About setting the 12 o’clock position with Ground Control,
Do you see what I mean?
I find it difficult to visually set it straight.
Now you might wonder “How straight is straight enough?”
Well 1/12 of a sprocket tooth distance is 3 degree. That is:
And this causes about 0,5 mm chain position error on a sprocket. If both sprockets have an error around 3 degree off. They either go opposite (one too high, the other too low) and the X, Y workspace is shifted like this: X shifted to the right from 0,55mm to 0,75 mm, and Y warped near side edges by 0,3mm.
Or sprockets have errors in the same direction (both too high, or both tool low). and the X, Y workspace is shifted like this: X expands 0,2mm to 0,3mm, and Y dips (or raises) at center top by 1,5mm.
That maybe not so much for you. But if you seek accuracy, everything adds up. And that one is scaling up if the 12 o’Clock error is greater that 3 degree.
But there is an easy solution to tune in better that 0,5 degree: using a LEVEL.
Well here I suggest to use a level like this.
Note 1: This picture is NOT showing a chain exactly positionned as in the calibration task. Normally the chain tip would be lying on the sprocket. But the point here is to seat the level on the top link while you tune 12 o’Clock position to get the bubble centered on the level.
Note 2: When you calibrate 12 o’Clock, you want to place the second link of the tip of your chain on the 12 o’clock top position. Then attach that second link to the sled. Here is an example on the ring kit:
And make sure to attach your chains together with a safety solution like this to prevent accidents when chain tip snaps off.
Here is a nylon rope, as thick as would fit the narrowest chain link, that I installed lately, (shown in a simulated chain snap condition):
Overall, using a level is easy and makes your maslow more accurate. Once this 12 o’Clock is set accurately. You can start exploring you chain tolerances.