How tight is too tight to lock down a tailstock?

[strantor]

A smart-ass might say "so tight that it breaks."

I might be that smart-ass. I have quantified exactly how tight is too tight. It's "normal tight" applied with a wrench that's about 6" longer than a "normal wrench."

I was trying to turn between centers without a lathe dog, with the work just held by pressure from the tailstock. The radius was small and it was working just fine with light cuts. Then I got impatient, wanting to take deeper cuts, but the tailstock was sliding back when I applied the needed pressure. So I added pressure. No more than felt reasonable, I didn't feel like I was reefing on it any harder than I have in the past. But then there was a pop and the tailstock bounced back and the workpiece fell out.

I snapped the cast piece that goes under the tailstock and clamps upwards against the bottom of the bed. My root cause analysis turned up the fact that I was not using my normal 6" wrench, but one that was about twice as long, and I probably had some trash in there that prevented the bottom piece from making good contact so I was wasn't just pulling on it, but trying to turn it into a Pringle.

I repaired it with super glue (seriously) and drilled/tapped a couple of 1/4-20 bolts through it. Haven't tried it yet, but I think if I dedicate a 3" wrench to tailstock duty it should hold.

Oh yeah, and here's a pro tip for if you ever break your tailstock clamp and try gluing it back together: a yuge c-clamp can secure your tailstock while the glue dries.

 

[TorontoBuilder]

a smart ass may also say you need a bigger lathe. I've never heard of this happening on a 33" x 80" tarnow

 

[strantor]

a smart ass may also say you need a bigger lathe. I've never heard of this happening on a 33" x 80" tarnow

Yeah, that hits close to home. I have a bigger lathe (18"x80", with removable gap to get 26" swing), I just haven't made time to get it operational. I keep buying tooling for this little guy because it's my only working lathe, instead of building up the cache I'll need for big guy. I'm wasting my time and money in more ways than I like to admit.

 

[Manual Mac]

glue??

 

[Just for fun]

A smart ass might say "Tighten to the point just before it breaks"

 

[Aukai]

Copy it with real steel.

 

[Aaron_W]

Curious what the lathe is. My first thought was something really small, Chinese mini-lathe or maybe an Atlas 6", but what I see in the photos looks more substantial like a vintage 9" or 10" South Bend or Logan maybe? Certainly makes breaking it that way even more surprising.

 

[strantor]

Copy it with real steel.

Yeah I will if my bandaid and bubblegum patch doesn't hold.

 

[strantor]

Curious what the lathe is. My first thought was something really small, Chinese mini-lathe or maybe an Atlas 6", but what I see in the photos looks more substantial like a vintage 9" or 10" South Bend or Logan maybe? Certainly makes breaking it that way even more surprising.

Logan 9", not sure of vintage, I believe it's from the early '60s.

I just torqued head bolts last week with a calibrated torque wrench so I have valid de-facto calibration cert on my right arm, and according to its muscular strain gauge the thing broke at around 30ft-lbs. I was surprised too, still am.

I think something had to have been jammed in there to upset the balance of forces and make it break. I'm sure I've put more torque than that on it before and it didn't break.

 

[strantor]

glue??

Yeah, super glue (CA glue). It probably won't help; if it holds, it will be the bolts holding it, but putting the glue on there was an added step that let me feel like I did everything I could to keep it together.

On the other hand, super glue has been known to be sufficient for temporarily holding workpieces to faceplates and such, so, ... maybe it was worthwhile? Yeah, I'm going to go with that. It was totally worth my time.