Embedded Files
Week 12: 2 Complete Axes
Week 12: 2 Complete Axes
Assembled X and Y Axes
Assembled X and Y Axes
This is the X-Y assembly for our machine. We did not have time to finish machining all the parts for the Z axis.
Beginning Z Axis
Beginning Z Axis
We've started the process for attaching the spindle and building the z-axis structure
Week 11: A Complete X Axis
Week 11: A Complete X Axis
Assembled X Axis
Assembled X Axis
This is our assembled X-axis. We were able to drive it using the controller Paul had set up for his machine.
Finished sizing a few more pieces so that they're ready to CNC next week
Some of the tasks we completed this week
<-- Also cleaned up the y-plate, involving manipulating and fixing the large heavy plate, and face milling the surface very carefully to maintain certain hole pairings at the same plane. Holes were also drilled through and only need to be tapped now, which can happen quickly at the beginning of the next session.
Week 10: Almost Done with an Axis
Week 10: Almost Done with an Axis
We almost finished assembling an axis, but we forgot to take pictures. All we have left to machine is the piece that connects the ball screw and the table.
A fixture was required for making holes in the long rails that could not fit into a CNC or drill press.
We have also finished most of the parts for the other horizontal axis.
Rails for Y-axis
Threaded 8020s
Hole making Fixture
Week 9: Working to Finish an Axis
Week 9: Working to Finish an Axis
We prepped a few more parts for CNCing for the Y-axis and tapped the holes in the motor mounts to finish them off.
In terms of overall progress, we only need to machine 8 more holes and modify some shaft couplers before we can assemble the x-axis. We have all of the parts for the y-axis cut to size and they just need to machine some features on a HASS.
Week 7: Still Machining Parts
Week 7: Still Machining Parts
Internal Frame
Internal Frame
An internal support frame made from 80/20 was added for rigidity and ease of connecting the shell pieces together.
External Shell
External Shell
The external shell has been modified and extended to accommodate the new frame.
We finished machining the X and Y motor mounts and bearing blocks and were able to slow down the CAM and salvage one of the parts that didn't work last week!
We started drilling the holes in the sides of these pieces but broke a bit so we will need to revisit the CAM and potentially use a larger tap + helicoil in order to salvage the part.
Progress on Z-axis Assembly
Design of Z-axis structure and drive system has been finalized
Initially, we were planning to use larger 23 mm rails compared to the 15 mm rails being used for the X- and Y-axis because of the long length of the cantilever of the Z-structure which results in larger moments on the linear bearings blocks. However, we already have quick access to 15mm rails, so we are planning to test the performance of the Z-axis using the 15 mm rails. The plate where the linear bearing blocks mount was left large to accommodate the larger 23 mm rails if they end up being necessary.
The main subsystem of the Z-axis that needs to designed is the support of the Z-axis when the mill is not powered. Because the Z-axis is driven using a ball screw, the drive system is back driveable when a motor torque is not being applied to the ball screw. We do not want the Z-axis to drop suddenly when power is shutoff to the mill. Some ideas include a damper system using a gas spring, a counter weight that balances the mass of the Z-carriage, or a break on the ball screw or Z-carriage that fails on when power is cut to the system.
Sources:
Discussion of Progress
Discussion of Progress
We have been making steady progress during lab sessions, but are concerned about being able to finish the machine with only a few lab sessions left and the new restrictions on accessing the shop outside of lab hours
Many of our supplies have just arrived and we are still waiting on other parts, so we haven't gotten to assemble/test a full axis yet even though we had initially planned to do that a few weeks ago.
Week 6: Continuing to Machine Parts
Week 6: Continuing to Machine Parts
Machining More X-Axis Parts
Machining More X-Axis Parts
Machining this axis is taking longer than we thought. We were able to finish cutting everything down to size and to cut out the features of a few parts. We have gotten a lot better at accurately machining parts down to size. Unfortunately the rails we are planning to use have an unknown shipping time, but luckily the rails in the kits are similar enough that we should only have to change 1 part as long as we get the ball screws we designed for.
The Smaller Parts
The Smaller Parts
We've prepped several more pieces of stock for CNCing and have some holes left to drill next week to finish off a part manually.
Week 5: Starting to Machine Parts
Week 5: Starting to Machine Parts
Epoxy Granite Structural Shell
Epoxy Granite Structural Shell
Rather than stressing over the aesthetics and finish of the epoxy granite, we decided to instead construct a shell around the structure. This shell functions as a structural support for the axes mounts (the 2 support beams in the middle) as well as a mold for the epoxy granite. Additional beams will be added to support the z axis as well. Dimensions are still being discussed since this is critical to the mounting of every other component in the build.
X-Axis CAD
X-Axis CAD
We decided to focus on making parts for the X-axis to fulfill the deliverable since it doesn't require the base design to be final.
X-Y Table
X-Y Table
The XY-table has been machined. The underside of the plate still needs to be faced. It serves as the connection between the X- and Y- axis, as well as providing the main mounting location for the X-axis frame and motor mount.
XY Mounting Plate
XY Mounting Plate
We finished the CNC work on the XY mounting plate, smoothing all sides and removing residual tabs. A few more holes need to be countersunk, but it is otherwise smooth and ready to go.
Assorted Smaller Parts
Assorted Smaller Parts
We didn't have time in lab to put everything on the HAAS to machine the holes, but we were able to cut most of the parts we needed to size and face them. We still have to cut one dimension on the Axis Table Mount and all of the X-Axis Frame bars.
They are labeled since we weren't able to hit the exact dimensions we wanted as we are still learning how to machine, but that is ok as we know which dimensions allow for larger tolerances.
Week 4: CAD, Drawings, and Design Updates
Week 4: CAD, Drawings, and Design Updates
Y-Axis CAD
Y-Axis CAD
CAD Link: https://a360.co/3lpMnJY
Y Axis Frame - the outer structure for the Y Axis which the linear rails sit on
CAD Link: https://a360.co/3llYtDA
Drawing Link: https://a360.co/2QbsNFJ
Side Bearing Block - supports the undriven side of the ball screw
CAD Link: https://a360.co/3eLUZJh
Drawing Link: https://a360.co/38SHoMN
Axis Table Mount - couples the ball screw and the table
CAD Link: https://a360.co/3cIO0hY
Drawing Link: https://a360.co/3bPNgrN
Side Motor Mount - For mounting the motor to the chassis
CAD Link: https://a360.co/3ltm4Cv
Drawing Link: https://a360.co/3eOs3At
Bearing Block Modified - Modified version of what comes in the kit.
CAD Link: https://a360.co/3bS77ql
Drawing Link:https://a360.co/3lpxZ4g
We are also working on:
Initial CAD for overall structure
Week 3: CAD, Drawings, and Design Updates
Week 3: CAD, Drawings, and Design Updates
The components we are ready to machine in the shop are:
Base plate for mounting parts (Mounts on X-Axis Blocks - designed to mount fixture plate on top)
CAD Link: https://a360.co/3rCUyou
Drawing Link: https://a360.co/30wsZkO
Z-axis spindle mounting plate
CAD Link: https://a360.co/2PYCqrj
Drawing Link: https://a360.co/2PXmXaP
We are also:
Creating a Bill of Materials of ready-made parts
Identifying/calculating critical dimensions
Calculating maximum forces each axis must withstand
Initial CAD for overall structure
Initial Structure
Initial Structure
Our chassis will be molded from epoxy granite. This material was chosen because of its vibration dampening capabilities and low cost. While 3D printing the mold for this chassis is certainly an option, the simplistic shape may allow the mold to be made from plywood, thus bringing the cost down even further. The guiderails in the y-axis and z-axis will be embedded into the chassis where the indents are. Dimensions for the structure are still fluid as OTS components are being finalized and will inevitably change the design slightly, but our aim is for the structure to be ~2-3 ft tall.
X-Axis CAD Beginnings
X-Axis CAD Beginnings
This week we started designing the X & Y axes. Each uses ball screws and linear guide rails. A standard T-Slot fixture plate is to be mounted on the X-Axis for workholding - either with a vice or with standard machine table clamps. The overall dimensions of the axes are still being determined as we move forward with the design.
X-Axis Beginnings: CAD Drawing
X-Axis Beginnings: CAD Drawing
This dimensioning style was chosen because the most important aspect of this part is where the holes are in relation to each other. The tolerances will be refined as we continue working on our design. Important dimensions can be confirmed using calipers.
Z-Axis CAD Beginnings
Z-Axis CAD Beginnings
This week we started designing the Z axis. The Z-axis uses ball screws and linear guide rails to define its motion. The spindle/motor assembly from shearline (P/N 6514) is aligned and bolted to a mounting plate, which is bolted to the Z-axis structure. The Z-axis structure is made of aluminum plates which are bolted together. The cavity in between the plates can be filled with sand or other type of material to provide damping to the structure. The overall dimensions of the axis are still being determined as we move forward with the design.
Week 2: Chosen Configuration & Actuators
Week 2: Chosen Configuration & Actuators
The configuration we chose for our desktop mill axes was that of a conventional turret-style vertical bed mill. We chose this on the basis that it was the most user-friendly design (as it is common and we all know how to use one) and the least risky from an engineering standpoint (by not having the heavy spindle unit moving around in multiple axes). Additionally, the use of a vertical bed mill over a vertical bridge mill makes the possibility of conversion to manual operation much easier to implement.
Our overall design strategy
Our overall design strategy
We aim to minimize the impact of inevitable (small) errors in manufacturing / tolerances, creating a smooth user experience and retaining the flexibility to have a manual override mode where one can operate the axes by hand.
For the XY stage, we seek to use ball screws to maximize overall efficiency. Though we considered using a ball screw for the z axis as well, there was concern about the additional safety precautions needed to ensure that the spindle head doesn't come crashing down due to gravity once motor torque is no longer being applied. We will decide in the near future whether it is worth pursuing mitigations for a z-axis ball screw; for now, our fallback is a simple ACME-threaded lead screw.
The guides for the axes will likely be simple linear rails, with blocks sliding along them on ball bearings.
If the team decides to continue pursuing manual override mode, an additional design consideration will be the inclusion of a quill-type mechanism around the spindle to enable z-axis pulldown, as seen in larger hybrid manual/CNC mills such as Prototraks.
Week 1: Configuration Possibilities
Week 1: Configuration Possibilities
Describe two milling machine configurations. Discuss the manufacturability, adjustability, and potential challenges of building a machine in those configurations.
Configuration 1: Vertical Bed Mill
Configuration 1: Vertical Bed Mill
Pros:
Standard configuration
Readily accessible tooling in LMP
Relatively small
Easy to use and setup parts
Good for simple parts
Cons:
Chips stay in piece during cutting
Leads to shorter tool life
Not as rigid as a Horizontal Mill
Cantilevered Z-axis structure leads to Abbe errors
Lack of symmetry in structure (open-frame)
Configuration 2: Horizontal Mill
Configuration 2: Horizontal Mill
Pros:
Better for cutting specific types of objects (e.g. gears)
Remove material faster
Chips fall out
Multiple cutters can be used at once
Better tool life
Can be more efficient
Cons:
Generally larger and more expensive
Not as common as Vertical Milling
Could be difficult to use
Requires unique tooling, not typically used in LMP
Configuration 3: Vertical Bridge Type Mill
Configuration 3: Vertical Bridge Type Mill
Pros:
Closed structural loop
Symmetric design
Length of cantilever of Z-axis does not depend on desired work volume
May be easier to achieve desired machine stiffness
Can use same tooling and fixtures used on traditional vertical knee and bed mills
Plentiful information on previous machine builds of this type
Cons:
Less accessibility to workpiece for fixturing and measurement
Mass of spindle, spindle motor, and Z-axis components move with X-axis motion
Rigid mounting of Z-axis to X-carriage may be challenging due to limited mounting surface area while trying to minimize mass and length of cantilever of Z-axis
Challenge is increased as Z-axis increases in length
Manufacture of bridge structure requires beams longer than the maximum desired X-dimension of the workpiece
More challenging to hold parallelism and squareness tolerance over long parts
Configuration Thoughts
Configuration Thoughts
The vertical bed mill seems to be a prime candidate for the configuration of our machine. Its operational simplicity, spatial efficiency, and capability to manufacture a wide range of parts are characteristics our desktop CNC mill should employ. One drawback to the vertical configuration seems to lie in its rigidity, so our team will need to take this into consideration when designing the structure. Also a vertical mill, the bridge type design has increased structural and thermal stability due to its symmetric-closed structural loop compared to the vertical bed mill which has an open structural loop. However, the bridge type design has challenges in manufacturing the structure of the bridge and designing the Z-axis which has an additional degree of freedom with respect to the machine structure compared to the vertical bed design. Horizontal configurations generally are more rigid than vertical configurations, but due to the narrower range of applications for manufacturing, we would like to model a configuration capable of manufacturing many different types of parts and not one designed for manufacturing a specific subset of parts. Furthermore, since the vertical configuration is more common than the horizontal, it will likely be less expensive to create and will have more available resources to guide us in the design. As result, the vertical bed and bridge mills are the two designs we are considering for our machine.
References:
Slocum, A. H. (1992). Precision Machine Design. Englewood Cliffs, N.J: Prentice Hall.
Marco Reps YouTube Channel: https://youtu.be/zvqjIOG0fi0
Page updated
Google Sites
Report abuse