Table Saw Alignment Tool Reviews

MasterGage Pro

by admin on Nov.16, 2009, under MasterGage Pro


What is included with MasterGage Pro

This section is a guided tour of my MasterGage Pro, showing each part, what it does, and how it works.

The “Base” is machined from a standard aluminum channel extrusion.

The markings on the surface are said by the maker to be laser “etched”.  This is somewhat of a misnomer, as etching is a chemical process involving photolithography.  The graphics on MasterGage are actually laser “engraved” (a machining process).  The results are very attractive and readable as shown in the photos above. The vertical rods are stainless steel.  The surface is black anodized, the protractor is red anodized.

The “Level Arm” is machined from aluminum bar stock. It’s surface is hard anodized. The two “V” groves ride on the stainless steel rods that are mounted in the main body allowing vertical motion with a range of about 2.4″. It’s position is secured by a spring loaded thumbscrew and “T” nut.

 

 

Two accessories are available which attach to the end of the level Arm. Left: “Point Indicator”, $29.  Center: “Dial Indicator Adapter Block”, included. Right: A short rod segment (included with my vintage model) can be inserted into the Level Arm as a measurement aid.

 

The rod on the back of each accessory fits into a hole in the end of the level arm and is secured by a #8-32 thumbscrew.

The dial indicator attaches to the “Dial Indicator Adapter Block” using a 1/4″-20 thumbscrew.  There are five holes available which allow mounting the dial indicator in a variety of orientations.

When pointed down, the dial indicator stylus would extend beyond the bottom of the base even when the Level Arm is at its highest position.  When placed on a flat surface the plunger is depressed significantly allowing for maximum height measurements of about 0.4″.   

My vintage model included two nylon spacers to be used on the back side of the dial indicator plunger.  These spacers retract the plunger so that the stylus does not extend beyond the bottom of the base.  Measurement range is limited more with this configuration. The current model MasterGage Pro comes with a 1/4″ travel dial indicator so the stylus does not extend beyond the bottom of the base and these spacers are no longer necessary.  Of course, this even further limits the measurement capabilities of the product. So, the maker offers the “Height Extension” accessory ($34) which raises the dial indicator making practical height measurements possible.

The broad “reference” edge of the protractor is shown here. It’s width does not facilitate gauging angled surfaces by sight.

The “Contact Bar” (included) attaches to the face of the protractor and provides a narrow edge for gauging angled surfaces by sight.  This was not included in my Vintage model but was offered as an accessory for additional cost ($14). 

The Protractor is calibrated by adjusting a set screw located in the center of the reference edge.  When the user is satisfied that the reference edge is square with the MasterGage base, then the pointer is adjusted so that it points to zero (90) degrees on the scale.

These photos show the magnets and bubble level accessories installed. They need to be removed in order to install the Miter Slot Cradle Bar.

Shown above is the Miter Slot Cradle Bar which came with my vintage model.  Miter slot width adjustment is made by tightening the setscrews on each end.  As the setscrews are tightened the bar is locally expanded.  The current model is a modified design which has three adjustment points utilizing the same basic method: tightening a setscrew causes localized expansion of a bar.

This is how the Miter Slot Cradle Bar attaches to the bottom of the base of my vintage MasterGage Pro.  Because of the fit, and the flexible nylon clamping mechanism, it cannot be tightened enough to prevent shifting even with minor pressure.  The clamping method has been modified in the current model to provide more acceptable stability. The Magnet and bubble level accessories interfere with the installation of the Miter Slot Bar and must be removed.

On my vintage MasterGage Pro, the Miter Slot Cradle Bar could also be attached to the side of the base.  This configuration is even less stable than attachment to the bottom.  The current model does not permit this particular configuration.

These are the “Precision Rods” available as a accessories on my vintage model ($7 and $9) but included with the current version of MasterGage Pro.

This is the dial indicator point set available as an accessory ($19).  It is made in China.

This is the storage case available as an
accessory ($49).  It is of high quality double wall
construction with a die-cut foam insert.

 

This is the manual which came with my
vintage model.  It is photocopied and illustrated with line
drawings.  Many pages are devoted to titles and advertising.   The current manual is much improved but still contains a
considerable amount of advertising.

 

These hex wrenches were included with my
vintage MasterGage Pro.

 

The “Made in China” dial indicator
available as an accessory for my vintage model ($93) is shown above. 
The mounting accommodates a standard AGD 2 loop back indicator so it
could be replaced with a better unit if one were so
inclined.

 

In its lowest possible position, the
stylus of the dial indicator ends up about 1″ from the table
surface.

 

The manual of my vintage
model recommends performing blade alignment with the base of MasterGage
Pro on its side.  In this configuration the stylus of the dial
indicator ends up about 3″ from the table surface.  Tilting the
dial indicator downward is unacceptably inaccurate.  The maker
suggests the use of an optional accessory: Master Plate ($49), a 3/8″
thick aluminum blade replacement plate.
 
This solution allows measurements across the entire 10″ blade width. 
However, it also magnifies the error produced by minor warps in the
table surface.  Such warps are extremely common around the throat
plate area, where the thin cross section of cast iron allows room for
operation of the blade tilt mechanism.

A new feature on MasterGage
Pro, called “Instant Recall” allows the user to quickly reproduce angular
and linear measurements that were previously registered using a “Memory
Link” in conjunction with a hole in the protractor or level arm. 
This feature is designed to improve the repeatability of the instrument.

Another new feature on
MasterGage Pro is an engraved Brass Name Plate to “personalize” it.

 

In the Metrology Lab

The maker claims various
accuracies and capabilities for MasterGage Pro.  So, I was eager to
test these claims.

The maker claims
that the body of the product is machined to tolerances of 0.0002″ on CNC
machinery.  Perhaps he means to say that the CNC machinery has
positioning or repeatability specs of 0.0002″.  It’s a common
mistake that many people make.  Any competent engineer or machinist
would say that it is not reasonable to expect such tolerances when
machining aluminum extrusions.

Six
surfaces of my vintage MasterGage Pro are said to be designed for use as measurement references (top, bottom, back, protractor edge, top of level arm, and
bottom of level arm).  To test these claims, I attempted to measure their accuracy (flatness, squareness, parallelism). Unfortunately, the
top and bottom surfaces of the base were not
sufficiently flat to prevent significant rocking on my surface plate, making such
measurements virtually impossible. The reason for this is fairly
straight forward:

The wall
thickness of the extrusion used is only about 3/16″ thick.  It
is not reasonable to expect such a thin cross section of extruded
aluminum to maintain sufficient flatness.  This is
likely the reason why the current MasterGage models utilize a
different extrusion design (with heavier cross section). I also checked
the top and bottom surfaces of the “Level Arm” to determine if they were
parallel.  Unfortunately, it too rocked on my surface plate so
measurements were difficult at best. 

On my vintage MasterGage
Pro, the maker claims that the vertical motion of the Level Arm can be
used in conjunction with the scale to measure angles using the dial indicator. 
Basic one inch trigonometry is proposed as the method. This assumes
several things which are not mentioned in the manual:

  • The
    tilt of the indicator must be adjusted to eliminate cosine errors. 

  • The base must not rock on
    the reference surface. 

  • The vertical travel must
    be precisely one inch; a difficult task using the supplied 0.020″/div
    scale.

  • The vertical motion must
    be square with the reference surface. 

To test the last requirement I
utilized the TS-Aligner calibration setup (above), replacing the MasterGage
Chinese indicator with a Mitutoyo 0.0001/div indicator (model 2804F-10).
The mechanism did not provide
consistent and repeatable vertical motion. It is likely why this
particular claim was left out of the current version of the manual.

The protractor
scale is graduated to 1/2 degree and the maker claims accuracy to 1/4
degree (visual interpolation as no vernier scale is included). Checking
the accuracy of the protractor was also made difficult by non-flat
“reference” surfaces but I managed very consistent results by
maintaining the same positioning.  In addition, the angle setting
squirmed when the locking knob was tightened making it difficult to obtain a
specific setting (but not impossible).  I started by meticulously calibrating
the protractor to
about 0.0003″ total error at zero (90) degrees (the flatness of the
protractor’s “reference” edge).  I then checked the full scale (45
degree) accuracy using the same setup used to verify my precision ground
steel angle blocks (see photo above).  My electronic gage measures in millionths of
an inch and has a total range of 0.003″.  The error was far more
than 0.003″ so I decided to adjust the protractor to “zero out” the
error and let the pointer tell the story.  As you can see, the
scale itself is off by a very significant amount, about 1/2 degree.  Not
quite believing my eyes, I repeated the entire procedure with the same
results.

 

 

 


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