How to replace the leadscrew shear pin on a metal lathe

[@KatyLynnWinery]

I appreciate your video. I am knew to the lathe about 4 months. I broke the shear pin this weekend and hoped I had not torn things up bad. I get it. Thanks.

[@keldsor]

Hi Rob ! Nice instructional video for people with that kind of leadscrew - well told and showed, I think ! Fortunately I have a leadscrew with a ball bearing clutch - unfotunately it's "open", but as long as you're holding it clean you should never run into a broken shear pin there, I beleave. I envy these leadscrew cover of yours - I've seen them before and investigated my lathe but it's too complicated to put them on mine ... so I'll just have to envy you ;-(( !

[@Xynudu]

Thanks Keld. It's a simple video, but hopefully it passes on some information on the subject. Your lathe clutch is a better idea for sure, but on small lathes it probably gets a bit difficult to fit. The covers are great, but restricting carriage travel is a downside. Cheers Rob

[@AmateurRedneckWorkshop]

G'day mate. Nice demonstration of pin replacement. My old flat bed lathe is not fancy like yours and does not have a shear pin instead it has a slip clutch so I can wreck it and it just slips then afterward their is no pin to replace. Keep on keeping on.

[@springwoodcottage4248]

Super useful video. Had I had a shear pin I probably would not have had to buy a new half nut when I had my crash. Unfortunately I don't have the excuse of a screw cover, so like today when I pulled a knife towards me and needed plasters when it slipped, I have to accept it was my stupidity.

[@Xynudu]

We all have those days. Something in the brain cells goes a bit wonky at times. Cheers Rob

[@iancraig1951]

Rob halfway through the video I raced outside to have a look at the two lathes I have---the little hercus doesn't appear to have one the hafco does but i have never busted a shear pin not ever and I hope that continues...I like all machinists hate crashes...Nevertheless a timely video...Regards E

[@Xynudu]

Hi Ian, Get some lead screw covers and I can say a crash will not be far away :) They are good, but have a major effect on critical carriage travel close in. The video I hope, shows just how important and simple a shear pin really is. A basic, safeguard that every lathe should have. Cheers Rob

[@turningpoint6643]

Yep a spring steel roll pin used as a replacement for a proper shear pin would be costly in parts. But not all lathes use brass, bronze, or mild steel shear pins. My small lathe is an Emco compact 5. They come from the manufacturer with aluminum shear pins. Smaller lathe, lower strength to the parts, so lighter breaking forces are needed.

[@aceroadholder2185]

Yes do get rid of roll pins and plain steel shear pins. Asian bench lathes are bad to be equipped with roll pins. Note that for some lathes there is a sketch showing how the shear pin should be made in the operators manual. Some directions call for necking down the shear pin in the two places where the driving and driven shafts interface. This is done because a full size brass or bronze shear pin may not protect the lathe's mechanism from damage. Make a few shear pins for the lead screw and drive rod (if equipped) and keep them in the lathe's tool box so they'll be at hand when you need them. In addition to the shear pins there is another useful addition you might want to make to your lathe. On my 12x36 Taiwanese lathe if you remove the chuck and run collets, the carriage way wipers can be crashed into the head stock and damage them if you aren't careful. What I did was make an aluminum piece out of 1/2 inch plate that bolts onto the carriage where the follower rest usually attaches. It hangs down enough below the carriage between the ways for a 1/2"-13UNC tapped hole through the aluminum. I screwed in a piece of 1/2-13 x ~8" all-thread with a jam nut to secure it in place. I slipped a rubber bumper over the exposed end of the all-thread and adjusted the length so that when the bumper hits the clamp under the head stock the carriage way wipers are just clear of the head stock.

[@juanrivero8]

I have to congratulate the manufacturer for putting in a shear pin in the first place. Not all lathes have them -- then you are in trouble.

[@robgerrits4097]

Would it not be easyer to mount a breakoff switch on the backside of the lathe that stops the motor before things go nasty? Nice Video.:)

[@Xynudu]

Yes that's a good idea. Whether it's easy or not remains to be seen :) Cheers Rob

[@aceroadholder2185]

Adjusting the switch to accurately recognize an overload might be problematic. It would have to be wired into a mechanical or dynamic brake of some sort to get the plot stopped quickly enough to avoid damage. The shear pin is much easier to deal with. Someone noted that they had a lathe with a slipper clutch... If you were shearing pins right and left, building a clutch might be easier than electrical switches. When you hear the clutch jump, you'd know that you were taking too heavy a cut and you need to back off a little. With a clutch you could use a torque wrench to adjust the break-away to suit your needs.

[@Xynudu]

Some lathes have a power cut out switch in the carriage stop (low voltage to a relay). That's another way to do it. Generally this sort of stuff is the realm of large lathes with plenty of room. Shear pins are as simple and compact as it gets. Cheers Rob

[@Mark6E]

Is the shear pin to protect the gearbox, my WM240 has neither. I expect the plastic gear would strip before any damage is done?

[@Xynudu]

Hi Mark, Yes, and also the change gears and their mounts. Cheers Rob

[@Xynudu]

A plastic or fibre gear is sometimes included in the gear train as a safety feature when a shear pin is not fitted. This is OK , but requires a replacement and even a teardown of the headstock on geared head lathes. Some (mainly larger Chinese) lathes have a roll pin in the leadscrew coupling, which could easily be replaced with a bronze pin as a simple modification. Cheers Rob

[@Rolingmetal]

I've seen people cut the lead-screw in half and insert a small adjustable clutch. Then you can leave and just run it up against a carriage stop.

[@Xynudu]

I did investigate that angle, but it would mean no more leadscrew covers, which I prefer to keep. Cheers Rob