Helical gears are often the default choice in applications that are ideal for spur gears but have nonparallel shafts. Also, they are utilized in applications that require high speeds or high loading. And whatever the load or quickness, they generally provide smoother, quieter operation than spur gears.
Rack and Helical Gear Rack pinion is useful to convert rotational motion to linear motion. A rack is directly teeth cut into one surface of rectangular or cylindrical rod designed material, and a pinion can be a small cylindrical gear meshing with the rack. There are several methods to categorize gears. If the relative position of the apparatus shaft can be used, a rack and pinion is one of the parallel shaft type.
I’ve a question about “pressuring” the Pinion in to the Rack to reduce backlash. I have read that the bigger the diameter of the pinion gear, the less likely it will “jam” or “stick in to the rack, but 
the trade off may be the gear ratio increase. Also, the 20 level pressure rack is preferable to the 14.5 degree pressure rack for this use. Nevertheless, I can’t find any info on “pressuring “helical racks.
Originally, and mostly due to the weight of our gantry, we had decided on bigger 34 frame motors, spinning in 25:1 gear boxes, with a 18T / 1.50” diameter “Helical Gear” pinion riding upon a 26mm (1.02”) face width rack since given by Atlanta Drive. For the record, the motor plate is definitely bolted to two THK Linear rails with dual vehicles on each rail (yes, I understand….overkill). I what then planning on pushing through to the engine plate with either an Surroundings ram or a gas shock.
Do / should / may we still “pressure drive” the pinion up into a Helical rack to help expand reduce the Backlash, and in doing this, what would be a good starting force pressure.
Would the use of a gas pressure shock(s) are efficiently as an Air flow ram? I like the thought of two smaller drive gas shocks that equal the total force required as a redundant back-up system. I would rather not operate the atmosphere lines, and pressure regulators.
If the idea of pressuring the rack is not acceptable, would a “version” of a turn buckle type device that would be machined to the same size and form of the gas shock/air ram work to adapt the pinion placement into the rack (still using the slides)?
But the inclined angle of one’s teeth also causes sliding contact between your teeth, which generates axial forces and heat, decreasing performance. These axial forces play a significant function in bearing selection for helical gears. As the bearings have to endure both radial and axial forces, helical gears require thrust or roller bearings, which are usually larger (and more expensive) than the simple bearings used with spur gears. The axial forces vary in proportion to the magnitude of the tangent of the helix angle. Although larger helix angles offer higher swiftness and smoother motion, the helix angle is typically limited to 45 degrees due to the creation of axial forces.
The axial loads made by helical gears can be countered by using double helical or herringbone gears. These arrangements have the appearance of two helical gears with reverse hands mounted back-to-back again, although in reality they are machined from the same gear. (The difference between the two designs is that dual helical gears have a groove in the centre, between the the teeth, whereas herringbone gears do not.) This arrangement cancels out the axial forces on each group of teeth, so bigger helix angles can be used. It also eliminates the need for thrust bearings.
Besides smoother motion, higher speed capacity, and less noise, another benefit that helical gears provide more than spur gears is the ability to be used with either parallel or nonparallel (crossed) shafts. Helical gears with parallel shafts require the same helix angle, but opposing hands (i.e. right-handed teeth vs. left-handed teeth).
When crossed helical gears are used, they can be of either the same or opposing hands. If the gears have got the same hands, the sum of the helix angles should the same the angle between your shafts. The most typical example of this are crossed helical gears with perpendicular (i.e. 90 level) shafts. Both gears have the same hands, and the sum of their helix angles equals 90 degrees. For configurations with opposite hands, the difference between helix angles should equal the angle between the shafts. Crossed helical gears provide flexibility in design, however the contact between teeth is closer to point get in touch with than line contact, so they have lower push features than parallel shaft styles.