Natural stone is used throughout the world for construction purposes and monumental sculpture; and is classified by several designations, depending on factors of hardness and appearance, such as granite, marble or slate. Natural stone shows up as architectural stone for such purposes as construction, flooring, countertops, cladding, molding, curbing and so forth. Large blocks of raw stone are used for funerary and monument projects and are frequently engraved to bear information or decorations.
CMS/Brembana's line of CNC machining centers provides the power, precision and capability—whether processing flat slab work, large raw blocks, or massive columns and objects of art—which the world's best designers, builders, sculptors and artisans depend upon to carry out their labors and work...
Architectural Stone - Overview
Incorporating architectural stone into building projects has a long and celebrated history in the construction of residential, commercial and municipal buildings and incorporates a wide ranging area of fabrication including building construction and ornamentation. Natural stone fabrication in this area leans towards softer stones such as limestone, sandstone, marbles and soap stones, but is not limited to these materials.
A more recent material employed in architectural stone applications, and in distinction to natural stone, is know as "cast stone" which simulates natural stone and is made from white or grey cement, natural sand, gravel or crushed stone and may also have added to it mineral pigments for colorizing. "Cast stone" is used most generally for outdoor applications and typically falls outside the need of CNC processing.
On the other hand, "engineered stone", also called "artificial stone", is a mix of quartz or natural material, resin and pigment and is cast using a vacuum oscillation process which forms sheets or slabs. "Engineered stone" is used almost exclusively for indoor purposes such as kitchen countertops and bathroom surfaces.
The individuality of projects for which natural stone is used tends to require 5 axis machines like CMS/Brembana's Maxima and G-Rex. These machines have the ultimate flexibility of 5+ axes and are only limited by the customers’ imagination and ability to create 3D digital models which correspond to their desire.
Maxima - 5 axis CNC machining center for architectural stone work
Brembana's Maxima CNC machines are oftentimes designated as Maxima MB (monobloc) construction—although OF (open frame) versions are available—and can be equipped with a maximum electrospindle of 40 hp and medium blade diameter.
Monobloc machines—besides being noted for their extreme rigidity—have shorter installation times due to the benefit the monobloc machine structure provides the technician in his assembling and calibration work as related to the machine's frame, since the machine is created in a "monobloc" construction.
Maxima can machine 3 dimensional pieces one day and counter tops the next. Maxima's machine base is very configurable with two X stroke options, four Z stroke options and Y stroke options too numerous to list. The Maxima type of CNC machine is able to accommodate two types of lathes—one fixed and one mobile. For a countertop shop looking to expand into architectural stone work or an architectural stone shop looking to add flexibility, consistency and control the Maxima is the perfect choice.
Speed MB 3/4 axis CNC machining center
For basic machining needs in the architectural stone sector Speed MB (Monobloc) is CMS/Brembana's workhorse. A 3-axis Speed MB meets all the standard machining requirements in a typical production facility—milling, drilling, lettering, profiling and polishing. All these varied machining operations can be easily handled by a 3 axis SPEED.
The standard Speed MB can produce a wide range of architectural stone parts—any stone slab or block component can be produced as long as it is made with a vertical tool.
Sprint - 5 axis bridge saw
CNC sawing machine designed for cutting marble, granite, natural and artificial stone blocks and slabs to the required size and shape.
Sprint is an ideal machine for building suppliers of interior and exterior floor and wall tiles, stairs, cornices, etc., as well as interior decorators and furnishing manufacturers such as kitchen and bathroom worktops, washbasins, sinks, tables, etc.
GIXA - 5-axis stone bridge milling machine
GIXA is CMS/Brembana's CNC bridge sawing machine with a even larger working envelope and designed to cover the same range of production requirements for cutting marble, granite, and stone blocks and slabs to the required size and shape.
GIXA is ideal for building suppliers producing exterior coverings, stairs, fireplaces, window sills, cornices, fountains, doorsteps, curbstones, artistic monuments, gravestones, etc.
G-Rex - the largest working envelope bridge saw with 5/6-axis
Large-sized machining center for the working of (ultra-thick) slabs, paving units and blocks of natural and compound stone. Its configuration can be customized according to the various needs; it is especially designed for marble workshops involved in architectural projects and in the building sector in general. Used in the fields of building , furniture, decoration, street furniture, funerary art.
- Large-sized workbench with Duralumin surface
- Bridge supporting and sliding structure on separate masonry or metalwork shoulders (Open Frame) to ensure sturdiness and rigidity for heavy-duty operations
- Operating unit equipped with an ISO 50 electrospindle
- Z axis stroke up to 2000 mm for ultra-thick workpiece machining
- Use of cutting and shaping diamond disks up to 1200 mm diameter and extra-long wheels for milling and polishing of shaped or convex sections and space-oriented surfaces
Black granite pillar base
Black granite pillar base machined on Maxima
The picture shows a large, heavy, solid pillar base, a typical architectural stone project, which has been machined from a block of black granite.
The following pictures will help to explain the steps of the process to go from the block through the various stages of the machining involved.
Using the blade horizontally for roughing passes
The block, in the shape of a cube is first rough sawn.
This part of the process will take repeated passes with the spindle head rotated horizontally using about a 14" diameter blade to bring the block internal structure to its approximate final shape with varying& depth passes of the blade.
5 axis angled compound cuts
Around the top of the block some of the excess granite can be removed with 5-axis compound angled cuts as seen in the picture.
Since the blade is 14" in diameter, the depth of cut will be about 3" with the rest being removed as shown in the previous picture, using multiple horizontal blade cuts to permit the excess to be removed more easily.
Staggered horizontal blade cuts
The majority of the excess stone is prepared for easy removal by carrying out a series of staggered saw blade cuts with the blade rotated horizontally.
The CNC movement of the blade around the block is made to correspond to the final block surface to be obtained when finished, therefore some cuts are deeper than others, depending of the final part geometry.;
View of the staggered blade cuts
This shot shows the block having been prepared with the remaining horizontal blade cuts.
The next step will be to remove the excess material left between the blade cuts.
The amount of material left between blade cuts is about the same as the thickness of the blade.
Removing the excess material
Once the blade cuts have been made, the excess material which remains is easily removed as shown in the picture.
A small hammer and an easy tap "breaks" off the excess material leaving some "rough" surface on the block, which can easily and quickly be brought to a finished condition than would otherwise be the case.
Segmented "roughing" tool to remove excess material
Following the removal of the excess material, the Maxima is equipped with a 150 mm diameter segmented diamond "roughing" tool to bring the surface to its final shape and dimensions.
The "roughing" tool is inclined in a 5-axis manner and the removal is carried out using the end of the tool, similar to a "fly cutting" operation.
The "roughing" operation
The "roughing" tool mounted in Maxima's powerful 40 hp electrospindle makes easy, and quick, work of removing the remaining small amount of excess material as can be seen the picture.
With the head inclined to the correct angle on the various faces, the final shape and size come out perfectly, as expected.
The pillar—ready for polishing
The pillar is now ready for final surface machining and polishing. The next steps in surface preparation would include the use of 4 additional diamond wheels of a progressively finer grit until the surface is ready for polishing.
Polishing is usually carried out by "hand" in this situation.
It is possible for Maxima to carry out such polishing operations with the use of a 2° "canted" wheel with the polishing material held to the wheel by Velcro. But the pad should remain in contact with the surface, and this would not be the case as the pad approached the edges of the various surfaces. So a hand polish will be used to finish it off in this case.
Columns—large turning work
Raw block for stone column
A raw block will be "turned" into a stone column on this Maxima.
In the image the raw block is placed in the machine and in a preparatory step a special "coring" bit is used to create the centering holes on each of its ends so that the block can be supported and mounted correctly in the CNC's 4th axis lathe device which is located within Maxima's work envelope.
When the coring operation is finished, the "cored" stone will usually remain within the coring bit and is easily removed by pushing it out with a screwdriver along the slots in the coring bit body. If it's still attached to the block at the end of the operation, a slight push against the core in the block with a screwdriver and it will break off at the base of the core and is easily removed.
Stone column - horizontal saw blade work
The second image shows the same block “chucked up” in a fixed lathe which is permanently mounted at the rear of Maxima.
In this picture can also be seen the “blade roughing” work under way, which is making many saw cuts into the piece at equal intervals, but always staying a safe distance away from what will ultimately be the finished surface.
Once this operation has concluded, the remaining material between the saw blade cuts can easily be removed with a tap by a small hammer and fall away, exposing the rough surface to be machined to the final surface.
Stone column - finishing cycle
The final image shows the finishing path work being done with the blade.
With closer inspection the blade can be seen to be carrying out the roughing work on the area to its right. The blade is about 4 mm wide and while the column is rotating continuously, the blade is also slowly moving from left to right in a spiral fashion with a "step-over" of about half its surface width.
Other tools could easily be brought in after this step to add carving, lettering, fluting, twisting or any other type of design—the images above are from an open frame (OF) Maxima.
Various architectural stone projects
Machining an ornate stone capital
Maxima ornately carrys out its carving work on 4 complete sides of this large Capital.
The clamping fixture is more about positioning than clamping.
Once the fixture is positioned the successive capitals only need be placed into the clamp and the same program run again each time.
Stone statute head - carving
Shown is a Maxima carrying out a carving project—the head of a statue from a temple being built in India.
There are several of these machines throughout the Indian continent doing this kind of dedicated work, as well as a number here in the US doing similar work.
Stone baptismal from a solid block
Maxima is shown machining a marble baptistry made from a solid block of marble.
As can be seen, the piece is too large for the table, but within the strokes of the machine—so the customer has fashioned a wooden support by which to carry the weight of the block and finish this particular piece.
Roughing large blocks of limestone
G-Rex Machines are OF (open frame) only type machines—as opposed to MB (monobloc)—and have a table that is mounted to the floor (or the floor may itself be the worktable) or some other device like a lathe.
G-Rex is also completely configurable with multiple strokes in X, Y and Z with a maximum blade size of 1.2 m or 48”. The G-Rex machine offers the largest working envelope for this machine style.
Here G-Rex is seen “blade roughing” a large block of limestone.
These projects generally begin as large blocks of stone brought in form the quarry. The blocks are then positioned in the machine for roughing. In many cases this roughing work is done with a blade as it is the tool which can remove the most material in the quickest time. Once the process moves to a milling tool the speed at which material can be removed slows considerably.
Stone column machining - standard, roped, twisted
The addition of an optional lathe makes a 5 axis machining center into an extremely versatile work center.
These lathes are not just rotating lathes, but interpolate with the other axes on the machine to provide the ability to do lathe work of standard columns like the one pictured above, as well as roped, twisted and open lathe work as shown in the example below.
Sculpting a marble bust
In this project the roughing work is done by use of successive milling passes.
Once the block is in place on the machine, a milling tool machines away the excess material.
From this point forward the process is the same using progressively finer milling tools until the desired finish quality is achieved.
Bas-relief work and architectural restoration work
What is bas-relief? Simple English Wikipedia provides the following definition:
Bas-relief is a type of sculpture that has less depth to the faces and figures than they actually have, when measured proportionately (to scale). This technique retains the natural contours of the figures, and allows the work to be viewed from many angles without distortion of the figures themselves.
Having explained what bas-relief is; it can also be said that architectural restoration is becoming a more important part of the architectural stone industry.
In some parts of the US and all over Europe it is possible to find hand carved ornamentation on building exteriors. Replacing these hand carvings for both safety and historical preservation reasons is driving much of this work.
As an example, say there are some original marble carvings on a municipal or commercial building or church that need replacing because they are starting to crack and are in danger of falling. You simply take laser scans of the carvings, remove the original carvings and put them in a museum. Use the scan flies to create new digital models and machine new carvings to put in place of the originals. The image to the left shows part of this process.
Large stone vessel machined
The images shows a very large stone vessel being machined in G-Rex.
The first step of this process is machining the outside bowl shape in an upside down position.
Large stone vessel - inside machining
Once the intended shape for the outside has been completed, the piece is flipped over and re-referenced.
The machining for the interior work is shown in this picture.
The work is being carried out with a extended milling tool, showing the need for well balanced tools and a very good spindle by which to power the tool through this process.
Stone moldings and lintels
Among some of the items required for architectural stone work are molding and lintels.
These are some examples of the types that are requested and produced on CMS/Brembana's CNC machining centers for architectural stone.
Machining of limestone cornice - building
A heavy limstone block is machined into a cornice for a building. The video shows:
- a look at the special tools and blades used, some of which will be mounted in extensions to permit access to tight areas
- the initial pass for the top reference surface
- the roughing blade work
- the milling passes to bring out the intended shape
- end milling tools for sharp square transition surfaces
- a view of the finished cornice
Overview of 5 axis machines working architectural stone
CMS/Brembana's Maxima is shown working on architectural stone projects including:
- exterior accent items
- building cornice
- granite polishing
- marble bust machining
- stone volute handrail with up-easing for stairway
G-Rex stone block cutting with large diameter blade
G-Rex is shown processing a large heavy quarry block of sedimentary stone approximately 20" thickness. The processing of the block will be done with a blade of 1200 mm in diameter (48"~).
G-Rex's work envelop can be configured as large as 4.25 m wide up to 7 m+ in length with 4th and 5th axes of 270° +/- and 100° +/- respectively.
The first work will be to "rough" the block to an approximate final size. G-Rex's large blade travels back and forth in deeper slices till the cut is finished. The 6 pole 220 Nm spindle of 31 hp makes easy work of this big job.
Next, G-Rex turns its 1200 mm blade on edge (horizontally) to shape the stone slab around its outside edges: large rounds on the corners while machining an ellipse shape on the sides.
Lastly. G-Rex uses its blade to cut a large opening on the inside of the block.
G-Rex polishing/surface texturing a thick slab
G-Rex is shown with one of its special heads for "brushing / honing / leathering".
Since most slab material available for production purposes already has a polished surface on it, when a surface of another type is needed, it's customary to take this available material and use one of the special CMS/Brembana heads that's available to give it a different look, texture, or surface preparation, which the market requires.
In addition, G-Rex (as well as the other CMS/Brembana machines for architectural stone) has available a complete range of traditional polishing heads to meet any surface polishing requirement.
G-Rex large stone column lathe
G-Rex machines a large stone column.
The first work is to machine the support and centering holes on both ends, which will be used to mount the block in the turning lathe.
The subsequent operations are as follows:
- tapping out the plug from the ends
- drilling a "rotational drive" hole for rotating the column about its center
- mounting the turning center
- rough blade cutting the surfaces with a number of slots, which when tapped with a hammer will remove the excess material
- roughing passes to "square off" the top and bottom feet of the column
- roughing passes along the length of the column to create the column surface
- change from blade work to end mill work along the length of the column
- milling of the straight slots from top to bottom along the column length
- milling the shape of the circular base foot at bottom of the column
- milling a convex shape at the top of the column head with a blade
G-Rex machining of "steeples"
G-Rex machines the 3D surface of a "steeple".
G-Rex is shown end milling a block of sedimentary stone. The end mill is mounted in an extension to make the reach into tight areas easier.
The 3D machining takes place on the surface and edges.
Maxima machining a granite curved arch molding with 5 axis saw blade
Maxima is shown using it's 5 axis capability with a 16" diameter saw blade to create a complex arch molding surface on a granite block.
The granite block is held by use of Maxima's vacuum clamping system.
The surface of the molding is refined by CNC control of the saw blade until a finished molding for an archway is revealed.
The use of the saw blade points out the important versatility which Maxima has. There is no need to buy a "form" tool to create this profile. The heavy amount of material to be removed and the creation of a perfect surface have both been accomplished without a "special" vertical milling tool being used, but rather a "standard" saw blade, used for many different purposes.