FAQ A: General Air Bearing Questions
A-01 What surfaces can I run New Way Air Bearings on?
Granite and hardcoat aluminum are the most popular choices. Ceramics and zero coefficient of thermal expansion glass are appropriate in ultra accurate applications. Air bearings can run on steel such as hardened steel bands or inserts, but there should be no oil on the surface, and steels used must not rust or corrode.
Also, because porous carbon air bearings do not have a hard face, they can be used against softer surfaces. Polymer and especially replicated polymers represent an opportunity for large cost savings in the production of precision guide surfaces. The surface finish should be 16 RMS or better. Local flatness-straightness (the area under a bearing at any one time) should be flat to within 50% of the air gap.
A-02 Will the air bearings fly on a ground surface, or must the surface be lapped?
New Way air bearings can operate on either a ground or lapped surface if the surface finish has an average roughness of 16Ra (u") or better. Grinding operations typically produce a surface finish of 8µ" - 63µ" Ra, where lapping will produce a surface finish of 2µ" - 8µ" Ra. Answer 2 is displayed to the right of question 2.
A-03 Can I fly porous media air bearings over holes or grooves in a guide surface?
You can fly the air bearings over holes or deep grooves in the guide surface as long as the hole is not so large that the air bearing is unable to support the mass on it without touching down due to the reduction of surface area that the air pressure can build up in. Also, make sure the holes or grooves do not have a raised edge.
It is much more difficult to fly over a seam; the height difference of the 2 sides of the seam must be small relative to the air gap, ideally 25% or less. If you have an air gap that is 10 microns, the height difference will need to be 2.5 microns or less . . . possible, but may take a lot of work to achieve. It is best to avoid this if possible.
A-04 Is there some relationship between the height of the air gap and the shear force?
The shear force loss (drag) is an inverse cubed function of the air gap.
A-05 Can I use New Way air bearings at high temperatures?
As of yet, we have no test data for air bearing performance at high temperatures. You'll need to proceed with trial and error testing to ascertain the viability of the air bearing at elevated temperatures.
Our bearings are designed to operate at or near a temperature of 20ºC (68ºF). At higher (or lower!) temperatures, our air bearings will begin to distort due to the difference in the co-efficient of thermal expansion and contraction between the housing material (aluminum) and the air bearing material (carbon). This dimensional change will affect the flatness of the air bearing, causing cupping (with heat) and convexing (with cold) and will affect the performance of the air bearing.
If your desired operating temperature is between 20ºC and 50ºC (122ºF), we recommend testing the air bearings to determine viability for your application. However, we do not recommend using these air bearings above 50ºC.
A-06 Do you have any information regarding the chemical resistance of your porous media?
The formulation of our porous media is a trade secret and so no information is provided regarding its chemical make-up. However, it is a good idea to prevent chemicals from coming in contact with the surface of the porous media.
If resins or materials are allowed to collect on the air bearing surface, it will locally restrict the airflow by blocking the pores in the carbon, and will then need to be cleaned in order to maintain airflow and proper performance.
Use 99% Isopropyl alcohol to clean the bearing.
A-07 I am using New Way Air Bearings in my assembly. What special precautions should I use to protect the air bearings during shipment?
Since air bearings operate with a very small air gap (measured in microns), it is usually impossible to fit any material between the guide surface and the air bearing. Therefore, extra precautions are necessary when an air bearing assembly is shipped with the air bearings installed and in contact with the guide surface.
One of the features of the New Way Porous Carbon media is that it will not scratch the guide surfaces and there is a very low risk of damaging the air bearings when shipped in place. This is not true for orifice air bearings that can damage both the guide surface and air bearing if the two surfaces come in contact. This feature allows the shipment of an air bearing assembly as a unit to reduce or eliminate the need to assemble the system in the field.
To protect the air bearings during shipment, you'll need to adequately restrict the relative motion between the air bearing mating parts, and protect the entire assembly from external damage, including vibration-induced damage.
When you are packaging lighter assemblies, restricting motion with packing materials and some reinforcing detail in the crate itself is sufficient.
For heavier assemblies, it is strongly suggested that you design and incorporate shipping brackets that mechanically connect the relative motion parts. The best shipping crate designs for air bearing assemblies not only constrain the movement of those assemblies, but fix the assembly in the shipping package.
If you need assistance, please contact New Way Air Bearings.
A-08 Will chemicals inadvertently applied to the surface of a bearing have an adverse effect on performance?
Because the bearings are porous, any fluids or chemicals that come in contact with them will be absorbed. New Way has not performed exhaustive testing on every possible chemical, so we do not know the full range of potential effects. We strongly recommend against allowing any chemicals to come in contact with air bearings.
A-09 What concerns should I have if air pressure to the bearings is interrupted while they are in operation?
Your principal concern should be safety. Will the machine operator be injured in the event of a bearing “touch down?” If so, then a low air-pressure alarm will need to be installed, along with a reserve air supply receiver. Since New Way air bearings use so little air, when the primary supply has failed, a small receiver (about 4 liters is typically enough) will provide enough time to shut down most machinery. Testing should be performed to ensure that the necessary emergency air volume is sufficient.
A-10 Will the machinery/bearings become damaged in the event of bearing contact with the ways?
New Way air bearings are finished to such a high degree of accuracy, and the ways or shafts that are used in applications are stipulated to be at 16Ra (µ in), the two surfaces are usually so smooth that there isn’t any damage. Further, the carbon/graphite used as a porous media in New Way’s air bearings is a natural bearing material in its own right, and will not damage shafts or ways in the event of contact. Neither will the bearings themselves suffer damage, as long as the contact is short, on the order of a few minutes.
A-11 What are the materials used in your bearings?
Anodized aluminum – with epoxy mounted carbon.
FAQ B: Air Bearings – Flat Round and Flat Rectangular
B-01 What maintenance do the porous media Air Bearings require?
New Way® Porous Media Air Bearings require no regular maintenance. Unlike orifice air bearings, New Way® Air Bearings are not susceptible to dirt or clogging. If you do need to clean the air bearing, simply wipe the bearing surface with alcohol and let dry.
B-02 What can I use to clean New Way Air Bearings?
Clean bearing & guide surfaces when needed, with air pressure applied, using ISOPROPANOL ALCOHOL ONLY. Do not clean air bearings or guide surfaces with acetone, ketones, MEK's.
B-03 How are the stiffness specifications for flat air bearings calculated?
Stiffness calculations shown on the product tables are measured with a known force applied to the air bearing housing and the displacement is measured.
FAQ C: Vacuum Preloaded Air Bearings
C-01 What is a Vacuum Pre-Loaded Air Bearing (VPL), and how does it work?
A Vacuum Pre-Loaded (VPL) Air Bearing uses externally supplied negative pressure, or vacuum, to create a force to oppose the positive pressure of the air bearing. In other words, vacuum is used to pull the air bearing closer to the opposing (or guide) surface without the need for an opposing air bearing or the addition of a load or mass to the bearing to create stiffness. Just like external pressure is supplied to the air bearing to create the pressure on the bearing face, vacuum is supplied to the air bearing to create the opposing force. One advantage to the VPL is that by adjusting the vacuum and pressure, the flying height can be changed to match the desired performance of the application. Incremental stiffness of the air film, with a light load, can also be achieved, depending on the application. The adjustability of the air film thickness can be used for focusing, squaring and sub-micro inch vertical positioning over a range of 1 - 2 thousandths of an inch. Another positive is that the bearing has a defined “settling time” – meaning that the height of the bearing does not fluctuate when in transition, and is naturally stable. This can be quite advantageous in demanding ultra - precision applications.
To achieve the same level of precision using opposed bearing preloading, you would need two flat guide surfaces that are parallel, instead of only the one flat guide surface of a VPL.
C-02 What size vacuum line should I use on a VPL?
As a rule of thumb, the larger the diameter of the vacuum line, the more performance you can expect in dynamic conditions. A smaller or restrictive line will create unwanted flow damping, which will limit performance. High, unrestricted vacuum flow can marginally improve the ability of a VPL to stay attached to its guide surface when it experiences dynamic forces near the design limit. Since the dynamic forces are unique to each design, you will need to test this for your particular application in order to quantify the benefit.
C-03 How can I test the VPL fly height?
First, you will need an air supply that can be switched on and off, as well as a vacuum line.
Second, you will need a device (or measuring instrument) that has an adequate range and appropriate resolution to measure the fly height. The range should be at least 75 microns, and resolution as needed for the application. New Way suggests using a capacitance probe, for accurately measuring the height of the bearing. One thing to keep in mind is that if you are using an inductance probe, your data may vary from New Way’s, since an inductive probe will take an “average” of peaks and valleys on the aluminum surface. One solution would be to use a gauge block, with a fine surface finish as the reference surface.
With these instruments in place, you are ready to test the bearings.
1. Record the bearing serial number (for your records),as well as the test instrument number and type.
2. Clean the bearing face with 99% Isopropyl Alcohol.
3. Put the bearing on the test surface, face down and apply vacuum pressure.
4. Place the measurement indicator in contact with the surface of the bearing at the test point location. At New Way, we test the 4 corners first, then the center.
5. With the measurement probe in contact with the bearing, ‘Zero’ the indicator.
6. Switch the air on to the specified air pressure and record the change in height.
7. Turn the air off and the reading should return to zero.
8. Repeat steps 6 and 7 several times, and record the average of the data. The difference in measurements should be very small – if appropriate significant digits are used, averaging should not be necessary.
C-04 Can I modify a New Way VPL by drilling into the housing?
We don’t recommend drilling into New Way VPLs. New Way will not warranty any bearing that has been modified.
C-05 Can I use the New Way Ball Mounting Screws with a VPL?
Sure you can, just understand that without any kind of restraint between the bearing and the ball, you must maintain positive pressure on the bearing assembly in order to keep the ball in contact with the bearing.
C-06 Do you offer a rigid mount for your VPLs?
Currently New Way does not offer a rigid mount for VPLs as part of the product catalog. However, if it is necessary, by special order one can be provided.
FAQ D: Air Bushings
D-01 What is the accuracy of these air bushings?
The accuracy of the path traveled by a bushing is determined almost entirely by the accuracy of the guide.
D-02 Can I use an air bushing for rotational as well as linear motion?
Yes, New Way air bushings are often used to support rotating shafts. It is also possible to allow the air bushing to rotate, but remember the need to provide pressurized air to the bushing.
D-03 Will the air bushing be damaged if it comes in contact with the guide?
D-04 How do I mount air bushings?
Two common methods for mounting air bushings in a standard New Way mounting block or bore in a custom housing are:
O-Ring press fit (flexible mount).
Standard New Way air bushings are supplied with 4 o-rings, two inner and 2 outer rings. The two inner o-rings form a seal to allow the pressurized air to supply the air bearing. An air supply hole can be located anywhere on the mounting block between the two inner o-rings. This mounting method allows the air bushing to “float” somewhat in the housing to allow the air bushing to align axially with the shaft and accommodate misalignments of air bushings and shafting of up to .002” (.050 mm). Install the two outer o-rings for a flexible mount with additional stiffness. Use Isopropyl Alcohol as a lubricant when pressing the bushings into a mounting block or housing.
Bonded in place (hard mount).
This method requires the use of 4 o-rings. The inner two o-rings form the seal for the air supply. The outer two o-rings form two annular cavities with the inner two o-rings. These cavities are filled with an epoxy that will fix the air bushings in precise alignment with the shaft. In this method, the air bushings are positioned in the housing with the 4 o-rings. Again, use Isopropyl Alcohol as a lubricant before pressing the bushings into a mounting block or housing. Align the shafts and supply compressed air to the air bushing via the supply hole located between the inner o-rings. The epoxy is then injected though holes in the housing so that the cavities between the outer and inner o-rings are filled. The air supply to the air bushing must remain on while the epoxy cures. If custom housings are used, be sure to supply an additional hole in the cavities so that the air can escape when the epoxy is injected.
D-05 What are the four O-Rings on an air bushing used for?
See "How do I mount air bushings?"
D-06 What epoxy should I use to hard mount an air bushing in a mounting block?
We recommend using 2-part epoxies that cure completely without special additional catalysts, have good bond strength to metals, and can readily be found in viscosities that lend them to this application. Shrinkage is typically not a concern in bonding air bushings in mounting blocks. Other properties such as out-gassing should be considered depending on the environment where the air bushings will be located. Most epoxies cure exothermally but with the amount needed to bond the air bushings, this should not be a concern.
Specifically the recommended characteristics are:
- A room-temperature cure epoxy with a reasonable set-up time or pot life for the number of air bushings being bonded – recommend 30 to 120 minutes.
- A cure time reasonable for the application – recommend 24 hours.
- A viscosity that lends itself to injecting into the hole provided in the pillow block or mounting block – recommend between 5,000 and 100,000 cP (centipoise).
New Way recommends using DWH-310FL Static Fitting Material manufactured by Moglice (see link below) for this application.
D-07 Can I use New Way air bushings at high rotary speeds?
The simple answer is yes, but we preface this with the statement that New Way air bushings are not tested specifically for high rotary speeds like an air bearing spindle. Through some cautious trial and error, you can safely test the operation of a New Way air bushing in your desired speed range.
The initial problem to solve will be selecting a coupling for the air bushing shaft that does not introduce any error motion from your driver due to the belt or motor's axis of rotation error, and/or vibration. A "Google" search on "Helical" or "Bellows couplings" will provide many options for couplings.
The air bushings include O-rings that allow the air bushing to be press-fit into a New Way mounting block - this will provide some compliance to mitigate this problem. (Remember to use Isopropyl Alcohol to lubricate the O-rings, before you press the bushings into the pillow blocks!)
Once the coupling is selected, and the air bushing is operated like an air bearing spindle, you may discover some heat build-up at around 50 meters-per-second (170 ft/s or 40,000 rpm for a 25mm OD shaft), due to the viscous shear of the air film between the air bushing and the shaft. You may actually need to grind the shaft down below the New Way recommended diameter in order to accommodate shaft diameter growth due to thermal expansion.
The heat gain is partly offset by the cooling of the air input into the air bushing, so it is difficult to predict when you will need to address the dimensional changes. Our suggestion is to incrementally increase the rotational speed by 7 meters per second (22 ft per sec or 5000 rpm with a 25mm shaft), until you begin to see a change. Since the air bushing is virtually frictionless, a good indicator is when changes in the current draw of your motor becomes non-linear.
As heat builds, the shaft will grow and displace the air film within the air bushing, and can come into contact with the Porous Carbon media. The air bushing should not be damaged, as long as the shaft finish is per the New Way recommendation (Ra 0.4mm, 16µ in) and the period of contact is brief; on the order of a few minutes. Let the shaft cool before trying to remove it from the air bushing.
Recommended Bushing Rotary Speeds: (50 m/s - 170 ft/s)
Bushing ID Speed (Rpm's)
0.25 Inch 140,000
13 mm 76,500
20 mm 50,000
25 mm 40,000
40 mm 25,000
50 mm 20,000
75 mm 13,250
If you need further assistance, please contact New Way Air Bearings.
D-08 How are the stiffness specifications for Air Bushings calculated?
Radial (normal) stiffness is measured with the bushing flying on a shaft of the dimension specified with the specified air pressure applied. A known mass is suspended from the bushing housing (without a pillow block) and the displacement is measured several times and averaged.
Pitch moment stiffness is measured with the bushing flying on a shaft of the dimension specified with the specified air pressure applied. The bushing is mounted in a pillow block and equal and opposite moment loads are applied at equidistant points from the center of the bushing. The displacement is measured and the stiffness is calculated using the known force applied.
D-09 How does shaft size tolerance affect air bushing performance?
The stiffness of the air film is inversely proportional to the air gap (smaller gap, more stiff). If mechanical stiffness is not important, a larger than recommended gap can be used but should be tested to assure it will function properly.
FAQ E: Precision Zone Air Bars
E-01 Can the Flat Panel precision chuck be operated at 50µm lift, or should 20µm - 25µm lift be used?
After reviewing design factors, a customer drew the conclusion that they needed 50µm of lift, but felt that other parameters would suffer (i.e. stiffness, air consumption, and accuracy). But since there was no data available, this customer worried that the chuck would not perform adequately.
The truth is that the Flat Panel Precision Chuck CAN be operated at 50µm. The air consumption is higher and the stiffness is lower than at the designed 25µm fly height, but not out of the range of viability.
Testing should be performed on the intended process to determine suitability.
FAQ F: Air Slide Assemblies
F-01 Specific Instructions for New Way® Air Slides?
When removing air slide unit from rail, the slide must be removed WITH 60 PSI AIR PRESSURE APPLIED. HOWEVER IT IS STRONGLY RECOMMENDED THAT THE AIR SLIDE UNIT NOT BE REMOVED FROM THE RAIL. PLEASE CONTACT NEW WAY FOR SPECIFIC INSTRUCTIONS.
Reassemble the air slide unit to the rail with 60 PSI AIR PRESSURE APPLIED. The air slide must be placed onto the rail so that the two alignment marks located on the side corner of the slide line-up with the two alignment marks located on the end of the rail.
DO NOT apply air slide unit to any rail other than the rail on which the slide unit was originally provided.
Air supply can be connected to any of the 12 ports fitted with brass hex plugs (box slides only).