tdculbert
Mechanical
- Jan 8, 2008
- 4
I'm taking a first stab at using standard fits (from ANSI B4.2) and running into some confusion:
I have a linear motion bearing riding on a shaft; the shaft is press fit into a plate and protruding through the far side. A second component will have a slip fit on the far side of the shaft.
The shaft & bearing I have selected from a catalog. Everything's nominally 6mm dia. The bearing stipulates that the shaft shall be class g6 (ie, 5.988 - 5.996). If understand the system correctly, this then is a hole-basis fit - the hole will have the basic dimension as one limit; the shaft is sized to provide the desired fit with this hole.
How now do I select a fit for this g6 shaft and a press fit hole that holds the shaft? This feels like it should be a shaft-basis fit, but I'm operating with hole-basis components. The shaft I'm stuck with is hole-basis, but the required hole will not will not have a basic preferred dimension as a limit like the bearing hole does.
One thought I had was to look at an H7/p6 locational interference fit for reference. This fit varies from 0 to -0.02mm interference. Applying this interference to a g6 shaft gives me a required hole of 5.984 - 5.988mm (+-.002mm? yikes!) which is nearly a R6 hole. So, if my logic is correct, a R6/g6 fit is a locational interference fit? A hole that tightly toleranced hardly seems appropriate though! And then I need to repeat for a sliding fit with the remaining component mating to this shaft, which will yield yet another really wacky-sized hole.
Obviously I'm pretty muddled with all this. Any guidance?
I have a linear motion bearing riding on a shaft; the shaft is press fit into a plate and protruding through the far side. A second component will have a slip fit on the far side of the shaft.
The shaft & bearing I have selected from a catalog. Everything's nominally 6mm dia. The bearing stipulates that the shaft shall be class g6 (ie, 5.988 - 5.996). If understand the system correctly, this then is a hole-basis fit - the hole will have the basic dimension as one limit; the shaft is sized to provide the desired fit with this hole.
How now do I select a fit for this g6 shaft and a press fit hole that holds the shaft? This feels like it should be a shaft-basis fit, but I'm operating with hole-basis components. The shaft I'm stuck with is hole-basis, but the required hole will not will not have a basic preferred dimension as a limit like the bearing hole does.
One thought I had was to look at an H7/p6 locational interference fit for reference. This fit varies from 0 to -0.02mm interference. Applying this interference to a g6 shaft gives me a required hole of 5.984 - 5.988mm (+-.002mm? yikes!) which is nearly a R6 hole. So, if my logic is correct, a R6/g6 fit is a locational interference fit? A hole that tightly toleranced hardly seems appropriate though! And then I need to repeat for a sliding fit with the remaining component mating to this shaft, which will yield yet another really wacky-sized hole.
Obviously I'm pretty muddled with all this. Any guidance?
