Many thanks to all who responded! So many clever ideas and forward thinking. The increased stiffness of the wire at 90° was kind of where I was headed with my thinking. Also the increased regulation capacity an advantage to 90° I think.
One more random thought.... the check end of the key sits lower than the front, yes? So as it rises the check moves farther away from the player until the key reaches level or parallel. The tail sits well below level so also moves away from the player ( i know... the whole distal proximal thing...) with a much shorter radius.
So as the key rises the check and hammer tail move away from the player but the hammer much more quicky. Arcing reduces the thickness of the tail and effectively its distance from the backcheck. Bill Spurlock had a great handout about this for the tail arcing jig saying with correct tail length and arc and correct check placement and adjustment that the space between the check and tail will remain roughly constant as they rise together. I have found this to be the case for me. The check being mostly parallel to the hammer head at rest also is a good starting point as to angle for me.
Not sure if I am even asking a question but definitely sure I am missing something. Mainly curious if my thinking is reasonably clear on these points.
Very grateful for the group.
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David Brown
Garland TX
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Original Message:
Sent: 10-03-2018 15:03
From: Alan McCoy
Subject: Replacing grand backchecks- Drilling angle
David,
Once I set up my drilling jig many years ago at the ~70 degree angle then drilling at that angle is as easy as drilling at 90 degrees (just being careful about bit drift). I always at least check to see if the holes were located where they should be. If they were and if they were drilled at an angle, great. If not, I plug and re-drill and/or re-locate the holes. I have pretty much always drilled at an angle because it makes sense to me that if I have to bend them at that angle, why not drill them at the angle and minimize the amount of bending I have to do. Thus I have plugged more than a few backcheck holes over the years.
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Original Message------
All-
A question for those of you who do this regularly. This relates to a new class I am preparing. When replacing grand backchecks , what is your drilling method- Use the existing holes regardless of their angle? Establish a new location and, if so, drill angled or 90 degrees to the key? Other than the potential for less bending, drilling the key and installing at an angle is more cumbersome for me than drilling 90 degrees. Is there a functional reason to drill at the desired 72 degrees that is talked about? It would seem to me the backcheck needs to occupy the same place in relation to the tail to function correctly regardless of how it is fixed to the key. Some difference in the resistance of the wire in check with a difference in angle? WNG drills at an angle. I guess it hasn't been talked about that I remember. Perhaps another instance of a traditional way being preserved. Perhaps I am also taking this a bit to seriously....
Many thanks in advance-
Best from Texas-
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David Brown
Garland TX
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