This is how I make 1/4" and 1/2" aluminum clamp collars.
A 1/2" collar is shown, but a 1/4" collar is the same except
that it has only one clamping bolt. A drill press and C-clamps is
a must for this, along with a 1" hole saw, tap, and the right
drill bits. I like clamp collars because they don't mar the shaft,
don't require a flat to be ground at any particular spot as set screw
collars do to work well, and they seem to have higher clamping
forces than set screw collars do.
I start with some stock 1/4" or 1/2" thick by 1" to 1.25" wide
and punch it with a center hole .5" from the end and a clamping
screw hole (or holes if I'm using 1/2" stock) .340" away from the
center on the edge. I then drill the clamping screw hole all the
way through with my tapping-size drill bit. I use 4-40 screws,
so I use a #43 bit for the first all-the-way-through hole.
I then open the hole up to the halfway point where the hacksaw
split cut will later be made using a 7/64 bit. Finally, I open
the hole up again with a (3/16"?) bit, just big enough for the
bolt head, leaving about .1" of 7/64ths between the bolt head
counterbore and the to-be-tapped #43 hole. You can see this
in the lower hole in the above right picture. The top hole has
had the first and second drills, but not the bolt head counterbore
yet. Then I tap the holes for 4-40 thread.
I open the center hole up to something a bit under 1/4" and
then, making sure the piece is clamped very solidly, go at it
with a 1" hole saw. It's not shown, but I also clamp an aluminum
heat sink block to the piece because hole saws try to get hot.
I go slow, use oil, and don't let it get very hot. I go until I'm
almost all the way through. If I remember, I don't unclamp
the piece for the next step, but I unclamped it here to take the pic.
Drill the center hole. You want this to be as close to the
shaft diameter as possible. I like to open holes up gradually,
1/16" or even 1/32" at a time. You might want to offset the
center hole away from the clamping bolt, or leave it in the
center. The one shown above is good in that I didn't have to
slot the part opposite the clamp screw. 1/2" thick aluminum
is strong enough that you may need to make part of the collar
thinner, depending on the shaft diameter. You can do this by
slotting it partway through with a hacksaw, or offsetting the
Cut the slot and test the collar out on the shaft. If it's hard
to clamp, you may need to slot the side opposite the clamp screw
partway through. Finally, what I do to make the collar's face nice
and flat and even so that it works well against a thrust bearing
washer (which is the entire point of all this) is tighten it on a
piece of shaft stock in the drill chuck and then gently spin it
against a clamped flat file. Presto! A $2 clamp collar with only
a few hours of work! :D