Todays Project - What did you do today?

[Mayhem]

Ken - that is almost how the end of the thread on the knee elevation screw looks on my mill. The top part of the thread in the nut is chopped out and I can only think that the knee was raised so the screw disengaged from the nut and then all hell has broken loose on the way down. I should take a picture of it. Last thing I want to do is wreck a new nut.

[PixMan]

Darren,

Flatting off the first thread at the point where is becomes "full profile" (beyond any leading chamfer) is called a "Higbee". I have no idea what or who that actual name or term relates to, but it's commonly used in armament breeches to afford positive engagement of two mating threads. A normal Higbee start would be blunt. On mine I tried to make it a little positive and sharp so it would act almost as a tap.

If yours is more like mine someone may have tried to do just as I did. Why, I have no clue. You should smooth it out if it's sharp.

[dallen]

made a set of training wheels for a friends plasma torch

   

[Hawkeye]

In firefighting, a Higbee Notch is a notch in one of the wrench tabs on each hose fitting. When you line up the two notched tabs and turn the fittings, the threads engage immediately. I had assumed that was the whole history, but I can see it originating with breech-loading artillery.

[Mayhem]

(01-20-2014, 11:28 AM)PixMan Wrote: ...someone may have tried to do just as I did. Why, I have no clue...

I've given up trying to figure out why (or how) someone abused this machine prior to me acquiring it. Either it was an machinist who didn't give a rats arse about his equipment, or someone who fancied themselves as a machinist but suffered from delusions of adequacy.

I think it is just more abuse but if I remember, I'll take a photo.

[Mayhem]

Nope - its abuse

   
   
   

[PixMan]

Good grief, that's mangled. It looks like the thread had only about 50% engagement for the time it was working. The thread form on the left hand screw doesn't look too good, and of course that last thread would need to be cleaned up.

[Mayhem]

What would cause the undercutting on the thread? I'm at a loss to understand how this happened. I noticed that Y-axis screw was the same. I forgot to check the X-axis. I wouldn't have left the factory like that would it???

How would you go about cleaning off the end? Should I grind it so there is a full profile on the end or taper it?

[PixMan]

Probably just excessive wear combined with a low rate of thread percentage for engagement. Looks like it was poorly lubricated.

The end of the thread appears to have been torn off. I don't know if the weight of the knee is hanging on it (doubtful) but perhaps when someone tried lifting the knee off the screw before it was fully disengaged from the nut that would have done it. You could just grind it clean to give it a good start without mashing a new nut. Truthfully I'd be looking for a new screw as those thread look beat to crap.

[Mayhem]

Thanks Ken - After I clean up the last thread, would the rest of the thread damage the new nut? If so, I may put it together with the current nut (of which the bottom 50% of the thread is OK). I could then make up a new screw (I would need the mill to cut the key slot).