Skyman2
Mechanical
- Aug 24, 2007
- 14
Folks, I just joined this forum and before you wonder, I am a EE by background rather than a ME as noted by the engineer type next to my handle - I misread the meaning of this selection when I registered on this forum.
I have a question related to guide pins. I have a mechanism in design for hobby purposes that uses two guide pins to define the "trajectory" of the mechanism these pins are attached to. The mechanism essentially has a base to which is attached a 12" arm. At the top of the arm is a 1 lb mass. The trajectory path or guide pin slots is curved in nature so that as the base of the unit traverses this trajectory path, the arm rotates by about 90 degrees from a vertical position at one end to a horizontal position at the other. When the base, arm and mass are in the horizontal position, the friction forces on the pins are quite large due to the lever arm effects of the 1lb mass. The pins are 3/16" diameter steel pins and they will run in guide slots made from either molded carbon or machined aluminum. The guide slots are blind in nature and are positioned either side of the base mechanism as a mirrored pair - the rails act as the two sides that contain the mechaism.
I need to find a way to significantly reduce the friction forces of these pins against the surfaces of the guide slots. The positioning of the pins cannot really be changed.
I have considered two methods to date:
1). Some form of dry lube laminate attached to the slot surfaces to create a bearing surface. This has fairly significant assembly implications and so I dismissed it.
2). Add roller bearings to the ends of the pins. On the base mechanism side of the roller bearing, add a thrust bearing and then a retining ring after that. The slot would be machined about 0.005" wider than the outer diameter of the roller bearing so that the outer casing can "roll" on the upper and lowersurfaces of the slot as well as the needles rotate on the shaft. As the outer casing of the needle roller rotates, that rotation is transfered to the thrust bearing therefore minimizing the frictional forces at this end of the bearing. The problem area is the other end of the roller bearing that is in the blind slot. There is a potential for the outer casing of the roller bearing to "rub" against the internal blind surface of the guide slot causing an increase in frictional forces. The end of the pins also control lateral play of the mechanism that sits between the two guide rail systems and has to be as close to the inner surfaces of each slot as possible.
Both methods represent problems. Does anyone have any ideas of how to produce a guide pin system that rides in blind guide slots and significantly reduce these frictional forces on all three surfaces of the slot?
I also just noted through the post preview function that I can add images. I will follow this post by adding some images that may help the visual aspect of the mechanism and the roller bearing solution I considered.
Thanks in advance.
I have a question related to guide pins. I have a mechanism in design for hobby purposes that uses two guide pins to define the "trajectory" of the mechanism these pins are attached to. The mechanism essentially has a base to which is attached a 12" arm. At the top of the arm is a 1 lb mass. The trajectory path or guide pin slots is curved in nature so that as the base of the unit traverses this trajectory path, the arm rotates by about 90 degrees from a vertical position at one end to a horizontal position at the other. When the base, arm and mass are in the horizontal position, the friction forces on the pins are quite large due to the lever arm effects of the 1lb mass. The pins are 3/16" diameter steel pins and they will run in guide slots made from either molded carbon or machined aluminum. The guide slots are blind in nature and are positioned either side of the base mechanism as a mirrored pair - the rails act as the two sides that contain the mechaism.
I need to find a way to significantly reduce the friction forces of these pins against the surfaces of the guide slots. The positioning of the pins cannot really be changed.
I have considered two methods to date:
1). Some form of dry lube laminate attached to the slot surfaces to create a bearing surface. This has fairly significant assembly implications and so I dismissed it.
2). Add roller bearings to the ends of the pins. On the base mechanism side of the roller bearing, add a thrust bearing and then a retining ring after that. The slot would be machined about 0.005" wider than the outer diameter of the roller bearing so that the outer casing can "roll" on the upper and lowersurfaces of the slot as well as the needles rotate on the shaft. As the outer casing of the needle roller rotates, that rotation is transfered to the thrust bearing therefore minimizing the frictional forces at this end of the bearing. The problem area is the other end of the roller bearing that is in the blind slot. There is a potential for the outer casing of the roller bearing to "rub" against the internal blind surface of the guide slot causing an increase in frictional forces. The end of the pins also control lateral play of the mechanism that sits between the two guide rail systems and has to be as close to the inner surfaces of each slot as possible.
Both methods represent problems. Does anyone have any ideas of how to produce a guide pin system that rides in blind guide slots and significantly reduce these frictional forces on all three surfaces of the slot?
I also just noted through the post preview function that I can add images. I will follow this post by adding some images that may help the visual aspect of the mechanism and the roller bearing solution I considered.
Thanks in advance.