Returning from an out of town consulting job, was near my metal supplier, so stopped to stock up.
misc tube scrap ( to make a proper S&W frame wrench) $1.75 from scrap bin
1 1/4" 1144 round, 2 ft, $15.54
1/2" round 4140, annealed 4ft, $11.68
3/16" round 1018 CR, 4 ft $ 0.80
9/16" round 1018 CR, 2 ft $ 3.68
1/2" aluminum 6061-T6, 4 ft $ 3.92
3/4" aluminum 6061-T6, 4 ft $8.92
total of a hair under $50 with tax. I think this is pretty fair $$ and it is nice to be able
to walk in and get what you want quickly. 1018 HR/CR, 1144, 12L14, 4140 ANN in stock.
That will make a lot of stuff for me, and I know exactly what I have, mark it all with
paint pen as soon as it hits the shop.
Next project will be a hand controlled axial tap/die holder. After watching my T&D maker friend
tap at 270 RPM with zero risk of breaking the tap.....had to have one. Knurled OD steel 1 1/4",
by 6-8" long. Bore and ream a 0.500" hole for 5" deep or so, one end. Drill other end to accept
a key type chuck (so it won't unscrew on reversing) mount, straight with setscrew is easiest but
knock yourself out cutting a JT2 or something if that suits your fancy. Center piece is a carefully
made piece about 7" long exactly .499 diam and polished. Mount the 1/2 rod in tailstock, slip
1 1/4" knurled piece over it, mount tap in the chuck. Spin up drilled workpiece and manually
feed in the tap. Your hand friction controls the torque on tap, if it sticks, it will spin if you
are holding it right. Once it bottoms, stop, then reverse the spindle while holding the knurled
driver again, back out tap. ZAP! tapped hole, at speed, no tap breakage. HAD to make one.
Will also make an alternate head to hold 1" dies, swap out the chuck with setscrew.
One comment on 6061-T6. Keith mentions 2024 and 7075, and all three machine like butter.
6061 in the most common heat treat of T6 (or T651) yields at 40,000 psi, ultimate is 45,000 psi. If you
pay extra for 2024, you can find T3 or T4, or T6 heat treats. T6 runs about 50,000 yield, T3/T4 maybe
a bit less in extruded, maybe 46,000, or maybe the same. So, about 15-25% stronger than 6061T6.
7075 gets you a bigger jump up, to 73Ksi yield, 83 Ksi ultimate. 7075 is about the strongest aluminum
alloy out there, and is used in forged form for AR15 uppers and lowers, with a milspec hard anodize to
give it wear resistance.
Another thing to keep in mind when choosing materials is whether droop or deflection is important in
your application. If you took a 1" round bar of steel and clamped it in a vise, then loaded it with a weight
a foot out at the end, and right next to it you did a 1" round aluminum bar, clamped and loaded identically, the aluminum
will deflect 3 times as much with the same load. Strength or alloy are not important (as long as you don't
over load it and get permanent deformation). So, 6061T6 is STRONGER than A36 mild steel, but will deflect
three times as much. A lot of times the deflections are small enough with either that it makes no difference,
wear, weight, ease of machining, etc. will lead your choice. But it is not well known that aluminum is 3 times
as flexible as steel. Said another way, 1/3 as stiff as steel.
Bill