Design and build a digital backstop for the workshop guillotine, utilizing the existing hardware of the previous backstop project as much as possible.

Team Members: Mark Buhagiar, Namitjira Skuthorpe, Adan Hoerner, Shaneel Prasad, Zhengyu Sun, Prama Nand

The Problem

Task: Precision electrically driven backstop with readout of distance to be fitted to existing workshop guillotine.

Problem: Re-design to ensure the backstop remains parallel to the blade within A mm over the blade length of B mm, under an assymetrical force on the backstop (through sheet being cut) of C Newtons.

Existing Hardware

Hydraulic workshop guillotine and existing backstop (student project with faulty bearing design).

Existing Part CAD Models (Group)

The modelling of the parts is to be shared by the group to allow rapid CAD assembly of various backstop solutions. When you submit parts you have modelled (or modified), put your initials at the end of the part name so we can keep track of your contribution.

To download, right click on file > save target as...


Inventor Models Inventor Models


Ass 1: Initial Concepts

1.1 Current Assembly. Assemble the current (faulty) design as an Inventor assembly using the parts supplied above. You don't need to go overboard - just show you can model and assemble it.

1.2 Parallelness: Sketch 3 concepts to address the problem of maintaining the backstop parallel with the guillotine blade. Include a description of operation and overall hardware, and the "issues" of the design (problem areas, critical factors, potential risks etc).

Send this by email as a IMAGE, WORD document or PDF to my email address, include name, subject, title and any pictures/illustrations/sketches. Hand sketches may need to be scanned or photographed (check it is legible).

Rules: You must include at least ONE new concept after the previous student's submissions.

bahugiar-mark.pdf (MB)


bahugiar-mark.pdf (MB)


nand-prama.pdf (PN)



rack&pinion.jpg (AH)


sun-zhengyu.jpg (ZS)


pulleys-800.png (NS)


parallelogram-900.png (SP)


offset-rail-TL.png (SP)


Ass 2: Select Best Design Concept

2.1 Selection process based on a number of criteria. Build a decision matrix (Pugh matrix) to compare the list of solutions. Factors could include: Cost, Rigidity, Reliability, Speed, Maintenance, Compactness, Re-use of parts, and (of course) SAFETY. Weight these factors by choosing suitable weights, score the factors on each design and tally the results to determine the winning design. This should be done using a spreadsheet (e.g. Excel).

Decision Matrix Tally:

2.2 Define the design variables; A,B,C. Blade must remain parallel within A mm over the blade length of B mm, under a force of C Newtons on one side of the sheet being cut. *(Comment on the Design Concepts for likelihood of compliance with these parameters. Some systems might be incapable of achieving the required parallel tolerance)


Ass 3: Data Collection for Components/Assemblies

Gather data on specifications for performance of critical components or assemblies such as;

  • Motors:
  • Bearings: linear-bearing_catalog-INA.pdf (6MB) Calculation of bearing load rating: (INA) (SKF)
  • Ball Screw: Ball screw notes. Ball screw catalogue
  • Hardware: Fasteners, adjustment, cables, etc
  • Ergonomics: Forces by a human (NASA)
  • Available Steel Sections
    Square Tube: 50x50x2, 50x50x1.5, 40x40x1.5, 25x25x1.5, 20x20x1.5, 16x16x1.2, 13x13x1.2
    Rect Tube: 40x20x1.5, 75x25x1.5,
    Flat Bar: 50x5, 25x5, 50x3, 25x3

Ass 4: Calculations and Design

4.1a Skewing Force and Bearing loads. Calculate the bearing loads under the skewing force stated in 2.2, and determine the minimum bearing spacing to satisy these loads. This is a very straight-forward exercise (in forces and moments) that you should be able to conquer all by yourself - esp with the hints I gave last term. Check mounting bolt diameters and shear forces.

4.1b Deflection. Determine the required bearing spacing and a suitable backstop bar structure that will satisfy the specified parallel tolerance. Demonstrate their compliance by calculation and/or FEA simulation on CAD. Use FEA to refine the design for minimum weight, ease of manufacture and reliable stresses at critical locations such as bearing mounts. Check mounting bolt deflection caused by clearance of the bolt within the holes.
See Backstop FEA

Complete the structural analysis to include the bearing support beam, the 2 mounting points on the guillotine and any bracing necessary to stabilize the backstop on the guillotine. You may need to adjust bearing spacing to improve deflection results once the bearing support beam is mounted, since it will seriously increase the flexibility compared to cantilevered frame alone. Note that an inboard mounted bearing support beam reduces moment and deflection.

4.2 Critical Details: Highlight all critical details that influence the parallel specification. Design any features needed to ensure this.

4.3 Adjustment: Design a method of adjusting the backstop to ensure it is parallel to the blade, or can be adjusted back to parallel in the event it becomes excessively angled.


Ass 5: Design Concept Report

5.1 Choose your design and justify using data. This is your submission on which design you are recommending for the guillotine backstop. You must be able to back your argument with hard data from previous assignments (esp Ass 4).


Ass 6: Shop Drawings (End of Semester 1)

This assignment must be checked 2 weeks before the end of Semester (Thurs, June 16). Submission is end of Semester 2 (Thurs, June 23).

6.1 3D CAD Assembly. Inventor assembly of your design solution.

6.2 CAD Detail Drawings. The drawings must provide adequate detail for construction and assembly, as per normal workshop standards. You do not need to include instructions for aligning the backstop to be exactly parallel to the guillotine blade, but you will certainly need to detail all fabricated componects and assemblies, showing fasteners, welds etc.

Inadequate/incorrect/incomplete engineering drawings will no be accepted. (You are leaving this job for someone to build!)


Ass 7: Controller Specification (Sem 2)

7.1 Current hardware: Measure the pitch of the ball screw and take data from the existing stepper motor (steps/rev etc).

7.2 Motor Selection: Determine the resolution, speed, torque requirements and specify a suitable motor type and ratings. The motor/s must operate at a safe voltage (i.e. "low voltage").

7.3 Resolution: Determine a realistic minimum resolution (in mm). Determine the number of digits required on the readout for the full range of motion to be recorded. (in mm).

7.4 Controller: Research a suitable controller. It needs to handle two steppers, end switches, input of coordinates, homing and zero-ing buttons, and digital readout of suitable number of digits.


Ass 8: Controller Programming (Sem 2)

8.1 Software and Hardware Testing: Develop test procedures and analyse system performance against relevant criteria. Recommend appropriate action. (In other words - check out if the controller can do the job, and if not, get it sorted).

8.2 Control Parameters: Measure and record relevant parameters for control programming - E.g. Motor speed, travel, steps per mm, total steps, etc etc. Compare these to any limitations of the controller and describe what effect this has on the solution.

8.3 Control Programming: Write code to that delivers a solution to an aspect of the project. Each student must submit their own separate code that addresses a unique part of the solution. Examples below;







Drive the motor to home position against microswitch

Prama - -

Develop acceleration code for ramp-up and ramp-down (in motor steps).

Adan - -

Interface with a keypad to enter the coordinate in mm.

Mark Spec Code

Show coordinates on a LCD display.

- - Code

Drive motor to a certain position in mm using above routines.

- - -

Program management and safety interupts.

- - - -


Relevant pages in MDME
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