Size chart for brass round head screws (used to lap muzzles)

[ohland]

I managed to stagger out of the basement after surviving hand to water heater combat.

Anyways, I see that James V. Howe in the book "The Modern Gunsmith" supposedly identified the screw size for brass round head screws used in lapping a muzzle.

I went through my electronic copy, but it isn't searchable (dow!)

Does someone have this info? Like to lap the muzzle on the old retrobate's 32-40.

[kywoodwrkr]

Were I to buy brass round head screws I'd go to McMaster-Carr
http://www.mcmaster.com/#machine-screws/=x1rrcc
and select the one whose head seemed to be correct for the caliber I was working with.
If you select one of the products McMaster-Carr can display the product detail.
You can even download an object to include in engineering drawings.
I'd also use the pan head screw type (sorry link went to general screw entry page) only because the 'edges' are all solid, ie no interruptions in head.
Downside of MMC is order quantity-answer is to share maybe?
X number of people go together and buy however many sizes, divide and mail splitting costs.
But then I also have tendency to over think a problem!
YMMV

[ohland]

pan head screw type

Uh, the wonders of using a round head when lapping a muzzle is that the round head is pretty much going to have the same radius presented to the muzzle, no matter if the screw is a few degrees off from the bore axis (within reason).

I have seen references to using a marble or a machinist's ball, dip in lapping compound and twirl in the muzzle. The screw can be used with a drill.

[montana_charlie]

Like to lap the muzzle on the old retrobate's 32-40.
... wink ! ...


This will take you to the page of offerings from McMaster-Carr in a brass, round-head, machine screw.
http://www.mcmaster.com/#machine-screws/=x1t2tg

Click on the (blue) stock number to see detail about any of them ... including the dimensions.


CM

[ohland]

Why nobody has seen this to be beneficial, I dunno.

Brass round head screw IMPERIAL dimensions for use in muzzle lapping. If you want metric, punch it in yourself.

Diameter Height
138769

NOTE: Looking at the screw head form, I see a transition from a radius to a cylinder (radius does not continue to edge of screw head). What this means is the four places to the right is just numbers. Thank God this is not calculating orbital re-entry. The height will be off that tiny bit of straight edge...

Parts of a Circular Arc
138776

NOTE: dia and ht are in inches, Angles are in decimal degrees.
#1: .137 dia, .061 ht, angle: 166.747, radius: .06896
#2: .162 dia, .069 ht, angle: 161.704, radius: .08204
#3: .187 dia, .078 ht, angle: 159.343, radius: .09504
#4: .211 dia, .086 ht, angle: 156.743, radius: .10771
#5: .236 dia, .095 ht, angle: 155.348, radius: .12078
#6: .260 dia, .103 ht, angle: 153.560, radius: .13354
#8: .309 dia, .120 ht, angle: 151.346, radius: .15946
#10: .359 dia, .137 ht, angle: 149.408, radius: .19425
#12: .408 dia, .153 ht, angle: 147.480, radius: .21250
1/4: .472 dia, .175 ht, angle: 146.232, radius: .24663
5/16: .590 dia, .216 ht, angle: 144.847, radius: .30945
3/8: .708 dia, .256 ht, angle: 143.492, radius: .37276

I wish that the arc standard was identified, it looks like MATH without alcohol will be required. We have diameter and height, pretty sure that the internet has widgets to do the number crunching... Might be DIN 86, looking for a good illustration...

Math stuff crunched by: The Complete Circular Arc Calculator
http://www.handymath.com/cgi-bin/arc18.cgi?submit=Entry

If I stuffed the numbers into the wrong variable box, by all means, say something...

Just guessing, I see the head angle diminishing with the increase of screw size, which in turn decreases the head height. Maybe the head height varies with size, as size increases, less height is required to maintain the cross-sectional area (strength) needed to prevent the screwdriver from tearing up the head...

Off-axis calculation: hmm, need to think. Done.

For a 32-40 groove size .322, closest screw size is #10, .359 dia, .120 high, 149.41 degree arc.
Plug in .359 (width of arc) and .120 (height of arc) results in a radius of .19425

Solve for how much the head of a #10 will stick into a 32-40:
.322 (width of arc), .19425 (radius of arc) means 111.95724 (angle subtended by arc)

Now it's 149.41 - 111.96 = 37.45. 37.45 / 2 = 18.725

So when lapping a 32-40 with a #10 round head screw, you can be 18.725 degrees off the bore axis and still present a congruent arc to the muzzle.

Yeah, baby... Groove diameter (width) and radius will give you angle. Take angle of screw head and minus angle of groove diameter, divide by 2, results in maximum off-bore angle.

:drinks:

[pworley1]

Thanks for that link.

[LAGS]

Has anyone ever used the Brass Hinge Pins from old antique door Hinges.
The old style with a ball end on top.
When I worked in demolition years ago, I would pull the old hinge pins that had a Round Ball on the end.
I used them to lap muzzles for may years.
And if you want one of a different size, you just spin it in your drill motor or press and reshape with a file. ( Poor mans lathe )
You can still find these hinges on old houses, at second hand building supply shops, and junk yards.
I noticed more of these used in houses or even barns built before the 1950's and have seen more of them on the east side of the U.S. than out west where I use to live

[crackers]

I'd skip the math and put a tap into a cap nut. Brass isn't necessary.

[ohland]

I'd skip the math and put a tap into a cap nut. Brass isn't necessary.

Oddly enough, while searching for suitable lapping compounds, I came across a number of posts where the OP uses... acorn nuts.

Lastly, brass is so retro, why not use it?