Whilst fitting the DRO I realised that I had created a space for a Sieg SX2.7 stiffening bracket. A bracket that could link the column and the base adding significant stiffness to the machine overall.
Whilst fitting the DRO I had to move the power supply case on the machine back 22mm. This was required to accommodate the Z-axis magnetic scale.
This made me think that I could perhaps add a bracket to the column/base and hence improve the overall stiffness.
So I looked around for some suitable metal plate. Must admit that one of my favourite suppliers is EKP Supplies. They had 6″ wide 1/4″ thick mild steel in lengths of 12″ and 24″. The 24″ felt a bit over the top. Also, as you can see I needed to machine the width down to 130mm if I was to accommodate the power supply case.
So, I bought 1off 1/4″ x 6″ x 12″ and 3off 1/4″ x 3/4″ x 12″. This combination would give me an overall plate thickness of 1″. Thicker than the 22mm I had gained with the DRO, but my initial thought was I would machine the beams down to a perfect depth.
The basic principle was to have a plate and to increase the bending stiffness with beams. This could actually have been made from aluminium. A full length aluminium plate and deeper beams might be an interesting experiment.
As mentioned earlier I machined the plate narrower where it aligned with the column. Hence it is 6″ (152.4mm) over the baseplate and 130mm wide at the column. I made use of the extra width on the base for fixing points. I used M5 capheads to fix the plate to the base and the column.
The beams are fixed to the plate with 3mm countersunk bolts. My initial thought was to fix with bolts and then weld them in place. However, I was concerned about distorting the plate by welding, but also the fixings were rather good. So I thought I would try it first.
Also, I have not used all of the fixings down the edges of the column. After drilling them I then thought they were a little over the top. I can always add them later if required.
I covered the edges of the beams with felt to stop it rattling on the case.
Also, you probably noticed that I didn’t machine the beams down to hit the overall thickness of 22mm. I decided to moved the case back 25.4mm, plus the thickness of the felt.
I don’t have an accelerometer and so cannot measure the dynamic stiffness. However, some time ago I compare this machine to my previous mill in terms of static stiffness.
I balanced weights on the head of the milling machine and measured the deflection. Thus allowing me to then calculate static stiffness in N/mm.
This gave me a good comparison and so I did this again with and without the plate fitted to the column/base.
The data table as created in Microsoft Excel.
I re-measured the baseline as the machine is older, plus the column has been removed and replaced since the first measurement. The added mass of the DRO readout might effect it.
Also, the measurement setup with the digital gauge position will effect the results. Hence for this back to back comparison I could ensure they were the same.
A simple comparison of the average static stiffness shows that the machine is now 1.5x stiffer with the bracket.
Sieg SX2.7 stiffening bracket works.
DRO and plate stiffener all in place. The cover is again fixed with 4off M5 bolts.
I now have a milling machine where the column has a 1.5x increase in static stiffness. A cost of around £45 for the plates and bolts. Overall this took me around a day to make and fit from start to finish.
The one thing I’ve not done is fixed the case to the baseplate. The case is quite thick steel plate and has a significant section.
I will look into this.