Acceptable thread tolerance help plz

[Piero]

Hi guys

Looking for a little help
I do own a machinery handbook but reading/understanding it is not my strong point

I have just purchased a motorcycle crankshaft.

I paid a lot off money for it as it was supposed to be one off the best

Unfortunately, I am not happy with the treads

The supplied nut for the clutch side slaps around too much for my liking.

I would like to verify it the threads are acceptable or not

I've never had to do this before.

 

[Erie Fred]

Try another nut ?

 

[Kram]

Unfortunately, I am not happy with the treads

The supplied nut for the clutch side slaps around too much for my liking.

I would like to verify it the threads are acceptable or not

Are they the same thread? What thread is it? Jt was supplied with the nut?

Can you get a better photo.

Measure it using the 3 wire method to tell you precisely how good the thread is. You can use any set of three identical wires, ~0.9 - 1mm is a good size. Drill blanks or the shaft of small drill bits, can work, provided they are the same.
Or 1mm tungstens..

 

[Piero]

The crank came with the nut

The size is 14mm 1.5 pitch

I have thread wires but I've never used them and I can't work out the instructions

In my machinery handbook, it does state for a m14 1.5 on a outside thread the min and max off the major sizes

The book says 13.968 max 13.732 min

I am at (see pic)

 

[Bouledogue]

Use your thread wires, as @Kram suggests. There are no doubt several Youtube videos on how to do it, but it isn't complicated. Just put two on one side and one on the other and measure across them. It helps to have been born with six hands, but I just use a piece of bluetac.

If you are unhappy with the result, either send it back or - if the rest of the machining is OK - make yourself a custom nut precisely to fit the threads. Just keep cutting and trying until it goes on.

 

[Smallfry]

Apart from the size, that thread looks very roughly finished, like it has been cut by hand

 

[Piero]

It does look rough

I will do the pin gauge measurements and report back

 

[Seadog]

Hi guys

Looking for a little help
I do own a machinery handbook but reading/understanding it is not my strong point

I have just purchased a motorcycle crankshaft.

I paid a lot off money for it as it was supposed to be one off the best

Unfortunately, I am not happy with the treads

The supplied nut for the clutch side slaps around too much for my liking.

I would like to verify it the threads are acceptable or not

I've never had to do this before.

The nut should be a nice close fit.

 

[Piero]

It wobbles more than I do after a long night on the beer

 

[Piero]

OK

Here's my results

In the pin gauge chart, it says to use .040 pins for a 1.5 pitch thread

See photos for results plz

Can and one please tell me what the pitch diameter is ???

 

[Bouledogue]

I get 0.501" / 12.725mm, but I am in a tractor so may have erred.

 

[E T]

I get 12.719 using the constance table that came with my set thread wires.

 

[Bouledogue]

I get 12.719 using the constance table that came with my set thread wires.

The slight difference between us will be due to my rounding error when going to inches and back again.

I believe this is undersized, is it not (have no tables to hand)?

 

[Piero]

My thread pitch pins says constant for 0.40 pins is 1.7490 in mm and .06886

See images

I'd like to understand what the maths are plz

 

[E T]

Substract the constant from your measured value and you get the pitch diameter.
Yours is way to sloppy. M14x1.5 should someting like 13mm I think.

 

[Bouledogue]

The following data-sheet shows the formulae, if the maths interest you.

https://www.threadcheck.com/technical-documents/thread-measuring-wire-formulas.pdf?srsltid=AfmBOop9d-KyL8K6cQ7bQ1awZTzPZZ-XKmEe-muI0sY-BLNanOVLEAlR

 

[E T]

6h tolerance M14x1.5 external thread should be 13.026-12.886mm pitch diameter.

 

[Piero]

This is my machinery handbook reference for a external thread

 

[Piero]

My book says for external 12.994 to 12.854

 

[Bouledogue]

My book says for external 12.994 to 12.854

Yes, that is the 6g (external) standard. @E T has also given you the standard for your nut: the 6h internal standard.

Either way, your external thread is a little under-sized. The nut might also be over-sized.