Edited 5 time(s). Last edit at 11/17/2013 11:39PM by nicholas.seward.

vinhdinh posted about whether threaded rod could be used to make a Rostock style printer . I made a lengthy post about the reasons you wouldn't want to do that. If any of you know me then you will know that I hate to be critical. So I started to feel bad and I decided to see if I could design a decent threaded rod bot. I got a glimmer of an idea and even though it doesn't fully fit with my design asthetic I decided I had to at least mock it up. I would be delighted if someone wanted to take the idea to completion.Design goals:*Make a Rostock style bot that is capable of high speeds with a threaded rod.*Minimize the number of components.*Eliminate all spherical joints in favor of 608 bearing joints.*Eliminate the smooth rods and linear bearings if possible.*Look cool.*Mount the steppers as low as possible.*Eliminate all unnecessary supports.Behold LISA Simpson. (LInear Simpson Alternative) As drawn she uses 1/2"-8 8-start ACME precision ground threaded rod . I was pleasantly surprised at the price of $56. (That is not cheap but remember I got rid of all the linear rails and bearings.) This setup will move the shoulder nuts at 240mm/s. If you desire more structural stability you can upgrade to 3/4"-6 2-start rods for almost the same amount of money. (However, that upgrade will downgrade your top speed to 80mm/s.)However, even with the skinnier 1/2" rods you can use some simple string to increase the rigidity of the bot. I don't see any reason to get fancier than this. I would test the rigidity without the strings first to see if the strings are even needed.The build volume as drawn is 6L. Biggest cylinder that fits in the volume is 165mm diameter x 200mm tall.The inverse kinematics on this are pretty close to the kinematics for the Rostock. However, the carriage rotation in coupled with its translation so you will have to do one trig calculation for each arm to adjust for that. That should be no biggie for an fast ARM processor.Rough Vitamin List:*6' 1/2"-8 8-start ACME precision ground threaded rod $56*12 R8ZZ bearing $34*12 608 Bearings $3*4 6702 Bearings $4******* VERY LOW COST ITEMS *******12 M3x5*14 M3x20*36 M3x16*52 M3 Nyloc Nuts*6 M8x55*6 M8 Nyloc Nuts*3/4" MDF FlatstockConcerns:*Backlash could be a problem then again it might not. If it is, I have some ideas on how to make the printed shoulder nuts wear compensating.*Friction. Lubrication is a must. I will need to figure out what grease is PLA safe.Future Explorations:*Design the hub pieces to be able to side step the threaded rod by an extra 25mm. This would give you a 50% bigger build volume. This would allow you to print a cylinder that was 210mm in diameter by 200mm tall. (Without this mod you can only print a 165x200mm cylinder.)*Play with mounting the extruder stepper on the hub.