Accurate Tape Measure?

[Tenson]

All my tape measures are crap; the hook at the start is not fixed and has about 0.5mm play, so it is impossible to accurately measure things like lengths of steel for my CNC machine frame.

Can you guys recommend an accurate tape measure where the hook is fixed precisely, or another way to go about measuring longer items?

[C_Bubba]

The movement of the hook is to have an accurate measurement of both ID and OD or length measurements. The movement is about the thickness of the hook.

[Tenson]

The movement of the hook is to have an accurate measurement of both ID and OD or length measurements. The movement is about the thickness of the hook.

Ahh I see, but still can anyone recommend an accurate item, rather than one where the movement is only about right?

[John S]

How accurate ? How wide is your stick of chalk ?

[C_Bubba]

I agree with John on this one. A "tap measure" is not a real accurate measuring device.
I would not even agree that the markings are real accurate! (precision)

[Jonathan]

i always measure from the 100mm mk.

Same.. it's the obvious solution.

Surely for a frame what's more important is to get repeatability since it's unlikely to make much difference if you measure 600mm and get 600.5mm as with the error you describe every piece will be 600.5mm. The frame will still be square etc, just negligibly off the size you wanted.

[JAZZCNC]

Tapes are for wood and rough material sizing, precision engineers rule is the minimum I would recommend and even then I'd double check every time.!

[Tenson]

How would you accurately measure 1800mm, Jazz?

[JAZZCNC]

How would you accurately measure 1800mm, Jazz?

Me personaly I would use my Rabone Chesterman No64R 1.5m rule and a 3.2.1 block as accurate marker then go again. Or. . . has john said use 2 rules, probably a 310mm engineers rule in this case.? I do have 1 mtr rule but don't class it has accurate enough to be called precision.! Still leaps ahead of a tape thou.

To give some idea of the quality and accurecy of a precision rule stamped on the Rabone is the warning "Only standard at 20c" and originally came with a certificate of calibration. I've had it for many many years and one of the nice things about living close to Sheffield is you drop across some high quality tools.
( If that border jumping gringo Bandit John S don't snaffel em first.!!!)

[John S]

put two one metre rules end to end.