Raquet becoming loose during stringing?

[orbit]

I string with an Alpha Pioneer DC plus, however I've been noticing that when I'm strining that sometimes the raquet gets loose, because the knobs on the head and throat of the racquet need to be screwed tighter later on. I believe it's happening when I"m doing crosses, and I always double check to make sure I'm mounting the racquet correctly. I just notice over time of stringing a racquet it slowly becomes loose, and then I have to retighten the knobs at the top and bottom of the racquet. Also sometimes near the end of the crosses when I'm pulling tension I notice that after a pull, the racquet all of a sudden shifts to the right or left depending where the string is being pulled, which is when I usually notice that the knobs are loose again. What is causing this? I'm pretty sure I'm tightening everything fairly well.

[dancraig]

Just reach over and tighten things down once or twice during the stringing.

[ls206]

The tension of the strings can alter the racquet head shape.
When stringing the crosses it will "squeeze" the racquet into a slightly longer oval shape which may explain why you need to tweak the racquet mounts.

[orbit]

Thanks for the replies. Well, I am working with a Dunlop 200g racquet from over ten years ago that I still use. I'm just worried all the time now that I'm putting too much stress on a racquet frame and don't want to break it, so when things come loose, it doesn't move much, but it worries me that it's causing extra stress on the frame.

[gavna]

Note that a 20 yr old 200G is going to flex all over the place......when new they distorted a tonne.

[SwankPeRFection]

This is most likely due to tower creep on the stringing machine. I have a new Pioneer as well and ran into issues with the outside towers that hold the racquet in place actually slipping on the tracks when tension is pulled. This causes the racquet to become looser as you continue to string. I suggest that you use a pencil or other marking device and mark the outside edges of the rails for the towers once you have them in place and tighted up. If they slip, you'll see the bottom of the tower move away from your pencil mark.

I called Alpha twice about this issue and they indicated that this is not a major issue and that they've only heard of it 2-3 times over several years.

I find the issue is because of the smoothness of the paint and the metal bases on the tower rails. They's just too smooth and the knobs don't grab on enough to keep it from slipping. Also, if you look under the table at the knobs, you'll notice that the washers they have on there aren't even big enough to grab the bottom of the table more than 1mm (if that) on either side. I had to get some larger washers (1.25" diameter) to help grab the entire bottom of the rail under there. Even with those big washers and there's still a bit of slip going on. I'm looking at possibly solving the smoothness of the surfaces to help with better traction, but I don't feel like ruining the surface just to fix an issue like this. All else fails, I may end up getting some hex screws for the bottom of those towers as I'm sure I can tighten those up more with an hex key than those small black knobs that come on the machine stock. Let me know if you need me to post some pics of the washers I used and how huge the difference in engagement on the bottom of the machine there is between the stock washers and what I'm using now.