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Adjusting Tapered Form

My Procedure:

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:


Taper Worksheet for Website.png

Strip in Planing Form

Station #65
Spec is 0.128"



At station #65 the depth was set to 0.131" with the intent of tightening the form after first pass and decreasing the depth to 0.128".
Before you do anything, go back with your depth gauge and verify #65 is at 0.131". 
If it is, well something's screwy and the fact remains you have to knock off 0.005".
12. There are other ways to do it, but as convoluted as this might sound I suggest:
Setting the depth gauge in the groove at station #65, turning the bezel on the gauge to 0.005", tightening the form until the gauge reads Zero.
13. Do this for all of them except for the stations that are already at spec.

Big time reminder - since this is your final time around and your last chance for glory, check the strip dimensions more frequently than before.


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