Metric measurements versus fractional - RC Groups
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Dec 21, 2009, 11:44 AM
Registered User

Metric measurements versus fractional

I often get a plan from my eastern European friend that was done in metric units of centimeters or MM. For it to be avaialblein USA I then have to convert a few things over to fractional sizes.

I have been using the Paperspace option (with the XP sub-option) for this in Autocad before I get going to a plot then. Involves a few K in size but works easy enough for me.

Do other users here have another routine to convert metric to fractional?

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Dec 21, 2009, 01:06 PM
Jim C Patrick
jcpatrick's Avatar
Scale the drawing and set the units to inches. Alternatively, you could set the units to inches and scale the drawing. ;-)
Dec 21, 2009, 01:18 PM
Gutless wonder
Guz's Avatar
Personally, I would just leave it alone. The US is one of three countries that still hold on to the old system.

Ever since I bailed and started using the metric side of my rulers, it's been so much easier to build things. The only hurdle that was somewhat difficult to overcome was drill bits, but I since finally broke down and ordered a set of metric drill bits life has been good.
Dec 21, 2009, 05:22 PM
B for Bruce
BMatthews's Avatar
I'd LOVE to use the metric system. It's so much easier overall. Sadly though since our balsawood supplies come from "that last bastion of Imperial measurements" (USA) I just go with the flow and stick with inches.

Canada went officially metric quite a while ago but there's still lots of imperial tools and supplies. Drill bit sets, for example, are still all fractional at most stores. You have to ASK for metric and at the smaller hardware stores there's no guarantee they have them. There's pleanty of other similar examples as well like screws, nuts and bolts. There's a metric section for them but it's seldom as big or well stocked as the fractional size area.
Dec 21, 2009, 05:59 PM
Prop Buster Extraordinaire
philba's Avatar
I was born and raised on the imperial system but have gotten to the point where I am comfortable with both metric and imperial. If something started metric, I just use it that way. Same for imperial. When I start a new design, a lot depends on the material I'm going to use. If it's foam, I use metric but if I'm using, for example, wood from the local lumber store then I'll use imperial. Metric is easier to use, though. When using imperial, I try to leave fractional inches as decimal - makes it a lot easier calculating a mid point for example.

I have memorized a number of conversions - 25.4 mm is 1 inch, 3/8 inch is a shade less than 1 cm. That helps speed things along.

For drill bits, I made up a chart, printed it out and refer to it all the time. I also use my electronic calipers on bits pretty frequently.
Dec 21, 2009, 06:00 PM
Reduce the drama...
rick.benjamin's Avatar
I keep a three column "cheat sheet" nearby.
Fraction, Decimal, metric.
Dec 21, 2009, 06:54 PM
Reduce the drama...
rick.benjamin's Avatar
an online conversion chart
Dec 21, 2009, 11:57 PM
Registered User
Joe'n Kody's Avatar
I hate and detest metric and I used to teach metric when I worked at college for 14 years!
To use millimeters for measuring lengths is only just ok and should be the proper unit for doing so up to 50 m. Centimeters is a load of rubbish! Meters are too big for small engineering drawings 'cos the decimal point is a nightmare.
Balsa that's made in "metric" is a pain. 3mm is often too small to replace 1/8". 6mm is the same, too small, its .014" undersize. 8mm is ok as 5/16". 9mm is not 3/8", nor is 10mm. 9.5mm equals .374", the only close conversion to any metric unit along with 0.8mm which is .031" or 1/32". You cant buy balsa in the proper sizes anymore. even the lengths are wrong, 1200mm is 3/4" short of 4'.
What I really hate is trying to understand the infernal units. eg, What's a pascal? Whats a megapascal? How does it compare to pounds? What about newtons? how many newtons does your plane exert? NO WAY. I hate metric. Kids at school have been deprived of the ability to "think" and work things out. I might be an old fuddy duddy but my brain is as sharp as a tack! Don't get me started on metric threads! or Liters for volume
When Australia went metric the conversion was litteraly overnight. This change almost sent the country broke. If any idiotic politition wants to change to metric in the US, take him (or her) out the back and help him change his mind using the leg bone from a roo or an emu.
So to work with a metric drawing, the best way as already suggested is to change the units of the drawing. This is easy to do by drawing a short line about 30mm long. Draw a verticle line near one end and then copy the line spaced 25.4mm away. Set the units to this measurement and call it "1.000". The zeros' aren't necessary but it looks better. All the dimensions will now be in the correct units, ie. Inches!!
Sometimes I will copy a drawing I see in a magazine and reproduce it on my Cad program. To do this I use my vernier calipers (I wish I had a digital set) but measure everything in mm's. This is the only time I use metric. Its because the eyes don't read the thous on the inch side of the vernier like they used to. I reproduce the drawing then change the units to inches as above. I then change the units to the actual dimensions I want and then print out the full size drawing. This works really great (for me anyway). My next projects will be the drawings for the sailplane "Paragon" and the fabulous .049 powered "TD Special". Doing this preserves the original drawing as best as I am able.
Hey Kody! What do you think of metrics?
Her reply ........

Dec 22, 2009, 07:13 AM
Closed Account
Metric measurements versus fractional The fractional measuring system is O.K. when your assembling things with a hammer. However, for other then material sizes and working in fractions less then 1/16th of an inch, I convert to decimals. Been working with the decimal system for a long time and it is just easier for me to think in this way.

As someone has said; converting is a simple equation and there are nice charts available for quick reference.
Dec 22, 2009, 08:29 AM
Registered User
Fractional?? Every thing has fractions including metrics. I do not believe "fractional" is a defined method of measurements, are you confusing it with Imperial or some other definition of measurements? i.e. a 1/4 inch is fractional, a 1/10 gallon is fractional, 1/8 meter is fractional but a foot, an inch, a yard etc. is not fractional.
Dec 22, 2009, 09:13 AM
Closed Account
Originally Posted by Rodney
Fractional?? Every thing has fractions including metrics. I do not believe "fractional" is a defined method of measurements, are you confusing it with Imperial or some other definition of measurements? i.e. a 1/4 inch is fractional, a 1/10 gallon is fractional, 1/8 meter is fractional but a foot, an inch, a yard etc. is not fractional.
Fractional is most certainly a "Defined method of measurement" What is 22' 5 & 5/8", if not a fractional method of measurement? The inch is divided into fractions: 1/2, 1/4, 1/8, 1/16, 1/32, 1/64, etc. The foot is divided into 12ths, the yard dived into 1/3rds and 1/36ths! The meter is divided into 1/10ths, 1/100ths, 1/1000ths, etc.

You lost me Rodney, I don't understand where your coming from!
Last edited by Mode One; Dec 22, 2009 at 09:20 AM.
Dec 22, 2009, 01:57 PM
Registered User
No, metric is a system of measurement based on meters, grams etc., imperial is a system of measurement based on feet, pounds etc.

Fractional is just a notational scheme equally applicable to either. 17.563 miles is as meaningful as 17.563 mm. One and five sixteenths of an inch is no more meaningful than one and five sixteenths of a metre.

Decimal notation is most common in any engineering situation these days whether the base units are metric or imperial. Fractional notation is only still retained where, for some perverse reason, materials are still made in historical sizes.

Converting a drawing from metric to imperial will not generally automatically produce fractional notation. A line 300 mm long will become 11.8110 inches not 11 and 13/16ths (give or take a bit) .

Dec 22, 2009, 02:10 PM
Registered User
Buran's Avatar
The metric system is far superior. It doesn’t get any simpler than base ten. What the heck do inches, feet, yards, ounces, and pounds relate to? When you study the sciences and advanced math, you WILL appreciate the metric system. I don’t see the U.S. changing anytime soon; we’re simply too lazy.
Dec 22, 2009, 03:34 PM
Registered User
Yep, every time I .....CAN... use metric, I do. Lots easier for this 70 year old mind to use than 1/32nds; 3/64ths; 5/8ths... etc.

No logic at all to stay with imperial and most countries have already seen the light..... Rich
Dec 22, 2009, 04:33 PM
Closed Account
The reason the U.S. hasn't converted to metric, is the cost of measuring equipment, not laziness. A lot of money has been invested in the inch. The fact that the machine trades are in the "toilet" during this recession and also that most new mics and calipers and other measuring equipment and automobiles can be converted to metric measurement by pressing a button should make the conversion a simple matter. Why it hasn't taken place is a good question, I think it was supposed to have happened in 1989! Maybe it's because your gov't doesn't want to spend your tax dollars on speed limit and distance signs. My guess would be this would be a significant cost!

Buran, could you explain to me the significance of the length of a meter and why this length is so much better then the length of a foot? Yes, working in multiples of tens is a better system, without doubt. However, now we are overlooking the nautical mile, which is a universal measurement equaling one minute of arc of latitude along any meridian. Certainly the metric system does not fit this system, which is used to describe where on Earth you are. 360 degrees doesn't make sense, either. Go out into space and now you have astronomical units and light years. You can go on and on with this stuff!
Last edited by Mode One; Dec 22, 2009 at 04:55 PM.

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