Still learning, if cutting material that is 4mm etc, do you want the focal length to be hitting the top centre or bottom??
I usually set the focal length to the middle of the material.
Centre focus for cutting and out of focus for engraving generally gives best result. If you focus on the top or bottom surface you sometimes get an angled cut. Engraving out of focus leaves a softer finish which is usually nice but can cause problems on very fine text.
thanks for your help
how do you set the focal lenght???
The focal length of these lenses are fixed. You can find your focal length by engraving a piece of wood on an angle. Start at the high end and engrave to the low end. You will notice the thickness of the engraved line changes with the height between the lens and the work piece. Where the engraved line is thinest is the focal length of the lens.
K40 laser usually comes with a 50.8mm (2") focal length lens.
@Daniel_Wood So, what you are saying is after the focal length is determined, one would adjust the head up or down to set the height for the job at hand, be it cutting or engraving?
Head cannot be adjusted, you have to adjust the work table that your work piece is sitting on. Most people remove the fixed bed, and install some type of adjustable bed, or just place blocking of various heights to get the work piece to the proper height under the head.
Here is something I found on ebay. Maybe it will work along with a bed change may be beneficial? http://www.ebay.com/itm/262150928817?euid=9ea9d4acf48f42d59e087b5cd9c2b1fd&cp=1
That head is too big and heavy for a K40 laser machine. Light Objects has an adjustable Z table that is designed to work with the K40 as well as a replacement air assist laser head with an upgraded focus lens. http://www.lightobject.com/Power-table-bed-kit-for-K40-small-laser-machine-P722.aspx and http://www.lightobject.com/18mm-Laser-head-w-air-assisted-Ideal-for-K40-machine-P701.aspx