BlondeBimbo

There is a half decent place in Whitburn itself. If you go out towards Blackburn, past the hillcroft into East Whitburn, then turn right onto hens nest Road, follow this until the side pavements stop just past the houses, there is a small lay-by on the left, this is a public footpath, follow this into the woods, there are several routes, but keep going up the hill. Go to the top locally know as 'pet cemetery' 55 degree 51' 47.5"N 003 degree 38' 50.41"W. There is a park style bench and a flat area which is fairly solid, there are trees to the north, but it has an elevated position looking to the South, East, and West. It is usually good for the geminids and the other meteors around this time, and is ok for an early sight of the conjunction, it's a bit of a walk but reasonablely dark, not as good as a drive-out type site of course, but just a few mins from East Whitburn, depending which side of Whitburn you're at, just a few minutes as well. It's a dark trail, so go during the day to get your bearings

Yeah it is a reducer - force of habit

Sorry to latch on to this thread, and your post in particular @RayD but I am also having problems looking at the Back distance on a similar setup to yours. I am looking at the Tak TKA36580L 0.72 flattener - it has a back distance of 72.8mm The Tak diagram shows this should have the 6A (TKA86200) rotator (M98F - M98M) then the 8A (TKA86003) adaptor (M98F - M54F) after it (these add up to 72.8mm themselves) , but then you need a M54M - M48? adaptor to go on to the EFW3 (21.8mm) and then the camera itself (19.5mm) - even if you can then remove the 7mm spacer this would give an additional 34.5mm beyond the flattener back distance without even including the additional adaptors needed between M54 and the EFW3! How did you get over this? BB

If you don't mind me asking btw, what 3d printer are you using? I have a 10s, and with pla, pteg, or any other filament, I cannot produce a thread this fine. I assume you are using something other than fdm.

Those figures look better, I did a quick manual calculation P = 1/24 =0.041666666"; H = 0.866P = 0.03608333" From the diagram, the pitch diameter reduction from major is H3/8 = 0.01353125" (each side) so twice this for diameter 0.0270625" so if we subtract this from the major dia of 2" we will get 1.9729375" - this would be the nominal or size of pitch diameter - for both ext and int threads, to add tolerance since you went for 3a (0.00436") this would give a range of pitch dia (ext) of 1.97294" - 1.96858" - appears to line up with your figures now. BTW external thread should be 3a, internal will be 3b - you have them the wrong way round With a 3a thread, it's dimensions should be within the range 1.97294" to 1.96858" - that is anywhere from nominal size down to 0.00436" below it. With a 3b thread, it's dimensions should be within the range 1.97294" to 1.97861" - that is anywhere from nominal size up to 0.00567" above it. So for your modelling, pick suitable figures within these ranges - as you will be specifying just the one set of dimensions rather than a range. One thing that appears to be missing in your thread specification is the thread angle, with UN threads it should be 60 degree, unfortunately there are others ( 55 degree, 47.5 degree and so on) so I am not sure which your software would pick by default. Oh, and I don't want to appear nitpicking but the thread designation 1-24 you have stated means a 1" diameter thread of 24tpi the standard designation for the thread you are specifying is 2-24 (3b)

Oops, just note the H for the thread depth in the diagram ( which you can calculate) is not the same H as the tolerance H - which is just the reference indication that the 4 applies to the hole - internal thread tolerance making the hole 0.0015"-0.0020" larger than size. (4L would apply the same 0.0015"-0.0020" smaller than size on an external thread) Only noticed the confusion once I posted! Hence Blondebimbo!

I understand that it's a standard uns thread form, so 2" would be the major dia, and 24 the tpi. (So the inverse is the pitch.) H can be calculated from the pitch as sqrt(3)/2 x P (0.866P roughly) the radius of the thread trough is not shown on the diagram attached but is 0.1443P Although if you are generating it in fusion 360 you can just insert the thread from the nominal and the tpi, and fusion will generate the correct form on either external or internal threads. You can also change the tolerance - being a uns type thread it ought to use the A/B tolerance scheme, so likely class 3A/B, ( you set it as 2) although more popular now is using the L/G/H system - typically the external thread is size (G) and the internal is oversize say 4H Your diameters are way out btw