jdowning
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Experiments with a CNC router - sound hole rosettes
Following on from my recent experiments with a 3D printer to produce sound hole rosettes I am now investigating what might be done with a CNC router
at minimal cost.
The machine selected for the trials is an upgraded generic version of the router kit described in this video.
https://www.youtube.com/watch?v=Y5nyjvytlBk
I took delivery of the router kit on January 15 this year and have since made a few trials but with this global pandemic and other priorities the
project has since been on temporary hold. Before memory fades further I will start this topic from the beginning covering modifications made to the
router, computer aided software (CAM) tested and 2D machined test samples made so far.
As with the 3D printer project posted here there is no guarantee that it will be possible to make rosettes successfully with a low cost CNC router but
'nothing ventured nothing gained'!
http://www.mikeouds.com/messageboard/viewthread.php?tid=18156
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jdowning
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For information this is the upgraded version of the CNC 3018 router that I purchased for just under CA$300 in January this year.
https://www.amazon.ca/dp/B07L4BJK82/ref=pe_3034960_233709270_TE_item...
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SamirCanada
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Hi John
Glad to have you back!
looking forward to read this thread!
@samiroud Instagram
samiroudmaker@gmail.com
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jdowning
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Thanks Samir!
These low cost CNC 3018 small desk top routers are light duty machines and not comparable with commercial CNC routers costing in the thousands of
dollars. Nevertheless I am using the router as an educational tool and curious to find out what might be accomplished with a cheap router.
The router has a working area of 30 cm x 18cm and height of 4.5 cm so should be capable of producing 3 dimensional carvings of those maximum
dimensions. However, for this project I am only interested in testing the router's ability to cut oud or lute rosettes so the requirement is for
either 2 dimension (2D) carving or so called 2.5 dimension (2.5D) carving (ie with some decorative surface profile detailing) with rosette thicknesses
of around say 2mm.
The unit was straight forward to put together and the frame is rigid once assembled. I have some reservations about the rigidity of the cutter head
that slides on 4 linear bearings on two 10 mm diameter rods mounted in the over head gantry. Initial test runs showed quite a bit of vibration when
cutting due to 'play' in one of the linear bearings. Parts for these machines are low cost and readily available. The suspect bearing was easily
replaced (the bearings cost about a dollar each). This reduced vibration levels but nevertheless there was still some flexing of the cutter head. This
will likely have some effect on precision of cutting but may not be problematic if dynamic cutting loads are kept to a minimum?
The cutting operation produces quite a bit of dust and chips that must be vacuumed up as work proceeds. Best kept separate from any computer hardware
to avoid dust ingress. I have an old desktop PC with Windows XP operating system that is dedicated to powering and controlling the router. The router
comes with a hand held off line device to control the router without PC input but I prefer the convenience of control with the PC.
The control board is fully enclosed with cooling fan and comes with GRBL(candle) v 1.1 firmware. The display on the PC monitor allows the cutter head
to be manually positioned to the required start point on the work - and then locked prior to start of cutting (important!). Cutter spindle speed can
also be adjusted to suit the work material and speed of feed. The tool position is visually displayed as cutting progresses which is a nice touch.
For the router to operate it must receive a set of instructions (GCode) defining the tool path to be taken. The coded instructions are fed into the
controller via a thumb drive. The GCode tool path is prepared separately using CAM (computer aided manufacturing) software - some freely available and
some quite costly dependent upon sophistication. More on this in my next post.
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jdowning
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Creating work with a CNC router (or milling machine) is a subtractive process (material is removed from a blank) and is a more complicated procedure
than 3D printing, an additive process where material - using slicing software - is built up layer by layer.
There are three essential steps
1) creation of the rosette model by computer. This may be as simple as an edited photographic image or line drawing as a jpeg file extension and
there are many free software programs (such as Inkscape) and on line file conversion facilities that may be used for this purpose.
2) The model file must then be processed by CAM software to create a machining tool path appropriate for the chosen brand of router. This is exported
as a .nc file extension for loading into the router controller. It is a set of instructions telling the cutter where to move relative to the work
piece.
3)The router is then able to machine the work piece.
I have chosen DeskProto CAM software initially for this project. It is free to use in a basic stripped down version for unlimited time - suitable for
beginners such as myself and comes with free reference manuals that explain all of the technical details as well as descriptive videos. There is a lot
of detail to explore that is best referenced here.
https://www.deskproto.com/
However, basic operation of the software by 'wizard' is easy to use for a beginner so there is no steep learning curve involved. Tool paths for 3D
machining as well as 2D and 2.5 D machining can be created. For this project - cutting rosettes - only 2D and 2.5D machining is of interest via Vector
machining or Bitmap machining. The latter may produce both 2D cutting as well as 2.5D relief carving (lithophane) that might be used to create
rosettes with surface detail carving?
A few test carvings were produced a few months ago - with mixed results - before the project was temporarily put on hold, so the results and problems
encountered will be discussed next before proceeding further with the experiments.
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jdowning
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Initial trial using Deskproto CAM software was to cut a .jpeg image in shallow relief as a Bitmap project using the Wizard based interface. I was
curious to see how the machining worked out with a view to eventually piercing right through a work piece with the cutter to make a rosette.
Two test runs were made the first in 3mm clear Plexiglas and the second in 3mm thick figured maple. The work blanks were screwed to wooden blocks
clamped to the router bed and cut with a solid carbide V engraving bit supplied with the router kit. Maximum depth of cut (negative Z direction) was
2.5 mm with the tip of the cutter zeroed on the upper surface of the work piece.
The software calculates depth of cut for black as zero depth and for white as maximum depth. A colour image is converted by the software to grey scale
the depth of cut depends then upon the density of grey for each pixel (ranging from minimum black to maximum white).
The attached portrait photograph was used for the test - well lit with no shadows that would distort calculation of depth of cut. Not a rosette but
bear with me!!
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jdowning
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The test in clear Plexiglas machined well without problem. The carved image (a.k.a Lithophane) can not be seen by back lighting but is revealed in
incident lighting by brushing a translucent white liquid over the machined surface. The fluid fills the deep cut areas in white.
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jdowning
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The trial with figured maple, back lit was also successful.
So much for the 'artistic' stuff. Next to try to machine a rosette as a Bitmap project
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jdowning
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Bitmap machining is a fairly slow process the cutter moving side to side across the work piece only advancing a fraction of a millimetre with each
pass of the cutter. To avoid spending too much machining time in the trials, therefore, relatively small sound hole pattern examples have been
selected for processing.
For the first trial a Nahat Eyun design has been used. The rosette will be cut in 2D so from a photo of an original Eyun the image was converted into
a plain black and white .jpeg image using Photoshop editing software. So in the Bitmap process pure black represents zero cutting depth and white the
set maximum depth.
This example will be a challenge to cut because of the fine detail and type of cutter used but the image may be made thicker with smoother edges in
places and larger in diameter to compensate if necessary. The diameter of this first test Eyun is about 5 cm
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jdowning
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The cutters supplied with the router kit are V shaped solid carbide engraving bits with a 20° included angle. This means that machined edges of a
work piece will slope at a 10° angle and will not be perfectly vertical.
Furthermore the cutters, being only half round in section, cut with greater dynamic forces (vibration) than a more delicate (and costly) parallel
sided spiral cutter might. See the attached image of the irregular 'straight line' cut on the Lithophane example in relatively hard acrylic plastic
(Plexiglas) previously posted. Part of this irregularity was due to slack in one of the linear slide bearings that has now been replaced.
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jdowning
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Mounting a 2mm thick work piece securely for machining so that it may also be easily released on completion without damage presents a bit of a
challenge requiring some experimentation.
To protect the router bed plate from damage and for convenience of set up and removal, each work piece is mounted on a scrap wooden block clamped to
the bed plate. The clamps provided with the router kit are not very good so a T-slot clamp and a couple of T-slot low profile work stops from Lee
Valley work nicely instead.
There are a number of alternative solutions to mounting the work piece on the block. If the machining operation pierces through the work piece to
greater than full thickness then the work piece must be uniformly mounted with adhesive so that it doesn't fall apart during machining. One method is
to first cover the underside of the work piece with painter's masking tape (weak adhesive so easier to release) and then stick the work piece directly
to the mounting block with either diluted hide glue or alternatively double sided adhesive tape.
Alternatively if the work piece is not machined quite to full depth leaving a small thickness to be removed by sanding after removal from the mounting
block then the work piece may be simply mounted directly to the block with four screws, one in each corner. This method has been successfully tried
with the Lithophane examples previously posted but not so far for a rosette.
The attached image shows an MDF mounting block clamped to the bed plate with a completed work piece held in place with masking tape and diluted hide
glue. MDF (medium density fibreboard) material has been found to be too soft for this application resulting in a rough, poorly defined machined edge
as the cutter breaks through the underside of the work piece.
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jdowning
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The first test with the Nahat eyun design, undertaken a few months ago, was to machine an African ebony work piece 1.3 mm thick using the Bitmap
process. As the cutter depth of cut was set deeper than the work piece thickness the underside of the work piece was covered with masking tape and
then glued to an MDF mounting board with water soluble fish glue. Upon completion of the machining operation the work piece was removed from the
mounting block with a thin metal spatula.
Apart from a couple of small missing pieces the rosette was complete although the edges are pretty rough looking. This may be because the tool path
was not set fine enough but also because the masking tape and support block material combination was too soft to support the cutter breaking through
the work piece for a clean cut at full depth? Anyway a good start that can only be improved through experience.
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jdowning
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An alternative method for cutting a rosette with DeskProto software (free version) is to use basic Vector machining where the machine path for the
cutter follows the lines and arcs of a 2D drawing or image. This is a much faster machining operation than the previously reported Bitmap machining
(where the tool path zigzags across the work piece advancing only a fraction of a mm at each pass). It should also produce smoother edges than
achieved so far with Bitmap machining. The free version of DeskProto only allows a single tool pass (several passes may be used in the paid versions
allowing roughing and finishing cuts for thick materials) but for rosettes only 2mm thick a single pass may be satisfactory?
The Vector operation starts with a DXF (Drawing eXchange Format) file that may be converted directly from a JPEG image file through free online
conversion sites.
Several test runs with different materials were undertaken earlier in the year before the project was put on hold. Securing each work piece to the
mounting block was the main difficulty - diluted fish glue worked for machining but separating the rosette from the mounting block (using moisture and
heat to soften the glue) without damaging the fine detail was difficult and no satisfactory versions of the Eyun rosette were cut - even when the
rosette diameter was increased to 6 cm.
The fine detail of the Eyun rosette is a challenge to cut in wood when the cutter is set to cut through the full depth of the work piece. More uniform
materials such as plastic or soft metal may be more successful such as this attempt in soft aluminium cut to almost full depth.
Note that all of these earlier attempts used the same V engraving cutters and were made before the loose linear bearing was replaced - so some tool
vibration may be evident causing rough cutting. Also when cutting through full depth the work piece should be mounted on a block of the same material
as the work piece to minimise tool vibration. Alternatively the work piece may be cut to slightly less than full depth and then the thickness reduced
by sanding - after the machining operation - to reveal the open areas of the rosette.
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jdowning
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As an alternative design to the delicate Nahat Eyun trial cuts were made using the central part of an original 16th C lute rosette by Giovanni Hieber
- a more 'robust' design that might better withstand the cutting and handling forces without breaking(?)
A hand drawn copy of the original rosette was made and a JPEG image prepared and converted to a DXF file extension for Vector machining. The hand
drawn rosette design has imperfections that the software will copy which may or may not be a good thing - rougher machined edges but representing more
closely a hand cut rosette? Smooth lines in the image may be achieved if necessary by processing in free CAD software such as Inkscape - a lot of
extra work so avoided for these preliminary trials.
Trials were made using spruce sound board material about 2mm thick and glued to a mounting block with diluted fish glue and a paper backing for
additional reinforcement - the cutter being set to cut full depth of the work piece. The results were pretty rough looking - again due to some cutter
vibration and perhaps material non-uniformity due to hard grain in the spruce. Separation from the mounting block without damage was again
difficult.
This summarises the results of trials completed earlier this year. Picking up this project and starting again the next trials will be Vector machining
in a close grained hardwood (boxwood) of the Eyun design, 6 cm diameter and 2.5 mm thick. Depth of cut will be 2.4 mm and after machining the
underside of the work piece will be sanded to open up and reveal the rosette design. This way the work piece may be simply fixed to the mounting block
with four screws allowing easy release without damage.
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jdowning
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The CNC 3018 Pro router is designed to work with a laser engraving head in place of the router motor/spindle. I originally did not intend to try laser
engraving/cutting due to the hazards involved but have now decided to give it a try to complete my cnc machining education.
I have purchased the SainSmart 5.5Watt Laser Module Kit designed to fit the CNC 3018 Pro router and am currently testing the installation to ensure it
works as intended so that it does not have to be returned. If OK then laser cutting of rosettes will be reported on this forum as a separate topic.
The kit comes with the laser head and control modules easily installed with wiring and mounting hardware and includes the all important safety
goggles. As laser burning produces fumes the router and computer were moved into my small workshop that has a fume extraction fan and is otherwise
enclosed for safety.
Control firmware for the router is open source LaserGRBL that also converts any image to Gcode for controlling the laser head movement. Like the
DeskProto firmware used for routing operations previously posted LaserGRBL can engrave photographic images (similar to Bitmap router operation) and
also engrave or cut to line drawings in Vector mode.
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jdowning
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As a preliminary functional test the .jpeg image of the B/W Eyun rosette previously posted was first converted to a line drawing using Photoshop
software. This was then loaded into Laser GRBL for auto conversion to GCode. The laser beam was focused onto a piece of plywood and a test burn
initiated. I need to have some practice at getting optimum focus to a fine point but this first engraved example with a relatively coarse focus
setting (it took 9 minutes to engrave) is the outcome. The laser may repeat the same path if required to cut completely through the work piece
(presumably setting the depth of burn a little deeper for each path?). Further experimentation will be required to achieve optimum settings but this
is a start.
The laser head will now be replaced by the router spindle to continue with trial vector machining of rosettes.
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jdowning
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The SainSmart website has an excellent set of articles for beginners on the basics of CNC machining and setup including laser engraving.
https://docs.sainsmart.com/article/9t96srkawt-introduction-to-cnc-fo...
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