Cheap digital vernier calipers/micrometer, any good?

I could do with a micrometer, digital would be even better. There are some really cheap ones on ebay, like this one [www.ebay.co.uk]
Are they worth it? I usually expect to get what I pay for, so I half expect it to be as useful as a chocolate teapot. It does say accuracy is +/- 0.02mm. Good enough for measuring filament and calibrating?

That looks to be the same as you'd find at a Harbor Freight in the US. I love mine and would be very sad if I had to go without it because I use it all the time.

Looks the same as the one I bought from Amazon that's been working well for me.

Great, I'll give them a go. Digital calipers in my local tool shop are around £40!

I have the 12" version, works well

I have one as well, from Harbor freight. was finicky when i first received it, but once i gave it the standard harbor freight once-over (disassembling, cleaning, reassembling) it works fine. uses a capacitive strip hidden under the ruler label, so maybe it was some grease or metal filings that were throwing off the readings.

Mine works fine.

One "quirk" of many of these inexpensive calipers is that they never turn off (mine is exactly like the one in that listing and has this quirk), the power button blanks the display, but it is still drawing current doing its measurement thing. The button cells can be a little expensive or hard to find uso I rigged up a holder for a single AAA battery with a real off switch and glued it in place. looks hacky, but my calipers are no longer dead when I forget to take the battery out before storing them. The AG13 battery most use is a alkaline 1.5V cell, not a lithium like other button cells, so a single AAA will do the trick.

If you're ok with a dim display the battery self-charges enough that it very rarely needs to be replaced.

If not..

10 pack. $2.15 shipped.
[www.dealextreme.com]
50 pack. $3.80 shipped.
[www.dealextreme.com]

The 50 pack is quite useful when your kids have a collection of Hexbugs!

Edited 1 time(s). Last edit at 09/12/2011 08:29PM by billyzelsnack.

I went ahead and ordered for £6.95, just got them this morning. Came with a spare battery, too! Plastic case is very cheap, and has cracked around one hinge already, but the calipers themselves seem surprisingly good. I checked them against my feeler gauges, very good accuracy and repeatability. The display does eventually turn itself off, but it's probably a good idea to lock the locknut during storage to prevent knocks opening the caliper blade and turning the display back on. Apart from the battery cover, there is a second removable cover above the battery compartment, which intriguingly allows access to some header contacts on the PCB. Anyone know what this is for?

@billyzelsnack - "the battery self-charges" - eh? Magic batteries?!

Edited 1 time(s). Last edit at 09/14/2011 08:59AM by droftarts.

Quote
droftarts
Anyone know what this is for?

Have you considered reading the user manual/pamphlet delivered with your tool?

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Thank you for your words of wisdom, Bob, yes I did read the instructions, that's why I asked as it is not covered by the brief documentation. I assume it's for an external readout of measurement. There was another thread on using these sorts of calipers to accurately position the print head; information on specification of this connection would be very useful for that idea.

If you bought the one on EBay (from your link) then it looks identical to the one I have at home.
I will take a look at it when I get home...
As a matter of fact, if you look at Amazon they have units from several different makers that all look identical which probably means that they are all rebranded from the same manufacturer.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

There are a number of interesting links in the Wikipedia article on digital calipers.

I suspect that Chinese Scales will give you the info you want, if not then take a look at Protocols of Digital Scales.

Edited 1 time(s). Last edit at 09/14/2011 09:55AM by rhmorrison.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

I have a very similar caliper, from mendel parts. Its branded Hogetex, the inch/mm button is slightly further left, it has a different looking scale, otherwise its identical.

From the instruction sheet:

3. With data output interface (optional), data can be input to a special printer or a computer via special cable for data processing and printing.

Interface Typeynchronous serial.
Data:Binary code, 24bits. Each datum will be transferred twice. The cycle is 300ms(20ms in fast reading state). Transmitting time:0.5ms

Four wires(from left to right): Negative power(-),Clock Pulse CP, Data D, positive Power (+). Pulse range of data:"0" Level <0.2Vm Level"1">1.3V. Clock Pulse CP:90Khz. effective for high electrical level.

Thanks Bob and Andrew, that's exactly the sort of information that I was hoping for, which isn't in my instruction sheet! Yes, I bought the version from ebay that looks very similar to the Amazon one.
Though I don't have any particular need for the information at the moment, at least it is in a relevant thread.

Which Harbor Freight model do you recommend?

I also have one of these and it is quite useful. I had mine for about 3 years before it finally got dropped, which has really messed up the readings. Oh well, worth it for the price just be careful about not dropping it or banging other tools into it. Precision tools cannot take much abuse, no matter how much or how little you spend on them.

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Germanicus

Someone already made an interface for these calipers :
[www.compendiumarcana.com]

And by shorting pins 2 and 4, you can add more functions :
[hackaday.com]
[www.justblair.co.uk]