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How much interference should I have to press a 1/2 inch OD needle bearing in a one inch OD aluminum gear? The gear is one I'm making for a reversing gear on 8X18 home lathe. Thanks for any help on this.
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How much interference?
- Thread starter yellow_cad
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I don't have the answer at hand and I have asked myself the same question. My thoughts are:
1. How much increase in temperature do you anticipate when this gear is running?
2. What are the expansion coefficients for Aluminum and Steel?
3. My "guess" would be .002-.004 less than the "expanded" diameter of the steel" as you are aware this can be a difficult problem. Hopefully someone with more knowledge than me will step forward.
Good luck
Ray
1. How much increase in temperature do you anticipate when this gear is running?
2. What are the expansion coefficients for Aluminum and Steel?
3. My "guess" would be .002-.004 less than the "expanded" diameter of the steel" as you are aware this can be a difficult problem. Hopefully someone with more knowledge than me will step forward.
Good luck
Ray
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Yellow,
A one in. O.D. gear with a 1/2" hole does not have that much room for the teeth. I am not sure what the application is but if this is the way it has to be done I would make a 1/2" hole and throw the bearing in the fridge and set the gear in the sun then press the two together using red Locktite when the parts are ready and that should work.
Paul
ps: Remember a 1/2" drill will make a hole bigger than 1/2".
A one in. O.D. gear with a 1/2" hole does not have that much room for the teeth. I am not sure what the application is but if this is the way it has to be done I would make a 1/2" hole and throw the bearing in the fridge and set the gear in the sun then press the two together using red Locktite when the parts are ready and that should work.
Paul
ps: Remember a 1/2" drill will make a hole bigger than 1/2".
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If I understand correctly, the gear will run on the bearing and the bearing will run on a shaft. If this is the case, it may not be necessary for the bearing to be affixed to the gear. I don't recall anything on a BB or NB being fixed to whatever was on. The clearance is very close between the two, but it's not an interference or shrink fit.
If you do insist on press fitting the NB into the gear, then consider something along the lines of 1/2 of a thousandth or less. Depending on what grade bearing you'll be using, more make damage the bearing or cause it to seize or function improperly. Additionally, pressing it into the aluminum may shear the aluminum.
If you do insist on press fitting the NB into the gear, then consider something along the lines of 1/2 of a thousandth or less. Depending on what grade bearing you'll be using, more make damage the bearing or cause it to seize or function improperly. Additionally, pressing it into the aluminum may shear the aluminum.
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On that size, I would go 0.0005 When it cools, it will be retained just fine.
Heat the gear, cool the bearing and she should be good to go.
0.002 to 0.004 is going to be a tight fit, and your probably going to kill the bearing pressing in.
Heat the gear, cool the bearing and she should be good to go.
0.002 to 0.004 is going to be a tight fit, and your probably going to kill the bearing pressing in.
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I'm thinking if you mic the needle bearing you'll find it to be oversize in the body, Assuming a stamped body. The spring of the stamped body should be all that is needed to fit a 1/2" hole. If it is a machined body then all bets are off as they are intended to be held by some other mechanical method and a press fit will deform them.
Steve
Steve
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On further reflection of this question... The bearing manufacturer's spec sheet for the bearing will invariably give min/max recommended bore size.
Steve
Steve
T
Tom Griffin
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Jim,
To answer your question I would need to know exactly what bearing you have because there are many types, but the most common type is the drawn cup. Stock Drive Products lists a drawn cup .500 needle bearing with a .3125 bore and the housing fit is .4995-.5005. Here's another source that goes into greater detail but produces the same results.
Companies like NTN also produce a needle roller bearing with much tighter specs, but all of those I found were metric.
Tom
To answer your question I would need to know exactly what bearing you have because there are many types, but the most common type is the drawn cup. Stock Drive Products lists a drawn cup .500 needle bearing with a .3125 bore and the housing fit is .4995-.5005. Here's another source that goes into greater detail but produces the same results.
Companies like NTN also produce a needle roller bearing with much tighter specs, but all of those I found were metric.
Tom
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If the intent is to run the NB directly on the shaft, the shaft material should be considered. If it is soft, it won't last long if there is much radial load. You can purchase inner races that are hardened, ground, and lapped that are designed to have needles on them. If you can turn the shaft down to accept one of those, you'd have a very nice bearing setup. Inner races are a light press, normally.
The outter race, with cage and needles should not be a high press fit. The shells are not that strong axially. I do mine with 0.0003-0.0005 interference, but no more.
The outter race, with cage and needles should not be a high press fit. The shells are not that strong axially. I do mine with 0.0003-0.0005 interference, but no more.
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Methinks you re putting too much thought into this.
Most simple lathes do not have bearings in the change gears or revesing gears, just a bronze bushing at best. Some just run Iron gears on steel shafts, like my 9 inch South Bend.
A needle bearing on a soft steel shaft will likely eat the shaft. Bronze wuld be much better.
I would just press in a thin bronze bushing, maybe an oillite. Press in, then ream to size afterward.
Heck, you could get by with no bearing or bushing at all with an aluminum gear. Just give it enough clearance for oil, maybe put an oil groove in the middle to hold oil, and possibly a small hole connecting with the oil groove to pump in oil.
The aluminum connecting rods below are for a high performance motorcycle engine, it will hit 7000 RPM at max warp. No inserts, the aluminum is the bearing material. A lot more severe duty than a lathe reversing gear. Note the oil groove I am putting in. This is a splash lubed engine!
Most simple lathes do not have bearings in the change gears or revesing gears, just a bronze bushing at best. Some just run Iron gears on steel shafts, like my 9 inch South Bend.
A needle bearing on a soft steel shaft will likely eat the shaft. Bronze wuld be much better.
I would just press in a thin bronze bushing, maybe an oillite. Press in, then ream to size afterward.
Heck, you could get by with no bearing or bushing at all with an aluminum gear. Just give it enough clearance for oil, maybe put an oil groove in the middle to hold oil, and possibly a small hole connecting with the oil groove to pump in oil.
The aluminum connecting rods below are for a high performance motorcycle engine, it will hit 7000 RPM at max warp. No inserts, the aluminum is the bearing material. A lot more severe duty than a lathe reversing gear. Note the oil groove I am putting in. This is a splash lubed engine!