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Posted by Joseph Gwinn on February 24, 2010, 9:05 am
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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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Posted by Steve Lusardi on February 24, 2010, 9:52 am
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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
>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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Posted by Larry Jaques on February 24, 2010, 2:00 pm
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On Wed, 24 Feb 2010 09:05:40 -0500, the infamous Joseph Gwinn
>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.
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.)
>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.
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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Posted by Richard J Kinch on February 24, 2010, 8:16 pm
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Joseph Gwinn writes:
> I just got a $30 Harbor Freight (item 47257) six inch digital caliper,
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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Posted by Don Foreman on February 25, 2010, 1:47 am
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On Wed, 24 Feb 2010 09:05:40 -0500, Joseph Gwinn
>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
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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> noodle factory, partly as an experiment, and ultimately to give to my 9 year