Rod Weighing Jig: Take 2
Just an update from this prior thread on weighing rod ends with a low cost home shop jig:
Low Cost DIY Rod Weighing Setup
A triple beam mechanical scale has been tried in place of the cheap electronic scale, and STILL showed repeatability issues related to side loading on the scale. This showed up a detail of the jig construction that was inducing side loads, and which could be easily fixed: The long length of the 2 pivots on the unweighed end are causing this issue.
If the 2 pivots at the far end are much longer than the weighed end pivot, and if you draw a line from them to the weighed pivot's point, this line is on an angle. If you move the weighed end of the plate up or down any tiny bit, then the weighed end pivot will move horizontally due to this angle, which will side load the cheapo electronic scales or bind the mechanical beam scale. Lowering the rod onto the jig also causes a slight vertical movement of the scale, and the same side loading or binding. See pix below.
So steel blocks were placed under the 2 unweighed end pivots and they were shortened to approximately the same short length as the weighed end pivot and everything re-leveled. The pivots all being equal length means that as the rod is lowered onto the jig, any vertical movement results in 0 horizontal motion; this avoids a side load on the scale.
With this change, the side load issues are essentially gone. Even with cheapo scales, a rod can be taken off and put back on and get 0-1 gram difference in an end weight, which is all these cheapo scales can resolve .... no 'tapping' on the bench to get things to 'settle out'. If the jig plate if lifted in a way that makes it twist a bit and set it back on the scale, then I can force as much as 2-3 grams variation. Before, if I did this, there would be up to 20 grams variation. Also, the long pivots may have been bending ever so slightly and also causing side loads to develop on the scale. Being short now, they are rigid.
Both the cheapo electronic scale and the beam scale work much, much better with the pivots all short. I measured all the big end weights for a set of a 8 rods with the beam scale and improved jig in a 'blind' test, i.e., not having the prior measured weights in front of me. Afterwards, I found 6 of the measured weights were 0, 0.5, or 1 gram off from before; the other 2 were 2 and 3 grams off respectively. The average difference was 5/8 of a gram.
.
Just an update from this prior thread on weighing rod ends with a low cost home shop jig:
Low Cost DIY Rod Weighing Setup
A triple beam mechanical scale has been tried in place of the cheap electronic scale, and STILL showed repeatability issues related to side loading on the scale. This showed up a detail of the jig construction that was inducing side loads, and which could be easily fixed: The long length of the 2 pivots on the unweighed end are causing this issue.
If the 2 pivots at the far end are much longer than the weighed end pivot, and if you draw a line from them to the weighed pivot's point, this line is on an angle. If you move the weighed end of the plate up or down any tiny bit, then the weighed end pivot will move horizontally due to this angle, which will side load the cheapo electronic scales or bind the mechanical beam scale. Lowering the rod onto the jig also causes a slight vertical movement of the scale, and the same side loading or binding. See pix below.
So steel blocks were placed under the 2 unweighed end pivots and they were shortened to approximately the same short length as the weighed end pivot and everything re-leveled. The pivots all being equal length means that as the rod is lowered onto the jig, any vertical movement results in 0 horizontal motion; this avoids a side load on the scale.
With this change, the side load issues are essentially gone. Even with cheapo scales, a rod can be taken off and put back on and get 0-1 gram difference in an end weight, which is all these cheapo scales can resolve .... no 'tapping' on the bench to get things to 'settle out'. If the jig plate if lifted in a way that makes it twist a bit and set it back on the scale, then I can force as much as 2-3 grams variation. Before, if I did this, there would be up to 20 grams variation. Also, the long pivots may have been bending ever so slightly and also causing side loads to develop on the scale. Being short now, they are rigid.
Both the cheapo electronic scale and the beam scale work much, much better with the pivots all short. I measured all the big end weights for a set of a 8 rods with the beam scale and improved jig in a 'blind' test, i.e., not having the prior measured weights in front of me. Afterwards, I found 6 of the measured weights were 0, 0.5, or 1 gram off from before; the other 2 were 2 and 3 grams off respectively. The average difference was 5/8 of a gram.
