Digital angle rule (protractor)

[transatlantic]

I want to pick up a digital protractor and it seems there isn't much choice really in the sub £50 range, other than the Trend ones. Anyone have any experience with them?

Digital angle rule 200mm
Digital angle rule 500mm
Digital angle finder 8 inch

Annoyingly, they don't seem to have much accuracy. The top 2 are only +/- 0.3degrees accurate, which for the 500mm one, seems fairly poor?

I work out that 0.3deg over 500m could result in up to 2.6mm or error. Thats quite a gap!

The bottom one has an accuracy of +/- 0.15

Also, what is the point of having a resolution of 0.1deg if the accuracy is +/- 0.3deg?

 

[woodpig]

I've got this one.

http://www.machine-dro.co.uk/digital-pr ... eries.html

Resolution is 0.05° but I don't know about the accuracy.

 

[Eric The Viking]

Gem Red also make one, but TBH the hinged-twin-ruler type of design isn't very accurate (in my limited experience).

Put one on a flat surface closed, and zero it. Then open t completely and see if you get 180 degrees. If you have an accurate square, check it from both directions at 90. If there's any discrepancy...

I have one. I don't trust it.

 

[Beau]

Lidl do one and from what I can measure it's spot on. When held up to a M&W square it reads exactly 90 degrees

 

[toysandboats]

Lidl do one and from what I can measure it's spot on. When held up to a M&W square it reads exactly 90 degrees

+1 for Lidl

David

 

[transatlantic]

Lidl do one and from what I can measure it's spot on. When held up to a M&W square it reads exactly 90 degrees

But I need one nooooooooow

 

[Honest John]

I have the Trend one and have no issues with it. I would be suspicious of any accuracy and resolution claims however as there is just too many areas where this could be compromised. Perfect on one use could be slightly different on another. That said, I have used my Trend to set up a mitre saw and a table saw sled to cut segments for segmented turning ring build ups, and have had good accuracy on every occasion so far.

 

[No skills]

Repeatability is what you need, if you can measure the same thing several times and get the same result each time then that's the best you can hope for.
Bonus time is if you have a very good engineers square to reference it against, if your sure your squares 90 you can check the protractor against it and see if it reads off and by how much - you can then apply this correction factor to any other angles you measure.

 

[Gerry]

You will find that manufacturers use the same digitiser circuits in both small and large measuring devices.
British standards allows for this by increasing the tolerance of measurement as the instrument gets bigger. So a 150mm Vernier would have a tolerance of measurement of +/-0.02mm but a 600mm vernier would be +/-0.06mm
Any measurment around nominal within those figures would be acceptable but in practice the measurement results obtained tend to be much tighter than this, The main factor of accuracy and repeatability being the operators touch and feel for the device.

Gerry
(Calibration Technician)