8. Computer controlled machining¶
group assignment
do your lab’s safety training . Test runout, alignment, speeds, feeds, materials, and toolpaths for your machine.
Individual assignment
Make (design+mill+assemble) something big (~meter-scale).
File Downlaod¶
Group Assignment_Test_RouterCNC
Software Used:
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Machine: ShopBot PRSalpha ATC 96-60-8
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Software: VCarve Pro
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Safety cautions
Safety cautions and procedures must be considered while working on Laser machines. Please read, understand and apply all caution signs.
ShopBot
The ShopBot PRSalpha ATC 96-60-8 is an affordable full-sized gantry tool for CNC cutting, drilling, carving and machining of wood, plastic, aluminum and other materials.
Machine Overview
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Specs: Cut/Movement Area (Length x Width x Plunge): 105” x 61” x 8” (2.67m x 1.55m x .2m)
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Step Resolution: 0.0004” (0.010mm)
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Positional Repeatability: +/- 0.002” (0.051mm)
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Spindle RPM: Max 18,000 RPM
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XY Move Speed (with full cutting force): Max 360”/min (9.1m/min)
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Z Move Speed (with full cutting force): Max 120”/min (3m/min)
If you are new to CNC milling, as I was, I definitely recommend perusing this guerrilla guide(https://lcamtuf.coredump.cx/gcnc/ch2/) to get an understanding of how three-axis machining works.
Also speak to your workshop supervisor to understand the machine you will be using.
Bits, Feeds, Speeds
The challenge of getting a good CNC cut is in selecting the best tool for the job (Bit), the optimal cutting speed (feed rate) and router/spindle RPM (speed of rotation) for your material.
Dust collection Bag & the compressor:
The CNC machine has a compressor attached to it, so that the cut particles do not fly around and mess up the lab.
Note:
Its important to wear safety protection whenever using this machine, esp. eye gear and gloves
Tooling Details:¶
- drill bit vs end mill :-
Drill bit can be differentiated by its pointed tip which is for drilling into the object whereas end mills have flat tips and they are for milling away chunks from the object. End mills give a flat cut while drill bit gives a curved cut.
- flutes :-
they are the spiraing sharp part along the surface of an end mill. They are for cutting through the object and for clearing the chips. Less number of flutes means chips will be cleared easily but the cut will be of rough finish. Higher the number of flutes we will get a smooth finish but the chips cut off wont be cleared effectively.
- up/down cut :-
if you hold the end mill by its head (the portion without flutes) and rotate it clockwise if you get the impression that the flutes are spiraling up then it is up cut and if it feels bke it’s spiraling down then it is down cut. Up cut is good for clearing the debris easily but results in a rough top surface while down cut is bad at clearing debris but gives a smooth top surface. Then there is something called center cut, where from bottom till middle it is down cut and from there till top it is up cut. This gives smooth top and bottom surfaces but very bad at clearing the cut out chunks.
Group Assignment¶
For the tests we used LMT.ONSRUD 57-287 , a downcut spiral bit. It has two flutes and a center-cutting tip. also we used LMT.ONSRUD 52-287 for the other part a similar Up Cut endmill. These endmills are designed for soft Wood, hard Wood, wood composite.
Up Cut Specification | LMT.ONSRUD 57-287
Down Cut Specification | LMT.ONSRUD 52-287
To minimize or eliminate runout “Runout is the tendency to spin the tool around a centerpoint that is not the tool’s center. It makes the tool wobble instead of spinning cleanly and increases chip loads” maximum part of endmill shank should be inserted to the collet. The end tip of endmill shank might flush with the collet and if possible it might go beyond the collet end. All ways, a clearance distance between the cutting edges and collet face should be maintained.
To tie the collet and endmill to the spindle, we used to supplied wrenches. A simple safety feature is provided in the machine that one of the wrenches is attached through a string to the “INTERLOCK DISENGAGED - ENGAGED” key. So whenever you need to use the wrench you have to remove the key and spindle cannot be started. Note that to fix the collet to the spindle the dust extractor should be removed first.
To tie the collet and endmill to the spindle, we used to supplied wrenches. A simple safety feature is provided in the machine that one of the wrenches is attached through a string to the “INTERLOCK DISENGAGED - ENGAGED” key. So whenever you need to use the wrench you have to remove the key and spindle cannot be started. Note that to fix the collet to the spindle the dust extractor should be removed first.
Make sure End Mill fixed !
Feed Rate
We used the Cutting Data Recommendations provided by the tool manufacturer to calculate the feed rate “Feed rate the speed at which the cutter engages the part and is typically measured in units/minute”. We used the data provided for Plywood (17.5mm).
Chip Load = Feed Rate / (RPM x # of Flutes)
where chip load in inches per flute, feed rate in inches per minute and RPM in revolution per minute.
Fixing The Work Piece
The machine has MDF sacrifice board fixed on bed. If the endmill penetrates the work piece the extra cut would happen on the sacrifice sheet. This way we make sure machine body and tool won’t be destroyed. Holes were drilled to work piece and wood screws used to fix it to sacrifice board. Note that when we work on software, we define “Boarder Gap” to be 30mm.
Group Assignment
Working with Rhino
for the group assignment we make 2 circular shape with different diameter (17.20, 17.30, 17.50, 17.80 ) with two different milling tool (Down cut & Up Cut) and the result was with 17.30mm the Playwood (17.5mm) is fit well !
we made some measure test for the part to make a comparison between the design and the actual output of the milling.
the image above shown that it’s fit with 17.3mm ( which is numbered with 3 in the red color)
Also we mae another test for the group assignment for the fit and the path to see what is the different between (Up Cut/Down Cut) and how is the board surface finish looks like !
Individual assignment:¶
I choose to make a swing chair for the Individual assignment, I chose this project because my mom told me she wants that chair. Yes!! this is the reason lol :)
I start with bring my board and measure thickness of it which is PlyWood material with 17.5mm thickness.
I designed the swing chair with SolidWorks software it’s awesome software allow you to design a model and assembly it to test is it fit or not.
Also I made a virtual sizing of the board seems like it on the shobBot with the actual size to see if my parts can be cutting in one board!
finally, with CAD design I moved up to drawing to export the parts to the Vcarce as DXD files.
Working on VCarve Pro
I used 17.5 mm latte The actual size should be used in machine software. Step-by-step guide for working on VCarve Pro is provided in week assignment section.
Tips(Additional)
While milling:
Sanding
While assembly:
Hero shoot !!
Problems and Solutions for the future:
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the holes for the bottom base were note alignment so I made some manual drilling.
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for the middle parts I couldn’t assembly them because the path wasn’t correct so I have to edit it in the original design or make more sanding for the joints holes.
After couple of weeks: Hero Shoot
