Armory Sponsor
Joined:
Oct 2024
Posts:
3
EE: 0% (0)
AK, USA
Posted: 10/6/2024 7:29:57 PM EDT
|
I'm building my first form 1 suppressor, and want to go to with 1.375x24 (Hub) threads. I'm finding conflicting info on the major and minor diameters. One source is showing 1.370 major and 1.335 minor, theoretical machinist is showing 1.372 major, but 1.319 minor. The major diameters are close enough, but the minors are .016 different... Any input on which is accurate? |
|
Thread specs aren't a set number, they're a range. http://theoreticalmachinist.com/Threads_UnifiedImperial.aspx If you're buying a mount and threading a tube, have the mount in front of you when doing so. Get close to spec and check fitment, take a couple thou, repeat. |
Husher of boomsticks
Joined:
May 2023
Posts:
519
EE: 0% (0)
CO, USA
|
1.366-1.372 is a normal MALE major diameter 1.331-1.338 is a normal FEMALE minor diameter Theoretical machinist calculators are accurate, but you need to know how to use them and differentiate between internal and external for different thread classes. You also need to pay attention to crest and root radius, because incorrectly formed crests or roots that give "in spec" major or minor will have pitch diameters that are not. You really want to target 1.345" male and 1.351" female pitch diameter with majors and minors in the range shown by TM. As I imagine you'll only be doing the tube, if you don't want to invest in gauges and micrometers, your best bet is to just check fitment as you go with all the mounts/adapters you plan to use, looking for smooth rotation with pretty minimal play. Plug gauges are expensive, I pay $350 for each side (GO/NO-GO) of my 1.3500" plug gauges. Yes, you can make your own plug gauges, but that still requires, at minimum, using a brand new full profile insert on material that will cut cleanly and be hard enough, and a using a calibrated thread mic or overwires to check P.D. I hard turn my shop made gauges for weird patterns out of full hard 440C, usually smoke at least one $30 Top Notch insert on each gauge cutting that 62 Rc material. Making accurate thread gauges requires good tooling, a rigid machine and a lot of thread cutting & measuring experience. |
Suppress all the things!
Joined:
Oct 2024
Posts:
4
EE: 0% (0)
AK, USA
|
DUH! Thank you! Of course the 2a & 2b threads have different specs. It would be a rather tight fit with 0.0" clearance between the male & female parts. It's obvious now! I will be using a factory made mount, so I'll have that along when it comes time to cut those threads. I will be building the end cap, and plan to use the same threads as it makes sense with the base material i'll be using. so I'll just thread both ends to work with the mount. and then build the end cap to fit. I'll pay attention to the root & crest radii. Thanks much |
Armory Sponsor