500 hundreds of a inch

[JulieB]

500 hundreds of a inch, dose A LOT of really bad stuff (to put it in simple form)

our 80-20 got messed up some how??? in two place off by 500 hundreds of a inch WHO KNOW HOW!!!
just take time to fix it NO BIGGIE

[Zippiot]

500ths of an inch is much larger than you think, a millimeter is 1/254 (if i remember correctly, maybe 1/245). and 1 millimeter is visible to us, it can be a huge gap with machinery or instruments. a nut that is 1/500ths larger than its bolt wont fit if that gives a better sense...

[JakeGallagher]

Originally Posted by JulieB

500 hundreds of a inch, dose A LOT of really bad stuff (to put it in simple form)

our 80-20 got messed up some how??? in two place off by 500 hundreds of a inch WHO KNOW HOW!!!
just take time to fix it NO BIGGIE

I don't understand...isn't 500 hundredths of an inch...5 inches?

[Zippiot]

must have been a typo, but i see your point. he probably meant 1/500ths. lol 5 inches

[Andrew Rudolph]

When someone says a 500th of an inch i think in decimal form, so In his case it would be .0500 which is 1/20 of an inch

[Tristan Lall]

This isn't rocket science:

• 500 × 0.01" = 5.0"
• 1.00" ÷ 100 × 5 = 0.05"
• 1.00" ÷ 500 = 0.002"
• 1.00" = 25.4 mm

Do you perhaps mean 0.05" (i.e. five hundredths of an inch)? That's not usually something to worry about, when it comes to structural framing. Similarly, it's positively inconceivable that you'd care about 0.002" (i.e. one five-hundredth of an inch) in your frame.

[Elgin Clock]

Ugh.. stupid scientific notations.

0.050 or 50 thousandths, is larger than you can think, and may affect form fit or function a bit with robots being 3 feet wide. (If it is an overall chassis cross member dimension).

But, to add to that, a standard dimensional tolerance is +/- .002 of an inch on the parts I make on CAD at work. (Small cable connectors about an inch long (or less) total.) Think: the connector at the end of the cable snake that invades your home and brings you your TV and cable modem services. About that size.

[Zippiot]

wow my math is off...haven't slept in 2 days...
1/20 is quite larger but .002 in microscopic ( 1/25.4 is 1 millimeter)
what and where exactly did this error occur and is it just annoying or is it a problem?

[Tristan Lall]

Originally Posted by Elgin Clock

0.050 or 50 thousandths, is larger than you can think, and may affect form fit or function a bit with robots being 3 feet wide. (If it is an overall chassis cross member dimension).

To put this in perspective, how many teams are sure that their frame is accurate (in two dimensions) to within 1/16" (0.0625")? (Answer: many, but not a large majority, I would imagine.) How many teams can further guarantee that their frame won't distort this much under normal use? (Answer: few.) If you're cutting with a saw, good luck--the kerf isn't always easy to judge.

Originally Posted by Elgin Clock

But, to add to that, a standard dimensional tolerance is +/- .002 of an inch on the parts I make on CAD at work. (Small cable connectors about an inch long (or less) total.) Think: the connector at the end of the cable snake that invades your home and brings you your TV and cable modem services. About that size.

I don't think that 80-20 structural framing is in the same league. Really, 2 thousandths is insignificant for the applications that 80-20 makes sense for. I'd guess that a change of 5°C would cause about that much in thermal expansion alone.

Let's see: Δd = d₀αΔT; for a 28" piece of framing, α = 23 × 10^-6°C^-1 (we'll call it constant for small ΔT), at 20°C, in 6101 aluminum (the closest I could find to 6105, which is actually used in 80-20); Δd = (28)(23 × 10^-6)(5) = 0.0032"

So if Δd = 0.0032", we're dealing with as much thermal expansion as we have machining tolerance, merely in taking it from the unheated cargo trailer to the pit area. That's why I think 0.002" is crazy, for our purposes.