Results 1 to 16 of 16
Thread: Starrett 98-12 Level
06-07-2006, 02:30 AM #1
I bought a Machinist level on ebay that needs to be calibrated. Any suggestions? Send Out? To Who? Do It My Self?
06-07-2006, 02:42 AM #2
Levels are self-calibrating by definition.
1) Put it on a surface plate with a metal right-angle clamped down as a position reference.
2) Note the reading.
3) Turn the level around 180º, locating it exactly in its original position.
4) Note the difference between this reading and the first one.
5) Adjust the level to reduce the error by 50%.
6) Turn it around again and check that this reading matches the previous.
Repeat to the desired level of accuracy (pun intended )
Obviously the level and surface plate must be clean and in good condition to achieve optimum results. If you don't have a surface plate a large piece of metal which is rigid and can be leveled will work.
Note that the reference surface need not be level. It must only be within the measurement range of the level being calibrated. But the whole process is more convenient if the surface is accurately level.
06-07-2006, 02:50 AM #3
Thanks Leigh, I've been meaning to post the same question about a leve I bought recently.
06-07-2006, 09:07 AM #4
That is the procedure we use to calibrate our precision levels. Starrett gives the same procedure in their introductory notes to the "Levels" section of their catalog.
When we do the calibrations, we make sure of the following:
1. Level and surface plate are at the same temperature. I call this "normalized"- probably a misuse of the term. I like to let the levels sit on the surface plate for a few hours, if not overnight if there are extreme temperature differences (like a level that was in its box out in a vehicle in winter).
2. Clean the surface plate and level contacting surfaces well.
3. Using the heel of your hand, swipe over the surface plate and level base to feel for any slight burrs or dings. If you feel any, stone them off using a small stone. For burrs or dings that you can feel, I use a "hard India" stone and something very light like "LPS" or similar.
When you are done with any stoning, wipe things down with lint-free wipers, such as "Kimwipes" (industrial grade tissues). At home, I use toilet paper.
4. If no burrs or dings are felt, I "kiss off" the contacting surface of the level. Lightly stone the level contacting surface with a smooth, hard Arkansas stone. I just give the contacting surface of the level a rub with the Arkansas stone, dry.
5. I use a "Sharpie" marker to outline the position of the level on the surface plate.
6. Position the level within the marked outline and note the reading. Follow what Leigh wrote to adjust the level. We call this "bucking in" the level.
7. When you are done with this "bucking in", you should be able to turn the level end for end and have the reading repeat.
A Starrett 98 level is a precision level and is fairly easy to buck in. One graduation on the vial = 0.005" per foot. If you do this exercise with a Starrett 199 level , one graduation on the vial = 0.0005" per foot. Starrett calls their 199 series levels "Master Precision Levels". I call bucking-in a 199 Level "Chasing my tail".
I have bucked in levels out in the field on any convenient flat surface such as machined & ground casing flanges on turbines. I have used the table of a Bridgeport or the flat way of a big LeBlond lathe as a flat surface to buck levels in. If you do not have a surface plate and put the level down on a flat surface, check that there is no "rock". The level must seat solidly on the flat surface.
If you use a piece of plate glass or a large flat piece of metal, you must make sure that level sits solidyl on it with no "rock". If you can;t come up with a surface the level will sit solidly on, you can create one. To do this, you will need to shim one end of the level so the ends sit soldily. You can use shim stock or even something like a playing card. I did this once or twice out in the field with a level that was out of adjustment. I was doing a favor to a friend of a friend. He had a small sawmill and was setting up an old wood planer. He had an old Starrett 98 level that did not repeat its readings and had no really good flat surface to calibrate the level on. The planer tables were about the best machined surfaces in the guy's mill and those tables were not quite flat as a result of wear and years of rough conditions.
Having no really good flat surface, I created a reference surface by shimming one end of the area the level was to sit on. The flattest surface was not realy that flat, and the level rocked a slight amount. I taped the shims down with ordinary Sctoch tape- made the shims large enough so the level sat on them, not the tape. I got the level bucked in fine and did the best I could with the old planer. Once you have the shims in place on the one end, you must not move them while you are "bucking in" the level. It comes down to establishing a solid reference "plane" or reference surface that the level is always seated in for adjustment.
The business of "Stoning" off surfaces is something I was taught to do routinely. Many machinists and toolmakers as well as millwrights will "stone off" contacting surfaces. You are not looking to take off any measurable amounts of metal. What you are looking to do is to insure there are no slight burrs or raised areas of metal. Routine handling of precision surfaces can result in these tiny burrs or raised areas. The heel of a person's hand is often the best means of detecting any such burrs or dings. You might be surprised to see that careful stoning and cleaning can make quite a difference in accuracy and repeatability of a precision level.
06-07-2006, 09:31 AM #5
[img]smile.gif[/img] Just for information, a 98-12 is a "machinist's" level, not a precision level.
06-07-2006, 01:59 PM #6
Good points re precision levels. I have a Mitutoyo that's good for .00025" per 12" (twice the sensitivity of the Starrett 199). If you want maximum accuracy out of that type of instrument you need to take the precautions which you mentioned.
But the level under discussion is a 98, and I believe the instructions I presented are appropriate for that degree of accuracy.
06-07-2006, 11:44 PM #7
There are a couple other things you should check on your new-to-you Starrett 98: First that the level vial is firmly attached to its carrier tube, and second that the vial is rotationally aligned to the base.
The outside diameter of the glass vial is slightly smaller than the inside diameter of the carrier. Traditionally the vial is fixed to the carrier with small plaster plugs cast over both ends of the vial, but some newer instruments use Room Temperature Vulcanizing (RTV) rubber instead of plaster. These materials are very stable when fully cured, are at least slightly adhesive, and don't shrink enough to overcome their adhesive properties when setting.
Be that as it may, I've found several instruments with a loose vial. A couple of times the vial has been loose enough to make an audible rattle if the instrument is vigorously shaken, although on an instrument like the Starrett 98 will make enough noise to obscure the vial rattle unless the rotating cover is held in place against an end cap while shaking the instrument.
Assuming that you have a good ear and a very quiet room, you should hear nothing except maybe fluid swishing when vigorously shaking the instrument up by your ear.
The other way to find a loose vial is to feel for it. Press your finger against the vial near an edge of the so-you-can-see-the-bubble cutout in the vial carrier and try to push the vial north, south, east, west, and down looking for any hint of movement independent of the carrier.
Level vials are very sensitive to thermal distortion, and in the time it's taken you to press the vial this way and that the heat from your finger has distorted the vial. Pick the instrument up, shake it for a few seconds to mix the fluid, set the level down -- out of the sunlight and away from heating or air conditioning vents -- and let it rest for 10 or 15 minutes before adjusting the vial as Leigh and Joe describe. (Incidentally, I'm with Joe on the importance of checking the iron for burrs and stoning off any you find . . . especially on a used instrument.)
After you've adjusted the vial tilt, "roll" the instrument around its long axis. You should be able to rotate the instrument through +/- 15 degrees or so without having the bubble change lengthwise position in the vial, which only happens if the vial's long axis is parallel to the long axis of the iron body. If the vial is rotated away from parallel to the body, the bubble will move lengthwise in the vial when the instrument is rolled.
It should go without saying, but the bubble moves to the high side of the vial. To adjust, loosen the top adjustment-clamp nut and move the now-loose end of the vial carrier end cap sideways to correct the error. I don't recall ever seeing a Starrett 98 that couldn't be adjusted within the factory clearance between the adjustment stud and end-cap hole, but I've had to open the hole in the end cap or file away a portion of the stud's thread to align the vial on some other reputable-brand millwright levels.
Incidentally, some instruments have very small setscrews in lateral holes in the vial carrier end cap. These setscrews bear against the sides of the adjustment stud, and are used to jack the vial carrier around when setting the vial axis parallel to the edge of the iron body.
Obviously you'll need to retighten the top adjustment-clamp nut and recheck the vertical and in-plane adjustment of the vial before you can consider your instrument properly adjusted.
Now let's go back and reconsider the thermal distortion of the vial for a moment. With the instrument set on a stable surface with the bubble reasonably centered in the vial, reach out and rest the tip of your index finger on the glass vial at one end of the see-the-vial slot in the vial carrier. In only a few seconds you'll see the bubble move, significantly.
Pull your finger away as soon as your see the bubble run.
Now just sit and watch. Note how much time it takes for the vial to reach thermal equilibrium agains, when the bubble will return to the earlier reasonably-centered position in the vial.
If you've not done this finger-on-vial demonstration before, I can just about guarantee you'll be amazed.
An aside to Leigh:
The vial in your Mitutoyo -- and most other European and Asian instruments -- is graduated in 2 millimeter increments, while that in a Starrett 199 -- and most other US and British instruments -- is graduated in 1/10 inch increments. For the same apparent specification (in terms of tilt / division), a vial with 2 mm graduations has a significantly shorter radius of curvature than a vial with 1/10 inch graduations.
Your Mitutoyo is more sensitive than a Starrett 199Z, but "twice as sensitive" probably overstates the difference.
06-07-2006, 11:59 PM #8
If the vial is bad, McMaster-Carr http://www.mcmaster.com sells a replacment for $66 under their catalog number 21515A29. I believe this is the mounted vial with the metal cylinder and cover.
Good points. Precision tools all exhibit some degree of thermal sensitivity (pun intentional ). As with any tool, you have to get familiar with it and work within its limitations.
Re the Mitutoyo level, I had never seen one of these before. It's an ebay find. Nice compliment to my Starrett 199 And it's shorter, only about 8" long, so it will fit in places the Starrett won't.
06-08-2006, 07:32 AM #9
Another thing to consider is the condition of the bottom of the level. You should be able to place the level on a flat known flat surface and push or pull one end and the level should not pivot in the middle. If the level swivels in the middle the bottom surface will have to be scraped. You should have pretty much even bearing across the entire surface but the points of bearing should be a little heavy near the ends. If you can move one end and the other ends stays put you are in pretty good shape. John
06-08-2006, 11:12 AM #10
If the vial needs to be replaced, see the writeup over on the HSM site:
Starrett Vial Replacement
I have the HTML page that is a dead link over there. If you need it, PM me and I'll send it to you.
I did this last year, and IIRC the final cost for just the glass vial was $20 (includes shipping) from Starrett. The "replacement vial" linked to at McMaster is a replacement vial "assembly" containing the glass vial, and the metal tubes; hence it is far more expensive. Interesting to note that from Starrett (prices current as of early last year), the replacement vial assembly was $51.20.
06-09-2006, 08:40 PM #11
Guy's, Your responses have been so helpful. I'll 'buck-in' the level this weekend. My next topic will be How do I use a machinist's level?
06-09-2006, 09:02 PM #12
The common usage is for setting up machine tools, particularly lathes since they're more sensitive to alignment problems. In concept you set the X and Y axes level, then by definition the lathe bed is flat and free from twist. This makes some assumptions about the condition of the machine, but that's a different topic.
And there are other advantages. For example, if you know your mill table is accurately level, you can use that information to set up a workpiece parallel to the table when a direct measurement might be difficult or inconvenient.
06-10-2006, 11:41 PM #13
Say I have a large bench saw (I'm a woodworker) Who is not afraid of metal and took two classes in machine shop practices at the local JC.
with the top around 36" square. Where do I start? How do I determine the high and low side? I do this all the time and it drives me crazy. Sometimes I end up shiming from .25" to .75" all around. Assuming the ground is flat, shouldn't on corner touch and the low side be .50" ?. I have fine hand skills and good judgement but getting something level without going around in circles and starting over just drives me crazy.
I think what I'm looking for is the methodology involved.
06-11-2006, 12:00 AM #14
"How do I determine the high and low side? I do this all the time and it drives me crazy. Sometimes I end up shiming from .25" to .75" all around."
Not really a bad idea to have a solid piece of steel plate under each foot anyway.
Now you measure or check the table top and determine which corner is the highest, that corner will not get a shim.
You will go around and around but never put a shim under the corner you originally determined highest. If it does become low you have simply added too much shim.
The shimming process should be slow and methodical. If you are not conservative enough with the shims you will chase the sweet spot around.
Heck, you'll end up with three inches of shim stock under each foot and she will still be out JRouche
06-11-2006, 01:05 AM #15
In this case you do want to go around in circles
Put the level in an open area where you can rotate it through a full 180º arc. Do so, and note the point of maximum deflection of the bubble. At that orientation, one end will point at the highest point of the table, the other end toward the lowest. Shim accordingly.
Many machine tools use a three-point suspension because it's easier to level. You could do the same with a saw provided you don't introduce instability. Put a support under two adjacent corners, possibly the two front ones. Then put a single support in the middle of the rear. Now it's very easy to level the machine front to back and side to side.
This approach might or might not be appropriate for your particular situation, depending on the rigidity of the machine and the size, shape, and weight of the work which it must support.
06-11-2006, 01:35 PM #16
There are two broad categories of machine structures to consider here. The first is the rigid machine that needs to be supported only to keep it from rocking, while the second is flexible and relies on its foundation to achieve planarity.
I would speculate that the maker of your saw thought his machine rigid, but he might have included jackscrews to adjust level at the four corners of the base anyway. I'll suggest a levelling technique based on that premise, which you can adjust to suit the actuality of your hardware if that's not the case.
1. Make a floor plate to place underneath each jackscrew. A 4 inch x 4 inch plate of 1/2 inch thick steel is about right. If you want, cement a layer of plumber's "rubber sheet packing" to one side of the plate.
2. Set the floor plates, with the rubber side down, on the floor where they will need to be to have the machine end up where you want it.
3. Adjust the jackscrews to the midrange of their travel and put the machine in place on the floor plates.
4. The machine will probably rock across one diagonal. Adjust the jackscrews as necessary to stabilize the machine.
5. Clean the machine table and the bottom of your properly-adjusted Starrett 98 level, stoning both surfaces to deburr if needed. Now set the level on the machine table, roughly centered between and parallel to the line connecting two diagonally opposite jackscrews. (Let me repeat that for emphasis . . . the level should be in line with diagonally-opposite jackscrews, NOT in line with two adjacent jackscrews.)
6. Adjust the two jackscrews in line with the level by equal amounts but in opposite directions to center the bubble in the vial.
7. Rotate the level on the table to put it on line with the other pair of jackscrews.
8. Adjust the other two jackscrews (that are in line with the rotated level) by equal amounts but in opposite directions to center the bubble in the vial.
9. Double-check both diagonals, tweaking the jackscrews as needed.
10. Finally, place the level in line with each adjacent pair of jackscrews to verify that the table is both planar and level.
11. Put your Starrett 98 away and go have a sasparilla to celebrate!