Roll pins

[steptoe]

Is there such a thing as a generic, or minimum, shear strength of a roll pin for a given size,?

I have a machine with a (circa) 5mm rill pin inserted, I'm not sure if its actually suitable, it certainly isn't original fitment ,

I would hazard a guess its putting up with near on 30ft/lb,

supported in centre (maybe 45%) and each end (25% each?), under stress .

 

[Sidewinder]

More details mate.

It can be calculated.

Now is it for example a shaft with a coupling over it IYKWIM?

With the pin through the two?

If so it is in quadruple shear.

You can measure the wall thickness of the pin and look at what the typical shear strength of spring steel is, then you can calculate an approximate shear failure load.

This will however, be related to the velocity, acceleration & jerk.

So, you would need the load time/velocity profile for the load.

 

[steptoe]

Ok, 

Its a slow steady smooth progressive loading, until no load, 

The best way I can describe is like one eye of a suspension/shock absorber, mounted between an eyed fork, so the load would (should) be evenly spread across the two ends of the pin.

I went to repair it last week, it was just a bit of bolt that had been used previously, all I had was a box of mixed roll pins from halfords.

I thought at least that would be better than a 5mm bolt.  

 

[apprentice87]

Hi Steps,

This might help...

http://www.spirol.co.uk/library/main_catalogs/SPIROL-Coiled-Spring-Pins-Design-Guide-us.pdf

john..

 

[Sidewinder]

John,

I'm going to go with it being a slotted pin rather than a coiled pin.

Ok, 

Its a slow steady smooth progressive loading, until no load, 

The best way I can describe is like one eye of a suspension/shock absorber, mounted between an eyed fork, so the load would (should) be evenly spread across the two ends of the pin.

I went to repair it last week, it was just a bit of bolt that had been used previously, all I had was a box of mixed roll pins from halfords.

I thought at least that would be better than a 5mm bolt.  

You have more cross sectional area of material in shear with the 5mm bolt than the roll pin, so it probably has a greater absolute shear strength.

 

[apprentice87]

Hi Paul,

Check out the tables the makers give for the shear strength of the things?? Seems a bit optimistic to me!! But they did not get them in halfords.

What about using a bit of 5mm silver steel??? It comes tempered so is not brittle..

[Could always get a proper parallel pin though!!]

john..

 

[steptoe]

http://www.halfords.com/webapp/wcs/stores/servlet/ProductMobileDisplay?storeId=10001&productId=256927&srch=roll+pin&categoryId=310504&langId=-1&catalogId=10151

In case there is a terminology issue

Not what I have, but the same thing, iykwim

Hi Steps,

This might help...

http://www.spirol.co.uk/library/main_catalogs/SPIROL-Coiled-Spring-Pins-Design-Guide-us.pdf

john..

Ye, thanks John, but as SW says,

Different to what I have,

I call them (yours) spring pins, (?)

Terminology is a batch,!!!!   :|

 

[steptoe]

John,

I'm going to go with it being a slotted pin rather than a coiled pin.

You have more cross sectional area of material in shear with the 5mm bolt than the roll pin, so it probably has a greater absolute shear strength.

So would I be better with say a bit of 5.5mm steel and just keep filing it until a sweet fit,?

The 5mm bolt was a bit slappy, held in with tape, its only about 15-20mm long

 

[apprentice87]

Ok then, 7/32 silver steel!! It is 5.556mm

Got a short piece here, 4 inch i suppose?? Will post it to you if it helps

john..

 

[steptoe]

Ok then, 7/32 silver steel!! It is 5.556mm

Got a short piece here, 4 inch i suppose?? Will post it to you if it helps

john..

That would be much appreciated John, if you think that would be up to the job,

And its obviously better than the current roll pin arrangement that is just waiting to break again.

I don't know any engineering places round here, and doubt anyone would be interested in selling me so little,,,

I've rang my mate today, its actually a bit of a heath Robinson contraption made for measuring compression on fork springs to make sure its a close (ish) matching pair.

He says about 12mm long, and thinks just over 5mm diameter, but hard to measure with the roll pin still in place.

 

[Sidewinder]

To be honest, I'd taper ream it & fit a 5 or 6 mm taper pin.

@steptoe, @apprentice87, John, I have taper pins I can send Steptoe, & I can loan the taper reamers out.  @steptoe?

What do you say?

 

[apprentice87]

I would agree, a taper pin in a suitably reamed hole wold be the best solution by far..

john..

 

[Sidewinder]

@steptoe, pins & reamers here waiting for you to say what you need.

Got to sort it out by tomorrow as I'm away all next week.

24 lg starts @ 5 mm & goes up to 5.46, 30 lg goes from 5 to 5.58, 40 lg goes from 5 to 5.77.

You can cut them down.

 I also have 6's

6x30 goes from 6 to 6.58.

The taper angle is the same, 1 in 48 or 50 I can't remember exactly now.

Just let me know, I have a padded bag here to send them in.

 

[steptoe]

@steptoe, pins & reamers here waiting for you to say what you need.

Got to sort it out by tomorrow as I'm away all next week.

24 lg starts @ 5 mm & goes up to 5.46, 30 lg goes from 5 to 5.58, 40 lg goes from 5 to 5.77.

You can cut them down.

 I also have 6's

6x30 goes from 6 to 6.58.

The taper angle is the same, 1 in 48 or 50 I can't remember exactly now.

Just let me know, I have a padded bag here to send them in.

View attachment 7746

View attachment 7747

Much appreciated @Sidewinder

I'd say 5.46 is plenty,

I dont have a lot of 'meat' to be able to take much out tbh

I think you have my address,,,,,,,,,,

is it 5.46 small or large end?

 

[Sidewinder]

Large end, small end is a few hundredths down on 5mm.  If it's only 5 you need then I'll only send the 5 mm reamer.

How many 24mm lg pins?

Do you have a tap wrench?

 

[steptoe]

I only need one pin,

might be an idea then to send the next size up one, the 5.58 one

yes, i've got a standard tap wrench.

 

[apprentice87]

Taper is 1 in 50 for a metric pin and the nominal diameter is the small end..

Imperial pins are 1 in 48 and the nominal diameter is measured at the large end..

john..

 

[Sidewinder]

I only need one pin,

might be an idea then to send the next size up one, the 5.58 one

yes, i've got a standard tap wrench.

OK no worries, I'll send both if you want, you can cut them down.

If you need to you can ream the hole out until the reamer is cutting full length of the hole, then drop the pin in, loosely, mark it, cut it to length, then brae it in.

John has given you the sizing data above.

Can you get in with a standard tap wrench?

I'll measure the reamer square after dinner & post it up, it will be about the same size as an M6 tap I suspect, but, I'll check & let you know.

 

[steptoe]

yes,

I have plenty clearance to access it,

its almost in free air, so to speak,

much appreciated guys,

I've prob only got about 5mm material left after the hole, so dont want to take too much out of it, IYKWIM

 

[Sidewinder]

Square on the 5mm taper reamer is 5mm, so the same size as an M6 tap.

So as long as your tap wrench will do an M6 tap, then fine.

You have email too, or will have shortly...