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tony ennis
01-29-2009, 08:40 PM
If I were going to place two spur gears on a plate such that they meshed, would the distance between their centers simply be the sum of half the gears' pitch diameters? That's what I gather from Machinery's Handbook.

Ex:

gear A is a 64 tooth gear having a diametral pitch of 16 meshes with gear B, a 20 tooth gear.

Pitch Diameter of A = 64/16 = 4
Pitch Diameter of B = 20/16 = 1.25

So I would place their centers (4+1.25)/2 = 5.25/2 = 2.625" apart.

And given the clearance is .157/diametral pitch = .0098, the centers need to be correct to within a a shade under .0049.

Ok, assuming that's correct, I have a metal plate all blued up. I centerpunch a divot for the first shaft. What's the right way to locate the other shaft, assuming it has to be at some odd angle from the first (not purely vertical or horizontal?

I'd be tempted to clamp the gears to the plate, meshed, with the teeth spaced by a few (?) thicknesses of aluminum foil, and use a transfer punch to mark the center of each gear.

The Fixer
01-29-2009, 08:47 PM
I can't confirm that your math (formulas) are correct but assuming they are... set your compass at the distance u want and scribe a circle around the center point of the first gear. you should be able to center punch anywhere in the circle that u want your gear to be.

al

oldtiffie
01-29-2009, 08:56 PM
2.625" centre distance is correct. Neglect "clearance" for this set-up.

For any centre-distance just centre-punch the first point, accurately (off a good rule will do) set a pair of dividers to 2.625" (2 5/8") apart, put one leg in the centre-punch indent and just swing an arc or circle of 2 5/8" radius with the dividers. Any point on the arc is the correct centre distance.

If the gears were manufactured correctly, "clearance" and back-lash were allowed for and incorporated into the manufacture of the gears.

"Gears" are not all that simple but they sure aren't real difficult either. They are often "talked up" to be more difficult than they are or need to be.

Get the fundamentals right and you will be on your way.

TGTool
01-29-2009, 09:16 PM
<snip>
So I would place their centers (4+1.25)/2 = 5.25/2 = 2.625" apart.

Ok, assuming that's correct, I have a metal plate all blued up. I centerpunch a divot for the first shaft. What's the right way to locate the other shaft, assuming it has to be at some odd angle from the first (not purely vertical or horizontal?
<snip>

If you actually know what angle the other gear is, you can use trig to figure the X and Y movements for which 2.625" is the hypotenuse.

tony ennis
01-29-2009, 09:30 PM
I suppose I should clarify a concern. How does one set calipers - or a compass - accurate to the thousandth? Regarding the clearance, am I not correct in that if the 2nd shaft is too close to the first by .005" the gears could crash?

My rather artificial requirement of the 2nd shaft not being in the 1st shaft's horizontal or vertical was to encourage a general purpose solution - like using a compass instead of a surface plate. Of course TGTool is correct in that I will probably know one of the other sides of the triangle and as such the surface plate is also a general solution.

Maybe my posts will be better if I get drunk first.

Robin R
01-29-2009, 10:52 PM
You should be able to set dividers accurately, by adjusting a micrometer or dial caliper to the required dimension, then carefully set the dividers to that gap.

oldtiffie
01-29-2009, 11:31 PM
OK - I will assume that this is not a "try on".

The end result will depend on three main items:
- that the gears are correctly manufactured;
- that the spindles on which the gears rotate are a good neat running fit in the gears; and
- the centre distance.

If the first two are correct, it only leaves the third (last).

Make two "Tool-makers buttons" each the same size but not necessarily the same size/s as the spindles that the gears are to run on. Set the first to the position of the first gear. Accurately (as you can - use a micrometer) set the second so that measurement over the buttons is:
= ((centre distance) + ((sum of the diameters of the buttons)/2))

The positions of the centres is now set accurately.

Put the plate with the buttons on the mill table and clamp it.

On each button in turn:
- use an accurate Test Dial Indicator (TDI) in your mill chuck and centre the mill spindle over the button;
- lock the table "X" and "Y" slides;
- remove the button;
- use a spotting or centre drill followed by a drill, say 1/32" under-size and drill the plate;
- bore the hole either exactly to size or bore it say 0.010" under-size, remove the boring-head, set an accurately sized or set reamer to size and ream to size.

There are other ways of doing it but the "jib-boring" approach has stood the test of time.

DRO's with or without slip guages are only two others of many.

If you want less accuracy or difficulty, move "down" from the "jig-borer" method.

The ultimate gears will have been made by a specialist gear-maker - hobbing/shaving/shaping etc. followed by high-tech metrology (not cheap).

It really depends on how far you want to go which may well be well in excess of how far you need to go.

A good read of "Machinery's Hand-book" and some good books on the subject might well be a minimum pre-requisite to even beginning the job - or worrying unduly.

I suggest that instead of theorising and worrying that you have a close look at the gears in your gear train in your lathe as well a gears in your lathe and mill geared heads - and even an outo-motive gear-box etc.

A lot will depend on the application.

Paul Alciatore
01-30-2009, 03:19 AM
You should be able to set dividers accurately, by adjusting a micrometer or dial caliper to the required dimension, then carefully set the dividers to that gap.

I beg to differ. Been there. Tried that. It is not that easy.

Divider points (and I have a Starrett so don't tell me my dividers are not high enough quality) are approximately cone shaped. If you are working with a small distance and put them between the jaws of a mike or caliper the distance between the points will be an unknown distance smaller than the distance set on the mike or caliper. Only when the angle between the divider's legs is greater than the cone angle of the points will the actual points rest on the faces of the mike or caliper.

And even then, it will be somewhat difficult to set the dividers to the correct distance. The slightest amount of pressure will easily close the dividers a bit while checking them this way so a very light touch is needed.

I find the best way is to use magnifiers. At least 10X, preferably 15X or evan 20X. I like to see the points sitting centered on the edges of the mike or caliper jaws. But you must shift your viewing position to be directly over each point as you judge it's location or you will get a parallax error. And of course the divider must not move when your head does.

Even with all of the above, it is still hard to adjust the screw/nut on dividers to the exact thousanth. And if you do, you must handle them very, VERY carefully when moving them to the work or you may easily disturb the setting you so carefully made. It does not take much of a shift in the nut's or screw's position to change the distance between the points by several thousanths. Remember that the points are at the end of the legs and the adjustment screw is in the middle at best, more likely even closer to the pivot point. It is a lever arm and any change in distance at the screw is amplifier at the points. So tenths at the adjustment become thousanths at the tips.

I would not argue with a master machinist who says he can use dividers at this level of accuracy. But a novice or even a moderately experienced person should not expect to get thousanth accuracy with dividers without a lot of practice.

If I were setting up two gears, I would first mount one of them and then mesh the second one with some shim stock between the teeth and use a close fitting transfer punch to mark the position of the second. Or use a short slot for the second one and adjust it during assembly. The size of the shim stock would depend on the pitch of the gears.

oldtiffie
01-30-2009, 04:28 AM
Let's put a few practicalities into this equation. We will start off with the very accurate (most are) "Machinists Rules" that are successively sub-divided into 1/64".

Put one point of the dividers into an etched mark on a good machinist's rule. Move the other across the rule. It is very easy to see where the moving point is.

First of all, 1/64" ~ 0.016" (16 thou). Halving it by eye is easy. If you are "off-centre" by 0.002" (2 thou), one side will be (0.008 + 0.002" = 0.010") and the other (0.008" - 0.002" = 0.006") a difference of (0.010" - 0.006" = 0.004") which at 1/4 of that 1/64" division is quite visible to the naked eye - better still with a loupe' or magnifying glass. There will be no (or negligible) "parallax" error as the points will be very close to the rule. So, getting it to within 0.004" is not too difficult and neither is getting it to within 0.002".

Transfer punches are a PITA as they must match the diameter of the bore/s very closely and the point of the transfer punch cone must be very precisely centred. Then, the chances are that the transfer punch needs to be followed up with a centre-punch and then the centre punch by a centre and/or spotting drill followed by one or more regular drills - all of which can each "wander off" bot laterally and axially and then by a reamer which will follow the drill just previous to it.

If I were marking it out I'd use a vernier or digital height guage (with a scribing point/edge) for accuracy or a surface guage or a scribing block and a flat plat (mill table or surface plate) with the job set up on a rotary table for the horizontal and vertical as well as any angular lines.

I can quite comfortably and repeatedly set a mill spindle axis over a line or intersection of lines within 0.002"

Its a matter of knowing what your tolerances and allowances and limits are and where your errors are of might be and acting and making informed judgments accordingly.

If the real requirements of or the gears is not too rigorous, I suggest that even badly meshed gears in the lathe gear-train rattle away in a dusty environment without a lot (or any) care and lubrication and by and large they do very well.

It is not uncommon for the pitch circles of gears to be eccentric to the bores and they oscillate in and out of mesh from "good" to "not so good". Set a pair of gear-train gears and set the back-lash and see if it is the same all the way through a complete rotation of each gear.

Oh dear - what to do?

Answer: bugger all. If it works its probably OK.

If you are cutting gears on a mill with the standard sets of gears for each DP and numbers of teeth, the only one that will be pretty accurate will be the first one in the set - even that is a compromise and the compromise gets bigger (worse?) the further up the number of teeth for each cutter you go. If you are plunging straight in for depth with your milling cutter using machine dials you are really trusting to luck unless you measure the gears against table in "Machinery"s Handbook" - or the like - using either a set of gear calipers or wires (2 or 3) with a micrometer. Seeing that the gear profile is concentric and symmetrical is another concern.

And that is not all of it - by far.

But in practical terms in many shop projects, most of it can be disregarded - up to a point.

I will not get into set-up and machine rigidity as common sense will soon identify any potential problems as well as their "fixes".

Why the diversion into gear-cutting when the topic is about setting gears up super-accurately?

Easy - because they are interdependent.

Just keep a sense of reality and perspective as well as a cool head and you will be OK most times.

Circlip
01-30-2009, 07:16 AM
Looking at the OP Tony this is a hypothesis? Machinery's calcs are based on a perfect world and we all know it ain't. This is why for super accuracy (??) one of the centres is either slotted or fitted with an eccentrically adjusted pivot. If you've ever watched the Discovery Channel's "How do they do it" or "How it's made" on ball races, the varying tolerance the individual balls are made to has quite a wide band.

Just remembered the Anti-backlash gears for "Important" drive systems,but they are usually lightly loaded. You want to play with the centres? make a depthing tool similar to the watch/clockmakers, but it has one fixed pivot with a hardened centre and a clampable sliding one in a slot in a piece of bar. Mount the gears, interpose a shim for clearence, clamp and bonk the pins on the plate you're marking.

Regards Ian

Richard Wilson
01-30-2009, 07:27 AM
Hi
All these are good answers, but if your gears are running on pins fixed in the plate, make one of them say 30 thou eccentric, then you have a way of adjusting out any error.

Regards
Richard

lazlo
01-30-2009, 11:02 AM
if your gears are running on pins fixed in the plate, make one of them say 30 thou eccentric, then you have a way of adjusting out any error.

camdigger
01-30-2009, 11:03 AM
Hi all

I know onlty what I was exposed to in gear class many moons ago...

1.)I must be misunderstanding a statement in the original post... Spur gears must have parallel axes otherwise, they will not make correct contact on the tooth faces. Parrallelism of the shafts is, IMHO as important as backlash.

2.) optimum backlash will improve the vibvration and noise from the gears meshing and reduce slop when loads are applied and removed, but are quite forgiving unless you're working with super high speed or horsepower.

3.) there has been no mention of the use of chalk on the good machinists rule to make the setting of dividers easier. Rubbing chalk into the division marks will make setting the dividers considerably easier.

My \$.02 cdn
YMMV
Cam

Lew Hartswick
01-30-2009, 11:36 AM
Off hand if youre using a center punch to locate the holes, a dress-
makers tape will be accurate enough to locate the other hole. :-)
...lew...

Swarf&Sparks
01-30-2009, 11:54 AM
I'm not in Tiff's class of precision, however....
presuming you are not using exotic alloys, a couple of NIB magnets make a sort of toolmakers button setup on the mill, using coax indicator or edge finder and some trig.

You may be surprised by the tolerances on these things.
I checked a pack of 5 (\$2 AUD) and they varied by less than .01MM in dia and thickness.
(by Moore and Wright mic.)

Oldbrock
01-30-2009, 12:22 PM
I'm with Oldtiffe, drill and tap 10-32 on each centerpunch mark, bolt on one toomakers button, stack jo blocks to centerdistance minus button diameter and hold the second button against the stacked blocks and tighten the second button in place. Dial in each button in lathe or mill, drill and bore to gear shaft diameter. The type of fit for the shaft to bore is up to you. Peter

oldtiffie
01-30-2009, 06:35 PM
If any of you even read Machinery's Hand-book you will see that it recommends/advises that back-lash, if insufficient, can be "adjusted" by taking a deeper cut.

Yeah, yeah I know about the involute curve, rubbing vs rolling, scrubbing, wearing etc. but that's the way it is.

Also for what its worth, the true involute curve is only at the pitch line as the curves on the gear sides/flanks above (addendum = 1/DP) and below (dedendum = addendum + clearance) are cycloidal, one above is epicycloid and the one below is hypocycloidal. So there goes the purist's "all involute" curves on "gear-set" cut gears.

Serves you bloody right for making a real mountain out of an imaginary mole-hill (most cases).

If hand-ground fly-cutters can do satisfactory jobs for many, then the question of super-gears and undue hype and needless worry - and bull-\$hit - are just a lot of hot air.

If you need the extra care - go the extra mile - otherwise give it a miss and just stick to doing what you have to and what you can.

So far I've heard bugger all about the gear material or the size or quality of the fits for the shafts and bores.

So let's not start hyper-ventilating needlessly.

Lets' have a look at a few instances that are subject to abuse that many may not even consider let alone do anything about - and possibly rightly so in many instances.

Who has actually pulled an entire mill or lathe apart and restored it to "as new specs"? There are some - for what-ever reasons, but many will just leave well enough alone and it mostly seems to work OK.

I hear a lot about change gears but very little about the gears in the quick-change gear-box or under the apron of the lathe or the lathe rack and pinion. Some of those parts are in use every or most times the lathe is in use. Heavy "flogging" and "making chips" can put huge loads right from the lathe spindle to the apron/carriage - most of it gearing, most of it taken for granted and most of it working pretty well. I should also mention the back-gear train on a belt-driven lathe. Its is in the way of any dust etc. that is about and despite some of the heavy loads it is put under, it too does pretty well.

There ARE times and places where precision gearing is required and the appropriate levels of skill and tolerances are quite justified.

There are times when people just want to make as exact and as good a gear as they can just for the sake of achieving it. That's fine too.

The trick is know the least or best level for the job in hand. By definition, anything less is inadequate and anything more will work as well.

Once that required level is defined, it is only a matter of working back-wards (mostly) to define the methods and processes that are necessary to acieve the required out-come.

I can see no reason why just about anyone and every one here could not make a satisfactory gear within the limits of their equipment. It is up to each individual to decide the "satisfactory" level for themselves. The decision is theirs alone. Anything from anybody else is just opinions and advice with none of it binding.

In case no one else does it for me, I will include myself as being firmly in that advisory and/or opinion(ionated??) category.

lane
01-30-2009, 06:53 PM
Let's put a few practicalities into this equation. We will start off with the very accurate (most are) "Machinists Rules" that are successively sub-divided into 1/64".

Put one point of the dividers into an etched mark on a good machinist's rule. Move the other across the rule. It is very easy to see where the moving point is.

First of all, 1/64" ~ 0.016" (16 thou). Halving it by eye is easy. If you are "off-centre" by 0.002" (2 thou), one side will be (0.008 + 0.002" = 0.010") and the other (0.008" - 0.002" = 0.006") a difference of (0.010" - 0.006" = 0.004") which at 1/4 of that 1/64" division is quite visible to the naked eye - better still with a loupe' or magnifying glass. There will be no (or negligible) "parallax" error as the points will be very close to the rule. So, getting it to within 0.004" is not too difficult and neither is getting it to within 0.002".

Transfer punches are a PITA as they must match the diameter of the bore/s very closely and the point of the transfer punch cone must be very precisely centred. Then, the chances are that the transfer punch needs to be followed up with a centre-punch and then the centre punch by a centre and/or spotting drill followed by one or more regular drills - all of which can each "wander off" bot laterally and axially and then by a reamer which will follow the drill just previous to it.

If I were marking it out I'd use a vernier or digital height guage (with a scribing point/edge) for accuracy or a surface guage or a scribing block and a flat plat (mill table or surface plate) with the job set up on a rotary table for the horizontal and vertical as well as any angular lines.

I can quite comfortably and repeatedly set a mill spindle axis over a line or intersection of lines within 0.002"

Its a matter of knowing what your tolerances and allowances and limits are and where your errors are of might be and acting and making informed judgments accordingly.

If the real requirements of or the gears is not too rigorous, I suggest that even badly meshed gears in the lathe gear-train rattle away in a dusty environment without a lot (or any) care and lubrication and by and large they do very well.

It is not uncommon for the pitch circles of gears to be eccentric to the bores and they oscillate in and out of mesh from "good" to "not so good". Set a pair of gear-train gears and set the back-lash and see if it is the same all the way through a complete rotation of each gear.

Oh dear - what to do?

Answer: bugger all. If it works its probably OK.

If you are cutting gears on a mill with the standard sets of gears for each DP and numbers of teeth, the only one that will be pretty accurate will be the first one in the set - even that is a compromise and the compromise gets bigger (worse?) the further up the number of teeth for each cutter you go. If you are plunging straight in for depth with your milling cutter using machine dials you are really trusting to luck unless you measure the gears against table in "Machinery"s Handbook" - or the like - using either a set of gear calipers or wires (2 or 3) with a micrometer. Seeing that the gear profile is concentric and symmetrical is another concern.

And that is not all of it - by far.

But in practical terms in many shop projects, most of it can be disregarded - up to a point.

I will not get into set-up and machine rigidity as common sense will soon identify any potential problems as well as their "fixes".

Why the diversion into gear-cutting when the topic is about setting gears up super-accurately?

Easy - because they are interdependent.

Just keep a sense of reality and perspective as well as a cool head and you will be OK most times.

The easy way is to use a Starrett master veiner caliper ether a 8 inch are a 12. set to correct dimension and turn them over you will find a little center punch mark om the head and one on the slide insert the divider points and set. now you have it set but be careful you do not put to much pressure on the are they will spring.

David Powell
01-30-2009, 07:00 PM
I enjoy making, repairing, fitting and assembling gears. Just watching them go round happily driving each other gives me a thrill. I am in full agreement with old Tiffee in that the important point is to consider the circumstances of use. One fellow I knew many years ago had a full size traction engine with very worn gears on the crankshaft, he built them up with weld, recut the teeth as best he could with fly cutters in an old mill, reassembled his engine,found they were very noisy,jacked the engine up, poured emery dust etc on the gears, and went to work leaving his wife to keep steam up and let the gears run in for a couple of days. To the best of my knowledge and belief that engine is still fairly quietly ,running with those gears 40 yrs later. Conversely, I spent quite a lot of working time shimming bearing blocks and replacing bearings and gears on one particularly odd ampoule filling machine to keep backlash to a minimum so that varying loads on the output end of a long train of gears didnt throw the timing out to the point the machine had failures at certain speeds.Yes gears can be lots of fun. Regards David Powell.

lane
01-30-2009, 07:03 PM
Another way is to set the plate at what ever angle you are looking far on the mill . Then put in one hole and dial of how far to the next. Once their depending on the size of the hole in the gear make a good fitting pin and put one end in the collet and the other end in the gear and turn the gears you can feel and see how they will work before you drill your hole . If all ok put the hole in at that location . If to tight are loose move in are out till you get what you want. Simple as that. That is how I do it. No calculations involved.

oldtiffie
01-30-2009, 08:20 PM
There are a couple of posts that I've left until now as I was sticking to traditional/usual stuff in the shop, but they are both too good to pass up commenting on.

I'm not in Tiff's class of precision, however....
presuming you are not using exotic alloys, a couple of NIB magnets make a sort of toolmakers button setup on the mill, using coax indicator or edge finder and some trig.

You may be surprised by the tolerances on these things.
I checked a pack of 5 (\$2 AUD) and they varied by less than .01MM in dia and thickness.
(by Moore and Wright mic.)

Excellent points Lin and a great example of lateral thinking and improvisation (you've always kept surprising me with that talent of yours).

The diameters are not important at all so long as you know the details of the sizes and that they can be placed accurately with minimal/no "damage" to the job - as I am sure you can.

For the info of some:
- 0.01mm ~ 0.0004" (4 tenths!!!)
- AUD2 x 0.66 = USD1.32 that is to say 26 cents US each!!

I'm with Oldtiffe, drill and tap 10-32 on each centerpunch mark, bolt on one toomakers button, stack jo blocks to centerdistance minus button diameter and hold the second button against the stacked blocks and tighten the second button in place. Dial in each button in lathe or mill, drill and bore to gear shaft diameter. The type of fit for the shaft to bore is up to you. Peter

Thanks brockley.

I deliberately didn't mention "slip guages" ("jo" blocks) as I am not sure that many have them but your pointing out about using them and "squeezing" the buttons is "spot on".

I did think of mentioning using adjustable parallels as they are cheap and very accurate and easy to set (with practice) as they can almost be seen as an adjustable slip-guage/"jo" block set. I had to "ease" mine a bit but they are excellent now - very smooth and quite accurate. They are great for measuring slots as well as in some awkward places:
http://littlemachineshop.com/products/product_view.php?ProductID=2552&category=

https://www.machineryhouse.com.au/Products?stockCode=Q260

Carld
01-30-2009, 10:07 PM
Just shove the gears together and measure the side of one hole to the side of the other hole and add the diameter of one hole to the measurement across the holes and use that as the center line. That assumes the holes are the same diameter. If not you should be able to figure the center distance between different diameter holes or you should quit doing machine work.

oldtiffie
01-30-2009, 10:53 PM
Just shove the gears together and measure the side of one hole to the side of the other hole and add the diameter of one hole to the measurement across the holes and use that as the center line. That assumes the holes are the same diameter. If not you should be able to figure the center distance between different diameter holes or you should quit doing machine work.

That's pretty well it in a nut-shell Carl.

Provided there is a small movement between the gears and a "click" when you hold one and move the other back and forth you are pretty well set to go. Providing the gears aren't so tight that they "foul" each other or "grind" and not so loose that they "crown" each other you are OK - set it somewhere in the middle and then if it sounds and feels OK, chances are it is OK.

Centre distance is only half the sum of the pitch circles each of which can mostly be got by measuring between the bottom of one cut and the top of the gear opposite and just taking off a "smidgen" (to allow for "clearance" in the dedendum). A carpenters rule is plenty good enough. Most gears are an even DP so a quick check of number of teeth/PCD will soon confirm it (or not!!).

I only use a carpenters rule as it is 1 metre long, is marked in inch and mm (built-in mm>inch>mm etc. conversion too), folds into four and has the ultimate contrast (black marks on a bright white back-ground). 1mm ~ 0.040". I can split a mm into four (0.010") easily, mm/8 ~ 0.005" and so on - all too easy.

Swarf&Sparks
02-01-2009, 01:30 PM
Mick, bear with me, some may not know the old dodge.

Once the buttons (magnets, whatever) are set up, use your calipers.
Measure outside dimension, then inside dimension, add and divide by 2.

This works also, for measuring hole pitch in a part, already drilled.
Works for odd-sized holes too :D

Gears, I'm less than familiar with. I just put the holes in the right place.

gellfex
02-01-2009, 05:27 PM
Maybe I'm missing something here, but I've found if you go tighter than the PD+PD/2 you're asking for trouble. All gears have backlash except special anti-backlash (and even they do if you over torque them), so why screw yourself? If you don't know the PD of your gear you can usually look it up in a catalog. by the teeth # and OD.

As for marking, why transfer to dividers, are you guys afraid to scribe using your calipers? I'll just scribe the line between centers and all the way to an edge. Then from that edge, mark the 1st center, zero the caliper, set it to the correct spacing and mark the 2nd. Spaced within the accuracy of a caliper, +-.001, plenty for anything we're capable of drilling, or prick punching.

Yes I need to occasionally sharpen my caliper tips, but I don't expect them to be immortal, they're a tool to be used as best keeps me going forward. They suffer far more when I drop them!:eek:

Paul Alciatore
02-01-2009, 08:42 PM
The easy way is to use a Starrett master veiner caliper ether a 8 inch are a 12. set to correct dimension and turn them over you will find a little center punch mark om the head and one on the slide insert the divider points and set. now you have it set but be careful you do not put to much pressure on the are they will spring.

I have a Starrett vernier height gauge, but it does not have any such marks on either side. I am curious as to how they are arranged. It would seem that they would have to be in the same position, one above the other, when the caliper is closed to zero. Or there would be a parallax error. Butr even that would produce some parallax error. Or perhaps they are offest by some fixed amount, like 1" or 0.1" that you have to add to the reading to get their actual separation.

Could you describe this feature better or perhaps post a photo. I may want to copy it on a cheaper import caliper.

lane
02-01-2009, 09:07 PM
I have a Starrett vernier height gauge, but it does not have any such marks on either side. I am curious as to how they are arranged. It would seem that they would have to be in the same position, one above the other, when the caliper is closed to zero. Or there would be a parallax error. Butr even that would produce some parallax error. Or perhaps they are offest by some fixed amount, like 1" or 0.1" that you have to add to the reading to get their actual separation.

Could you describe this feature better or perhaps post a photo. I may want to copy it on a cheaper import caliper.

Not on the height gages ,only the master veiner calipers 6, 12, 24 inch
When the caliper is closed up. They drill a hole through the sliding jaw but go just less than .001 breaking through. The tip of the drill may just scratch the surface of the beam. Not sure just how they do all that . but in the beam is a small divot like a prick punch mark with a circle around it. adjust caliper to size and insert one divider leg in divot on beam and other in divot on slide . Very accurate I have found. All of this is on the back side opposite the numbers.