Why am I sand bagging the milling machine? A great way to add damping to a structure is to use sand. Loud speaker stands are commonly damped using sand. Thus adding mass and damping to the structure. This means the stands don’t vibrate and so radiate sound.
The milling machine in question is the Sieg SX2.7 and just recently I increased the column stiffness using a steel bracket. The stiffening bracket bolts to the back of the U-shaped column and thus creates a void at the bottom of the column. The idea is to place sand bags in this void and hence reduce the vibration even further.
Making and Filling Sand Bags
The first task was to make up some sand bags. Well, actually these were made by my lovely wife.
They are roughly 3.5″ x 5″ and initially sewn along the sides leaving a small ~0.5″ gap to allow for filling.
They aren’t so easy to fill without a funnel. A piece of thin aluminium or cardboard rolled into a cone shape and taped works fine.
When filled with dry builders sand they weigh approximately 0.3kg each.
I filled 2 of the bags with cast iron swarf. I collected this some time ago when turning a cast iron flywheel on the lathe. These bags weigh in around 0.38kg each. I will keep these bags for use on the milling table.
Fitting the Sand Bags
The void in the column is quite large. This will accept a few sand bags. Thus adding weight and damping to the lower end.
The only small issue is the free end of the leadscrew as this is unprotected. Therefore, it could catch on a bag bag and lift it out of place or get stuck. A small protective cover might be needed for this.
I managed to fit two sand bags flat at the bottom of the void. I tamped these into place. One bag then fits vertically each side of the leadscrew.
The leadscrew being protected by a section of plastic pipe. This plastic pipe fits loosely over the leadscrew and just stops direct contact with the bags.
When looking from above in the next image you can see the plastic pipe.
I then refitted the stiffening bracket. At first I left all of the fixing bolts loose. I then tamped the bags down with the handle end of a hammer. This gently pushes them into the voids. Finally the Stiffening plate was brought up tight and then locked in place.
Now I have finished the sand bagging of the milling machine. I don’t have the ability to measure the natural frequency and damping of a structure and so I will have to rely on the feel I get when using it next.
Sand bag damping of sheet metal is not new. Using sand bags to dampen down structures is not new, not even to this blog. This tiny Genmitsu 3018-pro cnc is small, is not that stiff and not that heavy. Hence it is already at a disadvantage. However, the video shows the impact of adding bags of sand onto the table.