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  #1  
Old Mon 27 November 2006, 23:33
Gerald_D
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Hi All,

I am trying to figure out how to make the drawings inch-friendly. Putting decimal inches on the drawings is easy, but you guys don't have decimal tape measures, or do you? Digital calipers/verniers make it okay for smaller dimensions to be decimal, but what do you do when something has to be 129.55 inches long? How do you read the .55" on a tape measure that is marked in 1/16" increments? Or, are you so good at mental calcs that you know .55" equals nearly 9/16" but not quite?

Bottom line question is: How do you want inch dimensions to be shown on the drawings?
  #2  
Old Tue 28 November 2006, 09:20
Bob Cole
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Gerald:
As for me though I work almost exclusively in inches, I think that due to the problems involved with converting mm to inches especialy where dimensions between fixed points is CRITICAL {ie. mounting holes for wheels, or motors} I will just have my machinist work in mm.

thanks,
Bob
  #3  
Old Tue 28 November 2006, 10:03
Gerald_D
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Bob, AutoCad does the conversion for me, so that is no problem. Hardly anything on the MechMate must be made very critically - lots of things are adjusted afterwards with shims, eccentrics or slotted holes. I am just curious how you guys do the coarse tape measure stuff??
  #4  
Old Tue 28 November 2006, 11:36
Greg Waggy
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Since .55" is almost 9/16" but not quite, I would move to the 9/16", it would just make that point a bit stronger, unless it's a hole very close to an edge of the steel, then I would drop down 1/2" since that is another very common size. So for me, you can just use the decimal equivalents.
  #5  
Old Tue 28 November 2006, 11:55
Gerald_D
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Greg, without consulting a calculator, what is your quick gut feel of the decimal equivalents of:

1/16"
5/16"
11/16"
13/16"?
  #6  
Old Tue 28 November 2006, 12:03
Greg Waggy
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1/16" = .0625
5/16" = .3125
11/16" = .6875
13/16" = .8125

All I did was take my .0625 and mulitply by the numerator. I had to do the math in my head but that wasn't so bad. LOL
  #7  
Old Tue 28 November 2006, 13:52
Gerald_D
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If you guys are that comfortable with decimal inches, why aren't decimal tape measures more common?


I get the impression that it is okay (indeed standard practice) for the drawings to specify increments which are not available on the standard measuring tools. Strange....
  #8  
Old Tue 28 November 2006, 13:56
Greg Waggy
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Gerald, I guess the decimal thing is more along the lines used by machinists and the normal tapes are for carpenters. Heck, I didn't know this one existed. I'll have to look into one of these. This would be a GREAT addition to my tool box.
  #9  
Old Tue 28 November 2006, 14:19
Bob Cole
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Gerald: et al
I am incorrect in my thinking? Using your motor plate profile as an example. M5 10 322D, the drilling of the mounting holes must be very exact in relationship to the center hole for the motor frame, as well as the relationship to all other mounting point holes. I can't bring myself to "fudge" a little on the American measurements. That is why I will try to build according to the metric plans. They are MUCH more precise only because that is the native measure for Gerald.

I am making this assumption because we are trying to maintain .001 tolerances on our routing are we not? therefore we need to be carefull in ALL areas of our construction? NO?
  #10  
Old Tue 28 November 2006, 20:48
Charlie Trouse
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The tape is cool. Like the poster above I will have the machinist work in mm so I dont need the conversion. I think its actually worse to have both on there, say a guy on Monday cuts half your job in metric Wednesdays guy decides to use the Inchs on the drawing. Now the mathheads would tell you its just a conversion and the machine "should" all fit together like nothing happened. But.. I dont want that would you? Base ten is better anyway.
  #11  
Old Tue 28 November 2006, 21:03
Greg Waggy
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Actually, if you are right handed, as most folks are, the metric side faces you for very easy reading. I guess if you have enough money for a machinist you wouldn't want to spend the $9.00 on a tape and do the building yourself. I find the most pleasure of being able to say I built it from scratch and it works than say I built it from scratch but someone else cut out all the parts and made them fit. You may as well just buy a ready made CNC machine and assemble it.

Also, I build the electronics as well, so if something does go wrong I can fix that too.

Gerald was just asking how he could make his drawings "inch friendly" and I don't think there really is a need since we can find measuring devices that will let us use the metric system without all the calculations. OR as he pointed out a decimal system. There are even fractural tapes out there.
  #12  
Old Tue 28 November 2006, 23:20
Charlie Trouse
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If I could grind nine foot side rails with a $9.00 tape you bet Id buy it and skip the machine shop.
  #13  
Old Tue 28 November 2006, 23:22
Ted Gustafson
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For me expressing inch dimensions in fractions just ends up making for more conversions. Express them as .001" or .0001". The one who does the cutting or machining of the parts will end up doing it anyway. A person may well change a dimension here to match a standard inch size for shafting, bearings or steel material size as supply dictates. Just try and go to a bearing supply house here a get a QD taper lock bushing for a 42mm shaft. I have no problem working of metric drawings and doing any conversions myself.

Greg is correct here a machinests rule is marked in .01" or .001" graduations (but then some are in 1/128th of an inch) and a carpenters tape in fractions of an inch. You learn to live with it.
  #14  
Old Tue 28 November 2006, 23:29
Greg Waggy
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Ted, The one I showed above is marked in cm and mm on one side so you wouldn't need to convert anything with that. WOW 1/128th of a inch? Can you see the spaces between the lines?
  #15  
Old Tue 28 November 2006, 23:33
Gerald_D
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Bob asked some good questions: "I am incorrect in my thinking? Using your motor plate profile as an example. M5 10 322D, the drilling of the mounting holes must be very exact in relationship to the center hole for the motor frame, as well as the relationship to all other mounting point holes. I can't bring myself to "fudge" a little on the American measurements. That is why I will try to build according to the metric plans. They are MUCH more precise only because that is the native measure for Gerald.

The center hole of that motor mount plate is NOT critical. The motor swivels on a hinge and rides springloaded against the rack. It could be off by 3mm [1/8"] and you are going to see no difference in the precision of your finish cut job. Literally, you get that plate from the laser cutting guy ($4), center punch the four holes on the marks that the laser guy made for you, drill 5mm, tap 6mm, de-burr, de-grease, paint primer, paint finish. It is not a machinist job, it is a $4 and 30 minute job for a weekend in the home garage.

"I am making this assumption because we are trying to maintain .001 tolerances on our routing are we not? therefore we need to be carefull in ALL areas of our construction? NO?"

0.001 tolerances for wood routing is a whole big subject by itself: Are you measuring to the tips or the valleys of the wood particles? On a hot or cold day? What moisture content? How much did the cutter bend? How much did the plywood bow (warp) when you cut the skin only on one side? Etc. Etc. Notice that none of the afore-mentioned issues have anything to do with the precision of the machine. ShopBot are so bold as to claim positional accuracies of about 0.005" - the MechMate should be better, but I am not going get drawn into stating an absolute figure.

No, you do not need to be careful in ALL areas of construction. (Where you need to most careful is with workshop safety - pushing those rails through a bandsaw scares the heck out of me!). You need to be very careful with the final setting up, particulary getting the rails straight and the wheels to run true and gantry to run square. For the rest, the actual components don't need a high inherent precision.
  #16  
Old Wed 29 November 2006, 00:15
Gerald_D
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As for the drawing side of things, I'll stick with decimal inches for lengths.

Thicknesses is another area....gauges...and probably fractional inches??

Another subject is "implied accuracy"; If I give a dimension to 3 decimal places in the metric world it normally means the measuring tool and accuracy of the job should be down to the 3rd decimal place. So I talk of 3mm or 4mm plate, but not of 3.0 or 4.0 mm thick plate. You guys talk of 0.0625" thick plate which actually means about 1/16" thick - no need to put a 0.0001" precision micrometer on that. My point is that the 0.0625" implies a precision that was never intended - which could make things extremely expensive to build. Precision = Cost.
  #17  
Old Wed 29 November 2006, 00:27
Greg Waggy
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Gerald, You are very kind and generous. I, for one, Thank you for sharing all your hard work and answering questions.
  #18  
Old Wed 29 November 2006, 19:05
Ted Gustafson
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Greg there was a time I could see marks like that but it has long passed.

"implied accuracy" is not an issue if the accuracy you want is stated on the drawing. That is what it is and it matters not if 1/16" =.0625" I know is seems odd to you that just work with mm but we can work things out here on this side of the swamp. If you gave me a dimension in mm for a part and the accuracy needed I could make it or have it made. If you tell me to make something out of 3mm plate I would make mine out of 1/8" plate and adjust things from there if there are stack up issues.

Gerald, The work you are doing here is top shelf in my book. You must enjoy what you are doing as it reflects a great deal of time and just hard work on your part. You are what Ham Radio Operators call an Elmer. (The term "Elmer"--meaning someone who provides personal guidance and assistance to would-be hams)
  #19  
Old Wed 29 November 2006, 19:25
Greg Waggy
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Ted, I am on the same side of the swamp (as you put it), so working in mm is foreign to me as well. I was just saying that there are methods and tools out there to help us Yanks out with out a lot of conversion on Gerald's part. He has been kind enough to break his drawings down to inches in decimal form, there are even tapes out there, as he pointed out, that have that scale on them.
  #20  
Old Tue 12 December 2006, 15:48
Donald Neisler
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In the plate the v rollers bolt on, it has the Note A, I have not researched the option of the two hole locations. Is one v-roller compared to the other harder to find or prefered over the other?
  #21  
Old Tue 12 December 2006, 21:39
Donald Neisler
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Any one built/building one using standard measurements. 2/4/5mm steel here is not easy to come by. Any major changes?
  #22  
Old Tue 12 December 2006, 23:05
Gerald_D
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Donald, re the rollers; some guys want to upgrade ShopBots and keep the smaller rollers that came with the SB - they need to use a smaller, lower hole.

Re sheet steel, what are your popular thicknesses?
  #23  
Old Wed 13 December 2006, 08:00
Donald Neisler
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1/4", 14g. 16g, and etc. The shop that is quoting think found all the metric stuff, just gonna cost a little more.
  #24  
Old Wed 13 December 2006, 09:35
Gerald_D
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For the 6mm stuff on drawings 1040434, M510312, and M510322, use 0.25" (1/4")

For the 5mm gantry and Y-car ends (1020454 & 1030450), use 0.1875" (3/16")

For the 4mm plates on drawings 1030455 & 1040432, do you have a standard thickness between 3/16" and 1/8"? Maybe 5/32"?

For the 3mm gantry ends (1020456), use 0.125" (1/8")

For the 2mm of the Y-Car (1020422), use 14 gauge
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