Metric to american

What is your rule for rounding up when converting the metric to mm?
I do not round in either direction, it is normally obvious what the designers intention is by the tolerance call out for each dimension.
If a bore dimension is .625" +.001 -.000 the intention is a diameter that under no circumstances be less then .625".

If you are concerned about the 4th decimal place you can already make parts in tenths and need not be asking questions here, a grinding forum would be a better place for such questions.
 
I just don't understand why this country refuses to go metric. The imperial system is archaic. We are just being Luddites on this issue. It is time we bite the bullet and made the change. The vast majority of our manufacturing companies could do it over night, if it weren't for there current inventories.
Randy
 
P.Waller i just ask bc some measurements like 4mm converted is .1574803. The book of drawings in metric does not have any tolerances. Since my work is all mainly imperial im new to converting everything over and not sure what type of tolerance i should use when converting. Should i round the conversion to the nearest tenth? I guess im asking for your opinion.
 
P.Waller i just ask bc some measurements like 4mm converted is .1574803. The book of drawings in metric does not have any tolerances. Since my work is all mainly imperial im new to converting everything over and not sure what type of tolerance i should use when converting. Should i round the conversion to the nearest tenth? I guess im asking for your opinion.
Do you use machines that have graduated dials that resolve to 7 decimal places?
If the answer is yes you are in the wrong forum, if no they are like most hobby machines that are graduated in .001" divisions, ask yourself this question, "Self, how do I remove a 7th decimal inch (1 millionth) amount of material with a 3 decimal reading machine". The short answer is that you can not do so. It is likely that you could not measure it if you did manage to do so.

If the tolerance call out is +-.002" then you have .002" on either side, if the tolerance is 3 decimal places this means that in this example .0029" is acceptable as it is not .003"

Very simple, in your example above I would call that .157"

If the drawings that you are working from have no tolerance on the dimensions then someone dropped the ball, do not try it.
 
Ok thank you. Exactly what i wanted to hear. I still have my machines in storage but ik the SB lathe is dials and my mill does have read out.
 
Ok thank you. Exactly what i wanted to hear. I still have my machines in storage but ik the SB lathe is dials and my mill does have read out.
Much like "digital calipers" many DROs use 4 decimal displays, do not expect this sort of accuracy in use.
 
One of the best uses for even the cheapest DROs on a mill or lathe is to set mm or inches. I feel sorry for anyone with his calculator trying to hit 0.4863 by reading the dials.
 
What is your rule for rounding up when converting the metric to inches.
The precision to which you carry out conversions depends very much on what the requirement represented by the dimensions are.

A metric dimension may be listed as 22 mm but unless otherwise stated, I assume 22.00 mm which would be .8661". If that 22 mm is the i.d of a bearing to be a light press on a shaft, you better be working to four decimal places. On the other hand, if that 22 mm is the diameter of a crank handle, I would probably round it off to 7/8".

I carry all my calculations out to four decimal places. I know that bothers some people but I am used to dealing with it. Most of my work is done to thousandths so the extra decimal place helps to prevent stack up errors. An example would be 10 holes .5002" apart. If I round to .500" and start machining holes, by the tenth hole, I would be .002" out

Bear in mind that virtually all of my design work is for my own use. I am aware of what the functional requirements are and what kind of machining accuracy is required to meet the functional needs. If I were designing in collaboration with others and cimmunicating with those responsible for executing the design, as I did in my professional life, it is a totally different ball game.
 
I just don't understand why this country refuses to go metric. The imperial system is archaic. We are just being Luddites on this issue. It is time we bite the bullet and made the change. The vast majority of our manufacturing companies could do it over night, if it weren't for there current inventories.
Randy

DoD is pretty much the reason. They are the 600 pound gorilla in procurement. Going metric would necessitate a clean break in procurement and stocking. The public would freak out finding out that they would be spending billions on setting up, qualifying and then stocking metric hardware for the various programs. Then think of the logistics of having to handle both systems, in the same maintenance units, until all the imperial equipment was transitioned out. For some things, the equipment is in use for 40+ years...
 
I'm a Visual sort of guy, It helps me if I ~SEE~ rather than read or hear.

Upon buying my New PEC 6 inch scale, I had the typical choices, so I bought their Imperial/Metric scale.

It does 1/64", and inches decimal (100 per inch) then side two has Metric ( @ 0.5mm for 2 (or 4) CM, then the rest in 1.0mmm Plus CM's. The Fourth scale is (IIRC) 1/32 . I use this 6" scale for most of my work, as it is nitrided a "Gold" color and is plain easy on the eyes.

Using the Metric Side, even when DOING Imperial Work helps me "keep" them relatively "together" in my mind.

Note: the Company Incra Rules is my "Go To Ruler" for All Wood Working, and has been since 1989. their thin Stainless Steel is perforated so a .5mm Pencil will fit perfectly, the ends have a removable "Tee Square" that can slide so either top scale or bottom scale is "On Edge" with the Tee.

They Provide 1/16, 1/8, 1/4, etc. line markings & holes then, With a Unique system in the center of their Scales, (a series of Diagonal Holes Marked +/- ) one can Accurately Draw LINES to 1/64 inch Plus whatever inch distance from the scale.

They even have a 3X4 inch X/Y Plotter "scale". As Well as a Special Order for a Metric Based Scale Sized to the equivalent nearest Inch length say 75X100 instead of 3X4.

I do not work for, NOR Receive $$$ for "endorsing" their Products, I simply pass the information On as an Avid User.

As my STANDARD Pencil in my shop is a Metric .9 Milimeter lead, I once took the time to increase the holes in one scale to .9mm, But that is a Lot of work, you gotta be just a bit OCD to "do That" ! ! ! ! !

philip, Oregon is dry this week, Next week Fall will start!
 
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