Beam width too wide on horizontal cut...

[khumbu5]

Another one for you gents...

I'm putting a line round a design on some oak using a cut. The problem is that the horizontal lines of this square are quite a lot wider than the vertical.
The vertical is about what it should be in width but the horizontal line must be close to 0.7mm wide!

Any suggestions?

Ta in advance...

[PhillyDee]

Check you lens, mirrors and laser end of the tube. Might be cracked.