Chinese digital caliper - first report

I just got a $30 Harbor Freight (item 47257) six inch digital caliper, from the noodle factory, partly as an experiment, and ultimately to give to my 9 year old
nephew.
It is functional, albeit more crudely made and less accurate than a Mitutoyo (which costs four times as much). The random error of the 47257 seems to be about 0.002", largely due to head looseness. I tightened the head gib, and the error dropped to about 0.001", which is what HF claims. I don't know how well the gib adjustment will hold - the two adjustment screws seemed a bit loose.
The clamp thumbscrew (that locks the head to the bar) was bent, so I straightened it with an adjustable wrench. No idea how it was bent, as this takes some force. The caliper came in a plastic case, and shipping damage was not apparent.
The head slid reluctantly on the bar. This appeared to be due to a coating of blackish grease, which easily wiped off. But still there was too much drag and slip-stick. It turns out that the bar was precision ground but not polished, leaving grind marks perpendicular to the bar, so the grind marks were slowly filing away at the gib, which is brass. Not good, so I polished the grind marks by hand with crocus cloth. This helped immensely. I suppose that crocus cloth wrapped around a metal sanding block would do an even better flat polishing job.
After cleaning all the nasty grease away, I lubricated the caliper with pure lanolin (used for instance to lubricate brass musical instruments). Pretty smooth now.
The manual says that the caliper requires a SR44 (silver oxide) battery, but it came with two alkaline cells. Another corner cut.
I will use this caliper for a while in the shop and see how it goes.
Joe Gwinn
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You will find that not only is the Chinese caliper less accurate, they eat batteries at least twice the rate of a Mitutoyo. Steve

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On Wed, 24 Feb 2010 09:05:40 -0500, the infamous Joseph Gwinn

You realize that a few days or weeks of use would have made it much smoother, too, don't you? (Not near -as- smooth, but smoother.)

With all that time invested in the thing, that $30 HF caliper is more costly than the eqivalent Starrett. Ironic, ain't it? <snort>
Nice job, BTW.
-- "Politics is the art of looking for trouble, finding it whether it exists or not, diagnosing it incorrectly, and applying the wrong remedy." -- Ernest Benn
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Joseph Gwinn writes:

I have had nothing but success with these. I am still using the first one from 2003 and it still holds +/- 0.001". Maybe they are not as good lately.
Of course, I buy them on sale for $10.
More importantly, I test them in the store. Consider it field-level quality-control testing. Take your gage blocks with you, and go through the pile until you get the good ones, if there are any. The yokel store clerks will be respectfully baffled at your metrology expertise.
I have a nice campaign souvenir advertising the local board of elections supervisor elected official, who handed out free printed plastic sheet rulers. Whoever printed these things applied about a 0.9 shrink factor in the process, but no one else seemed to notice. Ludicrous and somehow quite appropriate for a politician.
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On Wed, 24 Feb 2010 09:05:40 -0500, Joseph Gwinn

Yikes, $30? Wait for a sale, mon! They're often on sale for about $15 and recently for $9.99.
I have several of them because I regard them as consumable, disposable and handy. I have a Mitutoyo at the lathe but I don't think it's any more accurate than the HF versions I have distributed around my shop, cars and various remote progeny who dream up "daddy do" projects now and then. Battery life is better in the Mitutoyo but the price difference would cover a couple of decades worth of batteries.
A digital caliper is no substitute for a micrometer, but it beats the hell out of a tape measure or a guess and often suffices in my shop.
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I'll keep an eye out. All the better for the nephew. But I wasn't going to wait, and I was already ordering some stuff.

Yes.
Also yes. Even if I have to polish the bar myself to get smooth action. I may use 600 or 1200 grit wet dry paper wrapped around a piece of HSS tool bit bar as a sanding block to polish the bar edges. The tool bit bar is ground quite accurately flat, and is a handy size.
Joe Gwinn
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Don Foreman wrote:

I've also had great luck with them and have a number of the 6" version and one of the 12" version. I'm not doing aerospace stuff so I don't need that many decimal places of accuracy anyway.
I don't have a problem with battery life, I just remove the batteries before I leave the shop, and only reinstall them when I need to use the caliper.
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wrote:

HF has several grades of calipers, I've been getting the "improved" models that have larger LCD displays lately. In-store price is $10-15 for the 4"-6" models. At least one model turns itself off until the slider is moved, then it picks up where it left off, no re-zeroing. Also remembers inch or metric. The really nifty one also does fractional inch. I use them in various tool kits for beaters, like with the wood planer, for closer-tolerance work I've got name-brand mikes and calipers. As you say, they beat using scales most times. I usually have a 4" in the pocket when hitting the hardware store. If you hit the internet, you can usually pick up the alkaline button cells for $4-$5/50. I go through a lot of them with various laser bore sighters and LED lights.
Stan
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I have the 4" and the 6" from HF. They work just fine in a work environment. Several of the guys have them now. Change the battery about once a year. Seem to be just as accurate as anything else, when measuring the same part with different brands. I prefer the 4" HF to my 8" Mitutoyo. It get into tight areas better. Yes there is a difference in the feel when you slide them open and closed, but they measure the same. When my 12 dial gives up I will get the 12" HF to replace it with. Since I don't use the 12" much I may never need to replace it. I have worn out 3 of the 8" digital Mitutoyos over the years and tossed them. Except for one I use for auto repair.
Richard W.
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[snip]
I am using the HF 6" the test in my shop. The 4" may be a good idea.
But I think it's worthwhile to hand-polish the bar to make the sliding action smoother.

I use the DRO on my mill for long items.

When a digital caliper wears out, what exactly goes bad?
Joe Gwinn
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The measuring surface wears out. So you get different readings at the bottom, center and top of the jaws. Adjusting the gib screws won't make up for wear on the jaw faces.
Richard W.
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I'd drop coin for a Mitutoyo 6" digital with carbide inserted OD jaws in an instant. Makes for a nice scriber for laying out a features on a detail. Uncle has an old Mitutoyo dial caliper with the carbide jaws.
Consider it a poor mans height gage.
Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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