This article contains images of the Mercury laser however the information is relevant to other machines as well.
Double images on a laser when engraving is most often due to a mechanical issue on the machine. This is why it happens when engraving raster images but not if cutting vector jobs.
To explain, the carriage head travels back and forth, left and right, across the material when engraving an image. With each pass across the material, the laser is being fired. This is true when the carriage travels left to right as well as right to left. Because the engraving happens in both directions, the travel time & path must equal one another in both directions. Any slight difference in the two passes may result in a flaw with the engraved image. This is all too apparent in the case of engraving a double image.
If the machine sits unused, with the carriage head resting in the same location on the rail, over time it may develop flat spots on the rollers where they contact the rail. The flat spots can result in the the carriage head jumping or skipping as the flat spot on the roller comes into contact with the rail.
You may be able to work the flats spots out simply by running the carriage back and forth along the rail by hand. In some cases however, replacing the rollers is required before good engraving can be achieved.
If the belt is loose the carriage head will hesitate when the machine reverses direction, causing a problem. When checking the belt tension, there should be no excessive slack in the belt when the carriage is placed in the center of the rail. The belt should be taut but not too much so. The main thing you’re looking for is that when the motor begins to spin in the opposite direction there is no slack in the belt. The slack would result in the carriage not being over the right area of the material when the machine begins firing the laser.
Here a few things which only take a few seconds and are a good idea to check every time before the laser machine.
– Make sure that the rail is clean. A dirty rail will shorten the life of the rollers and also cause the carriage to jump or skip.
– Make sure that the top and bottom rollers of the tool carriage head are clean and in good shape. Flat spots on the rollers can cause the carriage to jump or skip.
– Make sure that the belt has the proper tension.
Be sure to consult the your machine’s user’s manual for more information on tightening the belts.
First and foremost, take a look at mirror #3 (the one on left hand side of the rail) and mirror #4 (the one inside the laser head). Take these 2 mirrors out and put them back in, ensuring that they are seated properly and locked down so they can not wobble back and forth. They need to be absolutely stationary.
Second we need to look at some set screws.
All of these set screws are located on the right hand side or your machine. If you follow the rail to the right, you will see the large silver cylinder. In that area is where we will be looking for these set screws.
This is a picture of the entire right hand side assembly out side of your machine. Circled are top and bottom pulley set screws. You will need to tighten the top and bottom set screws. Sometimes the pulley’s have 1 set screw, sometimes they have 2. Find and tighten down all set screws on these pulleys.
This is where these items are when installed onto a machine. Unfortunately in this picture does not show the set screw itself, it wasn’t spun enough to show that.
But this picture does show the set screw turned where the camera could see it. (It’s a little blurry, sorry). 
Loosen all the set screws then rotate this flat spot until it meets up flush with one of your set screws. Lock it down then lock down all other set screws.
We need to make sure that your set screw is locked onto the center of this flat spot. It may be locked down but on the edge, which will seem tight but when the head starts moving left and right it will rotate from one side to the other when the left/right motion builds up enough inertia.
You can see this from the top where the silver c clips are with the 2 screws.
This picture shows the set screw on the motor itself.
It is a little bit easier to see and access these screws if you move the rail all the way to the front of the machine. You can then stick your head in the machine (it will be upside down but you will see what our pictures show).
Make sure both mirrors and all the set screws are tightened down onto the flat spot. Once that is complete, do some test engraving, let us know if the issue is or isn’t resolved.
If you would like to find out if new rollers are available for your machine contact Technical Support at [email protected]. Be sure to include the model of machine that you have, along with your contact information.
