Feather AT-9 Buffer
The Feather AT-9 has a rubber buffer which is held in the tube with a metal washer and a threaded end cap. The buffer has guide holes for the recoil spring and striker spring. Over time, the rubber had started to deteriorate. The previous owner told me the striker spring broke through the rubber and came out the back. He had a friend fill in the center of the washer with weld metal to keep the spring in. The washer didn't look very good, but the gun functioned fine. I figured I would leave it alone, but one day I almost couldn't remove the buffer (required in order to remove the bolt for cleaning). I realized the buffer swelled and wedged itself in the tube due to heat and humidity.
I measured the old buffer and the tube to design a new buffer. I decided to add a flange to the buffer to eliminate the need for a separate washer. The gun was made with easy to use, standard dimensions such as a 1-1/2" OD tube (1-1/4" ID). Most of the recoil energy is dissipated by the time the bolt reaches the buffer, so I figured I could get away with using aluminum with little rubber bumpers pressed in (as opposed to being completely made of rubber). Most of the construction was straight forward. I turned the buffer on the lathe and used the mill to drill holes for the springs and rubber bumpers.
I decided to use rubber grommets that I found at the big box hardware store, but they required me to cut an internal groove to hold them in place. I had to make a tool bit in order to make these grooves. I started with a piece of 3/8" W1 tool steel and turned down the end in the lathe so it would fit in the holes I drilled. I used the mill to remove material down to the center line (creating a cutting edge) and cut relief behind the tip (shaping the cutting tip). I realized the the bottom of the tool tip would rub inside the hole, so I put it back in the lathe, offset it, and turned more relief (interrupted cut; like turning a cam). I used a belt sander to put relief on the front edge and a stone to sharpen the tip. I didn't harden the tool since I had never tried heat treating before and I figured it would be fine for a few light cuts in aluminum.
I used the new tool in the boring head in the mill to cut the internal grooves. This tool can be used in the boring bar holder on the lathe as well, but the holes were offset from center, so the mill was used. To finish the buffer, I used Birchwood Casey Aluminum Black to color the new buffer (not shown). This product uses a chemical reaction to color the aluminum and attempts to match the color of black anodized aluminum. The color is close enough, but it is not very durable and difficult to get an even color on a large area. The rubber grommets were then pressed into place.
UPDATE (December 2014):
I made a design change to the rubber bumpers. I found a source for a more durable rubber material. It comes in the form of a long cord and I cut it into small rods. These are pressed into a tight fitting hole with a little bit of adhesive at the bottom of the hole to ensure they stay in place. This change makes the whole design more durable and doesn't require the use of the grooving tool I made. I still do not have a coloring process that I'm happy with. One of the version 2 pictures show my original buffer with the Birchwood Casey Aluminum Black. That buffer has only been inserted and removed from my AT-9 a handful of times and the coloring looks terrible. I'm still searching for a coloring process that is durable and I have the capability of applying.
I measured the old buffer and the tube to design a new buffer. I decided to add a flange to the buffer to eliminate the need for a separate washer. The gun was made with easy to use, standard dimensions such as a 1-1/2" OD tube (1-1/4" ID). Most of the recoil energy is dissipated by the time the bolt reaches the buffer, so I figured I could get away with using aluminum with little rubber bumpers pressed in (as opposed to being completely made of rubber). Most of the construction was straight forward. I turned the buffer on the lathe and used the mill to drill holes for the springs and rubber bumpers.
I decided to use rubber grommets that I found at the big box hardware store, but they required me to cut an internal groove to hold them in place. I had to make a tool bit in order to make these grooves. I started with a piece of 3/8" W1 tool steel and turned down the end in the lathe so it would fit in the holes I drilled. I used the mill to remove material down to the center line (creating a cutting edge) and cut relief behind the tip (shaping the cutting tip). I realized the the bottom of the tool tip would rub inside the hole, so I put it back in the lathe, offset it, and turned more relief (interrupted cut; like turning a cam). I used a belt sander to put relief on the front edge and a stone to sharpen the tip. I didn't harden the tool since I had never tried heat treating before and I figured it would be fine for a few light cuts in aluminum.
I used the new tool in the boring head in the mill to cut the internal grooves. This tool can be used in the boring bar holder on the lathe as well, but the holes were offset from center, so the mill was used. To finish the buffer, I used Birchwood Casey Aluminum Black to color the new buffer (not shown). This product uses a chemical reaction to color the aluminum and attempts to match the color of black anodized aluminum. The color is close enough, but it is not very durable and difficult to get an even color on a large area. The rubber grommets were then pressed into place.
UPDATE (December 2014):
I made a design change to the rubber bumpers. I found a source for a more durable rubber material. It comes in the form of a long cord and I cut it into small rods. These are pressed into a tight fitting hole with a little bit of adhesive at the bottom of the hole to ensure they stay in place. This change makes the whole design more durable and doesn't require the use of the grooving tool I made. I still do not have a coloring process that I'm happy with. One of the version 2 pictures show my original buffer with the Birchwood Casey Aluminum Black. That buffer has only been inserted and removed from my AT-9 a handful of times and the coloring looks terrible. I'm still searching for a coloring process that is durable and I have the capability of applying.