What are the recommended clearances for 1/4" and 3/8" steel shafts running in bronze bearings? The bearings are NOT oil-filled.
What method do you prefer for sizing these parts?
Camshaft and Crankshaft Clearances
Re: Camshaft and Crankshaft Clearances
I would also be interested in knowing what others are allowing for clearance. Two of my previous low rpm engines with 5/16th crankshafts had approx .001 clearance. These crankshafts will easily rotate with to the heavy side down with the rod removed. The current engine with 5/8th dia shafts have approx the same clearance or a 'few tenths' less and I would expect it to be fine also. On my first engine I turned the shafts to 5/16 and used stock oilite bushing only to find that they had more clearance than I liked so I made new ones. The extra clearance didn't hurt anything just a personnal preference I guess.
Bob W
Bob W
Re: Camshaft and Crankshaft Clearances
Hey Mosey,
Some study of ANSI standard fits listed in the Machinery's Handbook(MH) are helpful in deciding class of fit.
This would be a running clearance or RCx type fit. These fits follow a pattern of tight for close tolerance sliding fits as RC1 to loose as RC9 for sloppy fits with large tolerances.
Consideration to major temperature swings and location issues to thermal expansion are important. As a hollow shaft will grow more readily than a solid.
Speed as another factor can induce heat by friction. To tight a fit may cause them to sieze. More sensative as the diameter and surface area contact increase without oil pressure.
I tend to stick with the class RC5-RC6 fit for most things. Run in and assembly checking may push it to around RC7. As a general rule this works out to be about 3-5 tenths of a percent of the working diameters between 1/8 and 1". Use this rule inversely proportional. As in the larger percentage goes with the smaller shaft/bushing fits.
So to answer your question in a round about way? [img]/ubb/images/graemlins/smile.gif"%20alt="[/img]
.240*.5%=.0012
.375*.5%=.0018
Class of fits shown in MH are RC5=.001-.0025, RC6=.001-.0033 for diameter ranges .24-.40 so the above should be fine. Easily obtainable with a reamer or single point bored which I prefer.
Plain bearing fits can be used in a model engine also, but for the most part are described as fed oil under pressure. Beyond the scope of a simple posting to calculate oil flow and viscosity over surface areas and all the forces involved as outlined in the MH. [img]/ubb/images/graemlins/confused.gif"%20alt="[/img]
DC
Some study of ANSI standard fits listed in the Machinery's Handbook(MH) are helpful in deciding class of fit.
This would be a running clearance or RCx type fit. These fits follow a pattern of tight for close tolerance sliding fits as RC1 to loose as RC9 for sloppy fits with large tolerances.
Consideration to major temperature swings and location issues to thermal expansion are important. As a hollow shaft will grow more readily than a solid.
Speed as another factor can induce heat by friction. To tight a fit may cause them to sieze. More sensative as the diameter and surface area contact increase without oil pressure.
I tend to stick with the class RC5-RC6 fit for most things. Run in and assembly checking may push it to around RC7. As a general rule this works out to be about 3-5 tenths of a percent of the working diameters between 1/8 and 1". Use this rule inversely proportional. As in the larger percentage goes with the smaller shaft/bushing fits.
So to answer your question in a round about way? [img]/ubb/images/graemlins/smile.gif"%20alt="[/img]
.240*.5%=.0012
.375*.5%=.0018
Class of fits shown in MH are RC5=.001-.0025, RC6=.001-.0033 for diameter ranges .24-.40 so the above should be fine. Easily obtainable with a reamer or single point bored which I prefer.
Plain bearing fits can be used in a model engine also, but for the most part are described as fed oil under pressure. Beyond the scope of a simple posting to calculate oil flow and viscosity over surface areas and all the forces involved as outlined in the MH. [img]/ubb/images/graemlins/confused.gif"%20alt="[/img]
DC