WEEK 8: computer-controlled machining

In this week was to make something in wood using a CNC-Machine (computer Nuemeric control).CNC- machine is "computer controlled machine" like wasted in weeks past .

Here the file that we draw on a 3D/2D software first change to G-code .The G-code is the machine's language like path ,coordination speed will find through G-code by machine

Shopbot 3-axis CNC milling machine

Shopbot is high level production CNC machine which gives high perfomance ,speed,power for all cutting tasks.Here we can cut plywood ,timber and also soft aluminium by this machine . In our 3 axis machine the "BED" size is '4*8' feet


open or import vector design

select the regions to Vcarve or machine

specify the tool details and calculate tool paths

preview the job in any material

save the CNC code


Tolerance test

The group assingment was to find the Tolerance of the material to find this we drawn a comb structure with some female slots also give dimensions in the lowering order of the thickness of the plywood that we going to cut

Here the thickness of the plywood that we taken was "30mm" and put the slots with difference in" .1mm"that is the ranging was "29.8 to 29.5" .and it gives the tolerance as "29.8mm" that means it gave a tight fit in that slot.

Tolarence cut

Test for spindle speed,runout,toolpath,Alignment, Speeds and Feeds of SHOPBOT

For testing this we cut small square shapes at varying spindle speed,feed rate and depth. Shapes with similar rpm were clubbed together to create the toolpath.

The first test was for the RPM with varying feed rate and depth.It was found out that 12000 rpm and 10000 rpm gave a good cut of which 12000 rpm was finer and at 6000 rpm the tool got stuck and loosened.So when Rpm is decreased the quality is getting decreased The next check was for the feedrate we choose 12000rpm for testing and found out that at higher feedrate high frequency noise was heard.

RPM & Feedrate testing

So after discussing with our instructor we decided to have a final test with 9000 rpm at varying feedrate and we got the best result for 9000 Rpm,25 mm/sec feed rate and 3mm depth.It was also having the normal sound amoung these.

Final Testing

Runout a circle was cut and the measurements were taken at different points.Runout happens due to the inaccuracy of the rotary system (tool diverting slightly from the axis).This may be due to the problem with tighting the tool,wear and tear of the assembly,vibrations etc.Runout is calculated as the average of the maximum and minimum measurements we get

The runout was calculated to be 0.2 mm

MY WORK -Making Of A Shelf

There is somany ideas passing through the mind I decided to make a simple shelf in this week.The week was very special to us for learing about a new machine "prof.Neil" already told on the week Schedule make somthing big with using fit so I want to design the shelf using fits. So I just wrote a rough sketch on a paper for easy designing by using drawing softwares

Then I used "NX9 CAD" software for drawing of my model.Here I bulid up my shelf as a 3D model so it can give the correct dimensions in all parts and also in fits.So its help me creat all parts in the right manner.

drawing the shelf with line tool

In my model have a base,one complete back piece,and ten alling parts I already drawn the rough skecth so using the correct dimension I made The each part on the exact position using continuous line, after completing each part I extrude each part that in the wanted plane with the thickness of plywood that I am going to use.

building each part by part

Here I gave fit thickness as "12mm" that the thickness of the plywood that I am going to take cut .In group assignment we got the thick as .1mm difference from the plywood thickness eventhough it was very tough with fixing the parts so i go with the thickness of plywood .

here is the full model of my shelf in 3D

Here you can

After completing My model I want to change it into 2D so I exported it(file,export,Autocad DXF/DWG) by slecting parts as 3D object into .dwg file ,after exporting complete 12 parts each then I opend it into "AUTOCAD" one by one . In Autocad I changed each section 3D to 2D by deleting lines and sorted in the same plane(I selected top plane).

Changing the parts into 2D model the AUTOCAD is used for arranging the parts. I arranged all parts with in 8*4feet that is the full length of the shopbot bed and also plywood going to use. Here in arranging I try to save maximum space in the plywood

arranging parts

Here you can

Working In Shopbot

"V carve" is the software is using here for the shopbot ,Here I opened my model in "V carve" at the time there is an option apears that for giving the size& thickness of the metrial that we are going to use

giving thickness of plywood also width & height

After giving the thickness the second step is to give the tool path settings to becomes the skecth as a closed figure select the skecth the select join open vector which gives closed section then,

Dog bone

When tool passes through the inner edges cut inside the vector line it will not get the accurate fit because the tool can't make passes through the edges that the edges is not like 90 digree insted there is a curve for avoiding this we can give the "dog bones" ,like dog bone edges it makes a small fillet to the inner edges that gives a perfect fit .
For giving dogbone we can select the fillet in transform object and select the dog bone > then we can give the dogbone to the edges with the dia meter that we can mention at the inner edges

fillets in the drawing menu and selecting Dog bone fillet

Tool path settings

Select the tool : Here I selected 1/8" bit

Here the number of passes can be set ,it is depends upon the meterial type

Here we can give The "inside cut /outside cut" according to requirement,inside cut is given insted of giving pocket and outside cut for outlines

TAB option - giving tabs is prevent the material from shaking while cutting,then "Calculate"

Vcurve file you can download here


Before setting the origin we need to fix our bit on the machine ,for this we can manually fix it using the tools .

collectchunk and endmills

Here the collectchunk and endmills clean at each printing if not the dust particle will fill inside the gap and it affect the tightning of the bit.After cleaning tight the bit properly and notice the bit is too much inside .

fixing the bit using the tools

Here we can set Z-axis using alligator clip and zero plate these are electrically connected to the machine so machine can easly read the point .first connect the clip any where the machine which gives a green light when contact with the plate then place the plate above the material .The machine make contact twice with the plate takes zero settings in Z-axis

setting Z-axis with clip and plate

Then we can set xy-axis using control panal in the system after that we can start cut

control panel for setting xy axis


After setting all click to start cuting there is a window will appear asking with "starting router" at the time we want give rotate to the spindle otherwise it will brake the we can give ok.

starting router

cutting of the machine each parts by parts

cutting of the machine each parts by parts

After printing ,I shaked up each parts from the plywood and the give charming and clear finish to each edges using some tools I fixed it up to my self

filing each part for clean finish

building up each parts

shelf after fixing all parts

Error Occurred

Here I got one error in making of this shelf,At the time of fixing one part was entirely different in dimension it cause difficult in fixing the shelf .I think this is because of some problem occured in exporting into the.dwg file

The piece with different dimension

Then I decided to make one extra piece by measuring with tape ,I draw the extra one with correct dimension printed it makes a perfect joint


shopbot can cause some danger when it use so we want to take some precaution is more important .

Use Emergency stop switch if suddenly there is any danger

Use ear and eye protection when the using time

wear shoes when machining

oparate machine with a by stander

Always use sacrificial layer otherwise the bit can break

keep some distance from the shopbot when machining

Creative Commons Licence
shopbot by Abhilash Sp is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.