If you miter your tubes with a hole cut saw or hand file them with the help of a miter template, BikeCAD has always had you covered. Now, in BikeCAD version 21.0 we have the option to generate G-Code to cut both ends of the tube on a CNC mill.
To do this, we'll select File >> Export G-code for miters.
Before running through the input fields here, it should be mentioned that default values for these can be set in the Customize dialog box.
The first choice we make is which coordinate to associate with the rotational axis of the tube. Here we've chosen Y, which means the X coordinates will be measured along the length of the tube.
Next, we define the rotational axis range. We can associate it with the circumference of the tube, or we can enter a value that suits our particular CNC machine. Perhaps a full rotation is meant to be 360 degrees, or maybe one full rotation is simply 100 units.
Next we have the option to offset our tool path to account for the diameter of the cutting tool.
To make optimal use of the tube, you may choose to line up the tip of the base miter with the very edge of the tube. However, to adjust the placement of the butted section of the tube, you may wish to offset the entire cut by some distance from the end of the tube. And if you are going to apply some offset, you can measure that offset to the tip of the miter or to the deepest part of the miter.
If we wish, we can also check the box to create a hole for each water bottle boss.
If you have a unique application that may not use standard G-code, you can check the box to only print coordinates. If we do want to output the full G-code, we can proceed to input values for such G-code specific elements as the spindle speed in RPM, a slow feed rate for when the tool enters the tube and a fast feed rate for when the tool is milling the tube.
Z0 the start position of the tool measured from the tube centerline, the distance above the tube surface where we start the slow feed rate and the cut depth which is the depth into the tube that the tool will be plunged.
When producing a miter template, BikeCAD will show one curve to represent the outer diameter of the tube. It will also show a dashed line to represent the inner diameter of the tube. When generating a tool path for G-code, BikeCAD will follow whichever curve removes the most material at any given point.
When using a CNC mill, one must always ensure that the movement of the workpiece suits the rotational direction of the cutting tool. For this reason, you'll notice that the rotational axis coordinates for the down tube cut at the BB will start at 0 and increase in the positive direction while rotational axis coordinates for the down tube at the head tube end will start at 0 and decrease in the negative direction.
After saving your G-code you'll find three resulting files with the GCO extension. One for each tube in the main triangle.
If this becomes a routine procedure within your fabrication process, you'll likely want to use the same default settings each time. All these default settings are stored within the Properties.xml file which can be edited in the Customize dialog box. Click View >> Customize and scroll all the way to the bottom of the Startup tab. Click the Save settings button to store your preferences for all future design sessions.