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cnc strategies for machining helical shapes

by:QY Precision      2019-09-13
Spiral shape poses a particularly serious challenge to CNC machining.
The problem of rotating cutouts and fixing irregular bending volumes tests the courage of even the most experienced mechanics.
Small CNC machining spiral parts are usually manufactured with machines that provide continuous rotation of 5 axes, as shown below: there are very few 5-axis machines capable of handling any item with a size greater than 1 feet or so (if ever)
Providing this type of drive requires different strategies to make these challenging shapes.
The following instructable tests two strategies for CNC milling of spiral shapes in large format 5-axis CNC wood
From creating inventory in a way that limits waste and processing time, fixtures, and registration, to tool path creation.
A little context. . . -
When I was an artist at the Autodesk Pier 9 work store, the work was done --
The project that requires these strategies is to explore the entanglement volume of carpentry --
I will cover this a little in the next step-
The machine I use is DMS large 5-axis elevated gantry CNC with capacity of 5\'x 5\'y 3\' Za real beaut\'-
If you\'re fairly new to the CNC manufacturing field, here\'s a great crash course: the need for these strategies is the result of the climax of my research that I lived as an artist at the Autodesk Pier 9 workshop.
I started looking for new relationships between parts in the Assembly and developed a series of prototype joints.
Perhaps the most exciting of these studies is a series of entangled shapes cut from a spiral or spiral surface, so that the final parts can basically be screwed off from each other.
I started making versions of this idea on a larger scale, about the size of the human body, to face the challenges of manufacturing --
In particular, restrictions on materials and tools.
The image shows the parts developed in Fusion 360, essentially overlapping round cone shapes.
The Assembly tests a hybrid connection system where two objects are cut by a spiral shape and have the geometry of a friction-matched two-way ball joint.
For large prototypes, I chose a CNC milled mid-fiber plate mix for the spiral surface, and aluminum ribs and plates for the more original cone shape.
There are also some steel and rubber for spherical details.
In the plus bar, the mid-fiber board is quite cheap compared to the tool foam, good enough machine, and hard enough to be fixed together, because these shapes are usually gradually from thick to narrow parts
From below, the mid-fiber board is very porous and heavy, and the dust generated during processing is more like a smoke, floating gently in the air. . .
So dust collection is the key.
Not to mention the potential hazardous chemicals used to glue wood particles to medium fiber boards, namely formaldehyde.
I will definitely use the \"low formaldehyde\" version here.
In order to keep dust, waste, and machine time to a minimum, a clever new inventory creation strategy was used to enable me to perform only one finish while machining (no roughing! )
, And hollow parts to reduce the weight.
This process is outlined here ()
Created by a fellow artist, I will give a brief introduction below.
The goal here is to use the 2d CNC tool to create a rough shape from a laminated 3/4 \"slice that only needs to be finished.
Typically, materials that require long, dusty rough machining operations will be used as rectangular blocks.
These spiral shapes have a particularly high surface area and volume ratio, which makes this method particularly valuable.
The downside is that this process requires some different software, probably in addition to the software you use for design and CAM.
Fortunately, both are free products from Autodesk.
Step 1: offset and hollow
Export the geometrystl, import .
Meshmixer of Stl-
Offset geometry to ensure slice inventory (step 2)
Completely surround your shape.
I offset 1/2 \".
This also gives you some small error when you register the stock in the machine, although you really don\'t need it. . . -Make Solid-Hollow.
I dug up with 1.
5 \"wall thickness, so the finished part will be 1\" thick-
Export the result.
StlStep 2: Slice-
Import the hollowed geometry into 123d production-
Set the paper size and select the \"stack slice\" option-
I highly recommend using pins, which will make the assembly a breeze and your inventory will be stronger --
Export 2d drawings as well.
Stl step 3 of slice shape: import slice model-
Import the slice model into the CAM program and use this geometry as inventory in the settings-
In the case of fusion, the grid is first converted to BRep.
If your model has more than 10 k triangles like my model, re-import into the grid mixer and zoom out and try again. . .
Now cut the slice using the 2-axis or 3-axis CNC tool of your choice.
I used a 3-axis shopping robot with a 4\'x 8\' bed to cut slices from a 3/4 \"mid-fiber board\" with a 1/4 pin.
Also, I assemble using Titebond III wood glue.
To make the most of DMS\'s 5-axis function, I built a base to raise the parts of the bed by 1 feet.
This allows the tool to turn completely horizontally without a spindle or dust collection cover hitting the bed.
I adjusted the platform to be as long as my longest part in the Y direction and as narrow as my narrowest part in the X direction.
It is constructed as a 3/4 plywood box on a 3/4 plywood, extending to a threaded fixing hole on the DMS acrylic layer.
The general strategy of registering inventory in a fixture is that a unique rectangular mid-fiber board \"platform\" usually concentrates the footprint of each part on the box and docks the front edge with the registered block on the box.
The board is laser etched with footprint of the material to be processed and the center line aligned with the center line of the block.
The upper left corner of the block is used as 0,0 or work home.
Therefore, with this setting, we can use CNC technology to align the CNC machining materials very accurately to the plate and to align the plate to the fixture.
The same information you use in CAM software will appear on your parts and fixtures, so it\'s just a question of putting a very simple puzzle together --
This is a very precise set of relationships, all of which are CNC, with little chance of error.
With this generic approach, I went on to make two settings changes to produce these challenging shapes.
It is easier to mill shapes with convex and concave geometry and deep highlights using long tools (long reach).
Long tools want to be thicker in order to remain stiff under high loads, especially in the case of processing hard wood or steel.
Fortunately, the medium fiber board is closer to foam than hard wood, so I can use a fairly long tool without worrying about it.
Also, since I didn\'t do any rough machining, I didn\'t have to deal with any tool changes (
Except 1 with flip milling settings).
I used a ball nose 2 slot end grinding plate with a diameter of 1 in uncoated high speed steel with a cut length of 6.
I ordered these through MSC.
To drill holes in installation 2, I used 1/2 \"diameter 3\" length 3 slot flat head milling mounting type 1, trying to avoid the challenge of flipping milling by cutting the parts in half
Even with the ability of the 5 axis, these quasi-
The cylindrical/conical continuous rotating shape cannot be fully processed by 1 channel.
Again, there are no flat spots on these parts that can be easily and stably fixed to our base.
The two issues are strategically addressed by dividing these parts into two parts, but not ideal: professionals :-
The sliced surface provides a flat mounting surface-
Slicing in the right position will produce parts that can be completely machined without flipcons :-
The number of parts generated by the slice is twice the amount of work to prepare the inventory, and the time to develop the tool path is-
The process of clamping and gluing parts is an opportunity to lose the accuracy of the parts, and fortunately, in this workflow, I can\'t find a way to keep the origin between all exports and imports in the inventory creation.
So after preparing the slice inventory and importing its digital version into CAM software, the first step is to position the inventory model in space so that it completely surrounds your design model.
This is essential to ensure that any part of your geometry is not hung out of stock, so it does not exist in your machined parts.
Also, I increased the stock and model 1.
5 \"remove from the board, allowing the tool to cut all the way to the bottom edge without colliding with the fixture.
Next, I generated the Registration Board.
In Fusion, this means modeling your board to determine the size and generating a sketch that projects your inventory profile, the outline of the board, and the center line in 2d.
I cut my plate out of 3/4 \"with a rail saw and export the vector to.
Laser etching with large-format laser cutting machine.
I then connect the stock to the board that aligned the stock with the laser etching footprint.
You should expect the stock to be slightly wider than the profile, as the clamping and thickness of the glue will increase on all slices.
I used 2x4 (
Actual size 1. 5\" x 3. 5\")
Raise the inventory of the board to the right size.
I have had some problems anchoring the stock on the plate in a way that is hard enough to withstand the side pressure of the machine.
Finally, I used 5 lag screws with washers, through the bottom of the plate, through 2x4, into stock.
Finally, I connect the plate to the platform and align the etched center line with the center line of the registered block.
The image here shows the progress of the toolpath I used to carve this part.
While DMS provides 5-axis joins, my toolpath was created with the \"3\" Axis policy instead of the Real 5-Axis policy, which allows me to maintain fusion (
5-axis programming is not yet available in Fusion).
For Real 5-axis programming, I will use Inventor\'s HSM Pro, or FeatureCAM for Delcam.
This means that each operation has a fixed z direction.
To get to all the surfaces and corners, I found it best to split the channels into several directions to keep the tool as vertical as possible to the surface.
After trying to track and assemble all stock slices and trying to glue and clamp the final irregular shape, driven by the confidence to successfully register and process parts, I decided to address the challenge of flipping milling.
The new challenge here is to find a way to fix the irregular stock shape before and after the flip.
For initial positioning, our slice inventory strategy provides a fairly simple solution.
I just simply squeeze out 3 of them and slice them flat.
Now I have 3 fins and I can register them to the board using the same technique in setup 1
Project sketch in fusion of fin and laser etching.
I added a tag detail to the fins so they can be easily removed after flipping the stock.
To increase the rigidity, I made a four-tube all-in-one fixture with a shop robot, and the fins of the stock can slide and screw in.
The fixture is aligned with the etching and screws to the board, the stock screw is aligned to the fixture, and the board is again centered to the platform through the registration block. .
For the direction of the flip, I used the 1 \"wooden pin to support the irregular shape.
In fusion I created a sketch line as the axis of rotation and then copied and rotated the geometry.
I modeled and positioned 4 pins for the range of the shape and used combine> cut to subtract the pin shape from the model depth by about 1/2 \".
I then flipped the model back along the same axis and created a drilling operation as the last step in creating pin holes in the first direction of machining.
Similar to setup 1, I made a 2d sketch that projects the pin position onto the profile of the board.
Now, starting in the first direction, the board will have the laser etching position of the fixture and the Post that flipped the stock.
This gives me 4 precise mounting points for irregular geometry so that I can know exactly where the inventory is in space after flipping.
I used the chop saw to cut the pin into a size extracted from Fusion and made some collars from the 3/4 mid-fiber board with the Shopbot to increase the stiffness and screw into the real estate.
After machining in the first direction, I took out the stock from the fixture and cut the fins at the label with a saw.
I then remove the fixture from the board and connect the 4 columns aligned with the pin.
Then it\'s as simple as aligning the hole with the pin and installing it with mallett --
Get ready for the second round!
Same programming policy as set 1
While DMS provides 5-axis joins, my toolpath was created with the \"3\" Axis policy instead of the Real 5-Axis policy, which allows me to maintain fusion (
5-axis programming is not yet available in Fusion).
For Real 5-axis programming, I will use Inventor\'s HSM Pro, or FeatureCAM for Delcam.
This means that each operation has a fixed z direction.
To get to all the surfaces and corners, I found it best to split the channels into several directions to keep the tool as vertical as possible to the surface.
The picture above shows the final parts and assemblies after I finish, paint and add some metal cones and hemisphere to finish the geometry.
Ultimately, the flip strategy does save a lot of time in stock manufacturing and setup, and the flip strategy is very accurate due to the workflow of the CNC fixture.
The only problem is the rigidity provided by the pin fixture.
Since my parts are generally cylindrical (Long and narrow)
, The spacing of the pin on the x-axis is not enough to provide stiffness (laterally)
When processing long edges, under the action of the force of the tool, a little jitter will be generated.
I am by no means a very experienced programmer or machine operator, and I have learned some valuable lessons in the process.
It would be great if there were any senior mechanics that could provide some feedback, even CNC 101 tips that I might not have noticed. Thanks!
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