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6. Computer Controlled Machining

Group assignment:

  • Complete your lab’s safety training.

  • Test runout, alignment, fixturing, speeds, feeds, materials and toolpaths for your machine.

  • Document your work to the group work page and reflect on your individual page what you learned.

Shopbot

Shopbot is a CNC machine which is used for 3d carving, engraving, cutting boxes, making signboards and cutting different styles of letters and numbering. Not only that we can even make and assemble furnitures and make prototypes of our project before we actually proceed further. For the shopbot we are using CAM software which is known as V-carve which allows us to generate the tool path of our design before we start cutting the material. V-carve accepts both 2d and 3d files and for that we can create our design using any 3d modeling softwares like solidworks, fusion 360, Freecad etc...

So after we finish creating our design, we need to import it in the V-carve, than start processing the design by giving its dimensions, scaling arranging and laying out the designs and ultimately generating the tool path, saving and running the saved file.

Specifications of Shopbot Machine

  • Standard tool accommodates sheet material up to 4’ x 8’ with cutting/machining depth (Z-axis) of 6 inches.

  • Table size approximately 6’ by 10’.

  • Step resolution is .0005” or better depending on gear ratio.

  • Positioning accuracy is +/-.005” or better (no load).

  • Positioning repeatability +/-.003” or better (no load).

  • Cutting accuracy is approximately +/-.015” for heavy cutting applications.

  • X, Y rapid positioning speeds (‘jogging’) up to 600” (standard)/1800” (alpha) per minute.

  • Z axis move speed up to 360” per minute.

  • ShopBot Control Software reads .sbp (OpenSBP) Part Files as well as standard Gcode and includes a .dxf converter which allows conversion of files from CAD programs such as TurboCAD, DesignCAD, AutoCAD, Corel Draw, and SignLab.

Safety Precautions while operating Shopbot

  • Read Manuals and familiarize yourself with the tool’s operation and safety guidelines before use. Also, review manuals for any attached routers or spindles.

  • Make sure that the room under which you are operating shopbot should be fully ventilated.

  • Always follow these three rules while operating the shopbot which are to look, listen and smell. Always look whether there are abnormalities with machine or not,listen whether there are abnormal sounds coming from machine or not and finally be mindful and immediately stop the machine if you sense some smoke or something burning.

  • Always keep the first Aid kit ready and within your reach if incase there are some cuts, splinters and burns while operating the shopbot.

  • Place the endmill properly and firmly inside the collate and tighten the collate nut and also fixture the job piece properly on the sacrificial layer using clamps inorder to avoid the breaking of endmills.

  • Always wear the Personal Protective Equipments while operating the shopbot and by any means, one should avoid operating the machine under the influence of alcohol, drugs or when we are not feeling well.

  • Always keep the fire extinguisher near to machine so that we can act instintly, if incase the machine catches fire.

  • While operating the machine there should be atleast two people to monitor the operation and we should never leave machine unattended.

  • Carry the wired controller switch(control pendant) along with you which allows you to press the emergency button during emergencies.

  • Always keep the surrounding clean and free dust so that we may not fall or slipped off while operating the shopbot.

  • Never forget to put ON the dust collector system for shopbot because during the operation, it produces lot of dust particles which are harmful for our health in long run. So inorder to minimise the health risk we need to put on the dust particle system so that the surrounding remains free of dust. Not only that at the same we should also not forget to empty the dust collecting bag when it gets full.

ShopBot CNC Machining Processes

  • Firstly we cleaned the sacrificial layer and than placed our material on it and measured its length.

  • After that we put on the machine by turning the power switch ON and engage the key and later on disengaged the key inorder to change the endmill using the tools which are placed on the control box of shopbot machine.

  • We changed the endmill and fixtured the material tightly on sacrificial layer and measured the thickness of material that we are going to cut.

  • After that we did the calibration of XYZ and then opened the V-carve pro and then imported the Test design for our group.

  • We had given the dog-bone fillet and kept its radius at 2mm

  • After that we had given the toolpath for the design and for that we followed the steps as per the image displayed below

  • From the tool database, we selected the required tool and its default tool setups.

  • We had selected both the vectors alternatively and given the tool paths and for our Test design, we had taken white particle board of thickness 12mm and for our individual assignment also, we will be using the same white board only. After generating toolpath, we calculated and simulated to see how it will be cut by machine.

  • We had selected both of our toolpaths and saved the file.

  • Next we opened the Shopbot 3 from the desktop and clicked on Cutpart and selected the saved file.

  • After that a dialog box will appear, and we need to press ON on the control switch first then only click Ok on the dialog box.

  • Machine will start its operation and for the group we cut away slot and rectangle and tried fitting the joints. We had given the slot inside cut and the rectangle part outside cut

  • After we are done cutting of our design, the machine's spindle stopped and moved back to its origin.

  • We started fitting the joints together and in the first case we cut the slot from inside and cut the rectangle from outside and found that it fits perfectly.

  • In our second case we tried to explore more by cutting the slot from inside and rectangle on the line and found that there are small gaps in between the joints and it was not fitting properly.

  • Lastly in our third case we had cut both slot and outer rectangle on the line and found that, the joint was again not fitting.

Studying feed rates and Rpm of machine.

Inorder to experiment the feed rates and rpm of shopbot we had made three circle and tried cutting them with different feedrates and rpm.

  • In the first test we kept rpm as 5000 and changed rpm starting from 20 till 40.

  • In the second test we kept fixed feed rate value as 30 and changed its rpm starting from 4000 till 6000

Finally what we had concluded was that inorder for the best fitting and optimal joints we should cut the slot from Inside and outer boundary (rectangle part) from outside so that our joints will be fitting perfectly

This week we had lots of fun in learning one of the most versatile CNC machine Shopbot and in addition to that we were bit anxious and nervous thinking that whether we will be able to complete machining our designs on time or not as we were four in number. luckily all of us were able to complete machining on time despite having to stay bit more time in the lab on weekends and but we all were happy for the fruitful outcome.