Pop any pre-purchase question about compound miter saws
into any online newsgroup or forum these days and the names "Bosch" and
"Makita" will likely appear in some of the responses. These two brands,
along with one or two others have proved to be leaders in their class in
compound miter saw design and performance.
admit, I have often spent a good amount of time in the local hardware and
machinery houses examining the subject of today's review - The Bosch 3912
(GCM12) Compound Miter Saw. GCM12 is the model number outside of the USA.
It has always appeared to be a very solid machine with a very good angle
adjustment feature and innovative positive stop system for common angles.
Would the 3912 live up to my expectations? Let's find out:
Note, apart from differences in motor ratings and power
cords, the Bosch 3912 and GCM12 are essentially the same machine, so we
will consider both variants as the one machine for this particular review.
Where differences exist, we will mention those directly.
Packaging, Assembly and Manuals
The Bosch miter saw arrived safely and securely packed in formed
styrofoam within the box. Unpack the contents with care. You wouldn't want
to have your new tool safely delivered and then have it drop out of the
box causing unnecessary damage!
Assembly is quick and easy. The Bosch 3912 (GCM12) ships
almost fully assembled. All you need to do is attach the Dust Chute Elbow
and Dust Bag, attach the miter locking knob to the front of the table
(simply screw it in) and insert the included quick action clamp. If you
buy this saw, you will quickly note the absence of work support extension bars
commonly found packaged with other saws. I'm not sure why this particular
model does not include these, although they are available as an accessory.
If you are planning to use the saw in a miter station, you probably won't
need them anyway, but they would be handy to have if you are using the saw
on location and don't have a miter station or portable miter stand with
Along with the standard warranty and service leaflets
included in your package, you also receive a 35-page English manual in
black and white print. The manual is very clear and concise and print is
easy to read (it's certainly not a photocopied manuscript that you find in
some lower priced saws). Line art drawings along with step-by-step
instructions for performing all the adjustments and particular cuts
achievable with this saw make the manual a very hand resource you will
want to keep close by. Common angles and cutting information for crown molding and other tasks is included, which will certainly come in handy
for the home renovator or tradesman. Top points for manual production this
Checking for Out-of-the-Box Accuracy
I always like to check the out-of-the-box accuracy of any power tool I
buy or review. If it is accurate out of the box (without any adjustments
carried out by the user beforehand), it is a good sign of quality
assurance and indicates that the company's quality testing values are well
implemented in the production of the product. For a miter saw such as the
3912 (GCM12), checking the angle/miter accuracy of the blade vs table out
of the box is a logical measure. The manual offers advice on how to adjust
your saw before you begin using it to ensure it is indeed accurate in use,
but for the purpose of this review, I thought we would see how accurate it
was without any adjustment. So out comes my trusty handyman square and
small framing square, which is all I need to check the accuracy of the
blade and miter settings on the machine.
Firstly, I set both the miter and bevel angles to 0
degrees to check if the blade is at a perfect 90 degrees to the fence. For
this task, I used the small framing square. The result... Yes it's a
positive match. Blade is at 90 degrees to the fence. While in the same
position, I used the handyman square to check the blade is at 90 degrees
to the table. Again a positive result. I should now be able to cut
perfectly square cuts at 90 degrees to the fence. Next I set a 45 degree
miter angle on the table. This would tell us whether the hard detents in
the table base are accurate or not. Using the handyman square again gave a
thumbs up for a perfectly aligned 45 degree angle.
All looking good so far. Now I tipped the blade itself
to a 45 degree angle to the fence (for a bevel cut), lowered the blade and
checked the angle of the blade to the table with my handyman square. Hmmm
pretty much right on, but I noticed the tiniest inaccuracy at one end of
the square. I'm talking really small here. A pinhead ray of light right
near the back end of the rule. I took an angle setting gauge, set it at 45
degrees and measured the angle again. Still that slight inaccuracy, so I
adjusted the bevel angle on the saw ever so slightly (full instructions
provided in the manual to achieve this) to give me a deadly accurate bevel
cut. Not sure what was out here. Possibly just my eyesight as the bevel
angle gauge at the back of the saw is small (as most are) and its almost a
certainty that some error will result, so I wont put this down as an
out-of-the-box issue, because essentially, this saw has been the most
accurate out-of-the-box of about 3 other miter saws I have owned
previously. Quite exceptional accuracy really. Big points scored here!
12" Vs 10" and Cutting Capacity
Truth be told, unless you are planning to cut some big lengths of
lumber, 12" may be a little overkill for your needs. 10" saws will handle
most tasks, but it is always good to know you have those extra two inches should
the cutting task require it. Some have argued that the larger blade is
more prone to deflection. This is certainly true, but with a practiced
cutting action and rate of feed, this can be minimized. With the Bosch
3912 (GCM12) saw, your depth cutting capacity is 150mm. At 90 degrees you
can cut 200mm width stock and at 45 degrees, you can cut close to a 140mm
width piece of material. The 3912 does not have a sliding action, so
anything wider will have to be cut by other means unless you get a little
creative - but of course this also can often decrease the safety level in
use, so we will not advocate any other methods or workarounds here.
Motor, Blade and Blade Guard Features
The Bosch GCM12 features a 1800watt motor. Of the 3 other miter
saws I have owned previously, a 1200 watt, and 2 more 1800 watt saws, none
of them so far have ever stalled on me during a cut, so needless to say, I
don't expect the motor on the Bosch to stall either, and during testing,
we had no trouble at all. Plenty of power to cut through even the thickest
pieces of wood. The motor is rated at 8 amps with a speed of 4,300 RPM and
is double insulated for safety.
NOTE: The Bosch 3912 (US variant) has
a 15 Amp motor rated at 3.3HP!
Shipped with your saw is a Bosch branded 12" 40-tooth TCT blade (rated at max 5,000RPM) with anti-kickback design. It comes
pre-assembled to the saw and in testing cut quickly leaving a relatively
smooth finish. If you want to try cutting picture frames on this saw, I
would look at getting an 80-tooth fine cutoff finish blade for cleaner
edges. The 40-tooth blade supplied will handle most of your rough cutting
/ sizing / cross-cutting or crown molding needs with pretty good results.
12" miter blades aren't the cheapest chunk of metal going around so we
sufficed with the supplied blade and were quite happy with its
The blade guard is constructed of clear hardened plastic
and is quite tough itself. There is more than enough clearance between the
blade and the guard on all edges. In the saws upright position, the blade
guard covers about 98% of the blade itself with say only an inch of the
blade exposed at the bottom end of the guard. This is quite good in
comparison to some guards on other miter saws I have used, and provides a
high level of blade protection for the user. The blade guard also features
a small wheel at the bottom end to help roll over larger pieces of stock
as you lower the guard. It won't force the guard up into an unnatural
position, but does help in preventing the guard catching on the surface of
the piece to be cut.
A spindle lock makes changing blades a safe and
The electric brake system on the Bosch 3912 (GCM12) is a
nice feature found only on the more expensive saws. In simple terms, it
stops the blade a little faster which not only allows you to work faster, and
more safely, but also greatly reduces noise exposure, something which the neighbors will surely be greatful for.
Handle and Trigger Switch
Personally, I prefer the horizontal-style drop-handles over the
vertical-style when seen from the front of the machine. It just seems
easier to apply downward momentum to the horizontal style handles. As you
can see from the photos in the right hand column, the Bosch 3912 does
indeed have a horizontal style handle. You will notice it also has
vertical handle component just behind the trigger assembly. This is
actually a carry handle that can be used to transport the saw around when
it is locked in the downward position. The head locking mechanism is a
little more robust than on many other saws and I felt confident carrying
the whole weight of the saw on this handle kept in place by the locking
pin. It is a great design feature, particularly if you have a need to move
your saw around often.
The trigger switch which is located on the reverse side
of the horizontal drop-down handle and runs the full length of the handle, and
must be unlocked via either of the two red trigger-release switches before
it will start the saw. The trigger release switches are positioned so you
can easily use either hand to operate the saw. The handle and trigger is
overall, quite comfortable and easy to use.
Angle Adjustment, Positive Stops and Vernier Gauge
I will say now that what lured me to this saw was the positive stop
design that is implemented on this machine. It is the best and most
accurate I have seen yet. The table itself can swing left or right to 52
degrees. Positive stops are found at 0 degrees, 15, 22.5, 31.6 and 45
degrees left and right. The positive stops are exactly that.... positive.
You may have used a miter saw yourself in the past where the positive
stops are much less than positive... i.e. they have some play either way
of the stop that keep you guessing just exactly where the right setting
actually is. On the Bosch saw, the stop system is achieved by somewhat
triangular detents molded into the saw base under the miter gauge (see
photo right column). The miter detent trigger located under the miter
locking knob features a locking 'wedge' that perfectly fits into the
detents on the saw base. This prohibits any chance of movement or
free-play when the saw is locked into one of the positive stops. There is
virtually no movement at all. Assuming the accuracy of the miter gauge in
comparison to the saw blade is maintained, then these positive stops will
be dead on accurate all the time and you can set them amazingly fast when
you don't have to negotiate with slight movements around the stop
position. The 22.5 and 31.6 degree stops are primarily used for crown
molding, and I shouldn't need to explain what the 15 and 45 degree stops
would be commonly used for!
There is a provision on the miter locking knob to disengage the spring
loaded detent trigger underneath so as you pivot the table to whatever
angle, the locking wedge underneath will not engage into any of the hard
detent stops at the common angles. This is necessary if you want to use
any angle close to the hard detent positions, so the spring does not want
to throw the stop wedge into these detents. You disengage this by
pushing further up on the trigger underneath until the top component of
the locking assembly falls over a ridge/cleat to keep it in place. So you
have the best of both worlds!
The width of the angle markings themselves may be of
concern at first glance, as you may be doubting just exactly where an
angle setting should be, but I found in testing that if you align the red
marker on the indicator gauge to the middle of the angle mark on the miter
angle gauge, you are pretty much right on the accurate setting point for
that angle. No big deal, just something different from many other saws. It
didn't cause me a problem at all in testing and in use. The cast and
machined scale themselves will never wear off!
The pivot on the table is a relatively smooth action as
you go about setting your angles. You undo the screw clamp knob and then
release the spring loaded trigger (pulling it up) from its current
detent/positive stop setting (if it is engaged in one) and pivot the table
to the new angle, and then re-engage the locking knob to make sure it
doesn't move during a cut. This is all done with one hand easily. You will
note the weight of the saw above is much heavier compared to say a 10" or
8" saw as you would expect. This can make it a little tricky to fine tune
an angle setting at times, say for going from 25 degrees to 22.5 or even 26 degrees,
but its a minor issue and you get better with a little more nudging action
and practice. No real drama here.
The marker window itself features a unique vernier-style
system to help set angles down to 1/4 of a degree with a good level of
accuracy. Using a series of sub-markings on the gauge window itself
superficial to the more prominent, regular marker lines, you can
accurately set the miter angle to 1/4, 1/2 and 3/4 degree increments past
any whole numbered angle. Very useful indeed!
Bevel Angle Adjustment
Bevel angle adjustment is
achieved by loosening a locking screw at the back of the saw arm and
pivoting the whole top saw assembly to the left. Nothing unusual here. It's
virtually the same with most other miter saws except the bevel angle gauge
is situated on the front on the main pivoting saw assembly here, meaning you
don't have to lean over the saw or walk around to the back of the saw to
find or check your bevel angle setting. A well thought-out feature. We made
several 45 degree bevel/compound cuts during testing and checking the cut
angles revealed a good level of accuracy. Some where ever so slightly out,
but this was probably due to a bit of blade deflection when cutting
through thicker pieces of wood. Larger 12" blades are more susceptible to
blade deflection, especially if you try to cut too fast.
One very handy feature for the home renovator is the
addition of a positive stop at 33.9 degrees in the bevel arc. Engaging the
bevel detent pin just above and to the right of the bevel locking screw
will allow you to set a bevel angle of 33.9 degrees which is commonly used
for cutting crown molding corners. I cannot verify the accuracy of this
detent setting at this stage as we didn't have any crown molding
available. We did try to replicate it with some scrap wood and to the best
of our ability, it seemed to produce an accurate result.
Overall, we found the the angle adjustments and positive
stops to be very well designed and very functional and accurate in use.
Many other miter saw manufacturers could take a leaf out of the Bosch
design book in this area that is for sure.
Fence, Table and Hold Down Features
The table on the 3912/GCM12 measures 25" across. With the sliding base
extensions extended on both sides, this increases the length to around 28 1/4"
in total. What are the sliding base extensions you ask? Well, these
are small extendable tables that are featured on both ends of the saw
you can release with a hex-style wrench and extend out laterally. When in
the bevel cutting mode with the saw tipped to the left, there is much less
hand clearance for the user in relation to the blade in this position.
Extending out these bases provides more room for the operator to place
their hands to hold down material. A good safety feature.
The table pivots freely left and right throughout the
various miter angles.
This saw features a sliding fence on the left hand side.
The fence itself on the left measures 5" tall in total with
the top 3 1/2" of this fence being able to slide to the left, out of the
way for bevel/compound cutting. The sliding fence is held in place by a locking
lever that is easily accessed at the back of the fence. Having a sliding
fence is very handy to provide good support to the workpiece no matter
what position the saw is in, and also helps prevent chip-out on the back
of the piece when cutting through it. The right side fence does not have
this slide feature, but does have a machined, inset measure which allows
you to quickly measure the length of material to be cut. This measure only
extends to 12" and no numerical markings are found on the fence, so you
have to count notches so to speak, to find your length of cut.
Because this saw does not come with work support
extension bars as
standard, there is no real provision for a stop block to be used. You
could clamp one to either of the fences quite easily for cutting shorter
pieces, but for longer pieces you will need to purchase the extension bars
(which comes with its own little stop block) or set the saw up on a dedicated miter station
equipped with a stop if you want to cut many
longer lengths of timber to the same size quickly and easily.
What does come standard with this saw is a metal quick-action clamp for
securing the workpiece to the saw table for cutting. The clamp easily
slots into any of the 6 available clamp support positions machined in the
base. In testing, the clamp provided adequate support to the lumber being
cut and worked as we would expect it to. No problems there!
Like all miter saws, the dust collection bags they feature are
relatively useless in comparison to the total amount of dust created.
Connect a vacuum or dust collection machine to the port instead of the
standard dust bag and you will increase your chances of catching a little
more, but it still won't be adequate for indoor workshop use. You can
either use a suitable dust mask indoors and be prepared to clean up later
or if you are using the miter saw in a dedicated saw station, rig up a
dust collection frame around the back of the saw hooked up to your dust
collector. This will ensure maximum dust collection capability. The bag
will collect a little and it is better than nothing, but like every miter
saw on the market, it's really not that practical by itself.
Simply put, the drop/plunge action on the Bosch 3912 (GCM12) is one of
the smoothest around thanks to the quality spring mechanism in place (See
the first photo right column). Very little downward force is needed to
drop the saw, yet the spring is rigid enough to prevent a small child from
easily pulling the head down, or for it to fall down itself. The drop
action is very much in the same class as the Makita's drop
action. Very smooth and very accurate. There is no noticeable lateral
movement of the head assembly when lowering the blade.
Zero Clearance Insert
A zero clearance insert is provided on the Bosch 3912 (GCM12). This helps
alleviate any problems with chipout on the underside of the workpiece as
the blade passes through the bottom of the workpiece. It works very well,
but expect to have to cut into the insert a little more when you first
make a few bevel cuts which will widen the gap in the insert.
Alternatively, if you don't want to ruin your nice clean gap for normal 90
degree, straight-down cuts, then you could have two inserts, one for
standard cuts and one for beveled cuts, however, you would have to source
an additional insert plate from Bosch to do this. The plates are easily
removed and replaced with 6 holding screws.
Testing and Accuracy
During the test period, we cut all different types and sizes of wood.
The text above basically summarizes our findings with the saw regarding
individual aspects, but during each cut, the saw performed very smoothly
with little vibration and with good results all round. Even on larger
pieces, we were able to achieve excellent results in both smoothness and
accuracy of cut. Our picture frame test yielded good results, and only a
very light sanding of the joints was needed to make them picture perfect
(pun intended). Test cuts at various angles were verified by an angle
gauge as to being pretty much right on the mark. One or two cuts were
slightly out, perhaps due to a little blade deflection or slight movement
of the piece on the table during the cut. It is difficult to tell exactly.
Fence and angle settings remained rigid after cutting and no lateral
movement in the cutting head could be easily identified during the
drop-phase of the saw, or even in the stationary up position which
indicates a good level of quality, which in turn, did reflect in the accuracy of
the cuts. The hold down clamp worked well when it was called upon,
although I do prefer clamps that are in some way more 'fixed' to the base,
although they seem to be less versatile at times.
The Bosch 3912/GCM12 12" Compound Miter Saw certainly lived up to my
expectations for performance and accuracy. It's innovative design in the
positive stop angle arena is probably the best I have seen so far (I
haven't seen them all though). The build quality in all areas is easily
identifiable both in look and in function and performance. You can
certainly see where the higher price tag comes from in this item. Needless
to say, that money would be well spent if invested in this piece of
machinery. It is without doubt a worthy contender for any serious
woodworkers shop or contractor's worksite and one product I would happily
recommend to you all. The Bosch 3912/GCM12, in my opinion, is more solid
and better designed than any of its competitors in the same price range. I
would expect to get plenty of years of trouble-free service out of this
saw. Time will tell of course!
Bosch 3912 (GCM12) Photos
All photos copyright onlinetoolreviews.com. Use without prior
written permission prohibited
The plunge spring is of high quality producing a very
smooth drop action.
The Zero Clearance insert will help prevent chipout on
the underside of your workpiece.
The sliding base extension can be extended out (to the
left in this picture) to give more hand support area when cutting bevels
or beveled miter joints.
The switch/trigger handle is very comfortable and
trigger release switches are conveniently located for both right hand (as
shown) or left hand use.
The miter lock knob allows you to quickly lock they
table at any angle.
Miter indicators are molded/machined onto the base for
greater durability and accuracy.
Notice the almost triangular looking detents in the base
of the miter gauge assembly. These are the positive stop settings for
common miter angles. When locked in one of these positions, there is no
free-play at all!
Easily slicing through some 3/4" material at
And thicker material was again no problem.
Cuts came out pretty smooth considering we were
not using a fine cutoff blade
with more teeth.
Notice how we have the base extension extended
here for more hand support during this bevel cut. Fence has been
move to the left for blade clearance and better workpiece
Making a compound cut with blade at 45 degrees
and table at 5 degrees
Accuracy is right up there! Here we cut stock
for a picture frame with pretty good results!