World of possibilities
Cutting and speeds
World of possibilities
Such a machine offers a lot of possibilities…
You can :
- Cut parts for any wood assembly
- Cut boat forms or templates
- Cut vinyl (with special head), to make letters or decoration
See Thierry Monnot site tmonnot.free.fr/Fraisage/Vinyle/Vinyle.htm
with some examples of cutting tools ww.antaresinc.net/VinylPage.html
How does it works ? end of cutter is slightly behind the center of rotation of cutter support (offset). So, the cutter turns when we move it (as when you pull an object). Small diameter bearings can came from a destroyed hard drive (or small electric motors). Professional cutters are made in carbide, but you can make yours in old drills or spit nails.
The offset is set from 0.2 mm to cut films to 1mm to cut cardboard.
- Do engraving or 3-D parts for modelling, scenes, etc.
For example www.ronchinimassimo.com/millwizard.htm, in Italian, but photos are clear.
- If you add a rotating system, you can do turning.
Fist, some definitions :
CAD : Computer Aided Design. Computer tool to make drawings and computer models
CAM : Computer Aided Manufacturing. This is our aim !
2D : 2 dimensions, cutting parts, engraving
2D 1/2 : 2 dimensions, with some possibilities to manage tool depth, to creates decorations, for examples.
3D : 3 dimensions. Relief world is open to you... ball nose bits are used to obtain a smooth surface.
Bitmap image : Image constituted of many dots, as a photo or a fax.
Vector image : Image described by lines or surfaces. A CAM software must follow trajectories and needs drawings described by vectors.
We can transform bitmap images in vectors with a vectorisation software, which search lines of a drawing.
Free vectorisation software Wintopo allow that. You can download it on CNC25 site HERE (2.8 Mo)
A photo can be transformed in a 3-D volume based upon it's contrasts. Interesting results.
How to choose a software ?
You have choice. Began first by software you already are experienced with. As long as you can create files with DXF 12 format (which is the case of most CAD software), or files with a PLT format (which is the case of nearly all softwares), you can do the work.
Autocad is the most common, but i don't recommend it, except if you use it professionally. Personally, i hate from the beginning it's strange ergonomy and it's complexity (It is a software much older than Windows, and it have never followed any ergonomy standard), but this is the one i'm using (…), because i had the need to read files from my work. At the end, i finished to be used to...
You can do drawings with software as surprising (In industry) as CorelDraw, which, moreover, have a vectorisation function.
My personal choice will go on Turbocad, which have a good ergonomy and is relatively powerful but adapted for home use. LE version (Light Edition, 2D only) can be get freely (but you have to register).
The last possibility is to create directly your drawings in the CAM software, if it does have a CAD module. This is the case of NinosCFAO, presented herebelow.
Control software allow to run the router/mill with :
. Drawings done directly into the software. This is integrated CAD/CAM software
. Drawings imported from other softwares, generally in DXF or PLT format for 2D . STL format is also used in 3D.
In 2D cut, you have to add to the drawing complementary informations to défine interior or exterior cut, the kind of bit used and associated speeds.
Cutting order and entry point can also be redefined.
. A file created in a standard format called 'G-code' or 'ISO code'. That file can be written directly by experienced CNC programmers, or more frequently theses days, produced by another software. Such an interpreting software need small computer resources and can be installed on obsolete computers. A solution with two machines, one in office to generate the G-code, the old other one in workshop to run the mill/router.
Important points :
. Bit diameter must be taken into account. If the software don't allow that, you are obliged to do your drawing taking into account bit diameter, which will be impossible to change later. Recent software normally allow that.
. 'Attachs' or bridges. When you are cutting parts, to maintain the cutted piece in place and also left some stiffness to your plate, it can be useful to uncompletely cut the parts. Remaining links are called 'attachs'. In the case of my machine, where the plate is installed vertically, these attachs are compulsory because without, the cutted piece fall down and you risk serious problems.. Accelerations Management. A stepper cannot accelerate too much without loosing steps. So acceleration management is important especially if your machine is heavy, because that allow use of a good gear ratio to have strength, without decreasing the speed. But your electronic boards must have the ability to control stepper at high speeds (use of a PWM control, aka chopper).
In english Kellycam software is the best known (for amateur use)
You will find other miscellaneous software.
NinosCFAO, CAD/CAM integrated software for 2D and 3D, is remarkable, and it's evolving on fast pace.
It can import DXF and HPGL (.plt). It does have a surface modeller and can read STL format.
Manage accelerations, takes into account bit diameter and do have 'Attachs'. It can export to G-Code files.
It also does vectorisation and can build 3D volume from an image. Do you want more for an amateur software ?
License cost 70 Euros, with two installations or with a dongle 140 Euros. While originally only in French, there is now an English and Spanish version. Though, the helpfile is only yet in french, and need serious update. There is also a very active users forum, but also only in french.
To execute G-Code, quality DOS software, costing 20 $ (US), TurboCNC. It is the one i'm using now on a PC 486DX50. On this machine, it can output up to 9000 step/second, with fluid movements. No graphism.
What is G-Code ? see here on the manual of EMC (Linux)
To write, DeskEngrave, Freeware which output a G-Code which can be excuted on TurboCNC.
It exist miscellaneous other softwares.
The universal resource for CNC is Majosoft
A useful software to test parallel ports, parmon, on Fred Bulback's site www.geekhideout.com/.
On this site a dll (io.dll) allow direct drive of parrallel port pins, if you are tempted to program yourself.
My personal present setup :
. Autocad lite for 2D drawings, export to DXF V12 files, on a PC 2 Gz
. NinosCFAO for machining definitions, exported to G-code, on a PC 2Ghz
. TurboCNC as G-Code file interpreter, on a PC 486DX50 Mhz
Machining and speeds
Some definitions :
Cutting speed :
This is the speed of the blade when cutting part. For a given rotationnal speed, cutting speed increase with the bit diameter. This is why small bits must turn very fast. A router with variable speed control is required. Unit to give this cutting speed is usually meter or millimeters par minute. For exemple, one 6mm diameter bit turning at 15 000 rpm will have a cutting speed of :6 /1000 * 3.14 * 15000 = 283 m/minute.
This is approppriate to machine wood with carbide bit, but this is far from maximum speed.
This cutting speeed rely on 3 things :
- Machined material
- Bit material
- Your machine performances
Advance speed :
This is the speed of the router in the part. It is given in meter/minute or cm/minute.
It is given by the tuning of your machine/software, as defined in your cutting list.
Increase the speed give higher loads, so it is needed that your machine can :
1/ Arrive to that speed
2/ Maintain sufficient load at such speed
A lower advance speed generally give smoother surfaces.
But if it is too slow, you will burn material (if non-metallic). Cut material, don't make powder ! That will also decrease the life of your bit.
Load depends of all cutting parameters, but mainly from machined material, steel being the harder.
If you are obliged to reduce advance speed (because of machine limits or to have better finition), it might be needed to decrease cutting speed (say, rotational speed), to maintain a cut thickness at a minimum.
Our CNC routers not being professional mills, their stiffness is not that high. It means there are some risks of vibrations with hard materials. Also, that drive to some lacks of precision.
Cutting depth :
If cutted materials are relatively thick, it will not be possible to cut them in one time. It will be needed to make multiple path, by increasing the cutting depth between each path. To cut wood panel, for example, it is generally recommended to not have a cutting depth of more than one bit diameter. Some bits, like the helicoidal cutting bits allows higher depth, but be prudent, bit can be broken. Also that increase the load.
Here also, stiffness is a key point. Lack of stiffness give irregular loads and increase the risk of rupture.
What bit to use :
To contour, use carbide helicoidal bits (see photo). Don't use HSS bits, which don't last. Don't forget that ply and glued panels are very abrasive due to the glue. For wood and plastic cutting, use bit with one helice. For aluminium, brass and hard plastic, use bits with two helices and for steel use bits with 3 helices (sort of 3 teeth...)
See Antares inc, where you will also find vynil cutters, Ketele or BELIN Yvon S.A.
To not have to change router pinch too frequently, buy all your bits with a 8mm shaft, and avoid 6 mm shaft (in Europe ...).
Classical carbide bits box. Note dismounted bearing on one bit, which is required on a CNC. Oil after use. Classical bit 4 mm diameter, one teeth Diamond stone, fine (fine is red, medium is blue), required to sharp carbide bits. 18 Euros.
Manufacturer : DMT
CNC helicoidal cutting bit, solid micrograin carbide, very high efficiency, 8 mm diameter. Cutting height 22mm, 32 Euros/piece, and that is cheap !
to buy at reseller, but manufactured by BELIN Yvon S.A.
Choice, use and maintenance of bits is one key point of router use, being it manual or CNC'ed. This is also the most costly part. You will find all needed informations in specialised books.
If you are working with medium, bit will wear (because of the glue), so a small 'refreshment' of the bit with diamond stone after each use is desirable. To avoir corrosion, do a small projection of 'WD40' before tidy up (diamond stone is used with water).
You can machine a lot of materials :
- Wood and associated products :
No difficulty, but have a minimum advance speed to well cut and not burn the wood. Use carbide tools. A too small advance speed will decrease the life of your bits.
- Plastic :
No difficulty, provided you use appropriate speeds (to not melt the plastic)
- Composite materials :
This is a bit problematic, especially because of the toxicity of the chips. So, it is better to avoid, even if your aspiration system is good.
If you wish to cut carbon composite, you have to remember that it is an electrostic and high conductor material, and all your electric and electronic equipment will risk destruction by short circuit. If you insist, you will have to pressurize your electronic command box with fresh air taken outside.
- Aluminium and alliages :
No difficulty, provided you use appropriate speeds and lubricate. Loads are higher than for wood and you have to limit adavance speed. Otocoup machine cannot machine aluminium, because you cannot lubricate, due to the installation..
- Steel :
There is no special difficulty, but loads are high, and the stiffness of your machine must be sufficient to avoid vibrations. A screw transmission may be better to machine steel.
While less problematic than carbon, because less electrostatic, metallic chips are not that friendly for your electronic. Precautions are required, and your control box must be as tight as possible, and as far as possible from the machine (and in height). A good aspiration is required.
Bit diameter Rotating speed for wood machining.(for an advance speed from 300 to 1500 mm/min) Maximum rotating speed in wood 0-20 mm maxi (28 000) maxi (28 000) 20-25 mm 25 000 trs/min maxi (28 000) 25-35 mm 22 000 trs/min maxi (28 000) 35-50 mm 20 000 trs/min 20 000 trs/min 50-70 mm 16 000 trs/min 16 000 trs/min
More or less, you will be obliged to limit your rotating speed because your advance speed will not be sufficient.
In wood, advance speed is more or less limited by the stiffness of your machine. If you go too fast, when stopping, there is a mechanical 'release' which will modify trajectories. Beam of the machine have torsional displacment under load. When you stop, that came back.
Practical limits of my own machine (with cables and without steel angles) are now around 300-500 mm/min if cutting depth is not too high.
If you follow the drawings, your machine will be 2 to 3 times more stiff than mine (this is progress...), and i think you may go over 1000 mm/min.
Also, i've not yet tested the high efficiency helicoidal bit.
Beware, numbers hereabove are preliminary estimations. look at your machine and use your judgement !
Ears and eye protections are required.
And a wood part ejected by a machine run generally at a speed over 200 km/h...
Beware of the quality of your tools. This is high speed rotating equipment, and if you buy your bits 'made in China', you have to take your risks. This is of no interest, because they will not last, even if in carbide.
And don't forget, if you decrease advance speed, decrease rotational speed, to not burn wood.
-- Remaining to be builded --