Silver solder, then machine; Warning, beginner content

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R.G.

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My latest scheme involves turning a 5/8" stop on a 12" long 1/4" diameter rod with a coaxial 3/8" thread on the other end of the stop. As a semi-rank beginner, I have serious doubts about my ability to turn a longish skinny rod without massive errors. It's bad enough that I need to turn 1/2" of 3/8" thread. So I concocted the following plan. I'd appreciate any comments on the practicality of the approach.

1. Hacksaw off about 3" of 3/4" diameter mild steel rod.
2. Chuck it up in the 3-jaw, knowing full well that this is not perfectly centered, but as good as I can do without a 4-jaw. Leave about 2" outside the jaws.
3. Center drill the end.
4. Drill the end for 1/2" depth of 1/4"-minus x
5. Turn the diameter to 5/8" for 1/2".
6. Using a parting tool, plunge-cut the shoulder of the 5/8" diameter section 1/8" deep to get down to the major diameter of the 3/8" section to be threaded.
7. Do this several times moving toward the chucks till I get 1/2" of the 3/8" diameter section uncovered, pausing to turn the motor off each time I move the cutting tool and hand-turn the spindle to make sure I'm not going to hit the chuck.
8. Once I get to 1/2" of 3/8" section uncovered, part it off.
9. Unchuck, reverse and rechuck by the 5/8" diameter section, leaving the 3/8" section toward the tailstock. I think this leaves me all the concentricity on the 3/8" threaded section and the 5/8" stop and the 1/4" hole that I'm going to get out of a three-jaw.
10. Thread the 3/8" section.

Here's the question, finally.
That 1/4"-minus hole I drilled - what's my chances that pressing/loctiting/silver soldering a 1/4" rod into that will wind up with little runout? Do/did I need to turn it smaller, turn the 1/4" rod to a smaller diameter and tinker till I get a hard wringing fit? Suggestions? (leave out the one that I give up any thought of doing decent machining; I've already thought of that one myself) Or should I silver solder the rod in first?
 
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Let's see if I have this straight. You want a length of 1/4" rod with an upset on one end with a 5/8" head with a 3/8 - 16? thread under the head?
 
Tony Wells said:
Let's see if I have this straight. You want a length of 1/4" rod with an upset on one end with a 5/8" head with a 3/8 - 16? thread under the head?
Click to expand...

From threaded end:
- 1/2" of 3/8" thread
- 1/2" of 5/8" diameter (the "stop")
- 12" of 1/4" diameter shaft

with all sections as coaxial as possible.

I'm going to thread a 3/8"-24 drill chuck on the end. It's for a hand-tapper setup. The 1/4" diameter section slides/rotates in bushings in the frame.

Or will. :) I have the various rusty bits of angle and tube to make the frame. That's easy. Turning, not so easy, for me at least.
 
Your giving your self a fair bit of room for error, but for a hand tapper, you could very well pull it off. How much run out, well its going to depend on how much you can tolorate. Just do all you can to minumize it, let us know how it works out.
 
OK, may I suggest a slightly different approach. Forget the 3/4" stock for now. Get a 3/8-34 socket cap screw long enough to chuck a smooth shank above the threads. Chuck/face/centerdrill/drill and ream a 1/4" hole to depth. Part off to length. Now you can sweat the 1/4" rod in place. Take the 3/4 stock and drill/ream/bore a sliding fit on the 1/4" rod. Make it whatever length you need. Slip it down the rod against the 3/8-34 section and either set screw it in place, or solder it as well. The only hangup I can see is the 3/8-24 thread needing to run dead true with the 1/4" rod. If this is a problem, before mounting the stop collar, instead of using a bolt with the threads, sweat on a piece of stock that you can turn and thread after sweating it onto the 1/4" rod. Then put the collar on.
 
8ntsane said:
Your giving your self a fair bit of room for error, but for a hand tapper, you could very well pull it off. How much run out, well its going to depend on how much you can tolorate. Just do all you can to minumize it, let us know how it works out.
Click to expand...
I need all the room for error I can get.

The runout is going to be better than I can do holding a tap handle by hand, for certain.
 
Blue Chips said:
The solder needs wiggle room, but you don't want the finished part to wobble from the wiggle, so solder first and then turn/thread the larger part last.
Click to expand...

Ah. Good point.

OK, so I should revise procedure to chuck stock, center drill, then insert and solder the shaft; then chuck by shaft, turn down the larger diameter, turn down the smaller diameter, part, and thread?
 
That's how I'd approach it, R.G. A couple of points to keep in mind:

When you chuck the 1/4" shaft, leave only enough of it sticking past the chuck to get a dial indicator on it. If there is any amount of runout, mark the lowest point and shim the other side with aluminum foil, paper, or whatever to bring it closer to true. You may have to shim two jaws if the low point is close to the third jaw. Tighten the chuck firmly.

Take only very light cuts on the large part of your assembly. There isn't much holding power on a thin shaft, compared to the cutting force against the 3/4" piece. This is especially true if you had to shim the shaft. If the assembly slips in the chuck, you'll need to re-true it before going any further. If it slips in the threading operation, your best bet is to finish the threads with a die.
 
Not meaning to offend anyone, but I can't picture the need for a 1/4" rod when everything else is larger. Thinking I would thread the end of a 3/8" rod and fit/solder the stop collar on it.
 
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