wrote:
How can you tell.Â* Print it out at what scale ?Â*Â* and what precision. Don't guess and measure with a ruler.Â* Use a mouse and the CAD file and have the Cad program measure it.Â* CAD might scale a Tabloid into 11/17 with 3/8 borders or anything.Â* It is relative.Â* When 1:1 you normally use D and E size paper and make sure the CAD is printing at only 1"=1" or 10" or 5 or some even number. Cad fits a drawing into the paper size and the scale of ink vs Tube vs planned is always off. Martin On 3/22/2019 5:03 PM, wrote: On Wednesday, June 12, 2013 at 10:23:30 PM UTC-4, David R. Birch wrote: My company occasionally receives customer CAD files that have all or most dimensions in inch fractions. What puzzles me is that when I convert the fractions to decimal inches, the actual values turn out to be only approximations of the fractions. On one drawing, there was a line of holes regularly spaced and dimensioned fractionally from one end. Based on the fractions, the spacing seemed to be 6-11/32" hole to hole. After I converted the fractions to decimal, the location of each hole from the end was not an exact decimal equivalent and the hole to hole spacing was from 6.3405 to 6.3445". The distances didn't get progressively longer, just wandered around the decimal equivalent of 6-11/32". In another case on the same drawing, several hole diameters were given as 1/8", yet changing it to decimal showed one line of holes to be .173" and another on the same part .117". Why does this happen? How do you input 1/8" and get something other than .125"? David I posted this question almost 6 years ago and I don't remember whether I got any response. I received AutoCAD compatible files from a customer, either DWG or DXF, I don't remember which. The files were fractionally dimensioned, but when I checked the dims in AutoCAD, as we always did with customer CAD, I found the discrepancies as described above. There was no hard copy involved in this. David --- This email has been checked for viruses by AVG. https://www.avg.com |
#24
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Dimensions in CAD with fractions.
On 3/25/2019 7:39 AM, Jim Wilkins wrote:
"Martin Eastburn" wrote in message ... How can you tell. Print it out at what scale ? and what precision. Don't guess and measure with a ruler. Use a mouse and the CAD file and have the Cad program measure it. CAD might scale a Tabloid into 11/17 with 3/8 borders or anything. It is relative. When 1:1 you normally use D and E size paper and make sure the CAD is printing at only 1"=1" or 10" or 5 or some even number. Cad fits a drawing into the paper size and the scale of ink vs Tube vs planned is always off. Martin The X and Y scales of a paper print may differ because separate mechanisms control them. I posted this question almost 6 years ago and I don't remember whether I got any response. I received AutoCAD compatible files from a customer, either DWG or DXF, I don't remember which. The files were fractionally dimensioned, but when I checked the dims in AutoCAD, as we always did with customer CAD, I found the discrepancies as described above. There was no hard copy involved in this. David --- This email has been checked for viruses by AVG. https://www.avg.com |
#25
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Dimensions in CAD with fractions.
"David R. Birch" wrote in message
... On 3/25/2019 7:39 AM, Jim Wilkins wrote: "Martin Eastburn" wrote in message ... How can you tell. Print it out at what scale ? and what precision. Don't guess and measure with a ruler. Use a mouse and the CAD file and have the Cad program measure it. CAD might scale a Tabloid into 11/17 with 3/8 borders or anything. It is relative. When 1:1 you normally use D and E size paper and make sure the CAD is printing at only 1"=1" or 10" or 5 or some even number. Cad fits a drawing into the paper size and the scale of ink vs Tube vs planned is always off. Martin The X and Y scales of a paper print may differ because separate mechanisms control them. I posted this question almost 6 years ago and I don't remember whether I got any response. I received AutoCAD compatible files from a customer, either DWG or DXF, I don't remember which. The files were fractionally dimensioned, but when I checked the dims in AutoCAD, as we always did with customer CAD, I found the discrepancies as described above. There was no hard copy involved in this. David --- This email has been checked for viruses by AVG. https://www.avg.com Maybe the points were manually "digitized" from a paper print. https://en.wikipedia.org/wiki/Graphics_tablet "It can also be used to trace an image from a piece of paper which is taped or otherwise secured to the tablet surface." "These digitizers were... bundled with PCs and PC-based CAD software like AutoCAD." |
#26
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Dimensions in CAD with fractions.
On 3/25/2019 5:12 PM, Jim Wilkins wrote:
Maybe the points were manually "digitized" from a paper print. https://en.wikipedia.org/wiki/Graphics_tablet "It can also be used to trace an image from a piece of paper which is taped or otherwise secured to the tablet surface." "These digitizers were... bundled with PCs and PC-based CAD software like AutoCAD." I think the files were generated from some kind of art program, maybe Corel Draw. The customer was a UWM art dept prof who knew little about manufacturing. He wanted the finished project for an industrial show, but he kept modifying what he wanted just before we thought we were ready to cut metal. His changes meant we went way over what we had quoted. No one was happy. The geometry was so bad that I ended using their CAD for reference only as I redrew what they showed and made something I could use to produce programs for our LASERs. --- This email has been checked for viruses by AVG. https://www.avg.com |
#27
Posted to rec.crafts.metalworking
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Dimensions in CAD with fractions.
"David R. Birch" wrote in message
... On 3/25/2019 5:12 PM, Jim Wilkins wrote: Maybe the points were manually "digitized" from a paper print. https://en.wikipedia.org/wiki/Graphics_tablet "It can also be used to trace an image from a piece of paper which is taped or otherwise secured to the tablet surface." "These digitizers were... bundled with PCs and PC-based CAD software like AutoCAD." I think the files were generated from some kind of art program, maybe Corel Draw. The customer was a UWM art dept prof who knew little about manufacturing. He wanted the finished project for an industrial show, but he kept modifying what he wanted just before we thought we were ready to cut metal. His changes meant we went way over what we had quoted. No one was happy. The geometry was so bad that I ended using their CAD for reference only as I redrew what they showed and made something I could use to produce programs for our LASERs. --- This email has been checked for viruses by AVG. https://www.avg.com If he assumed from a previous job that it would be manually machined or the G-code typed in then only the dimension numbers matter, the drawing could be a freehand sketch. Paper drafting practice was not to measure dimensions off the print, except in architecture. Circuit board artworks were taped or plotted on more dimensionally stable Mylar. |
#28
Posted to rec.crafts.metalworking
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Dimensions in CAD with fractions.
On 3/26/2019 6:06 PM, Jim Wilkins wrote:
"David R. Birch" wrote in message ... On 3/25/2019 5:12 PM, Jim Wilkins wrote: Maybe the points were manually "digitized" from a paper print. https://en.wikipedia.org/wiki/Graphics_tablet "It can also be used to trace an image from a piece of paper which is taped or otherwise secured to the tablet surface." "These digitizers were... bundled with PCs and PC-based CAD software like AutoCAD." I think the files were generated from some kind of art program, maybe Corel Draw. The customer was a UWM art dept prof who knew little about manufacturing. He wanted the finished project for an industrial show, but he kept modifying what he wanted just before we thought we were ready to cut metal. His changes meant we went way over what we had quoted. No one was happy. The geometry was so bad that I ended using their CAD for reference only as I redrew what they showed and made something I could use to produce programs for our LASERs. --- This email has been checked for viruses by AVG. https://www.avg.com If he assumed from a previous job that it would be manually machined or the G-code typed in then only the dimension numbers matter, the drawing could be a freehand sketch. Paper drafting practice was not to measure dimensions off the print, except in architecture. Circuit board artworks were taped or plotted on more dimensionally stable Mylar. As I originally said, we were sent AutoCAD compatible files, either DXF or DWG. I discovered the problem when I brought the files into our AutoCAD and found their dimensions did not match their numbers on their file. AFAIK, at no time were dimensions based on a physical measurement of anything, all we had was a CAD file. Also puzzling is the fact that the message posted on 3/22/19 is a reply to a message I left 6 years ago and there is no new text on the post from . Another note: all is moot, since I retired 5 years ago. David |
#29
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Dimensions in CAD with fractions.
It is simple simple. Draw a Ruler in Cad. A 10" by what sub divisions you
want. Print it on the paper you will use and with the same commands. Take paper to table and with a precision scale measure the drawing ruler. First the long 10" then 5" then 2.5 and down see what you get. Make it 1:1 and print normally - e.g. some printers have size to fit. NO. Martin On 3/25/2019 5:12 PM, Jim Wilkins wrote: "David R. Birch" wrote in message ... On 3/25/2019 7:39 AM, Jim Wilkins wrote: "Martin Eastburn" wrote in message ... How can you tell. Print it out at what scale ? and what precision. Don't guess and measure with a ruler. Use a mouse and the CAD file and have the Cad program measure it. CAD might scale a Tabloid into 11/17 with 3/8 borders or anything. It is relative. When 1:1 you normally use D and E size paper and make sure the CAD is printing at only 1"=1" or 10" or 5 or some even number. Cad fits a drawing into the paper size and the scale of ink vs Tube vs planned is always off. Martin The X and Y scales of a paper print may differ because separate mechanisms control them. I posted this question almost 6 years ago and I don't remember whether I got any response. I received AutoCAD compatible files from a customer, either DWG or DXF, I don't remember which. The files were fractionally dimensioned, but when I checked the dims in AutoCAD, as we always did with customer CAD, I found the discrepancies as described above. There was no hard copy involved in this. David --- This email has been checked for viruses by AVG. https://www.avg.com Maybe the points were manually "digitized" from a paper print. https://en.wikipedia.org/wiki/Graphics_tablet "It can also be used to trace an image from a piece of paper which is taped or otherwise secured to the tablet surface." "These digitizers were... bundled with PCs and PC-based CAD software like AutoCAD." |
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