Hey Folks… 

I have a relatively cheap drum sander from HBM machines in Holland. Ive been using it for about 4 years no problems… in fact it has out performed my expectations. However about 6 months ago after a move i noticed something strange. It has started to sand unevenly but in the most unusual way… it is thinner on the edges than in the middle. 

I have spent a lot of time taking it apart cleaning it, greasing it. Everything… and to know avail. 

Eventually i cam to the conclusion that it must be the bed so i took the belt off and measured it with a straight edge… low and behold the bed is not flat it dips in the middle and using feeler guages i found out that size of the dip is approx the difference between the middle of a sanded board and its edges!!

As a guitar maker i thickness really thin boards (3mm / 1/8″) so there is a lot of flex in them. 

I guess this has to be the issue right? 

So my questions are these – 

1. Has anyone encountered this issue before? i.e. thicker boards in the middle than the edges. 
2. If so what was the issue. 
3. Can it be fixed and if so, how? 

Thanks for reading and thanks in advance for any help. 

Gary.