What’s the difference between a helical rack and ball screw assembly?

A helical rack assembly has a long linear gear that meshes with a rotating helical gear to provide linear motion. The Y-axes on both the CNT-950 and CNT-1000 are helical rack-driven. A ball screw assembly (as used on CNT’s X- and Z-axis assemblies) consists of a screw spindle and a nut, integrated with balls and the balls’ return mechanism. The screw rotates to convert rotary motion into linear motion, or torque to thrust, and vice-versa. The X-axis on the CNT-1000 is a rotating nut ball screw assembly where the nut rotates to create linear motion, while the screw is stationary.


What’s better, rack-and-pinion or ball screw?

The debate over rack-and-pinion vs. ball screw as the mechanical drive component in a CNC Router has been a contentious issue for decades. CNT uses both systems on all of our machines, based on which is best-suited for a particular axis or application.

Ball screws are best known for being very smooth and virtually friction-free. Their shortcomings include the need for precision alignment, contamination susceptibility, and the need for increased diameter and weight associated with length (span) to prevent whip or vibration. This, in turn, requires more gearing or larger motors to compensate for the weight and need to maintain rapid positioning speeds. CNT has been installing ball screws for over 20 years and has no difficulty with the alignment procedures involved in machine assembly. We provide wipers and air/oil pressurization on the nut to prevent contamination. We also limit the length and diameter to allow the best balance without sacrificing speed or performance.

Rack-and-pinion drives are best known for being rigid and not limited by length. When mounted properly, they provide years of use with minimal wear and are virtually impervious to dust and debris. Rack-and-pinion’s shortcomings include lower efficiency (due to higher friction), backlash caused by poor engagement of the pinion, and vibration caused by tooth profile. CNT uses 30-degree helical gear rack with a custom semi-topping profile to create ultra-smooth, low-friction movement with more teeth in mesh for power. Our unique pinion engagement system, combined with mapping software, delivers zero backlash and positional accuracy of ±.002″ throughout the entire travel distance of the rack.

Perhaps the best way to impress on you the rack-and-pinion vs. ball screw question is to look at CNC machines costing $100,000 to $300,000. You’ll notice that most of these machines use both mechanical drives on the same machine, just like CNT Motion.


What’s the difference between a stepper and servo?

Both stepper and servo drives provide basically the same cutting results. Primarily, a stepper is an “open-loop” system, and a servo is a “closed-loop” system. In a closed-loop system, there is constant signal feedback from the encoder (or motor) to the servo drive. This feedback tells the servo drive exactly where it is within its move. Thus, the servo drive can adjust its power output, as needed, to complete the move. The servo is more powerful, has quicker acceleration time and positioning speed. All of CNT Motion’s CNC machining centers are servo-driven.


What size machines do you offer?

Both the CNT-950 and CNT-1000 Series offer 48″X96″, 60″X120″ or 60″X144″ standard cutting areas. Special requests for custom lengths and widths on both models will be handled on an individual basis.


What HP spindle do I need?

As with most subjective questions, the type and thickness of your material, the type of tooling you’re using and the nature of your part(s) will determine what type of spindle you need. CNT Motion will happily assist you to determine the ideal spindle for your needs.


How much Z-axis travel distance is there? Can you make it longer?

The standard Z-axis throat clearance is 11″ on the CNT-1000 Series, but can be modified up to 48”. On the CNT-950 Series, throat clearances of 7″ and 11″ are available, although we have done up to 16”. However, the thickness of your decking material will reduce these amounts accordingly. Special requests for custom Z-travel distances will be addressed on an individual basis.


How accurate are your machines?

Each of CNT Motion’s machines has a positioning accuracy of ±.002 inches over the entire length of the machine. However, improper tooling and feed rates may affect accuracy.


How fast will my machine go? How fast can it cut my parts?

CNT Motion’s 950 Series has positioning speeds of up to 1000 inches-per-minute. The 1000 Series can traverse at up to 2000 inches-per-minute. However, your cutting speed (feed rate) will depend upon various factors, including:

  1. Rigidity of set-up — Vibration is a major source of tool wear and poor finish. The less vibration you have, the quicker you can feed your cutting tool, and, consequently, the smoother finish you will get.
  2. Machine environment — Other variables that affect every machining application are spindle horsepower, rigidity and runout, collet condition, fixturing system and tool sharpness.
  3. Number of flutes — Single-flute tools should generally be fed at a slightly higher rate (approximately 10%) than double-flute tools.
  4. Bit diameter — A 3/8″ bit can be fed 10% faster than a 1/4″ bit. A 1/2″ bit can be fed 20% faster than a 1/4″ bit.
  5. Depth of cut — Your feed rate should be decreased approximately 25% for each multiple of the depth of cut. (If depth is two times, reduce by 25%; if depth is three times, reduce by 50%.)
  6. Spindle speed — The faster the RPM of your spindle, the quicker you can cut your parts. Standard RPM on tool changers is 24,000.

Tooling catalogs will typically provide CNC machining feed charts as a reference tool. When buying tools, these guides can prove to be an invaluable resource. CNT Motion will provide a tooling catalog with each purchase. We also offer a 25% discount on tooling purchases. (Minimum order applies. Ask for details.)


How do you program the machine to cut parts? Is it easy to do?

WinCNC, the motion control software we use, is based on standard G-codes. The G-codes provide a source code comprised of inches/mm and axis movements, which can be edited and understood by others. Most CAM packages will generate G-codes from the drawings you create. It’s actually quite simple. Visit our Software page for more information about WinCNC.


What other software, other than what’s included with the machine, do I need?

No extra software is needed to actually run the CNC machine. However, your specific application will determine if you need any specialized software (AutoCAD, etc.) to create your part files and CAM them. Visit our Third-party Software page for more information about available packages.


How do I fixture my material?

The size of your part, type of material and production goals will determine the most-suitable method of holding your material in place. Generally, a vacuum system is the most-efficient method of fixturing your material. CNT Motion offers vacuum systems with either a regenerative blower or claw pump. A rotary blower is usually better for smaller parts. You can also mechanically fixture your material with clamps, screws or double-stick tape. These methods would most likely require you to use a tabbing method of cutting your parts. With tabbing, you edit a few very slight vertical Z-moves along the outer edges of your part file. This will leave the part attached to the main stock by small “tabs” similar to the way plastic model kits are made. Once cut, your part can be twisted free of the material and the remainder of the tabs can be removed with a sharp knife or sanding block.


Can I use your CNC machining center as a point-to-point machine?

Point-to-point applications would not make the best use of our machines. Point-to-point machining typically requires that your machine be able to perform end-boring functions, which require special head assemblies and fixturing.


Do I really need to enclose my computer?

CNT Motion strongly recommends that you use an enclosure to protect your computer controller from the airborne particulates typically found in a workshop environment. A pressurized computer controller cabinet comes standard with each of our machines to protect your computer. It also houses all of the electronics for your CNC machine.


Is a maintenance kit available for purchase?

Every one of CNT’s machines is designed with preventative maintenance in mind; so a formal maintenance kit is unnecessary. Upon delivery and training, your CNT representative will provide you with all the direction and information you’ll need to maintain your machine and keep it running optimally and without problems.


What kind of field support do you offer?

Our experienced technicians understand a broad range of automation applications and can provide support by phone or at your facility. (Some fees may apply.) Regional expertise may also be available. Additionally, each machine is pre-configured for remote desktop support. This enables our technicians to troubleshoot your system via an Internet connection. (High-speed Internet connection required for remote desktop support.)


Do you offer training?

Training in the operation of CNT Motion’s equipment is available at the time of installation. Additional training is also available, but our customers usually adapt to it quite easily. Contact us for details and pricing.


How long does installation and initial training take?

Since our machines are delivered completely assembled and pre-wired, installation usually takes half a day. Our recommended initial training lasts 2-1/2 days or more, if necessary.


How are the machines delivered?

Our CNC machines are delivered on a flat-bed truck, tarped and fully assembled. For unique loading dock requirements, special provisions can be made to accommodate your facility.


Do you offer leasing?

Leasing a CNC machine brings with it many advantages, including tax benefits and minimal up-front cash requirements. CNT Motion, in partnership with Leasing Resources, Inc., has made it simple and convenient. (Click here for a free quote.) You can use your own leasing company, if you choose.


Are there any machines in my area that I can observe?

CNT Motion Systems has customers throughout the United States and overseas. If there is one in your area and you wish to visit their facility, we will contact them and arrange a visit.


What type of warranty do you provide?

CNT Motion Systems stands behind every machine we build. And we back them up with a warranty that ensures quality and dependability. We warrant every component we manufacture against defects in workmanship, materials and construction when used under normal operating conditions and in accordance with provided specifications for a period of one (1) year from the date of delivery. We will repair or replace, at our option, any of our products found to be defective during the warranty period. Contact us for complete details of the CNT Motion Systems Policies Terms and Conditions. Download a copy of our product warranty.