Shaft won't fit bearing

[Steamchick]

Pete has the answer. Take heed. Surface finish is really like the cutting edge of a Hacksaw blade. For a bearing, you need to Linish the sharp peaks to microscopically flat surfaces and fine grooves (machined surfaces would destroy a plain bearing in NO_TIME!). So, with the shaft 0.001inch large, you need to smooth-off the surface peaks of the machining - Try a locking wrench (Mole grips) to LIGHTLY grip a piece of 400-grade emery on the freshly machined journal and after only maybe 5 or 10 slow rotations re-measure the journal to see how much it has changed the diameter. You need to be working to TENTHS of a thou, measuring with good calibrated micrometer, etc. as explained above.
LINISHING is for removing ONLY the peaks from the machining (so fine you may not really see them). NOT for removing metal to CHANGE SIZES. I used calibrated micrometers with a vernier scale on the barrel when I was and apprentice. And got a few things wrong before I got them right! I learned NOT to trust the scale of measurement for making cuts, but the MICROMETER for measuring the part after machining. If I want a 1 inch length at "size" I cut 1/10th inch and measure, then wave everything around and measure, and take the best and worst of 3 measurements as a guide, and make sure I am OK before making the full 1 inch length of cut.. Then check both ends of the 1inhch long cut and the middle, rotate 90 degrees and measure again, and rotate 90 degrees more and measure. Then I am sure of "size". stop at 0.001 in before "size" and linish the last thou. (You can't linish more than a thou on diameter - but you can Bodge the part out of true with coarse emery!).Checking fit with the bearing, as it may not be perfect! Don't use 2 Mics. They are NOT the same. at sub 0.001in. (unless in a calibrated measurement room and checked and set to be the same!). Use one, and measure internal sizes by using a comparator as above, then measure the comparator. I sue Drills and milling tools (the precision ground shanks) and Ball bearings (new, not worn) to confirm sizes of the micrometer, so I can check my technique is good. Calibrate YOURSELF: Measure something - precisely and carefully, Put down the tools. wave you hands around, and turn around, or walk around the workshop. Measure again. Repeat 10 times and do some statistics on your results. EXPECT them to vary by as much as 1 or 2 thou. - That is NORMAL AND HUMAN. But with practice, you can improve... and record the improvement. Do that daily for a week, and see what happens? DO NOT Kid yourself: Expect variation and you will find it. Expect perfection and you will find it - when it is not there... - and find that things don't fit when expected. We've all been there, or not made precision stuff. So this is just a part of improving your expertise.
Enjoy!
K2

 

[swarf]

How and what are you using to accurately measure the bore? Having to go .003" -.004" under size on the shaft means something sure isn't right. On smaller holes .0005" under on the shaft should allow the parts to slide together as long as the surface finish on both parts is reasonable and the bushing is bored and not a simple drilled hole. I could see the problem easily happening using calipers for the internal measurements. Due to there mechanical design, they simply can't make highly accurate internal bore measurements. In fact I don't rely on any caliper measurement I.D or O.D. that has to be accurate to less than about .005". And the smaller the bore the less accurate those caliper measurements are. It's due to the internal jaws not having a knife edge and instead they both have narrow flats for longevity and durability. Even when measuring something like a grooves or slots without any radius, I don't use the calipers reading at all. Instead I use mine as a gauge to find the slot width and then lock the setting. Then measure the distance across those internal jaws with a micrometer if the accuracy requirements are high enough. Anything more accurate for something like a slot, I'd use a set of telescoping gauges, stack of gauge blocks or my two point internal mikes.

But those telescoping gauges are also highly dependent on them being very smooth, well made, burr free and just as important, require some well practiced technique. With everything correct, they can be accurate to within a few 10ths. It does take quite a bit of practice with them and measuring known bore sizes to double check you can actually get accurate and dependable measurements though. I also take at least 3 measurements just to be 100% sure of an accurate size measurement. But measuring with any accuracy even down to a few 10ths is at least an order of magnitude tougher than being certain of your measurement at .001" Any caliper of any type most of us can afford are at best somewhere within about .003". And I can say that with some assurance after double checking myself and my own calipers against proper gauge blocks. Under less than perfect conditions and with parts still in a mill vise or lathe chuck, I wouldn't bet bet a dime on less than .005" unless it's by pure luck.

Yep calipers. I have telescoping gauges but have never used them. Might be a good time to start using.

 

[pete]

Then that's your issue, without an accurate measurement for bore size then it's pretty tough to come up with a shaft size that will fit first time. Calipers can only get you fairly close, and yes there still one of my most used tools. But you have to understand there limitations and when to start using better and higher accuracy measuring tools more suited for the task. My Mit. calipers even have a .0005" digit. For me it simply gets ignored since there mechanical design isn't capable of that kind of accuracy. In reality, that last digit is pretty much worthless.

 

[stevehuckss396]

I was just about to say what Green Twin said. Turn the shaft and then polish with sand paper. It's the poor man's grinder. Without that fine polished finish the bushing will wear out quickly. It's surprising how accurate in size you can get if you take your time and measure frequently.

 

[Richard Hed]

I notice that there are some people, notably Russians, who use a ballbearing tool to run over their cut to flatten down any microscopic burrs. I'm intrigued with this idea and could see it would be a very good tool in many cases. I'm thimpking, one could try this, then use the mic and fine sandpaper to get to the right spot.

 

[GreenTwin]

If the bearing goes near the center of a shaft, you can sand either end of the shaft for a sliding fit, and leave the center part a bit high for a slight inteference fit.

.

 

[minh-thanh]

Personally, I think it's not because of the surface
If the surface is rough, when measuring, we will also measure those high points
I think it's due to the way of measuring and the measuring tools

 

[Richard Hed]

Personally, I think it's not because of the surface
If the surface is rough, when measuring, we will also measure those high points
I think it's due to the way of measuring and the measuring tools
View attachment 158302

Yes, that's why I am intrigued with the ball bearing treatment. Have you seen those vids? I can find one if anyone is iunterested. They don't look difficult to make. ONe of the vids is of a person making one.

 

[swarf]

Just for the record. I'm no machinist, nor do I wish to be one. I take perfectly good material and turn it to swarf.
Im just a hack having fun with a cheap lathe and mill drill learning as I go and most importantly having fun.

 

[BaronJ]

Hi Richard, Guys,

Using ball race to burnish the surface is one way to obtain a relatively smooth finish.
But you do have to be very close to the right size !

 

[minh-thanh]

Yes, that's why I am intrigued with the ball bearing treatment. Have you seen those vids? I can find one if anyone is iunterested. They don't look difficult to make. ONe of the vids is of a person making one.

Yes I looked, I was planning to make one but after thinking,,,....it didn't seem suitable for model engine small parts..so I didn't do it

 

[Richard Hed]

Just for the record. I'm no machinist, nor do I wish to be one. I take perfectly good material and turn it to swarf.
Im just a hack having fun with a cheap lathe and mill drill learning as I go and most importantly having fun.

Most of us don't hold that against you. In fact, I believe that most of us admire your attitude. In ALL learning, it should be FUN! The greatest learners wer, of course, interrested in the tiniest of details which are always fun in digging out. I might be 75 but I still thimpfk like a kid (and act like it too) and love learning trivia. Trivia is what makes up the whole world. Witout trivia, the world would NOT go around. My point is, if it is not fun, why bother doing it?

 

[Richard Hed]

Hi Richard, Guys,

Using ball race to burnish the surface is one way to obtain a relatively smooth finish.
But you do have to be very close to the right size !

HOw would that work? I would thimpfk that the bigger the better but for small close work maybe need smaller.

 

[BaronJ]

HOw would that work? I would thimpfk that the bigger the better but for small close work maybe need smaller.

No the work needs to be close to size !
I use a 1" ball race mounted on a 1/2" square bar clamped in the tool post. Not that its critical, just about any ball race about that size will work just fine. Handy for truing up thin work held in the chuck as well.

Here is a picture of mine !

 

[Richard Hed]

No the work needs to be close to size !
I use a 1" ball race mounted on a 1/2" square bar clamped in the tool post. Not that its critical, just about any ball race about that size will work just fine. Handy for truing up thin work held in the chuck as well.

Here is a picture of mine !
View attachment 158303

Ah, I get it. The one I am talking about is not the race, it is a single ball bearing--the ball which is put inside a tool. So you get a rotating "point" pressing the work. The lrger the ball, the flatter is the "point".

 

[peterl95124]

When I started seriously machining in about 2009, the thing that held me back initially was impatience.
I expected to take a few cuts, spend about 2 minutes, and have a perfect piece/shaft.

I overshot or undershot every time.
And I was using vernier calipers to measure, which I discovered are good for rough sizing, but not good for final measurements.

And as others have mentioned, I discovered fine sandpaper, perhaps 600 grit or finer.
I eventually leaned to get the shaft about 1 thou oversized, and then use the sandpaper to take it very slowly down to final size, with a lot of measuring as I went.

Like everyone else, I had to learn how to do it.
We all have had to learn how to do it, and we all had to start with that first shaft.
Nobody was born with a micrometer in their hand.
.

exactly my experience too !!!,

machine to .001 oversize, use abrasives to get perfect finish and perfect size. I find that 600-grit wet-or-dry paper takes about a "half" (of a thousandth) at a time, and 1000-grit takes about a "tenth" (of a thousandth) at a time.

also I find that ball bearing bores vary depending on mfgr and lot, some will fit on a nominally sized drill blank and some don't !, and nominally sized "drill rod" varies too much to reliably fit into a ball bearing bore, I often end up using abrasives to finish and polish drill rod too.

 

[indian]

Try setting your compound slide over 5.7 deg, this gives you a ratio of 10 to 1 so you can machine tenths. And if you polish your cutting tool all will be well.

 

[pete]

You can also do what's called ball burnishing as long as there through holes. It does take a hardened ball bearing of the correct size. But it's forced through the hole using whatever you can come up with for a press tool. Done right, it can both smooth and size the hole to very close limits. For us, the standard practice is to make the hole first and size the shaft to that for your running, light / heavy press fit.

 

[kwoodhands]

Put shaft in freezer for 2 hours . Use heat gun to warm the bearing. Place the shaft into the bearing while the bearing is hot. I do this routinely with no reduction in shaft diameter.

 

[L98fiero]

Put shaft in freezer for 2 hours . Use heat gun to warm the bearing. Place the shaft into the bearing while the bearing is hot. I do this routinely with no reduction in shaft diameter.

The problem with that is that is the shaft or bore to bearing size makes the fit too tight, it will stretch the bearing inner race/compress the outer race and cause a reduction of clearances of the ball bearing, some is intended, that's why press fits are specified buy the manufacturers.

If it's a plain brass or oilite bearing, it's intended that they are a press fit to produce the required shaft clearance.