Press fit for bearing housing question

rich p · May 30, 2006

I have been machining bearing housings out of aluminum for the past few years, (4 per year for a machine) and I sometimes have trouble with the bearing pocket being hit or miss, too tight or too loose. The bearing o.d. is 1.575" and I am boring it about .0005 undersize. My question is how do you come up on a tight dimension? Between the aluminum being hot and expanded and the fact that the lathe cross feed is in .001 graduations, and I need tenths, I sometimes overbore. I am a machine mechanic, but I enjoy making parts for these older machines. Any help would be appreciated.

dsergison · May 30, 2006

#1. dont turn the handle a "whole" graduation!

#2. sand that last bit.

#3. use green locktite on the loose ones.

#4. make a go-nogo type gage. (more like a goalittlemore-good)

make the "goalittlemore" portion .001 under target. make the "good" .0002 under target. when your to "goalittlemore" make a few "spring cuts" - cuts with no more infeed. creep up on making "good" just fit.

if

jim rozen · May 30, 2006

Machine them tight by a thou or so, and heat
the aluminum housing for a shrink fit.

If the interior surface of the bore has a one
thou surface roughness, you might make them
even tighter than a one thou interference.

Jim

Jackmo · May 30, 2006

Two things I do is put an indicator on the cross slide of the lathe graduated in .0001, if you don't have one you could use a test indicator like you use on a mill to true up a vise. The other thing is I always open the begining of the bore to the bearing bore so the bearing can drop in so when you start pressing it will start straight less chance of not going in straight, now if the bearing is not very thick this is not a good idea just be careful.
Another thing is to try to avoid heat especially when trying to to the finish pass use coolant or even air to cool the part otherwise it will come out different when it does cool.

rich p · May 30, 2006

One time I bored the hole too tight and heated the housing. When it cooled, the bearing would bind up. How do you guys measure the bore. I have been using telescoping bore gages and a mic. But I creep up on it with my 6" vernier.

Jackmo · May 30, 2006

Inside mic's are good but the best is a bore gage you preset with gage blocks. I use telescoping gages a lot but never for critical measurements.
What size bore are you doing?

AlfaGTA · May 30, 2006

If You set your compound at 89* to the bed , every .001" of long travel will equall .0001" of cross travel. Should be able to split that easily to give .0001 on the diameter. Need sharp tools to get fine changes in diameter. Do not work too close for final cut. (tool needs some chip forming on top to be stable.
Dial bore gage set to a master is the key to size measurment. Inside mic is next best choice
Bore under and shrink fir as mentioned above.
Cheers Ross

jim rozen · May 30, 2006

Ah, vernier calipers.

You can't realistically size a bore to that
sort of tolerance with a vernier caliper.
No wonder you are hit/miss on them.

You need to change to some other kind of
reliable measurement tool, such as a telescope
gage and micrometer, or as mentioned, a go/nogo
gage that you make yourself.

Nothing more than a steel plug with various
diameters turned on its surface.

Jim

Anchor · May 30, 2006

like jim rozen said, vernier calipers are good for just like it sounds, very near. put a tenth indicator on your cross slide and just remember you are measuring depth of cut not off of the diameter.

Timw · May 30, 2006

A 1.575 bearing should actually be a 40 MM. Or by my chart 40 MM = 1.5748 . You might be loosing in the translation. Try to stay with the same manufacturer of the bearing might help too.

mjk · May 30, 2006

I do a bore that requires a press fit upon assembly. The bearing is 35mm od. I shoot for (0.0003/0.0006") under the design diam of the bearing.
This bore is done in a bronze casting when it's 75% thru the machining process and besides the time I already put in it, the casting is $$ and lead time is long.
I made a set of plug gages in steps that help me tweak the final bore.
I usually let the casting cool prior to the final bore attempt.
Although there are gages that can measure the actual size, the hour I spent making the gages has allowed 100% success with the bore.

jackal · May 31, 2006

Baldor electric motors show 1.5756 to 1.5761 on the size for that bearing. We do end bells all the time for Baldor and Mac-steel electric motors. When the bearing heats up under operating temp. it will grow. Also take into consideration the shaft may heat up and that will put pressure on the inner race of the bearing and the balls or rollers will in turn push on the outer race. Sometimes a little loose will keep a bearing alive better than the tight space shuttle tolerances. We get our tolerances out of an EASA electric motor standard book, and we use these fits on everything we do, unless specified otherwise. A little Loctite never hurt if it is slightly loose. I always cut the fit about .0015 under size and use a polishing stick ( broom handle 6" long with a slot cut in it for sand paper). Go from 60 grit to 120, 240 ,360,400. At the last use coolant or WD40 for a lube and it will shine up good.

Hope this helps,
Jackal

I never put a bearing directly in aluminum. We always have to put in a cast iron EZ sleave. It takes the pounding and will endure the load.

pepo · May 31, 2006

With a telescope gage and an OD mic you will always be undersize. Most of us put the gage in the hole at an angle,tighten the lock pretty snug and then pull the gage thru the hole.It is the only way you can do it and get the same reading twice.The problem is that the gage deflects back just a skoash.It is that skoash that you will be small. Try it,bore a hole to .5004 in any matl. with your telescope gage,bet you cant get a 1/2 dowel pin in it.My experience is that telescope gages are good for a thousandth and more.
As far as your bearing bore in the housing try boring the first .100 or so of the bore to a slip fit.(.0005 loose)Makes a big difference at assembly.

mjk · May 31, 2006

Jackal
I've popped a few Baldors apart, mostly their 1-1/2 single phase which if I remember correctly have a 6203 & 6205 in the end bells.
Their fit for the bearing in the bore is only a slight drag fit if almost a slide in fit. The fits on the shaft are a press and the end to end distance is captive by the bores in the bells,a retainer on the output shaft side and a spring washer in the fan end

metlmunchr · May 31, 2006

IIRC, the standard application on ball bearings is to have the interference fit on the rotating member. An application requiring interference on both OD and ID fits can increase cost by an order of magnitude, since roundness as well as diameter are both critical, assuming one is looking for decent bearing life.

gar · Jun 23, 2006

060623-1000 EST USA

AlfaGTA:

You have the best idea for an easy way to make fine adjustments.

But just a slight correction --- the sin of 1 deg is 0.0175 and so is the tan at this small angle. For 1 deg your multiplication is 57.3 to 1. For a 10 to 1 ratio you want an angle of 5.74 deg or 84.3 deg.

However, I like your 1 deg because on the compound because it requires 5.7/1000 on the compound to change 1/10,000 radially.

.

John Michael · Jun 23, 2006

A lot also depends on the shape of the bearing housing. If it does not nave a heavy cross section you have to be careful not to squeeze it out of round with the chuck jaws. Full wrap around jaws might be in order.

donie · Jun 23, 2006

jackmo best described tthe method I use includin a little lead in for the bore.
Bearing fitting is a big part of what I do. I recomend looking at the bearing manufacturers information on bearing fits rather than giving it a thou or half thou.
As jackmo decribed an indicator on the crosslide works good, this is the set up on my Monarch lathe.
http://www.metalworking.com/DropBox/_2003_retired_files/Don%20007.jpg

precisionworks · Jun 23, 2006

No matter if you're turning to an OD, or boring to an ID, the cross feed dial is nothing more than a reference. It's fine for roughing quickly, and it's OK if the callout is +/- .005, but it isn't meant for precise work.

I know someone will say "I can turn/bore to .001, using only the dial" - it is possible on a newer or lightly used machine that has tight gibs, an unworn crossfeed nut, etc. For the rest of the machines, the easiest way to hit a dimension is to stick a magnet-back dial indicator on the cross slide.

This allows dialing off single thousandths, even half thousandths. Even if your machine is pre-WWII, you should be able to do really fine work. If you don't have a mag-back indicator, a regular magnet base will work - it's nowhere nearly as solid, but it will do.
-----------------------------------------------

An ID micrometer is the most affordable & easiest way to accurately measure small bores. Mitutoyo makes a really nice one, but $200 is more than I had to spend. For around $50, J&L sells a ChiWan copy that is usable. Mine often gets used daily, either on the Bridgeport or on the lathe.

IMO, the advantage of an inside mike is the ability to feel bore contact, something that's impossible with telescoping bore gauges. They can either be directly read or read with an OD mike.

------------------------------------------------

Any caliper, vernier, dial, digital, is much like the graduation on the feed dial -- good for roughing & quickly getting close, not meant for bearing fit work.
----------------------
Barry Milton

RobBinIN · Jun 23, 2006

A bore that small is hella hard trying to measure with a rod or barrel style ID mic.

I say keep using telescoping gage and mic. Get a mag base indicator like the one precisionworks posted, but make sure you get a good one. The backs of the cheaper ones will pop right off.

bore it a thou or 2 under and polish it in with fine emery.

Press fit for bearing housing question

Cast Iron

Diamond

Diamond

Hot Rolled

Cast Iron

Hot Rolled

Diamond

Diamond

Cast Iron

Stainless

Titanium

Titanium

Hot Rolled

Titanium

Diamond

Stainless

Hot Rolled

Diamond

Diamond

Aluminum

Similar threads