Desde hace un tiempo yo tenía ganas de hacer un reductor a tornillo. Cuando decidí colgar del techo mi torno, estuve a punto de concretar el proyecto, pero finalmente, dado el peligro que representaba un peso elevado que eventualmente podría desplomarse en caso de falla, decidí comprar uno hecho, de esos que se usan para plegar y desplegar toldos metálicos.
Este tipo de reductor tiene varias características interesantes:
- Permite con relativa facilidad obtener reducciones muy importantes, del orden de 100 a 1, o más. Eso es mucho más difícil de lograr con engranajes.
- No necesita de una traba ni crique para mantenerse fijo en el lugar en que uno lo deja, porque al ser la reducción elevada y trabajar por fricción, el movimiento en sentido contrario es prácticamente imposible.
- Requiere de un solo engranaje, en el cual encaja un tornillo o sinfín cuya rosca tenga el mismo paso que el engranaje.
Cuando comencé a construir mi chulengo (próximamente subiré el instructable) decidí que era una buena oportunidad para hacer un reductor de ese tipo, dado que la fuerza necesaria no era tan elevada como para que una falla pudiera ser desastrosa.
Speed reducers are at the same time, and a for a physical law, force enhancers.
For some time I wanted to make a screw-gear reductor. When I decided to hang my lathe at the ceiling, I was about to do it, but ultimately, given the danger of a heavy weight that could eventually collapse in case of failure, I decided to buy one made, the kind that are used to fold and unfold metal awnings.
This type of reductors has several interesting features:
- Relatively easily allows to obtain very substantial reductions in the order of 100 to 1, or more. That's much more difficult to achieve with gear.
- No need for a lock or crick to stay fixed in place when one leaves it, because being high reduction and working by friction, the movement by itself in the opposite direction is almost impossible.
- Requires a single gear, which fits a screw or worm screw which has the same pitch as the gear.
When I started building my chulengo (instructable coming soon) decided it was a good opportunity to do such a reductor because the forces were not so high that a failure could be disastrous.
Step 1: Getting the Materials (conseguir Los Materiales)
I looked among my things and found an old bicycle rear sprocket, disassembled, 16 teeth. It had been discarded for wear, but for my need that is superfluous. Also found a piece of round iron of about 7 mm in diameter and long more than enough.
Step 2: Making the Shaft to the Gear (haciendo El Eje Para El Engranaje)
I soldered two concentric bushings to the gear to match their diameter to iron pipe that will receive movement. I took care of the gear is fairly centered.
Step 3: Doing the Screw Thread (haciendo La Rosca Del Tornillo)
Según mis consideraciones, con una vuelta y unos pocos milímetros más hubiera sido suficiente, pero decidí hacer algo más de dos vueltas, para que la fuerza quedara distribuida sobre dos dientes del engranaje. Creo que fue una buena decisión.
Cold rolled 8 mm iron around another piece of iron, 12 mm in diameter. In the first stage I did not care to retain the right step, I did that once I had created two laps of what would become the "thread" of the screw. As heart of this I used a piece of car steering, also ruled out through attrition. Tightly mounted two turns of wire on this axis 8 mm, approximately 13 mm in diameter. Then separated the coils by a chisel used as a wedge, to the effect that the separation between turns coincide with the distance between gear's teeth.
According to my observations, with a lap and a few millimeters would be sufficient, but I decided to do something more than two turns, so that the force remain distributed over two sprockets. I think it was a good decision.
Step 4: Welding the Thread to Axis (soldando La Rosca Al Eje)
Applied 4 tack welds: one at each end of the "thread" and two in between. It is not necessary anymore, because as explained before, there will be no high forces. Then made an eyelet with the same 8 mm iron and soldered it on the end of the shaft, to serve as actuator.
Step 5: Making the Support for the Screw (haciendo El Soporte Para El Tornillo)
I could not get among my things a pipe to serve as a hub, so I cut two pieces of the closest tube I found, made longitudinal cuttings and closed them around the shaft of the screw and soldered the edges of the joint. Temporarily mounted on the axle these improvised hubs and soldered them two separate iron brackets to mount in place.
Step 6: Assembling and Testing All (armando Todo Y Probando)
I put the bike gear on the pipe that it should move (its axis), and then mounted the screw with its bushings so that the screw threads fits into the gear teeth.
Step 7: Recalculating ...(recalculando...)
- La chapa del tambor donde estaban montados los soportes cedía ligeramente al hacer girar el tornillo, y entonces se perdía la buena relación entre el tornillo y el engranaje
- Los dientes del engranaje tenían el borde demasiado filoso y se clavaban en el hierro del tornillo.
The first test was a bit frustrating, because of two concurrent circumstances:
- The sheet of the drum where the brackets were mounted yielded slightly when turning the screw, and then lose the good relationship between the screw and gear
- Gear teeth were too sharp edge and is fixed on the iron of the screw.
Step 8: Successful Test (prueba Exitosa)
Una vez hechos esos ajustes, y corregidos algunos pequeños defectos de la rosca, el reductor funcionó perfectamente.
Overcome both problems was relatively easy. On one hand, an iron rod soldered linking bushings and secured to the gear support, making a more robust body. On the other hand, with the hand grinder modified the profile of the teeth to settle more friendly on the screw's surface.
After these adjustments, and corrected some minor flaws of the thread, the reductor worked perfectly.