Walt Galer
ArboristSite Operative
Howdy WRW,
No, not exactly. The reduced bite over the nose radius is the result of how far the cutter's top leading and following edges, (the Depthgauge and the topplate heel), are located in front of or behind the pitch centers (center of the rivets which are the centers of articulation).
If you have a part with a trailing surface, well back behind the rear pitch center, you have a "tail" that will rise as the chain turns around the nose radius, and joint out the cut either partially or completely, depending on the design.
This effect is what you were thinking of and is correct for the guardlinks. I was referencing the cutter's design itself.
The earliest example was the Pioneer pintail drivelink, then there was the Sabre tiestrap.
Most radical was the Windsor 50RS where the tiestrap ahead of the cutter extended back so far as to be the only depthgauge on the cutter. (This is a bit of a design trick, since you have to preserve reverse deflection capability in a chain design to allow the chain to flex backwards comming off of a drive sprocket, or if it strikes something). Only McCulloch with the "Pintail" sawchain, put a protrusion on the cutter. It was located on the sideplate of the cutter and none to satisfactory as a guardlink.
Very early in the industry Mall Tool made a "stiff back" chain. This was not a guardlink however but a centerlink AND sidelinks, that mearly stiffened the chain in a very illadvised attempt to "stabilize" the cut and make the very rough chain smoother. (wrong way to go! You need to make a chain more unstable to make it smoother cutting as a rule. (Oregon 91 is rougher that 1/4 pitch or Carlton N1C for this reason. Same mistake. Excessive stabilization in this case is due to too long of a part bottom on the cutter).
The idea of cutter heel interference is hardly new, but it was always something to be avoided, until the industry concern with safety came about in the very late '70's. Windsor pioneered the idea of reduced topplate overthrow heel relief angle well thrown back behind the pitch center, together with a fatter ramped depthgauge, to tame down professional chisel chain while preserving professionally acceptable levels of over-the-nose performance. This also gave a bit longer cutter for increased available filing life. The design was a collaboration at Windsor between myself and Gordon Porritt, a student engineer who did my dirty work and put it together. It was he who did the engineering layout I previously mentioned, and gave me 8 X 11 transparancies of them to use in instruction and sales presentations. The guy became a great chain engineer working in a very small company. Unfortunately he is no longer in the industry.
Regards,
Walt Galer
No, not exactly. The reduced bite over the nose radius is the result of how far the cutter's top leading and following edges, (the Depthgauge and the topplate heel), are located in front of or behind the pitch centers (center of the rivets which are the centers of articulation).
If you have a part with a trailing surface, well back behind the rear pitch center, you have a "tail" that will rise as the chain turns around the nose radius, and joint out the cut either partially or completely, depending on the design.
This effect is what you were thinking of and is correct for the guardlinks. I was referencing the cutter's design itself.
The earliest example was the Pioneer pintail drivelink, then there was the Sabre tiestrap.
Most radical was the Windsor 50RS where the tiestrap ahead of the cutter extended back so far as to be the only depthgauge on the cutter. (This is a bit of a design trick, since you have to preserve reverse deflection capability in a chain design to allow the chain to flex backwards comming off of a drive sprocket, or if it strikes something). Only McCulloch with the "Pintail" sawchain, put a protrusion on the cutter. It was located on the sideplate of the cutter and none to satisfactory as a guardlink.
Very early in the industry Mall Tool made a "stiff back" chain. This was not a guardlink however but a centerlink AND sidelinks, that mearly stiffened the chain in a very illadvised attempt to "stabilize" the cut and make the very rough chain smoother. (wrong way to go! You need to make a chain more unstable to make it smoother cutting as a rule. (Oregon 91 is rougher that 1/4 pitch or Carlton N1C for this reason. Same mistake. Excessive stabilization in this case is due to too long of a part bottom on the cutter).
The idea of cutter heel interference is hardly new, but it was always something to be avoided, until the industry concern with safety came about in the very late '70's. Windsor pioneered the idea of reduced topplate overthrow heel relief angle well thrown back behind the pitch center, together with a fatter ramped depthgauge, to tame down professional chisel chain while preserving professionally acceptable levels of over-the-nose performance. This also gave a bit longer cutter for increased available filing life. The design was a collaboration at Windsor between myself and Gordon Porritt, a student engineer who did my dirty work and put it together. It was he who did the engineering layout I previously mentioned, and gave me 8 X 11 transparancies of them to use in instruction and sales presentations. The guy became a great chain engineer working in a very small company. Unfortunately he is no longer in the industry.
Regards,
Walt Galer
