Basic idea: (simplifying)
1/4"-20 is consumer mount (small cams)
3/8"-16 is professional mount (big cams)
If your tripod has the smaller 1/4"-20 bolt, you can step that up with an adapter ring called a "bushing". You'll want a 1/4"-20 to 3/8"-16 bushing for that. This would be a good idea for you, since it will hold more weight because it essentially creates a bigger bolt size (well, for whatever a bushing is worth haha) and you won't have to get a titanium drill bit like C2V said to drill a new hole for the smaller 1/4"-20 bolt. I'd suggest chopping the track in half to 1.5' if you want to use it on the your DV-7000 often, so you get reduced weight on the tripod & reduced load on the sides (less flex) when you take your camera out to the extreme ends of the track. You can test it at 1000mm or whatever you ordered first, of course (report back if it works without any flex!). The threaded holes to mount the bolts in are created using 2 parts:
1. Drill
2. Tap
You first drill the hole, then "tap" the threads in. You don't want to use a 3/8" drill for a 3/8"-16 tapped hole because the hole would be too big for you to tap (if the hole is 3/8" already, and you slide a 3/8"-16 tap, there will be nothing to "tap" to create those threads!). So the measurements for the drill bits are:
1/4"-20 tap size = #7 drill bit size
3/8"-16 tap size = 5/16 drill bit size
Since the rail already comes with a bunch of 5/16" holes, all you need to do is pick one and tap it with a 3/8"-16 tap, then slap a bushing on your 1/4"-20 tripod to adapt it for the 3/8"-16 threaded hole that you created. That way your tripod's 1/4"-20 bolt is now a 3/8"-16 bolt (thanks to the bushing adapter) and your track's 5/16" holes are now 3/8"-16 threaded holes (thanks to the tapping). So now they're compatible and you can attach them easily :love4:
Do the same thing to the carriage (sled/platform/whatever) - you can use either 1/4"-20 or 3/8"-16, depending on what you want to attach to it. With your Velbon head, you'd use 1/4"-20, which would include a #7 drill bit, a 1/4"-20 tap, and a 1/4"-20 bolt. If you get a hex head bolt (like in the first post), then you can have something to push snug against the bottom of the carriage's 1/4"-20 hole (this way, when you screw the tripod head down, you can just tighten the hex head up flush against the bottom of the carriage to lock it into place). So let's take that and turn it into steps:
Tripod Workflow:
1. Remove the fluid head from the legs
2. Attach a 1/4"-20 to 3/8"-16 bushing to the 1/4"-20 bolt on the tripod head
Track Workflow:
1. Find a pre-drilled 5/16" hole near the middle of the track
2. Tap it with the 3/8"-16 tap (from the bottom, not the top)
3. Attach the tripod (with the bushing) to the track
Carriage Workflow:
1. Using a #7 drill bit, drill a hole in the center of the carriage (the sled piece)
2. Tap it with the 1/4"-20 tap (again from the bottom up, since we'll be attach the hex bolt underneath first!)
3. Attach a 1/4"-20 bolt (long enough to go through the carriage and allow you to attach the head) into the bottom and screw up until it pops out the top
4. Screw the fluid tripod head to the 1/4"-20 bolt coming out of the carriage and tighten the hex nut underneath with some pliers (you may need to cut off the bolt a bit with a dremel or something to adjust for the bolt length inside the tripod head, so it sits flush on the carriage)
Then just slide the carriage onto the track and rock & roll. Post pics & footage when you're done! You can use a 1/4"-20 hole on the track as well if you'd like (instead of a 3/8"-16).
rogar-BigGrin(DBG)
