Perhaps my thread is what your refering to. If you have some scrap 1/8 in plywood, six track nails and a sabre saw, your in bussiness to have one made in about ten minits.
Cut one piece about 4 or so inches wide by 7 or 8 in long for a base plate, edges dont have to be straight.
Then cut two strips from the side or edge of the plywood, using the factory cut edge (this is an accurate straight cut ) to make a percision jig. Cut both 1 in wide and to the lenght of the base you cut beforhand.
Nail one strip accross the top edge of the base plate with track nails, being sure to keep the factory cut towards the center of the base plate.
Lay your track ties against the nailed edge, hold the second ply strip against the other side of the ties, then nail in place. The track slot should be snug, but not to tight.
Now you have a perfectely straight sodering jig, that is 1/4 in thick that can easely slide under the track.
When sodering curved track nail the track up to 18 or so inches from the end, slide the jig under the track and soder the rail joiners, the groove prevents misalignment both horzizonal and vertical. and will be a perfect straight joint.
Takes a few second to get use to, but is easier to hold both tracks, sodering gun and soder, I tried the MFG type and is now a paper weight, this is much easier to use and hold track when in awkward positions.
If you use different brands of track you may have to make one for each, just mark the brand in the slot.
Hope this helps...John
John Warren's, Feather River Route
WP and SP in HO