Hello,
sorry about the wall of words, I don't think I can make it smaller, although not complicated to understand.
Background:
I have a bandsaw that needs bearing replacement. the guy I bought it from told me it was replaced only 5 years ago, but Both bearings are bad when I brought it home suspecting poor quality bearings or poor installation. They are 6003 bearings. I want to upgrade to seal bearings from shielded. I have tried a couple of trial and error methods to get this to work Without success.
parts
The wheel ( part 23) is made of aluminum alloy. Bearings ( part 19 and 27 A) are 6003. Parts 25 is a shaft ( not keyed, but friction fit) that is 17 mm in diameter ( unverified). As you can see from the picture, the shaft has a stop in the back for the bearing. I also don't have an inside micrometre to measure the Exact bearing diameter. The shaft is 17.05 mm I think, But this could be wrong, as my digital CalPERS are cheap.)
reassembly installation procedure, deduced:
- install bearings in wheel. Achieved with a small toaster oven at 200°F, as wheels are made of aluminum. Maximum recommendation for bearings. shaft at room temperature.
- part 25 must be slipped in through the back and not the front due to the bearing stop near the threads.
goal
I want to achieve an easy slip fit Using temperature differential for two reasons. The first has to do with Not able to swing a hammer anymore With a lot of force. The second, is that it seems to be a two-step process as the shaft if driven last with a hydraulicpress or mallet will be pushing on the inner race while the outer race is also under force,
damaging the bearing. My hypothesis is this is what happens five years ago.
My current attempts and/or strategies.
- ( failed Shaft/ success bearings in wheel, 310°F differential). the shaft and wheel are inserted in the oven together heated to 200°F. the shaft was cooled using dry ice is 109°F. I did not attempt to hammer it in, but tried placing. this may have been a mistake. two step process.
- ( Not attempted, 560°F differential, unknown if possible). I can replace the two bearings with high temperature steel shielded bearings which are much worse in performance. more expensive bearings at $15 a piece. I can heat to 450°F and drop in a dry ice shaft. I don't like this as the tire will need replacing every time this is performed. this is very difficult to remove without destroying. I'm assuming the bearing can take the 500°F and not just the grease which might be wrong. Making this an expensive bearing placement, Done often). I can't find a seal bearing for 6003 high-temperature steel[ opinion: bad solution, But may B only option]
- [not attempted, 360°F differential. bring the wheel my local nitrogen supplier in Toronto Canada. I called a guy and ask if I bring the one wheel. I told him it was 15.5 mm rather than 17 mm by mistake. He said this would fail and said don't bother coming.
- [ not attempted, 510°F differential] I could go back to my same nitrogen supplier and bring my small toaster oven ha ha. Or my heat gun. He might say no. I don't know if this would work
- different installation method not considered.
Please let me know how you think I should proceed. this is a real pain.
thanks
Step one is you need GOOD measurements. You've got to know how much interference fit you've got before you even consider how much temperature differential is going to achieve what results.
I don't see any spacer between the bearings. That gives you some options. They're a "flat" design, which probably has a proper name, but the inner and outer race are the same thickness. In other words, you can press one bearing with the other. That's a good degree of freedom if you're having to invent ways to do this.
I agree with others, there is no need at all to have both the inner and outer race pressed to an interference level. On the other hand, I've seen a lot of cases where this was done anyhow, for reasons outside of my pay grade. Or related to my price point. One of the two probably.
Unless this was high precision stuff (band saws are not), while you "might" find one, usually the tolerances in manufacture, even quality stuff, means that one machine might have a gentle tap fit with the bearings, and another might take all afternoon to beat together with a post maul. Make no assumptions based on what the fit "should" be. It "should" be what the bearing world would call "sloppy". If you could -count- on heating to a drop in fit, you would not be buying bearings for ten bucks.
My first inclination is that with an awkward setup like this, more than likely something unfortunate happened to the replacement bearings. And/or the replacement was the variety that can be had for two bucks and change, INCLUDING paying the postage right to your front door.... You can literally buy bearings that are made of unhardened steel, presumably mild, as they rust real fast as well, if you try to save enough money.....
I see two (plausible) options really, giving that I'm extrapolting that you have minimal tools for this, so there's my "overview" of what's got to happen. First, as I and other said, you need a good measurement of the shaft and the bearing. Verify that the fits are plausible (0.05mm or 0.002 inches is "probably" doable reasonably, if that's accurate and the bearings are dead on..., but you're at the far end of what that size ofmaterial is going to tolerate). This will NOT slip together with heat/cold levels that are plausible due to changes in metulurgy of the parts. It's gonna need pressing. Maybe a swing press, or maybe a proper press..... So the overview is this- I would start by pressing the two bearings onto the shaft, since that's going to take fixturing and force and what not. You'd need a driver (pipe?) that could press directly on the inner race. One race can press against the other with no issues. Second, I would take that assembly, and as you've already discovered, aluminum expands a LOT, so that assembly, and the easier fit in the wheel makes a good "second operation", since the press/interference is a lot easier to work with.
OR......... As has been mentioned, but I'll second because it just sounds so "wrong" for something as precise as a bearing- This is not a high precision thing. (Obviously some level of care is needed, don't "try" to screw it up and you'll do fine...). If you can spin that little shaft in a lathe, drill press, etc...... Once you've got the measurement situation figured out, spin the shaft and dust it off carefully and systematically with emery tape until you achieve a more plausible press/friction/ fit. Even a slip fit would be fine, given the nut that tightens the whole thing, although I'd want on the "just barely" slip fit range. Although it might well could survive some wiggling, you really don't want it wiggling...
