Making Machine Screws for Guns
A friend of many years standing, who is a good gunsmith machinist but not a real machinist, called the other day with a question.
He needed to know how to duplicate a couple of screws for a gun, for which Brownell’s was out of stock, (as was he) of screw blanks.
Now he knows how to cut a thread on a lathe, and how to thread a piece of stock with a Die and Die Stock, and he knows what size to turn a piece of stock to for a particular screw diameter and pitch, what he didn’t know was how to properly make the head of the screw so that it would match the existing screws.
You see, the head of a screw has proportions relevant to the shank, and no one ever told him this, but he could see that there had to be some way to make the new screws so that the heads would end up as perfect matches for the factorymade screws.
Lucky for him I remembered how this is calculated so I gave him the math and drawings of how it is applied.
Then I got to thinking that since a few folks here now have metal lathes at home, there might be some interest in how to make a screw beyond the simple single pointing of it on the lathe or using a die and die stock to make one out of a screw blank.
That’s pretty easy to figure out, and I will detail it here if someone wants to know the process, but you can find lots of You Tube videos that will show you how to cut a male thread with a lathe or by using a die and die stock.
The four screw types generally found on firearms are the Flat Head Filister, The Oval Head Filister, the Flat Head, and the Round Head, with that last one not often being seen.
The accompanying drawings show each type, along with the math to make one of them in any size and have it come out the same as a factory screw, matching proportions that is.
Just in case the text below the pictures isn’t legible, here it is again.
For a Filister Head Machine screw:
A = Diameter of the Body
B = 1.64 times A, then subtract 0.009 from the result, this is the diameter of the Head
C = 0.66 times A, then subtract 0.002 from the result, this is the height of the head
D = 0.173 times A, then add 0.015, this is the width of the slot
E = ½ times C, this is the depth of the slot
For Oval Head Filister Screws:
A = Diameter of the body
B = 1.64 times A, then add 0.009 to the result, this is the diameter of the head and the radius of the oval
C = 0.66 times A, then subtract 0.002 from the result, this is the height of the side
D = 0.173 times A, then add 0.015 to the result, this is the width of the slot
E = ½ times F, this is the depth of the slot
F = 0.134 times B, then add C to the result, this is the height of the head
For Flat Head Screws with a 82 degree included head taper for counter sunk holes:
A = Diameter of the body
B = 2 times A, then subtract 0.008 from the result, this is the diameter of the head
C = A0.008, then divide the result by 1.739, this is the depth of the head
D = 0.173 times A, then add 0.015 to the result, this is the width of the slot
E= ½ times C, this is the depth of the slot
For Round Head Screws:
A = Diameter of the body
B = 1.85 times A, then subtract 0.005 from the result , this is the diameter of the head
C = 0.7 times A, this is the height of the head
D = 0.173 times A, then add 0.015 to the result , this is the width of the slot
E = ½ times C, then to the result add 0.01, this is the depth of the slot
View attachment Screw Proportions 1.jpeg
A friend of many years standing, who is a good gunsmith machinist but not a real machinist, called the other day with a question.
He needed to know how to duplicate a couple of screws for a gun, for which Brownell’s was out of stock, (as was he) of screw blanks.
Now he knows how to cut a thread on a lathe, and how to thread a piece of stock with a Die and Die Stock, and he knows what size to turn a piece of stock to for a particular screw diameter and pitch, what he didn’t know was how to properly make the head of the screw so that it would match the existing screws.
You see, the head of a screw has proportions relevant to the shank, and no one ever told him this, but he could see that there had to be some way to make the new screws so that the heads would end up as perfect matches for the factorymade screws.
Lucky for him I remembered how this is calculated so I gave him the math and drawings of how it is applied.
Then I got to thinking that since a few folks here now have metal lathes at home, there might be some interest in how to make a screw beyond the simple single pointing of it on the lathe or using a die and die stock to make one out of a screw blank.
That’s pretty easy to figure out, and I will detail it here if someone wants to know the process, but you can find lots of You Tube videos that will show you how to cut a male thread with a lathe or by using a die and die stock.
The four screw types generally found on firearms are the Flat Head Filister, The Oval Head Filister, the Flat Head, and the Round Head, with that last one not often being seen.
The accompanying drawings show each type, along with the math to make one of them in any size and have it come out the same as a factory screw, matching proportions that is.
Just in case the text below the pictures isn’t legible, here it is again.
For a Filister Head Machine screw:
A = Diameter of the Body
B = 1.64 times A, then subtract 0.009 from the result, this is the diameter of the Head
C = 0.66 times A, then subtract 0.002 from the result, this is the height of the head
D = 0.173 times A, then add 0.015, this is the width of the slot
E = ½ times C, this is the depth of the slot
For Oval Head Filister Screws:
A = Diameter of the body
B = 1.64 times A, then add 0.009 to the result, this is the diameter of the head and the radius of the oval
C = 0.66 times A, then subtract 0.002 from the result, this is the height of the side
D = 0.173 times A, then add 0.015 to the result, this is the width of the slot
E = ½ times F, this is the depth of the slot
F = 0.134 times B, then add C to the result, this is the height of the head
For Flat Head Screws with a 82 degree included head taper for counter sunk holes:
A = Diameter of the body
B = 2 times A, then subtract 0.008 from the result, this is the diameter of the head
C = A0.008, then divide the result by 1.739, this is the depth of the head
D = 0.173 times A, then add 0.015 to the result, this is the width of the slot
E= ½ times C, this is the depth of the slot
For Round Head Screws:
A = Diameter of the body
B = 1.85 times A, then subtract 0.005 from the result , this is the diameter of the head
C = 0.7 times A, this is the height of the head
D = 0.173 times A, then add 0.015 to the result , this is the width of the slot
E = ½ times C, then to the result add 0.01, this is the depth of the slot
View attachment Screw Proportions 1.jpeg
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