Last Friday evening, a friend brought over the turntable base from his recently acquired Spinfire Blaze stringing machine. This stringing machine has fixed end posts that allow for mounting a tennis racquet with the side supports in the appropriate place. The problem is that my friend only strings badminton racquets which are smaller in size than tennis racquets. The badminton racquet can be mounted but then the four side supports are only supporting the racquet near the ends instead of near the middle as they should be.
After some taking of measurements with a badminton racquet mounted and a bit of scratching heads, it was determined that we need to move the end posts closer by 5-6 cm. The end posts are fastened by M6 bolts – with a four hole pattern that we saw is separated by about 2.5cm. Suddenly we had the light globe event – a bright idea, how about we mount the end posts by using only the two closer screw holes, which should move the posts together by 5cm. We did this and sure enough – the badminton racquet could now be mounted with good support on the sides – sufficiently close enough that now we could be confident of stringing these badminton racquets without worrying about the racquet head turning circular or breaking. Since it was getting late, we would leave this until I have some time during the day.
Today was the day to “relocate.IT” the end posts, that is. I stuck some stickers on the base where I expected the new hole to be, then measured across by 25mm and marked the centre of the hole. But when I look down the base, it appeared that the centres were not quite right. I had another bright idea, I could just drill a template – which is what I did. I got some scrap aluminium flats, and drilled three holes each 25mm apart. I could do this on my milling machine, because the X axis has a dial that has incremental marks every 0.02mm. Of course, a full rotation was 1.5mm, so a matter of a bit of maths or just counting the rotations, to get the 25mm required. Two holes were drilled at 6.5mm then the third hole was drilled at 3.3mm. I have an automatic centre punch which has a tip about 3.2mm in diameter, so by lining up the two existing holes on the turntable base, I could punch the centre of the third hole – the one I need to drill. After doing this, I could see that the punch put the centre where it should be, and a bit different from my original markings.
Here is a picture of the base with the two holes punched, the template and the automatic centre punch. Now to mount it on my little milling machine.
Here I have it mounted, and a center drill in the drill chuck – the center drill is used to start the hole, and allows me to adjust the X-Y table to properly center the marking, then drill it. The base is aluminium, so after drilling the center hole, I went straight to the 6.5mm drill. If this was a steel base, it is better to use an intermediate drill like 3.5mm before the 6.5mm drill.
After drilling both holes, it was time to swap the ends around and do the other two holes. Then use a countersink tool to clean up the edges of the hole so that it does not have sharp edges, then to reassemble the end posts. My friend also invested in automatic base clamps, so I installed the base clamps before I installed the end posts. The end posts have one control to move each pair of side supports in and out, so after mounting the end posts, I also had to mount an actual racquet, then adjust the end posts so that the side supports with clamp the racquet at the same point. Only a minor adjustment was required, then retighten the end posts.
And now here is the final product sitting on my tile floor. The result is that the posts have been moved 2.5cm towards the centre on both ends. Now my friend can use this machine to string badminton racquets.