Review By Dean Bielanowski  Bosch Website - http://www.bosch.com

Bosch 3912 (GCM12)
Compound Miter Saw Review

By Dean Bielanowski

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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.

I must 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 supports available.

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 time around.

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 performance.

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 trouble-free task.

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 table that 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!

Dust Collection
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.

Drop Action
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.

 

Conclusion
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
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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 90 degrees.


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 support.


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!

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