Machining tolerances

[BelgiqueB]

I need to have a shaft machined for a SKF pillow block, the bearing in the block is 22214E type and according to SKF the shaft (70mm) can have a dimensional tolerance marked m6, however I can't find how much exactly m6 means.

Trying to wrap my head around how the tolerance system works and starting to understand the shaft/hole tolerance system, but I can't find any reference to m6. Could someone point me in the right direction where i could find more info on this?

Thanks.

 

[waddycall]

This table has it as +30/+11 I think as it’s lower case
https://simplybearings.co.uk/shop/Seals-Info-Pages-ISO-Limits/c19_4746_4779/index.html?page=1

 

[Brad93]

You’re not going to hit that kind of tolerance easily, depending on what lathe you have. 70mm +11/+30 microns (70.011 - 70.03mm)

in inches, is 0.2756” + 4 tenths / + 11 tenths.

You’re talking about tool room accuracy.
The best you can do is get 0.276” then emery cloth to take off a few tenths.

If you have a nice DSG or a Holbrook or other sturdy tool room lathe discount my comments above.

 

[Kram]

Its easy enough. Id get it to +0.2mm and take a few passes with a light finishing insert, just takes a bit longer and more measuring.
Tool room lathe might do it in a single deep cut, good if you have a lot to do, but it can be done on any lathe without emery.

 

[Arc Tourist]

When machining to tenth's, temperature comes into play. The final few thousandths or tenths should be removed when the machine and the work have cooled down to ambient temperature, otherwise the part will most likely be undersized.

 

[Johnnybravo]

Taking pissy little cuts to try and finish is a total waste of time. You get a crap finish, the tip starts to rub, nothing happens, nothing happens, nothing happens. Oh ********, it’s undersize. I always subscribe to a finishing cut about the same as the radius of the tool.All roughing and finishing done with coolant so the part doesn’t get hot and turn out undersize because it needed to cool down.

 

[Seadog]

Setting the compound at an angle also allows finer cuts to be set even though the movement on the slide is relatively large.

 

[Arc Tourist]

Using a tool post grinder would be my first choice.

 

[Johnnybravo]

Using a tool post grinder would be my first choice.

Quickest way to ruin a lathe

 

[8ob]

Quickest way to ruin a lathe

Oh feck

I don’t know what the application is here but most of the gear we have that run shafts/bearings that size need the use of an induction heater to get the bearings on the shaft, gas axe is normally used to remove them. Shaft finish is important , won’t take long for a bearing to bed into the shaft leaving it sloppy if it’s as rough as a pipe thread to start with.

Bob

 

[Brad93]

Taking pissy little cuts to try and finish is a total waste of time. You get a crap finish, the tip starts to rub, nothing happens, nothing happens, nothing happens. Oh ********, it’s undersize. I always subscribe to a finishing cut about the same as the radius of the tool.All roughing and finishing done with coolant so the part doesn’t get hot and turn out undersize because it needed to cool down.

Out of the horses mouth from an actual machinist.

With all respect @Kram you’re running a chinese benchtop lathe, taking light cuts is not the way to get a shaft to size, you’re just going to put a crap finish on.

Most of my finishing inserts have a nose radius of around 0.4mm that’s the depth I’d aim to cut.

Having a look on Cutwel there are some 0.2mm nose radius inserts.

 

[Seadog]

 

[AndersK]

Why do you assume a lathe to be used for final finnish?

 

[Arc Tourist]

Quickest way to ruin a lathe

Perhaps by others.

 

[brightspark]

id only do it if i had to. then cover the lot with cloth and masking tape

 

[waddycall]

Taking pissy little cuts to try and finish is a total waste of time. You get a crap finish, the tip starts to rub, nothing happens, nothing happens, nothing happens. Oh ********, it’s undersize. I always subscribe to a finishing cut about the same as the radius of the tool.All roughing and finishing done with coolant so the part doesn’t get hot and turn out undersize because it needed to cool down.

When I had my small ancient lathe I used to take very fine finishing cuts using a hand ground HSS tool that was set to rub lightly. It’s a technique I read in LH Spareys book The Amateurs Lathe. It always worked well for me. Do the comments above also apply to HSS tooling or is it more relevant to insert type tools? Just curious.

 

[Brad93]

When I had my small ancient lathe I used to take very fine finishing cuts using a hand ground HSS tool that was set to rub lightly. It’s a technique I read in LH Spareys book The Amateurs Lathe. It always worked well for me. Do the comments above also apply to HSS tooling or is it more relevant to insert type tools? Just curious.

A shear tool

comments above relate to insert tooling

 

[mike os]

Turn to within 0.02, finish with emery paper or very careful application of a smooth cut file when cool.

Trial fit rather than measure

 

[Johnnybravo]

When I had my small ancient lathe I used to take very fine finishing cuts using a hand ground HSS tool that was set to rub lightly. It’s a technique I read in LH Spareys book The Amateurs Lathe. It always worked well for me. Do the comments above also apply to HSS tooling or is it more relevant to insert type tools? Just curious.

Carbide inserts.But you will find you are more likely to chip any tool with a small cut rather than with a relatively large cut. With slightly larger cuts the tip of the tool is better supported so less likely to chip.Getting it to rub slightly adds to the support of the tool but it’s not something that lasts very well. Nothing worse than trying to chase the last couple of hundredths on diameter and your tip is now past it’s sell by date/ rubbed away!

 

[ronan]

If its just a shaft going into a standard ball or roller bearing, then don't over think it. What is the actual job ?