Hi. I needed a wrench for my lathe chuck - 1/2" square drive. I took some 1/2" square, took one end down to 1/2" round, cut some 1/2" -13 threads on it and added a brass handle. I used threads because I wanted the brass handle, and the brass I had didn't really like being forged - sort of crumbly. 

 

So, my problem now is locking the threads. I considered using picture, I suppose I may jut do that, but I am wondering if a mechanical lock might be better? A keyway or something, perhaps? Wanted to know what some of you thought, curious for ideas. I don't want to go too crazy,just something that will lock but still be able to be removed if it needs it. 

 

I attached a picture: I still need to remove the top portion, for obvious ergonomics, though I was considering a cap nut with a saddle, so I left it. 

 

 

KISS?

Consider making it the conventional way. Design for its mechanical function rather than ease of construction. Avoiding filing the square drive accurately by using the 1/2" square is not the best starting point.

Use a heavier piece for the key or upset your half inch bar and put a hole through it to take the brass, or roll an eye on the end of the 1/2" to take the brass...That way the mechanical advantage is how it needs to be. The rotary drive is taken through a solid construction.

Your solution, as pretty as it is, is trying to impart torque by locking an ordinarily rotating system...not sensible engineering.

You might be able to lock it sufficiently with a lock nut, but as soon as you try using it you are likely to impart more torque through it than was used to lock the nut so it will never be solid.

From where you are now...in order of least work first:-

You could silver solder or braze it.

You could drill down through the threads and put in a roll pin or grub screw to act as woodruff key.

You could file the hole in the brass square and fit and rivet the steel into it. You do not need to make the brass hole square...just one corner would be easier, and round off three corners on the steel tenon.

Alan

well, i did keep it pretty simple. it's only a light duty wrench for the lathe chuck - i highly doubt it'll see more than 40lbs of force. I like your grub screw through the threads idea - that may work. i needed to be able to detach it for now so that when i get my new backing plate for this chuck, i can turn the brass handle down into something a little bit nicer. once i do that, i suppose i may just braze it. 

thanks for the ideas 

Its the light duty bit I was concerned about...last week I was cutting a thread on a bit of Ø20mm 316L stainless using a die stock and the lathe in slow mo. I was really having to lean on the chuck key to prevent the stainless from slipping in the chuck with the load.   Shiny hard material, small diameter, high torque operation, self-centring four jaw chuck...all things contributed...but it is not the only time I have had to heave on the key to the maximum of my strength.

You alone know exactly the use you have in mind for it so a lock nut may well be adequate...but you have created a problem that needs solving rather than designed the piece to avoid that problem in the first place!

I had to replace the drive wheel on a trommel for the community composting scheme recently. It was a rubber tyred wheel direct driven by the motor spindle. I had to push out the roller bearing it came with and replace it with a solid sleeve...Ø50mm (Ø2") OD and Ø25mm (Ø1") ID. I keyed the wheel to the sleeve and the sleeve to the axle by drilling along the joints and tapping for grub screws/drive keys. Much stronger than a pinch bolt at right angles to the axle. 

Alan

I have a number of chucks requiring various square drive keys......I use a square drive ratchet and appropriate reducers, I'd use a tommy bar and extention but don't have one handy! Yes at some point I will make myself a set to match each chuck.

What came to my mind was taking a nice long extension for a 1/2 drive ratchet and heating it in the forge and bending it into an L.  To make a pretty brass handled T I would have drilled and then filed the hole in the brass into a square and then forged the tang of the shaft into a matching square and seat it in the brass, Trill to length and then rivet the end of the shaft down onto the brass.

Pretty small lathe if 40'#s  is enough.