In Otherplan 1.0, we’ve made some adjustments that cause the 30º Engraving Bit to mill a bit differently than it did in previous releases. Because this update will affect the precision and accuracy of milled PCBs, we wanted to share a little bit of background on why we’re making these changes, and how they might affect you.
During in-house testing, we’ve seen results with our 30º engraving bits that don’t quite match our expectations. In particular, we’ve noticed that on PCBs milled with the 30º engraving bit, the traces seem to be narrower than they should be, and the spacing between traces seem to be wider than they should be. This is especially noticeable on boards with small trace pitch. Because even one thousandth of an inch can affect the success or failure of a board, we searched for the cause.
After looking into a number of potential issues, we realized that the issue was actually in software. The tool definition – the part of Otherplan that describes the exact shape and size of the tool – is slightly incorrect for the 30º engraving bits that we offer in our store. Essentially, Otherplan thinks that the 30º engraving bit is thinner than it actually is, at the depth it’s milling. Even though milling with wider parts of the bit will usually result in functional prototypes, the prototypes will not be as accurate as the designer intended.
In order to address these issues, we’ve made a few changes in Otherplan 1.0:
An updated definition for the standard 30º engraving bit: We’ve changed the tool definition in Otherplan 1.0 to reflect the true dimensions of the 30º engraving bits we provide in our store. You will likely notice few changes, if any. But if you are milling boards with very fine traces, you may find that some of the traces will no longer be able to be milled with the bit. (See below for details on what to do in this situation.)
New high-precision 30º engraving bit in Otherplan and in the OMC Store: For folks who do need accurate traces down to 6 mil, we’ve begun stocking a new 30º engraving bit that is the right tool for the job. This new high-precision 30º engraving bit has a tip diameter of 0.003 in, compared to the standard bit with a 0.005 inch tip diameter.
So, should you use a standard 30º engraving bit or a high-precision bit? Here are our recommendations:
- If possible, we recommend using the standard bit. Because the standard 30º engraving bit has a wider tip, it will be stronger and less likely to break.
- If you’re milling a board with small trace pitch, approximately 8 mil trace-and-space or less, we recommend using the high-precision 30º engraving bit.
- Finally, if you need to mill small traces but don’t have a high-precision bit handy, just select the high-precision 30º engraving bit option in Otherplan, but insert a standard 30º engraving bit. The dimensions of your trace and space won’t be perfectly accurate when you use the standard 30º engraving bit with the path designed for the high-precision 30º engraving bit, but you’ll likely still end up with a functional board.
These images, taken under a microscope, show the differences between the two tools:
The tool on the left is the standard 30º engraving bit with a 0.005 in tip diameter, and the tool on the right is the high-precision 30º engraving bit with a 0.003 in tip diameter. While the difference is small, they can have very different results when used to mill PCBs.
If you do encounter issues with trace accuracy, keep in mind that there are a number of factors that can affect the final product, especially when using engraving bits. Copper thickness, board flatness, trace depth, spindle runout, chip clearing, inaccurate tool location, and thermal expansion can all cause traces to turn out wider or narrower than expected. For best results, make sure to keep your Othermill clean, locate your tool before every job, measure the thickness of your material with calipers, and run the Othermill for a few minutes before beginning to mill.
If you have any questions about these changes, please feel free to contact us at firstname.lastname@example.org.