# Milling Machine Stiffness

So, here I am in the workshop with a dial gauge in the spindle and weights on the top of the milling machine, trying to measure the Milling Machine Stiffness. The head was locked in position. You don’t need to use more than one weight to get a stiffness value, I used a few weights and recorded the displacement for each case so that I could see if it was linear.

However, be extremely careful as there is a lot of weight and if they slip and fall they are going to damage you or something.

This was all about measuring the stiffness of the mill column, head etc – I think the main area of weakness in these machines is the column to bed interface.

The measurements were made in a mixture of units and then I finally arranged all of the data in excel so that I could calculate a N/mm final number.

As you will see I think there is a bit of an issue with the linearity of the data and so it is quite interesting to look at the data as plotted below. Basically, blue shows the Amadeal and orange the Sieg for both the tables and the plots.

We end up with a stiffness number of around 1200N/mm for the Amadeal Mini-Mill and around 5000N/mm for the Sieg SX2.7

When I look at the Mini-Mill with the tilting column you can immediately see the weakness in the column to table connection.

The Sieg SX2.7 has four bolts and a large footprint for the column mounting to the base.

A higher stiffness value means less chatter and more accuracy when machining. This also means you can take bigger cuts without inducing excessive vibration and hence chatter.

Only a few pointers around measuring the milling machine stiffness, but hopefully this will allow you to look at design elements of the milling machine more clearly.

#### Sieg SX2.7 Stiffening Bracket

A very simple mild steel bracket construction that has increased the static stiffness of the Sieg SX2.7 by a factor of 1.5