Post by springcrocus on Jun 5, 2018 16:22:03 GMT
I've never been particularly happy with any of the methods for producing the dimples on loco and tender steps. I have tried using a punch directly onto the underside of the tread with a backing block of wood, and lightly punching onto brass shimstock to produce an inlay for gluing or soldering into place. Others (like Bob) have produced elaborate punches that create the whole step in one action, or controlled-depth punches that produce one dimple at a time. I wanted something simple that was repeatable, easy to use, and didn't distort the tread. Most punch actions make the tread curve in the direction of the punching action and any effort to flatten the tread out again flattens the dimple pattern. The other problem is that these all work better if one has three hands, the third hand supporting the work.
My solution was to convert a heavy-duty leather hole-punch into a dimple-forming tool. The one I chose came from Amazon and cost £ 3.99 inc postage but I also purchased one of the sets currently available at Lidl which is also £ 3.99 but of much lighter construction.
The first job was to remove the brass anvil, which just punched out, and the rotating punch holder which was slightly more problematic. Although I used my advanced butchery skills (junior hacksaw, hammer, cold chisel, verbal encouragement etc) it would have been simpler to just drill straight through the carrier with a 5/8" drill. It was made of one of those horrible aluminium-zinc alloys and not worth trying to adapt. I also discarded the indexing spring as I only require one tool location and would like some fine adjustment of it's rotary position.
The tool carrier was remade from mild steel using the same dimensions as the original and a solid mild steel pin made to mount it on. The carrier has a flat milled on it and a 6mm reamed hole to locate the tool bit. The tool bit is from 5/16" diameter mild steel with a 6mm back and the front tapered at ten degrees except for the point which is forty-five degrees. The anvil mounting point was opened up to 6mm and the anvil made from 5/16" mild steel. The M6 thread on the back is to hold it firmly in position but allow easy replacement and the front has a 1/8" diameter nose with a small indent formed with a No.1 centre drill.
All the parts were fitted together and checked for alignment, followed by a couple of trial indents. This is a close-up of the tool.
I found that the tool bit had a tendency to rotate away from it's positon so an M5 bolt was used to lock the position after alignment. The hole on view at the back of the tool carrier allows the tool bit to be punched out if it get's stuck.
This final picture shows three different sets of dimples. On the left is 18swg material and the dimples are not particularly well-formed, the middle is 20swg brass and they are much crisper. On the right is 8 thou brass shimstock and the inset shows the graph paper that I used as a guide. It just needs a bit of care and attention to get a perfect pattern. Trying to indent 16swg material failed miserably but may just need more accurate and harder tools.
Now that the principle has been proven I am going to try different types of anvil, and may use silver steel which can be hardened for the tool bit. The other tool bits and anvils that I am going to experiment with are for riveting. I think it should be possible to squeeze copper rivets in sizes up to 1/16" and also the smaller brass sizes using this tool. Although there is limited throat depth, such a tool could still come in handy for things like the smokebox rivets (I hope). Whether this works or not, you folks will be the first to know.
Regards, Steve
My solution was to convert a heavy-duty leather hole-punch into a dimple-forming tool. The one I chose came from Amazon and cost £ 3.99 inc postage but I also purchased one of the sets currently available at Lidl which is also £ 3.99 but of much lighter construction.
The first job was to remove the brass anvil, which just punched out, and the rotating punch holder which was slightly more problematic. Although I used my advanced butchery skills (junior hacksaw, hammer, cold chisel, verbal encouragement etc) it would have been simpler to just drill straight through the carrier with a 5/8" drill. It was made of one of those horrible aluminium-zinc alloys and not worth trying to adapt. I also discarded the indexing spring as I only require one tool location and would like some fine adjustment of it's rotary position.
The tool carrier was remade from mild steel using the same dimensions as the original and a solid mild steel pin made to mount it on. The carrier has a flat milled on it and a 6mm reamed hole to locate the tool bit. The tool bit is from 5/16" diameter mild steel with a 6mm back and the front tapered at ten degrees except for the point which is forty-five degrees. The anvil mounting point was opened up to 6mm and the anvil made from 5/16" mild steel. The M6 thread on the back is to hold it firmly in position but allow easy replacement and the front has a 1/8" diameter nose with a small indent formed with a No.1 centre drill.
All the parts were fitted together and checked for alignment, followed by a couple of trial indents. This is a close-up of the tool.
I found that the tool bit had a tendency to rotate away from it's positon so an M5 bolt was used to lock the position after alignment. The hole on view at the back of the tool carrier allows the tool bit to be punched out if it get's stuck.
This final picture shows three different sets of dimples. On the left is 18swg material and the dimples are not particularly well-formed, the middle is 20swg brass and they are much crisper. On the right is 8 thou brass shimstock and the inset shows the graph paper that I used as a guide. It just needs a bit of care and attention to get a perfect pattern. Trying to indent 16swg material failed miserably but may just need more accurate and harder tools.
Now that the principle has been proven I am going to try different types of anvil, and may use silver steel which can be hardened for the tool bit. The other tool bits and anvils that I am going to experiment with are for riveting. I think it should be possible to squeeze copper rivets in sizes up to 1/16" and also the smaller brass sizes using this tool. Although there is limited throat depth, such a tool could still come in handy for things like the smokebox rivets (I hope). Whether this works or not, you folks will be the first to know.
Regards, Steve
