Precision Gages - Design and Use of Dow-Gages
The lever ratio in the Model 10 Dow-Gage as shown in the line drawing above is one to one within reasonable manufacturing limits. It is therefore pertinent whenever possible, to design Stage Sets so that Fulcrum Lever “A” is in a horizontal position when gage is adjusted to Zero with Master in place. If this is done as suggested thru the use of a few simple rules to follow, the Dow-Gage will repeat consistently, well within the allowable error of any AGD Indicator on the market today.
To accomplish this, Stage Sets must have, (1) The centerline of the Gage Pin, Square with Stage Face, (2) Gage Pin Face “H” or “J” must be PARALLEL with Stage Face “G” or “K”. (3) Gage Pin RADIUS “B” must be CONCENTRIC with outside diameter of Gage Pin.
To determine the proper length of gage pin in a Stage Set for checking an internal dimension, refer to drawing above titled MALE STAGE SET. In this case the proper pin length should be one and three sixteenths inch PLUS the “D” dimension PLUS the MEAN of the dimension to be checked.
To determine the proper length of gage pin in a Stage Set for checking an external length dimension, refer to drawing above titled FEMALE STAGE SET. In this case the proper pin length should be one and three sixteenths inch PLUS the “D” dimension MINUS the MEAN of the dimension to be checked.
While it is best that pin lengths are held within plus or minus one sixty-fourth of an inch, pin lengths with a wider manufacturing tolerance may be used without serious variation. Stage Sets manufactured by Dow Gage, LLC have pin lengths held within .010.
Because the indicator action is reversed when used with a Dow-Gage it is necessary that the indicator have the proper plus and minus signs in order to get the true direction of the error from MEAN ZERO. In order to determine the proper position of the plus and minus signs on the indicator it is generally true that a Stage Set for checking an internal depth dimension should have reversed plus and minus signs, ie: the plus mark should be to the left of Zero when facing the indicator. Indicator should have a balanced dial and for best results the hand should be set in the 6 o’clock position when at rest.
When the Stage Set is for checking an external length on the part it is generally true that the indicator will require standard plus and minus signs, ie: the plus sing will be to the right of Zero when facing the indicator. A simple rule to follow is that when the Gage Pin is above the Stage Face the indicator should have REVERSED plus and minus signs and when the Gage Pin Face is below the Stage Face the indicator should have STANDARD plus and minus signs. This rule applies to Stage Sets for checking the diameter of a taper but it does not apply for the checking of ANGLE of a taper.
To install a Stage Set on the Dow-Gage it is important to first provide indicator clearance as well as stage clearance. First loosen adjustable stop lock nut and unscrew stop screw so that fulcrum lever can be depressed well below horizontal position. Loosen indicator lock nut and raise indicator until depressed fulcrum lever does not influence dial. These are extreme precautions to prevent Stage Set equipped with snap ring on gage pin from jamming indicator or putting undue pressure on the stop.
Gage is now ready for Stage Set which can be screwed into base and tightened securely. Place Master in position and turn indicator adjusting nut, lowering indictor until indicator hand passes Zero approximately one quarter turn, tighten indicator lock nut and turn indicator bezel to read Zero. Remove master and depress gage pin until indicator hand passes zero by one half turn and adjust stop and lock in place. Reset bezel to Zero checking master several times. Gage is now ready for use.
With a little experience in the use of this versatile gage, Stage Sets can be changed from one to another in less than two minutes.
The general instructions (above) for the design and manufacture of Stage Sets for the Dow-Gage also apply to the Tacomp Stub except that for the Stub it is necessary that the gage pin have a SNAP RING and the indicator be equipped with a FLAT POINT (furnished with Stub).
Stage Sets for this unit are not limited as to size and may be as large as is practical to handle. The Stub may also be attached to large multiple indicator gaging fixtures or checking machines.
Dow Gage, LLC manufactures an extensive line of standard diameter Stages up to five inches for use with both the Dow-Gage and the Tacomp Stub.
Like the Dow-Gage, Stage Sets for checking almost any conceivable dimension can be supplied for this unit and the checking of dimensions while the part is still in the machine is simplified.
The Stub as well as the Dow-Gage can also be equipped with a FLUSH PIN ADAPTER allowing the use of simple and inexpensive flush pins, wherein tolerances as low as plus or minus .00025 can be accurately checked. A standard line of FLUSH PIN BLANKS is available from stock and Dow Gage, LLC is prepared to design and make special flush pins for almost any dimension.
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