There's never a design path that's all good or all bad. The cost of the lead screws (with some thread designs) is fairly high. That can drive you to a compromise that shortens the screws. In my case it drove me to a cheaper thread design screw. That made the cost delta associated with long screws pretty minor.
No matter what you do for rods, you still have the issue of nuts. I'm doing all the attach to the rods with nuts. I'm also going with the double nut drivers. In my case the cost of the nuts is actually higher than the cost of the lead screws. Yes, you can do things on the ends a different way. That would cut the nut budget in half. With these big heavy screws, I decided the overkill approach made some amount of sense.
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Some numbers:
3/4" shaft at 13.50 per foot. Five foot screws (in my case) x 3 needed = 15 feet total. That's $202.50 for the screws.
Nuts are $31 to $37 each depending on which ones. The minimum of three would be $93. For a dual on each driver that goes to $186. Put nuts on each end of the screws and you are at ~ $400 for nuts.
Total bill to Roton $600 or so for a big printer. Total bill with half length screws $500 or so. That's not a fair number if you shrink the printer 2:1, since you also would pull out a bunch of nuts as well. It's also not fair if you go with 1" lead 3/4" dia Torqspline at $43 a foot. Even at 7/16" Torqspline the numbers are more slanted towards the screw cost.
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The other tradeoff (mentioned multiple times) is that the 1/2" lead probably cuts down the max speed of the printer over the 1" lead. That could be a 2:1 hit. It could be less depending on a number of things. Once the print time goes over 24 hours, what's another day waiting :)-D
No matter what you do for rods, you still have the issue of nuts. I'm doing all the attach to the rods with nuts. I'm also going with the double nut drivers. In my case the cost of the nuts is actually higher than the cost of the lead screws. Yes, you can do things on the ends a different way. That would cut the nut budget in half. With these big heavy screws, I decided the overkill approach made some amount of sense.
----
Some numbers:
3/4" shaft at 13.50 per foot. Five foot screws (in my case) x 3 needed = 15 feet total. That's $202.50 for the screws.
Nuts are $31 to $37 each depending on which ones. The minimum of three would be $93. For a dual on each driver that goes to $186. Put nuts on each end of the screws and you are at ~ $400 for nuts.
Total bill to Roton $600 or so for a big printer. Total bill with half length screws $500 or so. That's not a fair number if you shrink the printer 2:1, since you also would pull out a bunch of nuts as well. It's also not fair if you go with 1" lead 3/4" dia Torqspline at $43 a foot. Even at 7/16" Torqspline the numbers are more slanted towards the screw cost.
----
The other tradeoff (mentioned multiple times) is that the 1/2" lead probably cuts down the max speed of the printer over the 1" lead. That could be a 2:1 hit. It could be less depending on a number of things. Once the print time goes over 24 hours, what's another day waiting :)-D
