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Furnace
06-13-2005, 09:04 AM
Could someone please tell me what would be a slight press fit for a bearing that has an .875 outside diameter. I need to bore a hole in a piece of 12L14 for this bearing and Im not sure how much to undersize this hole. If you cant tell Im new to all of this, so any help or sarcasm would be greatly appreciated.

precisionworks
06-13-2005, 09:08 AM
.8741 to .8745 is the chart recommended sizing.

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Barry Milton

darryl
06-13-2005, 06:20 PM
How are you measuring the bored hole? I only ask this because I had a bit of fun to start with when measuring a hole and expecting a good fit- to my horror the hole came out larger than I wanted despite me taking much care in boring it. That's when I learned that the dial indicator I used would read three thou small, with the hole therefore being three thou larger than indicated.

I don't know if this is a standard, but this slight overlap of the inside jaws prevents the thing jamming when you try to open it from fully closed. If this small overlap wasn't there, the inside jaws could 'pass' each other, preventing the caliper from opening.

If your final passes are to test fit something, you can take a few passes to remove small amounts of material each time, then test fit. Easy enough. But if the hole has to be a fixed size smaller than the thing that fits it, such as when needing a shrink fit of parts, or a press fit, then you'll have to be able to know exactly how large your bored hole is strictly by measurement. Do some experimenting on scrap to find out this difference in your indicator's reading between inside and outside measurements, and only then can you rely on it to tell you the true diameter of a bored hole.

Just thought I'd bring this up again for those who didn't know, or who have forgotten to factor this in.

[This message has been edited by darryl (edited 06-13-2005).]

Evan
06-13-2005, 06:40 PM
For that sort of work I will make a plug guage from brass. I cut it with a taper of .001 over one inch. This allows easy measurement to .0001 based on how far the guage fits in the hole. Be careful not to jam it in the hole.

Last Old Dog
06-13-2005, 06:41 PM
Darryl, is this bore measurement task a good job for inside mikes and a calibrated 0-1" outside mike? Or even a simple GO-NOGO gauge?



[This message has been edited by Last Old Dog (edited 06-13-2005).]

JCHannum
06-13-2005, 08:31 PM
The dial caliper has it's limitations in measuring inside diameter.

Depending on the size of the hole, small hole gages or telescoping gages are your best bet. Get good ones, Starrett, B&S, Mitutoyo or Lufkin. Avoid the low priced imports.

They take a little practice to get the technique, but once mastered, very accurate readings can be made.

Mike Burdick
06-13-2005, 09:23 PM
I think Evan brings out a good point here. Sure it’s nice to have just the “right” measuring instrument but - if not - one can make something very easily to do the job just as well – if not better!

Furnace
06-13-2005, 09:24 PM
I have a set of the hole gages but theyre imports, the few times Ive tried them I didnt trust them. Im going to try the go-no-go gage and see if I can get it that way. This is a mount for a bearing for my little 7x14 cross-slide, in case any of you have tried it. Thanks for the help.

JCHannum
06-13-2005, 09:41 PM
Loc-Tite products are the great equalizer in applications such as this. Especially in a lightly stressed installation as this, they can make life much easier.

A go-no go gage will only tell you if the hole is too large or too small, it will not tell you how much material to remove.

The tapered plug gage, if you can make one, will only tell you the diameter of the top of the hole, not if it is straight or tapered. It is also of little use in a shallow hole.

Get good tools and become proficient in their use. It is all part of the process.

Evan
06-14-2005, 02:42 AM
It works for me JC. I have built a lot of projects using ball bearings that are a light press fit. After a while you end up with a handy set of plug gauges. If you do the boring right the top of the hole should be the same size as the middle. If it isn't then you have more basic problems to deal with first. For my designs through holes are the rule. It is pretty easy to come up with ways to retain the bearings. Stepped shafts and collars come to mind.

darryl
06-14-2005, 02:52 AM
No arguement here, the proper measurement device is what should be used. Having no such inside measurement tools myself, I've learned to manipulate the dial indicator to the point where I can trust the readings to within a half thou or so. This certainly takes some learning and practise, but it can be done. I like to repeat the readings a few times, just to see if they are consistent, and if they are, then I have passed the test of taking a reading properly, and the indicator has passed the test of giving a consistent reading. While doing the multiple readings, I check to see that the indicator shows .000 when closed each time.
I always have a few bits of precision rod around, and I use these to check the indicator and the bored hole. I keep old ball bearing races around for the same reason. I have thought to do a slight 'taper grind' on the outside of an old race just to use it as a hole gauge when boring for that size bearing, but I haven't yet done that. I think that would be handy for whatever common sizes of bearing a person would normally use.

Your Old Dog
06-14-2005, 06:40 AM
And this from the peanut gallery.

I have a cheap chinese digital calliper.

why couldn't you shapen the outside jaws to a V shape, slip indicater inside hole, zero meter, bring it out and close jaws to get minus reading of hole.? Is that possible?

kap pullen
06-14-2005, 11:26 AM
A lathe mandrel (tapered) works as a nice gauge, and you can use it in the lathe as well.

Kap

Yankee1
06-14-2005, 02:19 PM
I would make it .001" undersize. If the bearing is on a shaft I would subtract the
amount the shaft is oversized and subtract the .001" undersize of the housing from the bearing ball or roller bearing original clearances.
example: If a bearing has an original roller clearance of .005" and is on a shaft that is .001" oversize and is pressed into a housing that is .001" undersized.
Then subtract .002" from the original .005"
roller clearance of .005",this leaves .003"
roller clearance. It is possible to take up
the entire roller clearance if these things are not considered. This would cause the bearing to run hot.

Evan
06-14-2005, 02:52 PM
0.001 undersize is far too much even for a tight press fit. Bearing manufacturer specs for a light press fit for that size of bearing in an ABEC 5 spec (+0 -.0002") call for -.0002 to -.0004 at the most for the outer race housing.

wierdscience
06-15-2005, 11:33 PM
I'm going with JC on this one,Loctite 271 and primer is what I use.

The bearing guidelines are only that,not hard and fast rules..0002" under might be fine for most applications,but not all.

Temperature swings and expansion will play a role in some situations,as will housing bore alignment errors.

Mcgyver
06-16-2005, 05:41 AM
<font face="Verdana, Arial" size="2">Originally posted by wierdscience:
I'm going with JC on this one,Loctite 271 and primer is what I use.
</font>

I don't think loctite will work that well - a press fit perfectly aligns the bearing whereas with the thou or two of clearance loctite needs anything can happen

Allan Waterfall
06-16-2005, 06:06 AM
I was told by the man that writes the gear cutting book that the film of Loctite tends to centralise the bearing in the bore,providing that your fit is within the the recommended clearance in the bore.

How true this is I don't know but it made sense to me.

Allan

JCHannum
06-16-2005, 07:08 AM
<font face="Verdana, Arial" size="2">Originally posted by Mcgyver:
I don't think loctite will work that well - a press fit perfectly aligns the bearing whereas with the thou or two of clearance loctite needs anything can happen</font>

There are billions of bearings out there retained in this manner, many on your own car if it was manufactured in the last twenty or thirty years.

Loc-Tite is an accepted method of bearing retention, and is the method of choice in many applications as it speeds machining and assembly as well as eliminating potential problems caused by stack up of manufacturing tolerances.

Swarf&Sparks
06-16-2005, 09:32 AM
I'm with YOD. I have the cheap digital calipers and have used that technique within 0.01 mm.

Mcgyver
06-16-2005, 08:56 PM
<font face="Verdana, Arial" size="2">Originally posted by JCHannum:
There are billions of bearings out there retained in this manner </font>

I don't disagree that its often used and btw it is clear to me that cars are put together in the most cost efficient manner possible.

However whether Loctite's a good approach or not obviously depends on the task at hand, right? Furthermore, that this assembly method is widely used in no way suggests that it is a substitute for, or delivers the same characteristics as a press fit.

As the thread is about bearing interference fits, and therefore implies that the characteristics of press fit are required, Loctite(with the usual slip fit) is a poor substitute as there is quite a bit of clearance. A press fit results in almost perfect alignment between bore and bearing - a characteristic not necessarily retained with 2 thou clearance and an adhesive.

I don’t think anything you are saying is incorrect, just that its not applicable if the guy needs the accuracy of a press fit.


[This message has been edited by Mcgyver (edited 06-16-2005).]

mochinist
06-16-2005, 09:22 PM
<font face="Verdana, Arial" size="2">Originally posted by Mcgyver:
I don't disagree that its often used and btw it is clear to me that cars are put together in the most cost efficient manner possible.

However whether Loctite's a good approach or not obviously depends on the task at hand, right? Furthermore, that this assembly method is widely used in no way suggests that it is a substitute for, or delivers the same characteristics as a press fit.

As the thread is about bearing press fit interferences, and therefore implies that the characteristics of press fit are required, Loctite(with the usual slip fit) is a poor substitute as there is quite a bit of clearance. A press fit results in almost perfect alignment between bore and bearing - a characteristic not necessarily retained with 2 thou clearance and an adhesive.

I don’t think anything you are saying is incorrect, just that its not applicable if the guy needs the accuracy of a press fit.</font>

A bearing doesn't necessarily go in stright and aligned just because it is a press fit, the installer still has to put it in correctly.

Like you said and I agree a press fit is better than using loctite(by the way don't use regular loctite for bolts, lotite makes a product just for this application), but alot of the homeshop guys probably don't have the expensive tools, or the now how yet to do a proper press fit, and the loctite will probably work just fine for their application. The way Evan described works really good it just takes more time than using bore gauges or telescoping gauges.

precisionworks
06-16-2005, 09:25 PM
Mcgyver, I vote with you. There are times that Loctite High Temperature Retaining Compound 620 http://68.72.74.116/PRODUCTS/620.htm is the product of choice. Usually when a bearing bore is already worn oversize, as 620, which is thick, slimy & nasty green will fill gaps up to .010".

But I would never consider overboring by even .001 for a bearing fit & using 620 to fill the gap. If bearing fits weren't critical, no manufacturer of bearings would specify tolerances in the single tenths. And Kennametal/Erickson would probably never sell another Tenthset boring head (of which I have three for just that purpose).



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Barry Milton

wierdscience
06-16-2005, 09:38 PM
271 doesn't require .002" clearence,the machined finish left behind on a +/-.000" fit is plenty.All that is needed is enough loctite to fill the surface finish of the bearing bore.Once it expands slightly the bearing is gripped over 100% of it's outer ring surface area,press fits no matter how accurate will not do that without distoring the outer ring.

Distortion in bearings resulting form press fits is very real,reguardless of the bearings size.

I prefer to call a press fit an interference fit and avoid the press all together.Cone heaters are a much better means of installing bearings.250*f thermal convection heating and they drop on on shafts,do the same to the housing and they slide in,much easier on the machinist and the bearing.

BillH
06-16-2005, 09:43 PM
I made a Go-nogo guage for my locomotives tenders bearing boxes, works great, find out really quick if your there yet, and to within .001.

Mcgyver
06-16-2005, 10:01 PM
<font face="Verdana, Arial" size="2">Originally posted by wierdscience:
271 doesn't require .002" clearence,the machined finish left behind on a +/-.000" </font>

you're right & I know, I more threw it out there on the basis that if a guy is loctiting to avoid turing to tenth's, there's a good chance we're talking a 1 or 2 thou slip fit.

you're also right to point out it's an interference fit and it is nice to do as a shrink if possible. if it is a press I usually counter bore a wee bit in at say 0.0000/+0005 or as best i can, to start the bearing and ensure the press starts accurately - don't know if that's sop, but works for me

i checked and the 620 is applicable for press fits (Loctite's words, kind of surpised me that they recomend for intereference fits) - maybe thats the best way to go, a very light interference fit to ensure alignment but not distort and some good green goop to hold it all together


[This message has been edited by Mcgyver (edited 06-16-2005).]

wierdscience
06-16-2005, 10:44 PM
Oh what the heck there has to be at least 20 different ways to do the same job http://bbs.homeshopmachinist.net//biggrin.gif

On the critical bearing fits for small od bearings I use a neat little trick I picked up from a local insturment maker.

I keep a selection of nice shiney new bearing balls handy.If it's a through bore all I do is bore it .001" undersize,lube up the bore and ball with grease and shove the ball through with the press.Presto,perfect hole size everytime.A real life saver when you need to machine 300 holes to an exact size quickly on not so perfect machines.

mochinist
06-17-2005, 02:01 AM
<font face="Verdana, Arial" size="2">Originally posted by wierdscience:
Oh what the heck there has to be at least 20 different ways to do the same job http://bbs.homeshopmachinist.net//biggrin.gif

On the critical bearing fits for small od bearings I use a neat little trick I picked up from a local insturment maker.

I keep a selection of nice shiney new bearing balls handy.If it's a through bore all I do is bore it .001" undersize,lube up the bore and ball with grease and shove the ball through with the press.Presto,perfect hole size everytime.A real life saver when you need to machine 300 holes to an exact size quickly on not so perfect machines. </font>

I have read about that but never tried it, I think they called it ball sizing which would make sense.

JCHannum
06-17-2005, 07:17 AM
The application in question is a bearing for a leadscrew for a cross slide, 0.875 OD. This is a place for nice work, but hardly requires a high degree of accuracy or strength.

Furnace was looking for a light press fit, anything close to 0.875 + a bit will satisfy the needs for strength and accuracy in his application. Since this is the question, Loctite is a more than adequate answer.

Loctite can be used up to 0.015" gap with success, and is a valuable tool in the MRO industry to salvage or get a machine back into operation while waiting for an opportunity to repair correctly, or for a part to arrive.

Further, it is frequently used to improve a good fit, and increases the strength of any assembly. The 680 series can be used in this application, and will add 4000# shear strength to the assembly. If the assembly is fixtured properly, inaccuracies in alignment will be canceled out, and a degree of self alignment will be achieved.
http://www.loctite.com/int_henkel/loctite_us/index.cfm?&pageid=130&layout=1

I feel that sometimes, people unnecessarily stress high accuracy and claim to be machining to 0.0001" as a form of self gratification. This is seldom needed, and probably puts a burden on beginners, thinking they have to work to this precision, or they are a failure. Nothing can be further from the truth. In most cases, +- 0.005" is good, and in this case, -0 +0.001" would be workable, if missed, Loctite will take care of it for the next 100 years or so.