Helical gears tend to be 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 often provide smoother, quieter operation than spur gears.
Rack and pinion is utilized to convert rotational movement to linear motion. A rack is straight teeth cut into one surface of rectangular or cylindrical rod formed materials, and a pinion is a small cylindrical equipment meshing with the rack. There are numerous ways to categorize gears. If the relative Helical Gear Rack placement of the apparatus shaft is used, a rack and pinion belongs to the parallel shaft type.
I have a question about “pressuring” the Pinion in to the Rack to lessen backlash. I have read that the larger the diameter of the pinion gear, the less likely it is going to “jam” or “stick into the rack, but the trade off may be 
the gear ratio enhance. Also, the 20 degree pressure rack is preferable to the 14.5 level pressure rack because of this use. However, I can’t find any info on “pressuring “helical racks.
Originally, and mostly due to the weight of our gantry, we’d 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 because supplied by Atlanta Drive. For the record, the motor plate is definitely bolted to two THK Linear rails with dual cars on each rail (yes, I know….overkill). I what then planning on pushing up on the motor plate with either an Air flow ram or a gas shock.
Do / should / may we still “pressure drive” the pinion up right into a Helical rack to further decrease the Backlash, and in doing this, what would be a good beginning force pressure.
Would the usage of a gas pressure shock(s) are efficiently as an Air ram? I like the thought of two smaller force gas shocks that equal the total force required as a redundant back-up system. I would rather not operate the air flow lines, and pressure regulators.
If the thought of pressuring the rack isn’t acceptable, would a “version” of a turn buckle type device that might be machined to the same size and form of the gas shock/air ram work to change the pinion placement in to the rack (still using the slides)?
However the inclined angle of one’s teeth also causes sliding contact between the teeth, which generates axial forces and heat, decreasing effectiveness. These axial forces enjoy a significant role in bearing selection for helical gears. Because the bearings have to endure both radial and axial forces, helical gears need thrust or roller bearings, which are typically larger (and more expensive) compared to the simple bearings used in combination with spur gears. The axial forces vary compared to the magnitude of the tangent of the helix angle. Although larger helix angles provide higher velocity and smoother motion, the helix angle is typically limited to 45 degrees due to the production 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, although the truth is they are machined from the same gear. (The difference between your two styles is that double helical gears have a groove in the centre, between the tooth, whereas herringbone gears do not.) This set up cancels out the axial forces on each group of teeth, so larger helix angles can be used. It also eliminates the need for thrust bearings.
Besides smoother motion, higher speed ability, and less sound, another advantage that helical gears provide more than spur gears may be the ability to be utilized with either parallel or non-parallel (crossed) shafts. Helical gears with parallel shafts require the same helix position, but reverse hands (i.e. right-handed teeth vs. left-handed teeth).
When crossed helical gears are used, they could be of possibly the same or opposing hands. If the gears possess the same hands, the sum of the helix angles should equivalent the angle between your shafts. The most typical example of this are crossed helical gears with perpendicular (i.e. 90 degree) shafts. Both gears have the same hands, and the sum of their helix angles equals 90 degrees. For configurations with opposing hands, the difference between helix angles should equal the angle between your shafts. Crossed helical gears provide flexibility in design, however the contact between teeth is nearer to point get in touch with than line contact, so they have lower pressure capabilities than parallel shaft styles.