Fixing a disk to a shaft with set screws (disk is too large for them), or?

take your brass disk with a 1/4" hole in it.--- drill two holes through the sides and counter sink for cap screw head bolts. ---then saw a thin slit through the disk to make two halves to make a split collar. ---enlarge the holes in the counter sunk side half so the cap screws will slip in ---and thread the other half side for your cap screws to tighten your halves together snug on your shaft.--- by loosening your cap screws you can easily reposition your weight for desired adjustments. ---in other words just make a split collar of your brass disk. very simple
Dave
 
Drilling on an angle without a mill can be pretty tricky. As mentioned, cutting a key way, especially in brass, is pretty easy. Brass is a wonderful material to machine. The only problem, really, is it tends to grab unless the tool has a proper rake. This includes drills. The best option is to grind a relief on any drills used for machining brass. Alternately, one can simply drill in small stages, starting with a fairly small drill and moving up in small increments. This is especially true on a drill press, which probably does not have a semi-fixed spindle. On a lathe with a solidly set tail stock it is not quite as much of an issue.

A set screw hole does not have to be drilled with extreme precision . If you take care in finding the Top Dead Center of the cylinder along a radial line in the vice, a drill press should be easily accurate enough. Be sure to start the hole with a center drill, going very slowly. Check your work several times, and don't just pull down on the quill handle. Rather, poke gently up and down to get the hole started. Once started, all subsequent drilling operations will follow the original path faithfully, as long as you do not use too small a drill bit at the outset. If the depth of he hole is too much more than ten times the diameter of the drill bit, the drill can begin to wander as it moves down in the material.

I would not attempt CA adhesive unless the torque on this cylinder is going to be quite low.
 
So many good ideas!

But this is my very first project, and so I should limit myself to simple techniques that a beginner can execute on a lathe. Some of the above feels a bit intimidating.

I've been considering threading the rod and disk too. This can be advantageous since I will need to mount a "flag" past the disk; a thin rod of (maybe) spring steel that can register on an optical sensor. That could be mounted in a small brass holder and threaded onto the end of the same thread that holds the disk.

The problem with threading the rod is that I think I'd have to reduce the diameter of the rod a little before using a die, e.g. to slightly under 1/4" or for 6mm threads (I have a few metric dies, but none in that crazy Imperial system at the moment), and since it's rather long I'd have to stabilize the end (it's 36" long) sticking out the back of the lathe. I can do that, but it's the "what ifs" that worry me. I'd need a plan B, like reaming out the threads to 1/4 inch anyway, and all that without removing the work from the chuck.

So a question is whether 6mm inside threads in the brass leaves enough room to "correct" it to a clean 1/4" hole if I needed to. I have some smaller brass and some other 1/4" steel stock that I can practice on before possibly ruining the disk or the end of the Invar rod that I'm using for the project.

Another question about threading is whether a half-inch of it can be expected to be as square as a tight sliding fit can be (or better)?

Otherwise, I'll try for a tight sliding fit first, and figure out what approach (glue, a key, etc.) feels right after that. I'm mostly figuring this out as I go anyway.

(The torque on the disk will be quite low, by the way, at least unless I drop it. And I don't have a drill press. I will be buying a small mill soon, though.)

Thank you all.
 
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If you thread at a slow spindle speed, whip should not be a concern.
single point thread both, so they are a good fit.
I was going to suggest just that idea.

PS finer the thread, the finer the adjustment.
 
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If it were my project, I'd drill and tap the brass for 1/4" NPT. Then, a 1/4" NPT brass plug
(available off the shelf) can be drilled axially to barely pass the rod, and slitted. Those NPT threads are
tapered, so tightening the plug will close the slits, squeeze it down onto the rod, locking it all in place.

Drill a scrap (extra credit for tapering the hole) and tap it to hold the plug
for its clearance hole drill operation. A lathe and a tap make this a relatively easy task.

You might be able to get the hole into a 1/8" NPT plug, but... that's trickier.
The square drive head standard is only 9/32" across flats, drill a 1/4" hole and it'll be flimsy. You
could, though, fabricate your own plug with any head you want.
 
We had same problem with a project.

Here is one possibility, using random sized for demonstration...

Drill a 1/4 inch hole from side into center as if you were going to use set screw.

Next, enlarge hole only near top to correct size for the setscrew that you wish to use, must be larger than 1/4.

Next, cut a length of 1/4 round to make a sliding plug that fits in the above hole between setscrew and shaft.

Sent from my SM-G781V using Tapatalk
 
An update: I finished the basic machining of the disk.

I first practiced threading using a die on some spare 12L14 steel rod I had. I don't currently have the ability to do single-point threading, and the results with the die were not ideal. I subsequently abandoned this idea as being too imprecise. So for simplicity it was going to be a pressed or shrink fit or a glued fit. I have reamers in 0.249, 0.25 and 0.251, and I found by practice that the 0.25 reamer was most suitable.

I then mounted the 3" disk into my 4 jaw chuck. The Sherline has a 3.5" swing, but I discovered to my dismay that the diameter of the assembly was about 0.15" too big - the outside jaws of the chuck would hit the bed.

Luckily, I did have a riser for the head as well as a taller tool post. What I didn't have was a riser for the tailstock, which meant that I couldn't drill the hole! So I decided to reduce the diameter of the disk enough to set it up again without the riser. I faced one side and reduced the diameter as far along the edge as I could, then reversed the disk. Now gripping the reduced diameter, I was able to put it in the lathe without the riser.

The disk was sitting on parallels in the chuck, and I clocked it in to about 0.5 thousands. I faced the other side, and gingerly reduced the diameter of the remaining shoulder. I was very pleased to see the disk come out with only the most minute seam along the edge, which vanished after a bit of scotchbrite. I then drilled it in stages and reamed it.

It's still in the chuck as I think about what comes next. I'm curious about how parallel the two faces of the disk came out, and how square the hole is to the second face, but the little Sherline appeared to do everything precisely despite exceeding its standard work envelope, and all went well.

Thanks again.
 
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