Design alternatives options & decision matrices :

 

 

 

1. Design #1: Standard Simple Design

The standard simple design started as a cheaper model to the datum, but not a budget design. A goal in formulating this design was to make a machine cheaper than either the two main benchmarks, that being the ShapeOko and the X-Carve. Standard parts, like balls screws, linear rails, and stepper motors were included. Quality is where the differences are in theses machines. All the subsystems that were standard to the designs were chosen, but if they could be cheaper than that part would be selected. Tolerancing on these parts was not as good, but it was a compromise for the cost. To clarify, if a ball screw used on the X-Carve was $150, and the cheapest ball screw possible was 50 dollars, a ball screw of around $100-120 was selected. A simple xyz gantry was decided due to its simplicity. The gantry system, (Z4) with a box design enclosure, (N3) could be set up with relative ease, making this a plus in the pugh chart. The workholding selected was a T-slotted plate, [9]. Standard to most milling machines, theses plates are versatile and intuitive for users to work on. One add on that was particularly unique in this design was the interchangeable workholding piece (10-11). Although the machine would be designed with a T-slot, it would allow the user to change the base plate to any base plate they would need. Currently this add on would be unhelpful, but it was put in place with the intent to help further development for this project, (i.e. 3D Printing heated plate).

2. Design #3: The Budget Design

Design 3’s goal was to make a working machine that would get the job done on the cheapest budget possible. The enclosure original design was pieces of plexiglass ridged up on removeable stands. After use of the machine the stands could then be packed away on, or clipped to the machine for easy storage. After reworking the idea, subsystem design (N1) was a replacement to the unsafe plexiglass shields. Belt drives, (C2) were also used instead of ball screws for this machine, due to their inexpensive cost. This was a major downside to this design, however, do to the likeliness of inaccuracy. Rubber belt drives can be toleranced really well, but due to the estimated forces linked with cutting aluminum, it was considered to be high enough to potentially stretch or break these drives. Most of the subsystems in this design can produce a tolerancing between 0.001-0.005 inches. Unfortunately combining all these together allowed for too much risk of play throughout the entire machine. This design was helpful to get some simple subsystem ideas, but after taking a second look it was clear that it would have been a poor choice to be a selected design.

3. Design #4:

In design 4 we did 7 different types of design. Then, we add all of designs together to produce new design for CNC router table.these designs are A1 for Baseplate. for the Drive we used C1 because it is fully staple and that make it more accurate ,for XYZ movement we used Z9 and A9.for Rails we used the mor safety and more efficient design which it G6. and we used N9 Chip Clearing. The unique parts of design was in enclosure and frame design. for enclosure,we designed it to be like a box N3.for frame we used the vertical frame Z9. the pros for this design are Sturdy Frame,Limited Deflection during operation,Chip Clearing,Safety and Tolerance. the cons are it is not Design Ease, it is not Able to clamp work pieces in place, it does not have the Ability to be converted into 3D printer or laser cutter in future,expensive Cost and Maintenance Complexity.

4. Design #7: Datum

Design 7 was the design most similar to the machines talked about. A standard safety enclosure was chosen, and frame design was based off of the XYZ gantry system in both the ShapeOko and X-Carve. A small difference between the datum design and the benchmarks is the rail system. In both the benchmarks, a slot block rail, (similar to design G6) and simple bearings rails, were used to move all gantries. In the datum design, the rail system is system is formed with square stock, and roller bearings pressing against each edge, as seen in (G10) in the Appendix A. This system was used mainly for the simplicity and cost. A downside to this design is possible chips getting lodged into the bearings, breaking the rails, and the manufacturing of the rail would have to be custom. Unlike the the benchmarks, the datum would also have a chip clearing system. A fan, placed on the spindle itself, allows for the chips created by the mill to be force away for the the area, clearing and cooling all at once. This is another reason the box enclosure was chosen for this design, because from research, these chips can be flung at high velocity and could possibly injure the user.

5. Design #8:

This design is one of the design selected because it is the second highest score in the Decision matrix. This design uses a simple cube covering the whole device as the safety enclosure and is depicted in appendix A as (N3). it uses a set of slots in the base plate to allow for clamps that slide in the slots to be placed anywhere in the work area. the frame used is in the shape of (Z2) in that the z axis moves at the end of the vertical pier. the rails used are (G6) and they are the highest precision and strength rails we could find. it has an addon design for chip clearing that involves a container being designed around the spindle bit made of brushed that  will conform to the changing workpiece and prevent chips or saw dust from leaving the work area. attached to it is a vacuum hose that is intended to remove the chips in an orderly way and prevent them from building up around the tool head.The pros for this design are Design Ease,Construction Ease,Sturdy Frame,Limited Deflection during operation,Chip Clearing,Table mounting capability and Tolerance. the cons are it is not Able to clamp work pieces in place,Overall Area of Machine, it does not have the Ability to be converted into 3D printer or laser cutter in future,and the Transparent safety Shielding.

6. Design #9: XY Table

In design 9, we did attach an air-compressor. The enclosure called bread box as Appendix A (A-6) which looks as a door, baseplate called T Slot (N-5), the drive was a double lead screw(C-3 and A-9). While the X-Y-Z axis we did use the XY table. For the frame it was made from the wood (Z-2), and the rails was linear bearing(C-1, Z-2). For the chip clearing we did use the fixed nozzle(C-6). There was some  pros such as ;  the design ease, construction ease, sturdy frame, the deflection is limited during the operation  and the chip clearing system will work very well. But the cons in this design was more than the pros. For example; it’s really difficult to clamp work pieces in place and convert to 3d printer. Also, the overall area of the machine, the cost and tolerance weren’t appropriate. While the maintenance complexity and transparent safety was one of the most cons in this design.

7. Design #10: XYZ Gantry

Finally, design 10 didn’t have a chip clearing system or any add-ons. Simply, it had what called enclosed box for the enclosure (Z-5) and the frame too, the base plate was a scrap heap (G-15) , the drive is a linear belt (G-4)  while the rails was a diamond (G-10) and X-Y-Z axis was X-Y-Z gantry. For the cons, the design ease, construction ease, sturdy frame, cost, drive speed and table mounting capability were good enough for this design. Also, the ability to convert to the 3D printer and the maintenance complexity were working very well. In the other hand the ability to clamp work pieces in place,chip clearing system and tolerance wasn’t good enough for this design. More cons, was the safety and transparent safety shielding.

2. Designs Selected

The decision matrix used to rate the chosen designs did so based on several important engineering requirements, customer needs, and requirements generated for this purpose, given that any requirement alone, would satisfy the total needs of the system. Weight, cost, maintenance, and tolerance were each given by the customer needs. Cost and tolerance were rated with the greatest importance having a combined weight of 41%. These requirements were very important to the customer. Lifetime, dimensions, and emergency stop systems were engineering requirements which did not have a significant weight to the customer, but were discussed with him in some form and were based on information received from him. The remaining requirements, (reliability of clamp, force per axis, and custom parts) were created by the team to help quantify the difficulty of designing, constructing, and operating the device. These accounted for one quarter of the weight in the decision matrix.

1. Rationale for Design Selection

From the decision matrix, Designs 4 & 7 have been selected to show to the customer (with the team's recommendation) for him to choose what he believes fulfills his needs best. They were the highest scoring. By convergent design, designs 4 & 8 and designs 7 & 10 were extremely similar with a difference of only a few parts at most. The team had decided to present to the client both an XY Table design and an XYZ gantry design because the XY Table (4 & 8) design will best meet the tolerance and deflection needs of the client while the XYZ Gantry (7 & 10) designs will more easily meet cost constraints.

1. Design 4:

Design 4 scored lowest on the weight because it is expected that it will be made entirely of metal and in certain parts the metal plates will add significant weight over design 7 & 10 which will have no equivalent parts. The cost sored low because this design uses expensive rails with a greater number and possibly length than the other design. Additionally the significant amount of solid metal in this design will increase costs over the other design. Its lifetime scored higher because this design has components intended to be high accuracy and quality (reducing wear) and components to protect those high precision parts. Ideally this machine should have a life and maintenance comparable to a professional grade machine. This design was rated low on its size because it has components (namely the pier) that extends our significantly past the cutting area while the actual cutting area (rails included) is otherwise comparable to xyz gantry designs. This design has the highest score for its clamp because it uses a vice type clamp that will maintain an unyielding hold on any work material. It also has the highest rating for force per axis because of the inherent design. There are no parts that can deflect to the point of breaking on an XY Table design because the axes are laid out flat with almost no moment arm. The pier is a significant moment arm but during the detail design phase it will be determined how much material is needed to resist all forces applied. This design scored average on number of custom parts because the total number of components is less for this design but a significant portion of the components used will still need to be custom. This design scored average for maintenance because this design has high precision parts that will need more frequent maintenance but also is intended to protect the high precision parts to reduce the need for major maintenance. Lastly this design scores very highly (but not best) for tolerance, because as stated earlier there are little to no structurally weak moment arms that can result in deflection.

2. Design 7:

Design 7 scored highly on weight because it uses a stronger frame shape that can easily be made of wood (and retain a high strength) which can save weight over using a steel or aluminum frame. It also has fewer thick metal parts than other designs. It scores average in cost because it uses the same expensive rails (among other rails) as design 4 while also having higher quality and number of drive screws (Ball screws). Its lifetime is rated at average because it uses some cheaper parts that may not last long to cut costs and also uses less accurate and reliable structural parts for the X axis which may result in unforeseen wear or permanent deflection over time. It has the highest score for overall space because its footprint is only slightly larger than the total necessary travel size. It also has a highly rated score for clamp reliability because of its improved vacuum table design. This design has been shown (during research) to be able to strongly clamp work pieces in a reliable way. This design scores worse for force on the axes because this design has small parts and some thin rail/structural members that may not be capable of withstanding significant cutting forces. This design has many parts of which a significant portion will have to be custom designed so it scores poorly on that criterion. This design also makes use of parts that may never need maintenance (except replacing) and protects those that do by keeping them away from the damaging chips cut off of the material. Lastly its score on tolerances is very average because on some of the axes issues less accurate parts and has a potential for significant deflection in the x and z axes.