"soft" roll pins?

[dobbslc]

Is there such a thing as a soft roll pin like an aluminium one?
I broke the teeth off the bevel drive gears to the table on my lathe a while ago and it cost £60+ for new ones!
I nearly did it again yesterday....
I though if I had a soft roll pin connecting the drive though to the table it would act as a sacrificial pin.
Thoughts please.

 

[Maker]

I think shear pins are usually hardened, this way they'll snap rather than bend/deform.

 

[Spark plug]

What your looking for is a shear pin.

But why is this happening, sounds like there is something wrong if your loosing teeth off gears.

 

[Onoff]

I have read that it was common on some school lathes to use brass shear pins where safety was paramount in case of a jam etc. BUT then also that it was a frequent replacement item anyway as the brass would, over time work harden. A bit here too:

http://bbs.homeshopmachinist.net/archive/index.php/t-35143.html

 

[pedrobedro]

We used to have a scrap cutter at a firm where I worked. It was like a shear and used for cutting bar and pipe to fit in the foundry and it had a wooden pin to stop it from wedging solid if anyone got too enthusiastic.

 

[CompoSimmonite]

My old Johnson outboard had a standard split pin holding on the prop that acted as a shear pin. It even came with a "genuine" spare !

 

[gordon stephenson]

As stated above, make one yourself, What diameter is the pin? I think I would prefer to use aluminium etc, If not a solid pin it could be drilled down the centre to give a wall thickness that would do the job.

 

[mike os]

What are you doing to break them?

 

[MattH]

My Cardif lathe specifies a brass shear pin in single shear on the leadscrew.

 

[dobbslc]

What are you doing to break them?

Originally I let the cross slide drive itself to far over so it hit a hard stop and the gears went SCRUNKLE!
It took about 3 months to get new gears at £60!

Yesterday I was machining something up close to the chuck and nearly did the same with the table, I had the piece supported with the tailstock and a dead centre and to get the tool to the end of the part I was making I had to move the tool post close to the the right side of the table this meant the table was too far across to the left.
Lesson learnt now.
The shear pin would at least stop any more smashed gears.
Getting parts for Chester lathes can be a PITA so I don't want to break any more.
I have just had a look at it and could make a stop switch that would kill the motor if I got too close again.

 

[Wendelspanswick]

Originally I let the cross slide drive itself to far over so it hit a hard stop and the gears went SCRUNKLE!
It took about 3 months to get new gears at £60!

Yesterday I was machining something up close to the chuck and nearly did the same with the table, I had the piece supported with the tailstock and a dead centre and to get the tool to the end of the part I was making I had to move the tool post close to the the right side of the table this meant the table was too far across to the left.
Lesson learnt now.
The shear pin would at least stop any more smashed gears.
Getting parts for Chester lathes can be a PITA so I don't want to break any more.
I have just had a look at it and could make a stop switch that would kill the motor if I got too close again.

What about loosening the belt drive so that the belt slips if it all goes tits up.

 

[mike os]

hate to say it.... but pay more attention, crashing machinery like this is going to break something serious sooner or later and may even end up injuring you

 

[Spark plug]

As Mike os says you should stop before the critical point then finish the last little bit by hand.

 

[Robotstar5]

...I have just had a look at it and could make a stop switch that would kill the motor if I got too close again.

Known in the trade as an ultimate limit switch

 

[dobbslc]

Known in the trade as an ultimate limit switch

That's the one I'm thinking about.. It's a last resort to stupidness!

hate to say it.... but pay more attention, crashing machinery like this is going to break something serious sooner or later and may even end up injuring you

Your right, it's happened once and nearly twice. I'm still learning how to work a lathe but sometimes cock it up!

About the belt slip mentioned above, it's run fairly loose but will still do damage as the torque is multiplied many times before it gets to the carriage drive gears.

 

[mike os]

Only problem with limit switch is the inertia. .. machine keeps running for a few revolutions if power is lost unless braked

 

[dobbslc]

True But I'll set it a few mm before the hard stop.