PDA

View Full Version : Starrett Calipers ...



thejerradsays
10-27-2008, 07:32 AM
I calibrate gages for a shop in Houston, and new API standards state that all tools on the floor used in any part of production must be calibrated.

I ran across a pair of 0-6" Starrett Dial Calipers that have an issue. The needle rests at zero at the bottom of the dial. This is purely aesthetic as the calipers are both within tolerance and have repeatability.

Is there something I can adjust to bring zero back to the top of the dial? I was thinking slight adjustments to the track that the gear runs along, or would I have to disassemble the whole gage?

Lew Hartswick
10-27-2008, 05:00 PM
What does it matter where the Zero in on a dial????
...lew...

topct
10-27-2008, 05:29 PM
I believe there is a way to reset the needle. Some one here knows how.

b2u44
10-27-2008, 05:35 PM
I've seen this kind of thing happen for two reasons...


First (and mainly on cheap calipers), the pointer can sometimes slip on its shaft when the caliper is closed (too) quickly.

Second, the pinion gear can skip a tooth on the rack which is normally caused by stray metal chips. If a small piece of shim-stock is placed on the rack while the caliper is being closed, it can lift the pinion off the rack. Then, just close the caliper by a small amount, remove the shim, and test the dial's position. It can take several tries to get the "reset" correct. This method might seem overly aggressive, but my Mitutoyo caliper comes with a shim-like tool and instructions for this purpose.

thejerradsays
10-28-2008, 08:13 AM
Thanks for the info.

The machinist is complaining about the zero being at the bottom now, making it an issue. As I said before, the calipers are accurate and within tolerance so it is purely aesthetic.

The machinist has gone on the warpath now, telling machinists to take their personal tools home so that they cannot be damaged. This is actually a big help to me, because these new API regulations are a pain in my behind.

Once again, thanks for the advice.

thejerradsays
10-28-2008, 10:48 AM
Tried the shim tactic. Worked great. Thanks again.

Paul Alciatore
11-02-2008, 11:32 AM
Interesting. I would guess that the pinion that rides on the rack is spring loaded to maintain intimate contact.

I have an import caliper that I dropped once. Ever since then, the zero has been off by about 5 or 6 thousanths from the top. I have checked it against my mike and other calipers and am confident it is accurate (+/-0.001") but it is puzzling. It seems to me that if it skipped a tooth, it would be off in a multiple of 0.025". So I wonder what happened here. No obvious way to disassemble or I would have done so.

dutchw
11-02-2008, 11:53 AM
Paul
I have several brands of dial calipers and all of them have a moveable bezel. Just reset the bezel to zero.

DutchW

b2u44
11-02-2008, 12:27 PM
Paul,

I've rebuilt several calipers and they have all had 2 gears that run on the rack. The gears are spring-loaded onto their hubs so that one always pushes on the left side of the teeth and the other always pushes on the right. Basically, the springs keep torque on the gear shafts. This eliminates backlash problems and keeps the dial from jiggling left/right.

I seem to remember that I had to remove the clear, plastic dial-cover first. (I used a suction cup to pull it off) Then I pulled the dial off of the dial's shaft, followed by the knurled ring. There were a few screws under the dial's face that held the caliper together. Be careful if you decide to take a look at the gearing because it's spring-loaded. I don't remember the details about how to rewind the springs except that there was a way to use a pin/drill bit/pick/etc. to lock the springs until the cover was replaced.

For your caliper, it may suffice to remove the clear cover and then remove/reinstall the pointer on its shaft. As I mentioned in an earlier post, it seems like the pointers on import calipers tend to be a bit loose so they can shift on their shaft.

Paul Alciatore
11-03-2008, 09:09 PM
Thanks guys, it's nice to know the way in. And yes, I have simpily reset the bezel with the zero line. Since it is working, I may just leave it alone and recheck it occasionally. I'll try to go in if it becomes inaccurate.

JMI
11-27-2008, 10:24 AM
Like that shim stock idea!

Had a similar problem, albeit not quite as bad and contacted Starrett. This was their response:

"Remove the four screws from the metal plate below the dial there should be one screw in each corner. Lift the plate up with the dial and you will find the small pinion gear hanging down below the plate. Rotate this gear to reposition the needle to zero then reattach the plate with the screws."

Jim

rebel54
11-27-2008, 11:13 AM
I had a Starrett caliper. The problem with this caliper is the rack is not covered. The Machinist will sometimes have dirty hands which transfers metal grit onto the rack which will get caught in the gear that turns the dial. Which on course will make the gear jump teeth. This will happen again with this caliper, the shim is the way to get the pointer back inline.

RobbieKnobbie
12-08-2008, 11:39 AM
Thanks for the info.

The machinist is complaining about the zero being at the bottom now, making it an issue. As I said before, the calipers are accurate and within tolerance so it is purely aesthetic...

Perhaps the machinist in question would consider taking better care of his gear? I've worked in shops where every guy used his own tools... you'd ALWAYS see mics and calipers laid out on the bench next to the job. A rag was laid out and everything was kept out of the path of chips etc. These tools rerely needed recalibration because they were well taken care of.

I've also worked in shops where the company supplied the tools... mics laying on top of machines, covered in chips and oil. Calipers left where ever, you get the idea. After a while the company got tired of replacing expensive tools so they started replacing them with the cheapie MSC brand. Then the guys on the floor started complaining that the tools were no good and constantly needed to be recalibrated.

So much is dependant on the culture in the shop!

J Tiers
12-11-2008, 09:48 PM
The very worst tool abuser at work is the guy who owns all the shop tools, the business owner.....!

I find the calipers under a wrench, or in a pile of tools all the time..... We aren't a machine shop, but electronics consultants. But we do a lot of electro-mechanical stuff, so we have mechanical stuff to be measured, trued, fixed, etc. I usually end up doing it if it's "machinist type work".

The boss is also an engineer, and he is the worst for losing, misplacing, and damaging tools. Ownership is not a universal cure-all......