Reaming in aluminum

[Belding]

Hi all,

I am going to be reaming a 1/2" hole in the bottom of a steam engine connecting rod made of 6061. I want to press an ABEC-5 brearing into this hole. The bearing OD has a tolerance of +0, -.0002. I am not sure what size reamer to buy. I can get a .499, .4985, .498. Can I expect the reamer to make a slightly oversized hole? For example if I get a .499 reamer with a cutting diameter tolerance of +.0002, will my hole come out to .4992? I plan to drill 1/64 under then ream. I am relying on an interfence fit to hold the bearing in place. Seems to me an interference fit of .0005 would do nicely. I realize there are probably a hundred different variables that would affect my final hole size, but if everything works correctly what can I expect from the reamer?

thanks
Zac

[blackbeard52]

A one thousandths press is probably all you will need. I would try the reamer on a piece of scrap to see the fit and then use it on the rod .. I frequently use an old trick of freezing the bearing and warming the rod to make assembly easier.

just my .001

bob

[RMM97502]

Belding,
You are correct in that there are a number of ways to achieve this task. Reamers are usually pretty predictable, however, they can at times cut over what you expect them to. I never use a reamer for critical parts; i.e. single part orders, something where I want to hold a couple of tenths (.0002"), and so on. Better to be safe and take a little extra time than to chance a reamer cutting oversize. In cases like these I have had more luck with boring the holes. Despite some beliefs, you can hold a couple of tenths all day with a standard boring head instead of needing a tenths adjustable boring head.

As for the interferance fit, is this a bearing that can be frozen? Liquid nitrogen or dry ice works well, provided it will not affect the bearing in any way. Something else to help would be to heat the aluminum part slightly but be careful that you don't distort the part in any way.

hope this helps and good luck

[cam1]

Or ream on size or slightly below -.0001, and use a small amount of Loctite cylindrical retaining compound, press fit.

[blackbeard52]

I agree with Belding, However I assumed you didnt have the tooling or didnt want to go to that much detail. (not that .0002 is not much) I dont freeze it completely..Just lop it in the wifes freezer for a couple of hours...never has hurt any I have used.

Good luck

Bob

[Belding]

Thanks for your help,

I think I will go with the .499 reamer and use loctite if I have to (rather not)


zac

[dertsap]

you would be best off if you bought an adjustable reamer , a .001 pressfit will probably leave a bit too much material to get a proper fit

[cam1]

There is no shame in using Loctite, a very good and proven product. Used in many Aerospace applications.What's a .0005 radial gap to fill with something that will not come loose until you want it to.

[dertsap]

Originally Posted by cam1 There is no shame in using Loctite, a very good and proven product. Used in many Aerospace applications.What's a .0005 radial gap to fill with something that will not come loose until you want it to.

it's far better than having too tight of a fit , but a .0005 gap is a lot and probably best to avoid


the red loctite " bearing and retainer compound " is pretty good stuff , got to beat on it pretty hard with a hammer to budge the stuff , they also have a permanent compound that is black ,there is no getting that stuff apart without breaking something , ive used it only once but it impressed the heck out of me
even if you do get a good size for a nice press fit i would suggest using a little compound for the added assurance

[cam1]

It is a steam engine.......In my last life I was a heavy equipment mechanic, and we used that product alot of times on bearings that had spun on shafts and never had a problem with using Loctite. I agree that a light press fit would be desirable at the running temperature of the engine, however if the reaming or boring job were to go sour ,point, then the "can of goop" solution is viable.

regards

[Belding]

Thanks guys,

I will go for a light press fit- .4995 reamer
and if I don't get it I will use locktite.

zac

[cam1]

OK, so we whipped this horse to death.
Go with a .4996 (ha ha)

cheers