Sacrificial pin

[Bernard StartParticipant @bernardstart12493]

Sacrificial or shear pin.

Hi everybody I have made a stupid mistake on my Amabl250Fx550 lathe.

I have driven the saddle under power into the head stock. Ouch!!

The leadscrew pin has sheared and I hope no other damage.

The debris looks like the pin was brass 3mm dia. 21mm long.

Any comment Please before I make a new one.

Is it any old brass or are there any special methods or precautions.

Thanks and best of these times to everybody.

Bernard

[noel shelleyParticipant @noelshelley55608]

Try magnet on the wreckage. If nothing happens, and it looks like brass use 3mm brass rod. If it breaks too  easily then try one of the stronger copper alloys. Noel.

[SillyOldDufferModerator @sillyoldduffer]

I used any old Brass, and it’s fine.  You don’t want anything too strong because, in the event of a crash, shear pins have to break before the machine is damaged.  Steel is asking for trouble.

Also, avoid soft metals like Aluminium alloys.  Their problem isn’t lack of strength, it’s that they tend to distort and stick in the hole when the remains are knocked out so the new pin can be fitted.

Isn’t it wonderful that a lathe can make the parts needed to fix itself!

Dave

[Harry WilkesParticipant @harrywilkes58467]

Dave in a previous life I had the pleasure of keeping an old Binks chain on edge conveyor going it was old and worn out (just like me). When we loaded it with the heavier brake discs we sprayed it would often take the shear pin out so when we turned up a new one out of brass we would do around 20 and hang them up in a bag next to the drive 🙂

H

[Howard LewisParticipant @howardlewis46836]

Having done something similar, which bent the drive shaft and the integral gear, found that the Leadscrew and Feedshaft were secured with rollpins, by the factory!

(It started life with a 2 hp single phase motor but was fitted from new with a VFD and 1.5 hp three phase motor).

They were replaced by 5 mm brass shear pins, with a 2.5 mm hole drilled through, to weaken them.

Howard

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