Thread: Shaft clearance

Hi David,
A good rule of thumb is 0.001" per 1" of shaft diameter for bronze bearings.
It would pay to look at the 'Limits, Fits and Tolerances' charts to gauge the type of fit you are after.
I would look at building the shaft up with weld rather than bronze. Try to keep the shaft and bearing as dissimilar as possible.

Phil

Like this
Limits_and_Fits11.jpg

Would applying heat to the shaft risk distorting it? Or weakening it?

Would you be boring out the bronze bearings and bushing them? That is something I myself would probably do, as I expect they are now egg shaped...

You can buy plain bronze bushes if they are a standard size..

I can't understand why you would want to build up a shaft, with as little wear as that, to suit well worn bearings.

Nev.

Originally Posted by SurfinNev

I can't understand why you would want to build up a shaft, with as little wear as that, to suit well worn bearings.

Nev.

Good point Nev,
I should have read that properly.
I would just replace the bushes David.

Phil

Hi David,
How big are the bearings? I probably have some LG2 here that would suit, depending on the OD and thickness.

Cheers,
Ew

Originally Posted by Steamwhisperer

Hi David,
A good rule of thumb is 0.001" per 1" of shaft diameter for bronze bearings.
It would pay to look at the 'Limits, Fits and Tolerances' charts to gauge the type of fit you are after.
I would look at building the shaft up with weld rather than bronze. Try to keep the shaft and bearing as dissimilar as possible.

Phil

Like this
Limits_and_Fits11.jpg

Hi we all run here 0.002 per inch half a thou a side for lube is a bit on the marginal size especially round here the cockies are a bit light on for oil cans grease guns re babbbits on vintage engines usually 0.0025 -0.003'' per in that was in the days of thick treacle oil now with modern multi grades a lttle loose. 0.02cents worth John.
One thing one would presume that those bronze inserts be the split type cast iron housings.old trick was to reduce the ovalility and resize the bore diameter been a poor practice over the years with may a good engine rooted by ''ham fists''.

Originally Posted by Steamwhisperer

Hi David,

Limits_and_Fits11.jpg

Thanks for that table Phil, I was wondering about how to calculate diameters for shrink fits, and there it is!

Regards
Ray

Phil
I know I have said it before, however your mention of "Thous" & half thous" is something I understand & is very meaningful to me.
Are there others out there who think the same?
regards
Bruce

Originally Posted by Abratool

Phil
I know I have said it before, however your mention of "Thous" & half thous" is something I understand & is very meaningful to me.
Are there others out there who think the same?
regards
Bruce

Showing our age . I am happy to use both metric and imperial but I visualise in imperial. Half a thou is instantly clear to me but .02 mm requires some thought.

I am currently using an imperial lathe which came without a cross slide wheel so I had to make one. I cut a shallow groove to fit a 375mm length of stainless metric tape measure for markings. This means that 3cm on the tape equals 1 thou movement. I machined the handwheel to suit this length. The handwheel from this lathe is actually on the new lathe but luckily it still has its metric dial intact. Just the wheel got broken by the previous owner of both lathes, my work.

Dean

Originally Posted by RayG

Thanks for that table Phil, I was wondering about how to calculate diameters for shrink fits, and there it is!

Regards
Ray

No worries Ray,
I could probably rustle up an imperial one if you like

Originally Posted by Abratool

Phil
I know I have said it before, however your mention of "Thous" & half thous" is something I understand & is very meaningful to me.
Are there others out there who think the same?
regards
Bruce

Hi Bruce,
did you notice that table is in metric? I did that on account of how this new fangled metric stuff seems to be taking off
Give me imperial anyday

Originally Posted by Oldneweng

Showing our age . I am happy to use both metric and imperial but I visualise in imperial. Half a thou is instantly clear to me but .02 mm requires some thought.

I am currently using an imperial lathe which came without a cross slide wheel so I had to make one. I cut a shallow groove to fit a 375mm length of stainless metric tape measure for markings. This means that 3cm on the tape equals 1 thou movement. I machined the handwheel to suit this length. The handwheel from this lathe is actually on the new lathe but luckily it still has its metric dial intact. Just the wheel got broken by the previous owner of both lathes, my work.

Dean

I know exactly what you mean Dean. I can visualise imperial and have to stop and convert metric back to imperial so I know how much I can expect to be taking off.

Thank goodness, I was beginning to think that I was the only person in this world who just cant hack the metric stuff.

Eddie

Originally Posted by TKO

Thank goodness, I was beginning to think that I was the only person in this world who just cant hack the metric stuff.

Eddie

We were born in the wrong era Eddie, although we are both clearly from different era's.

My father, had he been alive would be 89 this year. He actively converted to metric with a calculator, remembering all the conversion factors or looking them up. He did this for all sorts of things such as a figure he read in the paper and used to tell whoever was around. I believe this was his way to keep up in a changing world.

Spare a thought for the modern generations and the trouble they would have converting back to imperial and then trying to understand the answer. I think I am fortunate to have gone thru the conversion to metric during my schooling years.

But I still mostly visualise in imperial. Up the empire!

Dean

Originally Posted by Oldneweng

We were born in the wrong era Eddie, although we are both clearly from different era's.

My father, had he been alive would be 89 this year. He actively converted to metric with a calculator, remembering all the conversion factors or looking them up. He did this for all sorts of things such as a figure he read in the paper and used to tell whoever was around. I believe this was his way to keep up in a changing world.

Spare a thought for the modern generations and the trouble they would have converting back to imperial and then trying to understand the answer. I think I am fortunate to have gone thru the conversion to metric during my schooling years.

But I still mostly visualise in imperial. Up the empire!

Dean

Trained in imperial and metric I think feet inches hp not killer watts. For micro thoughts always relate to 0.040'' equal 1 mm.

A maths teacher at a secondary school here told me teenage kids are dead in the water with fractions. unless they got older parents who care and take the time to home teach kids they the majority are lost they think in multiples of ten.
Music uses fractions when written.
He also told me that most entry exam maths questions always have fraction problems.or the obvious reasons.
Old heads are hard to readjust but in reality tens are an easy figure to work with. Cheers.

Thanks for lots of replies. Rule of thumb fits good guide, thanks. The bronze bushes are flanged both ends (my TAFE machining and fitting book calls them combination bearings). They are split and cast about 100mm long and exterior is hex shaped to lock into hex shaped housing. Bearings worn nearly round - 38.32mm in direction that takes most thrust and 38.00 in direction that takes least thrust. So only 0.02mm out of round (that is a whisker less than a thou out of round, thou being 0.0254mm exactly). I have to turn the shaft down as it is really badly scored - I guess at least 0.5mm. That makes the shaft well undersized. I propose to rebuild shaft as I am assuming that replacement bearings to fit these housings hard to get (saw is 1950's). I toyed with idea of building up with arc weld - would be easier for me - will pre-heat shaft and stitch slowly to avoid too much localised heat. Hopefully not bend shaft that way. Once have shaft re-turned, will bore out bearings to smallest to 38.32mm which is size of most worn dia.