Helical gears tend to be the default choice in applications that are suitable for spur gears but have non-parallel shafts. Also, they are used in applications that require high speeds or high loading. And whatever the load or rate, they generally provide smoother, quieter procedure than spur gears.
Rack and pinion is useful to convert rotational motion to linear movement. A rack is straight teeth cut into one surface area of rectangular or cylindrical rod designed materials, and a pinion is definitely a small cylindrical equipment meshing with the rack. There are several methods to categorize gears. If the relative position of the apparatus shaft is used, a rack and pinion is one of the parallel shaft type.
I have a question regarding “pressuring” the Pinion into the Rack to lessen backlash. I’ve read that the bigger the diameter of the pinion equipment, the less likely it will “jam” or “stick into the rack, but the trade off may be the gear ratio enhance. Also, the 20 level pressure rack is preferable to the 14.5 degree pressure rack for this use. Nevertheless, I can’t discover any information on “pressuring “helical racks.
Originally, and mostly because of the weight of our gantry, we had decided on larger 34 frame motors, spinning in 25:1 gear boxes, with a 18T / 1.50” diameter “Helical Gear” pinion riding on a 26mm (1.02”) face width rack because given by Atlanta Drive. For the record, the engine plate is definitely bolted to two THK Linear rails with dual vehicles on each rail (yes, I know….overkill). I what then planning on pushing through to the electric motor plate with either an Air flow ram or a gas shock.
Do / should / can we still “pressure drive” the pinion up right into a Helical rack to help expand decrease the Backlash, and in doing so, what will be a good starting force pressure.
Would the use of a gas pressure shock(s) work as efficiently as an Atmosphere ram? I like the idea of two smaller drive gas shocks that the same the total push required as a redundant back-up system. I’d 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 might be machined to the same size and shape of the gas shock/air ram work to adapt the pinion placement into the rack (still using the slides)?
However the inclined angle of the teeth also causes sliding contact Helical Gear Rack between your teeth, which produces axial forces and heat, decreasing performance. These axial forces play a significant part in bearing selection for helical gears. As the bearings have to endure both radial and axial forces, helical gears need thrust or roller bearings, which are typically larger (and more costly) compared to the simple bearings used with spur gears. The axial forces vary compared to the magnitude of the tangent of the helix angle. Although larger helix angles provide higher speed and smoother motion, the helix position is typically limited by 45 degrees due to the production of axial forces.
The axial loads produced by helical gears could be countered by using double helical or herringbone gears. These plans have the appearance of two helical gears with opposing hands mounted back-to-back, although in reality they are machined from the same equipment. (The difference between the two styles is that dual helical gears possess a groove in the centre, between the the teeth, whereas herringbone gears usually do not.) This set 
up cancels out the axial forces on each group of teeth, so larger helix angles may be used. It also eliminates the need for thrust bearings.
Besides smoother movement, higher speed capacity, and less sound, another benefit that helical gears provide over spur gears may be the ability to be used with either parallel or non-parallel (crossed) shafts. Helical gears with parallel shafts need the same helix position, but opposite hands (i.electronic. right-handed teeth versus. 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 equivalent the angle between the shafts. The most typical example of this are crossed helical gears with perpendicular (i.e. 90 level) shafts. Both gears possess the same hands, and the sum of their helix angles equals 90 degrees. For configurations with opposing hands, the difference between helix angles should the same the angle between your shafts. Crossed helical gears provide flexibility in design, however the contact between the teeth is nearer to point contact than line contact, so they have lower push features than parallel shaft designs.