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Taig z-Column Stiffening
Taig mill w/ base plate and stiffener
While assembling my Taig milling machine for the first time, I became quite concerned looking at the vertical column. It uses a friction clamp between two 3" diameter steel round sections to hold the column vertical. This design would be ok except for the fact that all of the clamping pressure is being done by one nut on the back side of the box tubing. This is extremely poor design, giving the column a degree of freedom when zero degrees are needed. It also doesn't help that the spindle can be located about 15" above the bolt, giving any side forces a 15:1 mechanical advantage over the nut. After assembling my mill and frustratingly tapping the column dozens of times trying to get it dead perpendicular to the table, I eventually got it set. Once again, this is an area of adjustment that Taig could have improved upon.
I'm sure that Taig Tools had a good reason for designing the mill like this, it was probably done so that the head could be tilted if need be. Or maybe it was purposefully made weak so that the column would tilt rather than overload a spindle bearing in the case of extreme loadings or tool crashes? But if the latter was the case, the mill should have come with exact torque specifications for the nut, which it did not. Therefore, I'm going to assume Taig did not purposefully design the clamp to slip.
Recently however I was several hours into a project of mine (machining a pump impeller) when the head finally tilted. The piece was ruined. I also know that I was not overloading the machine because I was only taking a .050" deep pass in 6061 Al using a 1/4" end mill at 2600 rpm and 6 ipm. The side forces should have been minimal. The ruined impeller can be seen below:
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And of course, the above pictures are worthless without knowing what the finished product should have looked like:
So I figured it was finally time to go ahead and not only brace the z-axis to make it stiffer, but also to make it easier to adjust the head. The first thing I did was grab a spare piece of 1/2" steel plate to make the base plate. The largest piece I could snag from scrap was 13"x16". Using that, I drilled holes for the mill feet to bolt to (1/4"-20) and then drilled 4 holes to attach rubber feet to, then another two holes for the extra column (all 5/16" through holes). A dimensioned drawing is available here if you want to make your own baseplate:
The column itself was made out of some mild steel 1.5" box tubing, 18" tall. A plate was welded to the bottom with triangulation to add the stiffness needed to keep it in place. A 3/8" hole was drilled through the top of the box tubing in order to accomodate the bolt holding the tie rod in place. On the opposite end of the tie rod, a nut was welded to the box tubing. This wasn't a necessary step, a nylock nut alone would have been enough to hold it, but I originally wasn't sure if I was going to use a nylock nut or just a jam nut.
For the tie rod, I took some 3/4" steel tube and cut it in half. I then turned down the ends of a solid 3/4" diameter piece on a lathe in order to fit inside the 3/4" tubing. I milled wrench flats on the the solid stock, then welded it to the tube. After that, I welded a 3/8" fine threaded right hand threaded nut inside one end of the tube, and a 3/8" fine threaded left hand nut on the other end. This allows for easy turning of the tie rod to push the ends in or out, adjusting the tilt of the head of the mill. See below for a picture:
In order to mount the tie rod on the vertical column of the mill, I had to drill a 3/8" hole in the back of the column, which should not be the least bit harmful.
The feet for the plate were made out of 1" thick rubber scrap, I'm not sure of the exact material though. The rubber feet were cut to roughtly 1.5" squares, and had a 5/16" through hole drilled in them, followed by a .4" deep 1/2" diameter countersunk hole using an endmill. This was the toughest part since the rubber wanted to deflect rather than cut, and it took some patience to let the drill/endmill run for a few minutes to clean out each hole.
See the picture at the top of the page for a finished view of the setup. I will update this page with how well the brace works once I get some more testing done. As far as the tie rod, it definitely makes it much easier to dial in the head. My head is now perpendicular to the table within .002" across a foot long length, which is well beyond what the Taig needs since the largest tool being used will never be anywhere close to that diameter.