Harbor Freight (Cen-Tech) Digital Caliper #93940

I've been picking up more eBay and Harbor Freight stuff lately, as I segue into retirement. I feel like a squirrel getting ready for winter. I don't want to run out of tools before I die and I'm afraid I won't be able to afford them after I retire.

I ordered a pair of these 6" digital calipers for $15.99 from the Harbor Freight website, figuring I couldn't go too far wrong for that price. I received them in the mail today and eagerly opened the package. Disappointment.

They powered up but the LCD was reading random digits, unrelated to the slide movement. I changed the battery (they come with a spare) but that made no difference. I removed the battery for 30 seconds to "reset the circuit" as recommended by the manual. No change.

Just before I pitched them into the trash, I became curious. They must have been designed to function - how hard could it be to fix them? I peeled off the label covering the screws on the back and ignoring the warning label, "Do not disassemble the Dial Caliper," I tore into them.

There wasn't much inside, just a "reader" board inside the plastic shell. I noticed two pieces of plastic tape between the plastic shell and the metal frame of the slide. It appeared to be a rudimentary shim, but I reasoned it might be elevating the reader from the scale far enough that it wasn't able to "read" it (also, the stationary scale is black on dark blue background which might also make it difficult).

I removed the questionable "shim tape" and reassembled the calipers, inserted the battery, and they worked perfectly. These are actually a pretty fair knock-off of the Mitutoyo digital caliper. They have a thumb wheel, metric/inch reading, zero button, and auto on/off. I'll check them tomorrow with my gauge blocks and see how accurate they are but so far they look pretty good and they feel just as smooth as my old Mitutoyo dial caliper.

Reply to
Jim
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Hasn't been my experience.

Perhaps you are using the wrong batteries?

Reply to
Richard J Kinch

Yes, it suprises me that I need a battery about every year and a half even though I only have the unit on for a total of, maybe, 2 hours. It is a small expense however. I suppose the shelf life of the battery is probably close to the above mentioned interval. I bought a 6" and a 12 " approx. 4 years ago. Best purchase I ever made.

Ivan Vegvary

Ivan Vegvary

Reply to
Ivan Vegvary

I have all , the black ( 2nd gen') and the newer large digits LCD ( 3rd generation ) ..

The 2nd generation , eat batteries .

The 3rd gen' claim they last longer .

The distance from the PCB to the capacitive rectangles can be surprisingly large . Dick Martin in CA made some PCB with little rectangles cut into the PCB , 28 inches long , to put under all common caliper heads . They work .

I took an old 12" HF apart and dropped the head on that long PCB and it slid along nicely and read +99 all the way to -99 inches ! Thus the HF 12" , first generation head can read 200 inches . So i put that on my HF mill/drill as a DRO .

I have the 36" calipers also . They have 2 memories , so you dont lose when you go from ABS to relative .

Notice all the Mikes have ambiguity on the .0001 verneir ! ENCO included , so i sent them back . But Long ago i got ENCO with all 10 numbers ( 0-9 ) , today China has only 5 numbers

Some 2nd gen' are bent . Mitutoyo is twice as repeatable as China .

They all have a Open Drain Fet , just hook a positive voltage to a pull up resistor ( about 5 to 20 Kohm ) to the ouput and they send out a stream of coded data .. I have the info somewhere ...

v Jim wrote:

Reply to
werty

The problem is that, when you turn a digital caliper off, you only turn off part of the circuitry. And the cheaper calipers (HF) tend to draw more current than some of the more expensive ones while in this standby mode. If you don't use the calipers all that often, you can remove the battery when not in use.

OTOH, the batteries are relatively cheap.

Jerry

Reply to
Jerry Foster

Any of local fairs or Dollar Stores carry those batteries, 12 for $1. Problem solved :)

These calipers are true workhorses. Jaws are more excellent, hardened and everything. I scribe with mine quite extensively - helps a big time for quick layout work

Reply to
rashid111

The Chinese scales (and most of the Japanese) just switch off the display to keep the reference. The circuit with the capacitor-array is running all the time and with always the same speed.

A note to the cells: They often are selling crap. You need SR-type for longer live.

Nick

Reply to
Nick Mueller

no, there are two variants of these, and I've not been able to distinguish them - but all the HF ones I've bought eat batteries - leave them OFF in the case for 6 months, battery is dead - solution - remove battery when not in use. Or, my solution - go on e-bay and buy a Mitutoyo solar powered one for $45 and quit worrying about batteries.

Reply to
William Noble

There are two chemistries that the batteries fitting these calipers use. One is called alkaline and the other is silver oxide. The LR44 battery is the alkaline type and the SR44 is the silver oxide type. Many battery packages will say that the LR44 can be used instead of the SR44. This is true but the LR44 voltage drops quickly whereas the SR44 doesn't. The caliper thinks the battery is dead when the voltage drops below a certain level. So even though the caliper won't work, or has a flashing display, the LR44 battery will still work in an LED light or similar application. I have found that even my Mitutoyo calipers get about 45 days with the LR44 battery. The SR44 batteries will run the same calipers for about 20 months. I'm pretty sure the LR44 will deliver more milliwats over its lifetime than the SR44 will, just at a lower voltage. ERS

Reply to
Eric R Snow

I've often felt it would be nice to rig a battery disconnect switch on my dial caliper, 'cause I could care less about whether it holds it's zero setting between my roughly once a month usages.

But, so far that project has seemed like "A long run for a short slide" so I leave rhe battery in and just make sure I replace the "spare" in the caliper case right after I have to install it.

Jeff

Reply to
Jeff Wisnia

The batteries in the Harbor Freight calipers are SR44.

Reply to
Jim

The paper "shims" between the plastic shell and the metal frame were only .003" thick. This was enough extra distance to keep the caliper from reading correctly.

Reply to
Jim

My experience is, that the distance can be up to 0.3mm. But the closer you get, the more stable the reading is.

Nick

Reply to
Nick Mueller

No they don't. You're mistaking alkaline for silver oxide.

Reply to
Richard J Kinch

My Mitutoyo caliper does not do that.

i

Reply to
Ignoramus16418

LR44 and SR44 are both 150 mah cells, the difference is the voltage droop on the alky LR44. SR44 is the same as 357/303. Energizer also has a 357/303H that is 175 mah. 357's from some some other mfrs are 165 mah. As Nick noted, there are cheap cells out there but they have very poor life. Go name brand -- Energizer, Renata, Varta,Duracell etc.

Check out

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Good prices for Energizers, $1.95 shipping. Silver oxide batteries have good shelf life (90% capacity after 5 years at 20C, longer in the fridge) so it makes sense to buy a half dozen or so and be done with it.

Reply to
Don Foreman
0 .3 mm about 0 .012" .... the old 12" HF i bought would read at a higher gap than that . I still have some 12" ..

I buy $2 ( for pack of 10) 1154 batts from

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, last long time .

anyone have the HF 36" calipers ?

They were $25 , so i picked up 4 ...

What do you think of my idea of hacksawing a Mit digi-mike ? Turning it into a ht gage . I will set it to zero on some dedicated 1-2-3 blocks .

The common way to do this is a funny looking mike with a vertical shaft with many 1" spaced discs ,

. Then move your ht gage/DTI up to it to set the ht gage . It has no range , my idea has 1" range ...

Reply to
werty

According to Jeff Wisnia :

[ ... ]

Well ... the battery holder in my Starrett digital calipers just needs to slide about 1/8" to disconnect the battery, so I put it away just like that. As a result, the batterys in that (which normally die rather quickly) outlive those in the Mitutoyo calipers.

That's what I do with the Mitutoyo ones, since they were not considerate enough to make a battery compartment like that on the Starrett which eases totally disconnecting the batteries.

Enjoy, DoN.

Reply to
DoN. Nichols

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