Helical gears tend to be the default choice in applications that are ideal for spur gears but have non-parallel shafts. Also, they are utilized in applications that want high speeds or high loading. And whatever the load or velocity, they generally provide smoother, quieter operation than spur gears.
Rack and pinion is utilized to convert rotational movement to linear movement. A rack is straight teeth cut into one surface area of rectangular or cylindrical rod shaped material, and a pinion is usually a small cylindrical gear meshing with the rack. There are several ways to categorize gears. If the relative placement of the gear shaft can be used, a rack and pinion is one of the parallel shaft type.
I have a question about “pressuring” the Pinion in to the Rack to reduce backlash. I have read that the bigger the diameter of the pinion equipment, the less likely it is going to “jam” or “stick into the rack, however the trade off may be the gear ratio boost. Also, the 20 level pressure rack is preferable to the 14.5 degree pressure rack because of this use. However, I can’t discover any info 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 since supplied by Atlanta Drive. For the record, the electric motor plate is definitely bolted to two THK Linear rails with dual vehicles on each rail (yes, I understand….overkill). I what after that planning on pushing through to the motor plate with either an Atmosphere ram or a gas shock.
Do / should / may we still “pressure drive” the pinion up right into a Helical rack to help expand reduce the Backlash, and in doing so, what will be a good beginning force pressure.
Would the use of a gas pressure shock(s) are efficiently as an Air ram? I like the idea of two smaller drive gas shocks that the same the total push needed as a redundant back-up system. I would rather not operate the air flow lines, and pressure regulators.
If the idea 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 shape of the gas shock/air ram work to modify the pinion placement into the rack (still using the slides)?
However the inclined angle of the teeth also causes sliding contact between your teeth, which generates axial forces and heat, decreasing effectiveness. These axial forces perform a significant function 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 usually larger (and more expensive) compared to the simple bearings used in combination with spur gears. The axial forces vary in proportion to the magnitude of the tangent of the helix angle. Although bigger helix angles offer higher 
acceleration and smoother movement, the helix angle is typically limited to 45 degrees because of the creation 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 reverse hands mounted back-to-back again, although the truth is they are machined from the same equipment. (The difference between the two styles is that dual helical gears have a groove in the centre, between the teeth, whereas herringbone gears do not.) This arrangement cancels out the axial forces on each set of teeth, so bigger helix angles may be used. It also eliminates the need for thrust bearings.
Besides smoother motion, higher speed capability, and less sound, another advantage that helical gears provide more than spur gears is the ability to be utilized with either parallel or nonparallel (crossed) shafts. Helical gears with parallel shafts require the same helix angle, but opposite hands (i.electronic. right-handed teeth versus. left-handed teeth).
When crossed helical gears are used, they may be of possibly the same or opposing hands. If the gears possess the same hands, the sum of the helix angles should the same the angle between your shafts. The most common exemplory case of this are crossed helical gears with perpendicular (i.e. 90 degree) shafts. Both gears possess the same hands, and the sum of their helix angles Helical Gear Rack equals 90 degrees. For configurations with opposing hands, the difference between helix angles should equivalent the angle between the shafts. Crossed helical gears offer flexibility in design, but the contact between teeth is nearer to point get in touch with than line contact, so they have lower drive features than parallel shaft styles.