Adjusting Tapered Form
1. Using a Sharpy I write the station number beginning with 90" at the first station (bolt) and then number each one up to, in this case, 45"
2. Using the rod's taper chart of "1/2 d" (distance from triangular flat to apex), each dimension is increased by 0.003".
I put blue painter's tape at every bolt and write the final dimension on the bottom and the increased dimension on top.
3. The form is adjusted at each station to the top number. The extra 0.003" gives some cushion if your taper gets off.
4. Rather than start the planing at the point on the strip where the 90" dimension should be, begin about 3" ahead of it. That is to say the strip butt would be placed at 93"
5. Plane away according to SOP looking at both ends and the mid-section to make sure you still have an equilateral triangle.
6. When you're only shaving steel, move the strip to it's final distance and plane until it's even with the form.
7. CRITICAL STEP (where I have to start thinking):
Take three measurements at each 5" station and if they aren't too out of whack - let's say a difference of 0.0015" -write the "average" down on a chart.
8. Do this for every strip - tedious but worthwhile.
9. The measured 1/2d on some stations is where it should be - 0.003" above the spec. That's good, but for most there's a bit of a difference - sometimes it's at spec or even below. It seems intuitive that you would adjust each station 0.003" to spec, but it obviously isn't a sure thing.
10. Write the discrepancy number in Sharpy next to the station so you won't forget to do it
How did the 85" station, which was set 0.003" above spec end up at spec? You had your Spotify playing Jason Isbell instead of Blue Oyster Cult or vice versa? The 60 groove had a smidge of cane shaving there? Who knows?
11. Adjusting form to correct discrepancies: