7th week Assignment

Computer-Controlled Machining

NSCP

Group Assignment

Safety Training

On march 6th, at night we receive the CNC reinforce and safety training, it was held in spanish by Víctor Pimentel. The review was undertake also with the CNC machine to make us note some key this that we need to remenber to avoid personal accidents.

  1. Use auditive protectors
  2. Use facemask
  3. Use protective glasses
  4. Use safety gloves
  5. Mantain safety distance to aovid electrostatic discharge

To avoid machine damages

Fab Lab Esan has a 1.52 x 2.44m ShopBot. We review the Vcarve software in order to know Shopbot's functional details, we focused on 1/4" down-cut end mill as follow:

  1. Regarding cutting parameters, we have 0.25 inches of pass depth and as step over 0.1 inches.
  2. In terms of feeds and speeds, we have that the CNC works with:
  • Spindle speed of 14000 r.p.m,
  • Feed rate of 3 inches/sec, which refers to how quickly the end mill moves in the X and Y directions and
  • Plunge rate of 1.0 inches/sec, refering to how quickly the end mill moves in the Z direction

To avoid machine damages

Design, Vcarve Pro and Shop Bot Features

Then, we worked within Vcarve Pro ShopBot Edition Software, and proceed as follow:

Group Assignment Results

CNC router offers many options of different types of joints, we are going to describe each result analysis

Tolerance Test

First we create a basic serial of sloting fingers with different sizes going from 14.25 mm uo to 16.25 in order to find out material tolerance (MDF 15mm). We find out that to obtain a manageable pressfit the tolerance reach 0.75 mm. However, our instructor suggested that for our final individual assignment was better to consider 1 mm tolerance. This because we will have to many different pressfit and we will have cumulative errors to manage

We tested 0.75mm tolerance with diferent joints, and we registered some problems:

When testing wedge joint, as shown in pictures below, the wedge mortise extended into tusk mortise. However, the wedge did not fit in, we conclude that accumulative error cause this result

After comparing snap-fit and flexure fit we notice, as shown in the photo, that snap fit fail due to widht irregularities, but flexure design allows to buffer those differences

We also test snap and fingers joints. As shown in photo (a), snap fail because we could not achieve the final lock. The beam design was too slim, and if we force the bending it would broke. In case of the fingers joint (b), we made a mistake and only consider 0.75mm tolerance. However in this case double tolerance is needed

Finally, we compare press-fit versus press-fit with chamfer. We find that the second one allows a perfect fit, while the first present son fit errors. We also tested T-Bone fillet orientation to anotate how this coud be hidden


You can get access to the testing file here.

Individual Assignment

Choosing and Bechmarking

To choose something big to build, I focused on finding something to solve a problem at home, so it could be useful and doesn't become waste at the end of the course. Thus, looking around I notice that I have problems on how to organize and exhibit my vinyl records. As you can see on on photo (1) I modify a DYI shelve sell by Playwood Peru (2). However due to vinyls weight, the plywood is buckling, also It doesn't have specific are to place the record and dvd players and for the special cleaning materials.

Prototyping and Designing

I started a web search to find some ideas that could be fabricated. I found a first example (1) at Autodesk Instructables, but I considered to small. Then I found a vinyl storage and turntable cabinet (2) fabricated by Wax Rax, a botique that use machines to develop customized storage, stands and cabinets. Thus I decided to design something inspired on that design but customize to cover my needs.

Scketching, and Designing

At the begining I was trying to think how to replicate the previous design (1), then I tried to spare at both sides of the turntable my vinyls storage (2), but I considered to small. Then I found a vinyl storage and for the final scketch I decide to fabricate something modular with places for my speakers (3).

I use Fusion to develop my design, I design in different files each vinyl storage part. I extruded each 2D design. and finally projected each view to obtain each .dxf file to work on Vcarve.

Using Vcarve

To start within Vcarve software it is important to set up the material, in this case I worked with OSB (18mm) and then I established material margins (2440x1550 mm) just using ruler options, nnd add aditional lines to set screws margins that we will need to use to fix the material to sacrificial table

We must import each .dxf file (1) to distribute them into the milling space. Then, we need to establish tool radiues (3.2 mm - considering 1/4" down cut end mill) (2) and choose fillet type. I select T-Bone fillet for those geometries presenting angles (2), and Dog Bone fillet for those with 90° angles.

Then we need to obtain Gcode files that we will use to fabricate our design. It is recommendable to start with pocket toolpath. I select 9mm cutting depth (half of material width), assigning 1/4" end mill and choosing climb as a cutting direction. Then we could visualized thoolpath direction and movement on 2D and 3D views respectively.

For inside and outside toolpaths, we select 2D profile toolpath option. Selecting 20 mm as cutting depth to secure milling efficiency (a). Choose 1/4" end mill and 3 pass to mill, this because we need to consider that depth cutting must be around end mill diameter (b). Finally, we need to add tabs, for this we need to analyse each toolpath and the distant between each geometry.

We obtained Gcode files for the other two profiles, interior (a) and exterior (b) toolpaths. Also include one to reference screws drilling, because we need to stabilize the material so we avoid problems during milling (c) and (d), we must choose each profile and be sure that only that file have been selected on the check box. Otherwise we could have problems during the milling

Using the ShopBot

We need to start the CNC machine (1) and Shotbot Software, here we need to move the end mill on X, Y (0,0) and then make descend Z axis just a little bit to proceed with Z axis calibration (3). The software advice us to colocate the plate to continue (4).

I upload each profile, in the following order: (1) drilling (for screw drilling guidelines), then pocket, interior and exterior toolpath.You can find profiles files here
We need to open the files, press CNC's start buttom, verify that the end mill is turning and push the green bottom that appear in the screen.

I prepare every piece by sanding them, finding a correct order to ensamble them, and proceed manually using rubber hammer. We can observe a musical note at the side. You can observe the final module with a vinyl record. The design allows us to appreciate the vinyl art.

You can get access to the vinyl stand design files here.

You can get access to the Vcarve files here.

Reflections

  1. It is recommendable to model your product, or in this case furniture, digital assembling, prior to machine, in order to avoid problems with press fits
  2. Eventhough OSB material declared width by supplier was 18mm, it is neccesary to measure the real widht because it is not perfect, and exist differences and we need to take that into account while designing
  3. Security measures with CNC Miling machine are very important, not only for individuals security, but to avoid any kind of equipment damages, and end-mill lost.
  4. A totally recommended OSB as material for furniture machining, because it allow us to build something that could last longer in comparisson to MDF. And could even last more by recovering it with some chemical product