====== Epilog Laser Focus Instructions ======

{{ :focus-menu.jpg?direct&200|}}===== Use the Cutting Table ====

The Epilog laser focus is calibrated for the cutting table. I have not tested it with the engraving table.

===== Use Manual Focus =====

Usually proper focus is important to achieve the desired results. After some tests, I found that manual focus is much more reliable than autofocus on the Fusion Pro 48. I recommend everyone use the manual focus method. If you don't remember how to use manual focus ask someone for help or message me on WhatsApp to make an appointment.

===== Focus = Material Thickness =====

Under normal circumstances the distance shown in the Focus Menu should be about the same as your material thickness. For instance, if I'm engraving on 1/4 inch ply, then after manual focus the focus menu should show about 0.25. Error is often in the range of 0.03, so a number between 0.22 and 0.28 would be normal. If the focus plane is different from the thickness of your material then check for warp. You should also check that your material is flat against the bed. If you push down on your material and it goes down then it isn't flat. If your material is flat and seated properly and the focus error is greater than 0.05 then ask someone for assistance. See "How focus numbers work" at the end of this page for more details.

{{ :auto-focus-off.jpg?direct&400|}}===== Turn off Autofocus in Job Manager Dashboard =====

Auto-focus should always be turned off in the dashboard.

===== How focus numbers work =====

The number on the focus menu is the elevation of the focal plane above the cutting table. If you put a piece of paper on the cutting table and use manual focus (very carefully, the motors could push a hole through the paper) then your focus plane should be at almost zero. If you put 1/8 inch ply on the table and focus correctly then the Focus menu should read about 0.125. Under most conditions your focal point should be at the top of the material, which is at an elevation above the cutting table equal to the thickness of your material. Advanced users might want to put the focal point inside the material. If you do that then you are more skilled than me and don't need to read these instructions.

===== Focused for Maximum Intensity =====

The laser is focused for maximum intensity which is slightly different that the waist of the focused beam. When I say focal plane I'm talking about the plane of maximum intensity not the plane where the beam is of minimum diameter. This is possibly a nit-picky deatil since it is likely that the two planes are very close together.

===== The Cutting Table is not Perfect =====

The cutting table is not perfectly level. Nothing is perfectly level. By focusing on different spots on the Fusion Pro 24 table I measured 0.000 at the top left (0,0) corner of the table, 0.025 at the centre of the table, and 0.064 at the far corner (24,24). So you can expect variation on the order of at least 0.035 due to variations in the cutting table.

===== How much variation in focus depth is acceptable? ======

This is an interesting question. Lasers usually form gaussian beams. For a thorough discussion on the propagation of a gaussian laser beam you can find papers like this on the internet [[https://www.brown.edu/research/labs/mittleman/sites/brown.edu.research.labs.mittleman/files/uploads/lecture21_2.pdf]]. A simple euclidean geometric approximation, assuming that the unfocussed beam width is 1mm, the focussed beam width is 0.13mm and the focal length is 2 inches, gives the table below.

|  distance from focus (inches)  |  beam diameter (mm)  |
|          0.000                 |         0.13         | 
|          0.010                 |         0.13         |
|          0.020                 |         0.13         |
|          0.030                 |         0.14         |
|          0.040                 |         0.14         |
|          0.050                 |         0.15         |
|          0.060                 |         0.15         |
|          0.070                 |         0.16         |
|          0.080                 |         0.16         |
|          0.100                 |         0.17         |