.578-28 thread question

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ezed
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.578-28 thread question

Post by ezed »

I am planning on doing Form 1 for 45 suppressor and would like to thread it to match my .578-28 suppressors. From what I have read, this is a "special thread", but there are 37/64 -28 taps available that some say would work. What do you guys say? Is this tap the same as the standard .578 - 28 threaded pistons?
Thanks
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L1A1Rocker
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Re: .578-28 thread question

Post by L1A1Rocker »

http://www.brownells.com/gunsmith-tools ... 24321.aspx

I'm assuming that you will start your threading by single point threading on a lathe and finishing with a tap?
ezed
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Re: .578-28 thread question

Post by ezed »

I was leaving that open until I found out if they were, in fact, one in the same.
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Re: .578-28 thread question

Post by David Hineline »

It's just math 37 divided by 64 equals .578125
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ezed
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Re: .578-28 thread question

Post by ezed »

yes it is simple math for finding the diameter, but threads can be cut be cut "special", and it is done all the time.
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yondering
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Re: .578-28 thread question

Post by yondering »

If you're going to cut the threads on a lathe, why bother with a tap?
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Bendersquint
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Re: .578-28 thread question

Post by Bendersquint »

L1A1Rocker wrote:http://www.brownells.com/gunsmith-tools ... 24321.aspx

I'm assuming that you will start your threading by single point threading on a lathe and finishing with a tap?
If you are starting single point on a lathe why would you not finish the job?
ezed
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Re: .578-28 thread question

Post by ezed »

guys, the point of my question was to determine if the threads for the .578-28 were standard, so that these 37/64-28 taps, or a standard threading insert would cut the correct thread form (if single pointing it on the lathe), would work. OR if they were they had a "special" profile which required a special ground tap or single point insert.
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T-Rex
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Re: .578-28 thread question

Post by T-Rex »

In your OP, you stated that you wish to match existing threads.
Ok, so they're .578-28.
What classification are they?

There is more than one way to cut a single pitch.

The other issue, we are wondering about, is how do you plan on aligning the tap? A suppressor mount needs to be 100% true. You will not get this from simply putting the cap in a vise and tapping.
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Bendersquint
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Re: .578-28 thread question

Post by Bendersquint »

ezed wrote:guys, the point of my question was to determine if the threads for the .578-28 were standard, so that these 37/64-28 taps, or a standard threading insert would cut the correct thread form (if single pointing it on the lathe), would work. OR if they were they had a "special" profile which required a special ground tap or single point insert.
.578-28 and 37/64-28 are not the same, they have different specs...if they didn't then manufacturers would call it 37/64-28 and not .578-28. ;)

The profile is a standard 28tpi profile so inserts that can cut 28tpi will work fine.
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Re: .578-28 thread question

Post by Delw »

ezed wrote:guys, the point of my question was to determine if the threads for the .578-28 were standard, so that these 37/64-28 taps, or a standard threading insert would cut the correct thread form (if single pointing it on the lathe), would work. OR if they were they had a "special" profile which required a special ground tap or single point insert.
The profile is a standard 60º thread profile.
the -28 means 28 threads per inch.
the .578 is the major dia of the thread, even if your going a internal thread you figure out your thread depth and all thread date by the major dia.
The reason they call is a "Special thread" is none other cause its not a standard thread like a 1/4-20 1/4-28 heres another example 1/4 is standard, 1/4-28 is NF ie national fine 1/4-36 is nef National extra fine 1/4-72 is special all the same profile just different in threads per inch.
"Special" is just a term used frankly for nothing.

some thread profiles are"
60º standard threads unless other wise specified
j thread which has a specific root radius its the exact same as a 60º standard threads just specifies and exact root rad.( mostly aerospace work)
acme thread
buttress thread
and many more

the 2a-2b designation is tol on the PD ie pitch dia . this is pretty much standard for most nuts and bolts
the 3a 3b designation is a tighter pitch dia used for close tolerance threads





word of advice on inserts.
unless your cutting a ton of threads in certain pitch DONT use designated inserts cause they are useless. for any other thread pitchs you cut.
what those inserts due is also skin the minor and or major(depending if you have id insert or od inserts) to give you a burr free thread. if your thread depth isis deeper you will also cut your minor or major deeper which will be wrong for the thread spec. use a single point threading tool and debur the thread its that simple.


you can look up all thread data on the net there are plenty of places.
all you need to know is the thread pitch and major size it will spit out all the info you need to know. even stuff you didnt want to know.

you can only check a I.D. thread with thread guage or a mold and a comparator with get you close. or you can find a bolt that matchs and cut until it feels right.. (not good idea but it works)
O.D. threads you can check a varity of ways. thread gages, thread mic comparator thread wires(MOW)

Hope that helps

Delw
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Re: .578-28 thread question

Post by AC_2250 »

To get the tap drill size, divide 28 into 1, subtract this decimal value from the .578" diameter. This will give you the correct tap drill size.
Center drill and step drill until you get the correct size. Lightly chamfer the hole, and using plenty of Tap Magic, tap the hole.
milsurpcollector1970
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Re: .578-28 thread question

Post by milsurpcollector1970 »

Im no expert on building suppressors but a few suggestions

Get yourself a copy of the machineries handbook old copies are fine the info doesnt change mine is from 1958
It will have all the info you need about everthing to do with threading and about 1000 more machining operations.

Become familiar with how to check thread size using the 3 wire method.

Since you are cutting a thread to fit something aread made use that as a guide.

The tighter the fit the better.

I see that you are turning interior thread on a endcap

Take a piece of scrap and thread it .578-28 cut it to what ever standard you want 2a or 3a and measure it using the 3 wire method to make sure its properly cut

This will be your threading checker for the endcap or just use the barrel to check it.
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