Press fit dimensions?

[tevans9129]

For the ignorant, I would think that metals and sizes would play a part in press-fitting one metal into another but my question is, how does one determine what the dimensions should be? As an example, .500 male brass into .500 steel, should the male be .500 or .5005 or what? Thanks for your thoughts and comments.

 

[doc1955]

Proper press fit size depends on the dia size the bigger the dia the more interference you want as far as which causes the interference I would pick the softer metal, now thats just my preference.

 

[RReid]

From my 1920 Machinery's Handbook. Only the most up to date info.

 

[nautilus29]

I'm sure if you looked in the machinery's handbook you'd find some press fit dimensions for different sizes, materials. That being said I think a rule of thumb for brass bushings is .0005 to .001" press per 1 inch of diameter.

 

[nautilus29]

From my 1920 Machinery's Handbook. Only the most up to date info.

Haha well there you go.

 

[SmithDoor]

For the ignorant, I would think that metals and sizes would play a part in press-fitting one metal into another but my question is, how does one determine what the dimensions should be? As an example, .500 male brass into .500 steel, should the male be .500 or .5005 or what? Thanks for your thoughts and comments.

For ball bearing for 1.500 od I using 0.000,2".
But you are press brass to steel are planning in finishing the bore after pressing in to the steel?

Dave

 

[ajoeiam]

For the ignorant, I would think that metals and sizes would play a part in press-fitting one metal into another but my question is, how does one determine what the dimensions should be? As an example, .500 male brass into .500 steel, should the male be .500 or .5005 or what? Thanks for your thoughts and comments.

I would suggest that you obtain a copy of the Machinery's Handbook in an edition say from 24 or so to the new one - - - IIRC 30 (or is it 31).
There are not one or two but likely some about 20 pages of 'fits'. Which 'fit' you use is prompted by what you're trying to do.
If you're pressing stuff together galling can quickly become an issue.
Technique has, iirc, been discussed here more than a few times.
I will admit that I view my copy of Machinery's Handbook as a primary tool not only for the doing stuff but for the theoretical process and design information included.

 

[Steamchick]

Ajoeiam has the right answer. I regularly used the same machinery's handbook, or other Engineering almanac, with the appropriate tables for fits. As I was working on car engines (e.g.) the engine blocks made from cast iron, with steel tubes fitted followed the tables. But when I did some calculations for aluminuim blocks and steel tubes, the fits didn't work. The expansion and contraction difference between steel and aluminium from -30C to + 85C block temperature meant the steel either cracked the block at coldest, or the tube became loose at top temperature. So a sliding fit (at factory 20C) with a dot of loctite cured all evils, when durability tested at the extreme temperatures. (From Cold start -30C in Finland, up to the hottest block temperatures when pulling fully laden going up a mountain pass, with max trailer load, in the Middle East or North African mountains and Saharan temperatures).
But of course you just want the simple answer, so follow the tables.
If using 2 different metals, "choose the fit half way between the 2 figures quoted in the tables" was the crude-rule used in another design office where I worked 35 years ago.... That was for bronze bushes pressed into stainless steel plate, or stainless steel parts pressed into gun-metal castings, -25C to + 70C. - It worked.... Probably the same design technology that Goldstar experienced post stone age, but some modern engineer will have a computer programme to work it out now.

K2

 

[SmithDoor]

I use Machinery's Handbook copyright found 1941 and 1958 was best ones. By 1970's the machinery's handbook had less usable data and harder to find.
Even the Machines books from 1910 has very good data on shapping tools.

I took key copy and enlarge pages out books and put plastic binder for shop uses.

Dave

Ajoeiam has the right answer. I regularly used the same machinery's handbook, or other Engineering almanac, with the appropriate tables for fits. As I was working on car engines (e.g.) the engine blocks made from cast iron, with steel tubes fitted followed the tables. But when I did some calculations for aluminuim blocks and steel tubes, the fits didn't work. The expansion and contraction difference between steel and aluminium from -30C to + 85C block temperature meant the steel either cracked the block at coldest, or the tube became loose at top temperature. So a sliding fit (at factory 20C) with a dot of loctite cured all evils, when durability tested at the extreme temperatures. (From Cold start -30C in Finland, up to the hottest block temperatures when pulling fully laden going up a mountain pass, with max trailer load, in the Middle East or North African mountains and Saharan temperatures).
But of course you just want the simple answer, so follow the tables.
If using 2 different metals, "choose the fit half way between the 2 figures quoted in the tables" was the crude-rule used in another design office where I worked 35 years ago.... That was for bronze bushes pressed into stainless steel plate, or stainless steel parts pressed into gun-metal castings, -25C to + 70C. - It worked.... Probably the same design technology that Goldstar experienced post stone age, but some modern engineer will have a computer programme to work it out now.

K2

 

[Iampappabear]

If you don't have a Zeus book in your pocket you are missing something!!! You will find everything you need on limits and fits all one one page plus all kinds of useful information for the machinist.

As you will see from the image, I have had this one a little while paying a whopping one pound twenty pence for this copy but as it is still in almost daily use for the last 40 years, I guess I got my moneys worth.

 

[Charles Lamont]

Why on earth does anyone need bother going to look it up in a book of tables? This is the simplest of arithmetic that anyone on this forum can surely do in their head?

 

[Steamchick]

Fair comment Charles, but not all heads are the same, nor do they all have the same training. If you would like to share the equations and standards you have in your head, I am sure some of us will agree, and others will have an opportunity to learn. (I.E. me). We mostly join these forums to share our knowledge, and learn from each other. I learn a lot ( as well as spouting a lot of drivel....) but it is good to talk to clever people, who are prepared to share their knowledge and expertise, and often opinions, without prejudice.
Regards,
K2

 

[awake]

Proper press fit size depends on the dia size the bigger the dia the more interference you want as far as which causes the interference I would pick the softer metal, now thats just my preference.

Hmm ... since the interference will be between the two metals, I'm not sure it would matter which one was oversized or undersized?

 

[tevans9129]

Fair comment Charles, but not all heads are the same, nor do they all have the same training. If you would like to share the equations and standards you have in your head, I am sure some of us will agree, and others will have an opportunity to learn. (I.E. me). We mostly join these forums to share our knowledge, and learn from each other. I learn a lot ( as well as spouting a lot of drivel....) but it is good to talk to clever people, who are prepared to share their knowledge and expertise, and often opinions, without prejudice.
Regards,
K2

Amen!

 

[tevans9129]

Thanks to everyone for sharing your knowledge and "opinions". It has finally occurred to me that I need to become more friendly with my Machinist handbook.

 

[tevans9129]

For ball bearing for 1.500 od I using 0.000,2".
But you are press brass to steel are planning in finishing the bore after pressing in to the steel?

Dave

Yes, in one scenario.

 

[ajoeiam]

Hmm ... since the interference will be between the two metals, I'm not sure it would matter which one was oversized or undersized?

It 'could' matter.
The material that is being inserted - - - - if you 'are' pressing it into the out material well if this 'shaft' (I'll call it) has a tendency to gall and is softer than the material its being into then you are far more likely to have issues than if what you're inserting is something more like a 12L14 which really doesn't tend to gall.
So it might not matter which material has the 'added' (to cause the interference) most of the time but I can see instances where it would matter. Collecting this with the common sizing of hobbyist projects and you're less likely to run into issues than when you playing with a 5" dia shaft going through a very heavy attachment - - - - that's when this kind of thing gets very carefully produced - - - - - its not a lot of fun when what you're doing is at last stage of manufacture and it gets foobared - - - - bosses tend to get quite grumpy at those kind of times!

 

[clockworkcheval]

In professional manufacturing designing and producing a good pressfit is complex at best. Materials, elasticity, wall-thickness and surface finish are just a few variables. We hobbyists have the luxury of not being able to make to measure. In Europe a quality 6 tolerance on shafts means a tolerance field of 11 microns up to diameter 18 mm, and 16 microns up to diameter 50 mm. A quality 7 bore tolerance means a tolerance field of 18 microns up to diameter 18 mm and 25 microns up to diameter 50 mm. As hobby machinist we can expect to work to a tolerance of plus/minus 0,01 mm or a tolerance field of 20 microns. Therefore we can not expect to manufacture to the exact required dimensions. And working to a tolerance on a shaft is usually easier than on a bore. The practice in my group therefore is to make to fit: first make the bore, by reaming or boring and/or honing and subsequently making the shaft to fit the bore. We do measure the bore as a guidance, not expecting to get the exact measure. In testing the fit we use the first few millimeters of the shaft as probe before making the final cut.

 

[Steamchick]

Thanks Cheval. Very good information.
Of course, in mass production, bore gauges are often air gauges, or lazers nowadays. Whereas as a hobbyist, I have to use traditional bore gauges (expanding feeler type on my small bores), replicating "the feel" in jaws of the micrometer. I think a tolerance of 0.002" is brilliant for my work! Otherwise, I use the plain shank of drills, etc. and mic those as gauges. Then follow the practice you detail of "sizing the bar" to the bore. - Even down to honing with fine emery to get the last thou of fit. A locking-jaw grip is a useful tool to apply the pressure onto the emery for the fine polishing, or even good quality a adjustable spanner with ground parallel jaws.
K2

 

[ajoeiam]

In professional manufacturing designing and producing a good pressfit is complex at best. Materials, elasticity, wall-thickness and surface finish are just a few variables. We hobbyists have the luxury of not being able to make to measure. In Europe a quality 6 tolerance on shafts means a tolerance field of 11 microns up to diameter 18 mm, and 16 microns up to diameter 50 mm. A quality 7 bore tolerance means a tolerance field of 18 microns up to diameter 18 mm and 25 microns up to diameter 50 mm. As hobby machinist we can expect to work to a tolerance of plus/minus 0,01 mm or a tolerance field of 20 microns. Therefore we can not expect to manufacture to the exact required dimensions. And working to a tolerance on a shaft is usually easier than on a bore. The practice in my group therefore is to make to fit: first make the bore, by reaming or boring and/or honing and subsequently making the shaft to fit the bore. We do measure the bore as a guidance, not expecting to get the exact measure. In testing the fit we use the first few millimeters of the shaft as probe before making the final cut.

Respectfully - - - - I would disagree!!

I have been able to achieve a shaft precision of 0.0000"+0.0005"- on a lathe with an total error range of some 0.023" in the same length.
In theory what you say is correct - - - - but then practice theory is all too often shown to be - - - - well less than correct.
Was this precision easy to achieve - - - - !@#$%^ NO!!! It was very very stressful and very not easy - - - but it WAS POSSIBLE.
This means that the possibility of a quality level is dictated from the 'office' - - - - if the office says you can't do it - - - you'll not even get the opportunity. If the office says you 'can' do it - - - - you've got to haul it out.

If you design using somewhat standard shafting (when shafts are called for) you can easily purchase this nice T & G (turned and ground and sometimes that includes stress relieved and, more rarely, even other features) and it will likely measure between 2 and 3 tenths under nominal and the rating is +0.0000"-0.0005" . It then behooves you to create the bore to your required dimension (hard press, press, interference, sliding and/or running) fit. So instead of requiring machining on 2 surfaces - - - bore and shaft - - - machine 1 - - - it makes life easier and things go faster.
Some would then argue that you can't machine a bearing - - - rightfully so - - - - now you machine the shaft - - - - and its funny that most bearing IDs are just so and give that recommended fit for the bearing on a standardized shaft. This is where that turned and ground shaft, due to its very slight undersize of nominal, is not quite as useful.

IMO hobby machining can be as good as any commercial - - - - if care is taken. Is it always as good - - - - I'd be willing to bet not.
But then I've had to fix enough commercially produced stuff that wasn't up to snuff either so the capability is not always reflected in the reality either.