CMMXYZ Resource Center

The Ultimate Used CMM Machine Buyers Guide

What are the benefits of purchasing a used CMM Machine?

The first questions many prospective buyers ask are:

  • What are the benefits of purchasing a used CMM?
  • What to look for in used CMM equipment?
  • What are the risks associated with the purchase?

The major benefit is the immense cost savings usually 50% and sometimes greater than the cost of a new machine.  Used CMM machines are also available for immediate delivery and are not subject to the 6 to 10 weeks waiting time for a new one.

Mechanically coordinate measuring machines have not changed much in the last 30 years, only the machine controller and software has undergone significant modernisation in recent years.  Therefore, many companies who own older machines decide to retrofit their existing equipment with new software and controllers as thousands of dollars can be saved.  Because the majority of CMM’s use frictionless air bearings their mechanical structure is subject to minimum amounts of wear and can outlast several controller and software retrofits.  Our knowledgeable service and sales staff at CMMXYZ can help explain the benefits of retrofitting a Used CMM.

Where to buy used CMM Equipment?

When you buy a used CMM from a dealer authorised by the Machinery Dealers National Association (MDNA) you receive important guarantees you don’t get when buying from individual sellers or auctions.  MDNA dealers will refund any machinery that is proven to be mechanically unsatisfactory or repair it at the dealer’s option.

Purchasing used CMM machines at an auction is an extremely risky proposition unless you are an expert and can thoroughly assess the machine’s condition and value. An authorised dealer MDNA dealer takes away the risks associated with purchasing used CMM Machines.

Here at Canadian Measurement Metrology, we specialize in high quality used CMM machines and equipment. You ca

n learn more about our company and our industry experience.

Retrofitting a CMM

Retrofitted and rebuilt CMMs (another option)

Occasionally the CMM dealer will install a new control system on a preowned CMM, and usually accompanying this will be the latest software.  This is usually a great option for a purchaser when considering an older CMM that has obsolete electronics and software.  This allows the buyer ownership of state-of-the-art metrology equipment, at a significant reduced cost from new.

What brand of used CMM is the best to buy?

An independent used CMM machine dealer, such as CMMXYZ has a large inventory of coordinate measuring machine brands to choose from.  The following brands are the most popular: Zeiss, Hexagon (Brown and Sharpe, DEA, Sheffield Leitz), Mitutoyo, L.K., Wenzel and  Coord 3.  All the machines are mechanically and electronically reliable and will provide years of trouble-free service, if maintained properly.  What separates these brands are the probing systems and proprietary software, in 95% of the cases, these machines will be capable of measuring most parts, the exceptions being gear measurement, aerofoil measurement and special applications systems.  In this case, only certain brand names can be considered.  However, any one of the brands could be recommended.  Hexagon and Zeiss machines hold their value more than the other brands, probably because they have the lion’s share of the CMM market.  Better deals can be found when choosing Mitutoyo, Coord3, Wenzel and LK.

 

Software training

 

The importance of software.

When buying used CMM equipment it is often advisable to purchase a used coordinate measuring machine with the OEM recommended software for that brand.  For instance, Hexagon machines and PC-DMIS software, Zeiss CMMs and Calypso software, Mitutoyo CMMs and Cosmos.  Because these three manufacturers represent the largest share of the market It is often easier to find CMM programmer’s that can already run the latest CMM software. Should you ever wish to trade your machine or sell it, its worth much more with the OEM software on it.

99% of all software products sold for coordinate measuring machines can utilise a CAD model and therefore most of them can perform well on the average coordinate measuring machine.  The top five recommended retrofit software products are: Polyworks, PC-DMIS. CMM Manager, Calypso and Open DMIS. Each one has a substantial user base and offers plenty of support

Parts and service.

Spare parts on the basic mechanical frame of the CMM are usually easy to find even if the machine is over 20 years old. Components such as motors scales and encoders as well as air bearings are easy to source. Machine controls and jog boxes are usually obsolete after 5 to 10 years but boards etc. can be sourced from aftermarket suppliers who stock these out of production items. The computer system and software have an even shorter lifespan, for instance an upgrade to the current version of windows often leads to a new software purchase due to compatibility issues.  New software releases often will not work on older computer hardware, it’s important to pay attention as CMM software is expensive. It’s a good Idea to discuss these matters with your independent CMM service provider as they know how to install used CMM parts.  An OEM may not be as helpful, and may not know sources of obsolete components.

What size of used CMM do I need?

A coordinate measuring machine useful measuring capacity is usually described as strokes in XY and Z. The measuring range of a CMM is normally described in millimetres, for instance a machine with a range of 28 inch by 40 inches by 24-inch XYZ would be a 7.10.6. Bear in mind the physical size of the machine is not indicative of actual measuring capacity.

Purchasing a CMM machine for a specific family of parts or a certain part requires some forward planning, first let’s take a look at the long axis or Y (this is usually the axis from the front to the back of the machine) is this long enough for the part to comfortably fit in the measuring area, or are there diameters that need to be probed and are there recesses that require access?  It’s usually a good idea to add at least 8 to 10 inches additional per side, in this case, if you have a 20-inch-long part, we would recommend a 36-inch measuring range.  The same basic arrangement goes for the x-axis (or the axis running from left to right).  The z-axis or the vertical axis requires a little more thought, remember, the probing head fits into the base of the Z ram and normally this takes up 10 inches of z-axis clearance.  So, in this case, if we have an 18-inch-tall component, then a 30 z-axis would be appropriate in most cases.  Of course, if you have deep bores or other hard to reach areas, then additional clearance needs to be added in order that the probe can index into the area.  Remember, no one ever regretted purchasing a larger machine than was necessary.

Do I need a Manual or DCC used coordinate measuring machine.

Used manual coordinate measuring machines can be purchased very cheaply.  This is mainly because very few are sold and there is little demand.  If you are looking for something that can be occasionally used, and only basic measurements taken then perhaps a manual CMM might be just right for you.  If however you’re looking for comprehensive measurements on parts, or measuring production components, then, a DCC machine is a better investment, today’s software allows a DCC machine to be programmed just as easily as a manual one.

Different types of coordinate measuring machines.

There are four basic types of coordinate measuring machines, which is right for you?

Bridge Style CMM.

The 3-D bridge style CMM machine is by far the most popular style coordinate measuring machine.  It allows movement along X, Y and Z axes in the coordinate space. Due to their basic structure and simplicity of build, bridge machines have become extremely popular.   Bridge style CMM machines have a low cost to build and the ability to maintain accuracy and repeatability over the long term.  The average bridge machine is a free floating gantry structure supported by a granite surface plate. Most of these machines run on air bearings to allow friction free performance.

Bridge style CMMs are usually more accurate than other styles of coordinate measuring machines.  They are certainly your best bet when considering a used CMM machine for machined parts with tight tolerances.

Cantilever CMM.

Most cantilever machines today are usually intended as shop floor hard bearing machines, they are generally used for measuring small parts as they provide open access for the operator on three sides.  The x-axis measurement beam is attached at 90° to a rigid structure housing the y-axis.  This limits the size of the X beam because of inherent rigidity, making the machine suitable only for smaller components.  As a shop floor CMM.  The cantilever machine excels because it lends itself well to automatic loading and unloading.

DEA Lambda CMM

Gantry style CMM.

 

Gantry CMMs are generally used for measuring extremely large parts or components that are too heavy for a standard bridge CMM.  A gantry machine can be mounted on a large steel table or bolted directly to an isolated foundation.

The advantage of these systems is that parts can be wheeled in at floor level without distortion to the main machine structure. Additionally, the X carriage can be moved out of the way to facilitate loading by overhead cranes.

Manufacturers of gantry machines require strict adherence to foundation requirements in order to meet structural integrity of the gantry.

The average configuration of a gantry style CMM is 2 or 3 upright columns at either side of the bridge supporting 2 square sectioned Y axes beams.  These beams are usually situated 6 -8 feet above the ground and allow free movement of the X axes.

Horizontal arm CMMs.

The configuration of the horizontal arm coordinate measuring machine is quite different from the three other types in that it consists of a vertical column (X, axis) and horizontal arm.  (Z axis) mounted on the x-axis.  The entire assembly is then mounted on the y-axis (or the long axis) that runs along the length of a surface plate, or beam.

There are two basic types of horizontal arm coordinate measuring machines:

  1. Plate mounted. Here the column is mounted on a large surface plate, usually made of steel.  The machines may run on top of the plate or are mounted on the side of the plate side mounted horizontal arm machines provide greater area for measurement on the plate and increased stability for measurement.  Plate mounted horizontal arm machines can also be configured as a dual arm system.
  2. Runaway mounted. As the name implies the machine runs on a dedicated beam.  There is no integral plate.  This design provides the utmost in flexibility because it can be used singularly or as a dual arm machine for measuring large components.  Normally, automotive bodies and trim are measured on these machines.  The dual arm machines allow measurement of both sides of the component simultaneously, parts can be wheeled are pushed into the measuring volume or an independent plate can be added.

 

Horizontal arm coordinate measuring machines are the least accurate of the four types of CMMs, however, they have some decided advantages.  They can measure large automotive thin wall parts mounted on fixtures that represent car body position, normally these components are quite tall and narrow, yet require access from both sides.

Were do I install my used CMM?

The Quality lab.

 Installing your used CMM in the Quality Lab is the first choice of the majority of CMM installations, as it is certainly a better working environment than the shop floor.  The lab provides a stable measuring environment where temperature humidity and vibration are controlled.  The coordinate measuring machine works optimally in these conditions, maintenance is also kept to a minimum when dirt and contaminants are not an issue.  All manufacturers of coordinate measuring machines provide specifications for optimal machine function.  When these specifications are not attainable it is acceptable to derate the coordinate measuring machines performance.  Therefore if choosing a high accuracy coordinate measure machine it’s important to fully understand the manufacturers restrictions for optimal performance. In all cases measuring machine accuracy is closely tied to temperature and vibration control.  We recommend seeking advice from the used CMM supplier, they will be able to help you in assessing the potential environment for your used CMM machine.

 

Shop floor CMM

 

On the Shop floor.

Shop floor machines are becoming extremely popular, they do not replace a lab-based CMM, but they add some tangible benefits to the production process, with fixed gauging being extremely expensive many companies are turning towards a flexible measurement solution.  The coordinate measuring machine can be easily programmed to accommodate engineering changes on the part or reprogrammed for completely new parts.  This of course is not possible with fixed gauging; shop floor coordinate measure machines provide the benefits of real-time process monitoring with the same temperature and environmental conditions as the manufactured parts.

Shop floor CMMs may be manually loaded, automatically loaded and unloaded. Not only can they monitor and report dimensional conditions, but they can also be programmed to make corrections directly to the machine-tool.  Shop floor machines differ physically from the lab machine, the machine must be thermally stable and predictable.  Most of these machines are equipped with temperature sensors that notify the software of changes in environment so that the software can make corrections to the dimensional results.  Machine guideways are normally covered or protected from dirt and contaminants.   As a rule hard bearings are preferred, as air bearings generally cause internal contamination of the machines ways and guidance system.

What type of Probing is best for a CMM?

When choosing a used coordinate measuring machine.  It is often wise to consider the type of probing that the machine comes with, the type of probing directly influences the selling price of the coordinate measuring machine as well as its effectiveness in programming and measuring your parts.

Fixed and manual heads.

A fixed probe head requires building a Christmas tree structure for different angles required to measure the part, or if a probe changer is present the machine would drive to the changer and replace a probe with one more suitable to measure a specific feature.  A fixed head probing system requires preplanning prior to the measurement of any part, and the building of specific probe attitudes.

A fixed probe head in some cases possesses many positive attributes that may be required to measure specific parts, fixed probe systems can be more accurate in high precision applications than an indexable head.  Many fix systems have the capability of carrying extremely long extension bars (800 mm) without discernible loss of precision.  Notable manufacturers of these heads are Hexagon (Leitz) and Zeiss.

Manually indexable probe heads must be indexed to position and are generally not suitable for fully automatic operation of the CMM machine

Motorised indexable heads.

When utilising an indexable probe head, it dramatically speeds up programming time when the machine is utilised in learn or teach mode.  The probe can be indexed into any position necessary for the measurement of the part without changing setups or requalifying the probe, during the inspection process no operator intervention is required, speeding up part measurement times.  Notable manufacturers of indexing probe heads are: Renishaw, Hexagon and Zeiss.

five axis probe

Five axis probing systems.

This is the latest development available for CMM probing and really has not been available on used CMM machines until the last couple of years, you now find these systems are becoming more popular in the used CMM market.

What is five axis measurement?

In the conventional coordinate measuring machine, the machine itself performs all the movements to acquire the data, the problem is that errors in the machine structure are amplified, irrespective of the probing accuracy.  Five axis technology overcomes this issue by using an articulating head that moves in 2 rotary axes as it measures.  This allows the coordinate measuring machine to minimise movement along a single vector while measurements are being taken by the probing system.  The probing head being much lighter and dynamic than the coordinate measuring machine can quickly follow changes in the geometry of the part without introducing dynamic errors associated with conventional two axes systems.  The benefits are faster speeds and shorter measurement times.  Currently the Renishaw Revo is the only example of this technology for coordinate measuring machines.

 

Scanning and tactile probing.

Tactile (touch) probing can be found on 90% of used CMM machines available today, however, newer machines built in the last five years are available with scanning probes.  For most of the measurement jobs out there today, tactile probes are more than adequate, for coordinate measurements and feature locations they perform well, examples of tactile probing are TP 20 and TP 200 probes available from Renishaw.

Scanning probes work better on newer CMM frames that have smoother dynamics and more precise positioning controls.  For profiles and form deviations scanning probes provide more accurate data and save time, as they collect thousands of points per second, they also can operate in single touch mode for optimum flexibility.  In fact, most coordinate measuring machines less than 10 years old can be fitted with a scanning probe at a minimal cost.

 

The importance of packaging, shipping, installation and calibration of a Used CMM machine

Okay, you’ve just bought a used coordinate measuring machine, what happens next?  The three most important steps that will guarantee a fully operational and trouble-free coordinate measuring machine for years to come:

CMM packaging

  1. Packaging

Preparing the machine for shipment to your facility

CMMs are extremely sensitive high precision measuring instruments and require specific preparation and packaging for relocating.  The biggest concern is physical damage to the CMM table and superstructure because most CMMs are designed and built as a single unit, is it extremely important that the manufacturer’s shipping braces are used for that specific machine type.  This bracing immobilises the structure and all the moving drive axes and prevents damage to the bearing surfaces and insurers components do not shift during transportation.  Our recommendation is that a fully authorised CMM service company is contracted to do the machine tear down and bracing, experienced CMM service companies also have all the packaging materials necessary to make sure nothing is damaged.

  1. Shipping

When a coordinate measure machine is to be moved any distance (no more than four hours driving time).  It is recommended to fully crate the machine and contents.  Smaller machines that are fully skidded can go in the back of a dry van trailer, its generally good for freight less than 5000lbs. Larger machines require flat bed trailers with step decks that allow for the extra height of most CMMs.  Another consideration for flatbed transport is for freight protection, to protect freight from the elements during transit, in fact Conestoga style trailers are mainly recommended.

 

  1. Installation and calibration.

If possible.  It is better to have the used coordinate measuring machine dealer install and calibrate your machine, should there be any problems during installation, or repair is necessary, it can be fixed without delay. All reputable used machine measuring machine dealers will want to make sure that the customer is looked after.  When this is not possible, then it is better to ask the dealer, who he recommends in your area to do the installation and calibration.  The dealer will ensure that anyone who is installing the machine and calibrating is proficient.

Final word of advice on buying Used CMM Machines:

Try to view the used machine before purchase.  Ask for references.  Visit the dealer’s premises.  A little bit of due diligence pays off and ensures that your used coordinate measuring machine purchase is a successful one.  If you are looking for a used CMM machine or just have questions feel free to contact us for more information.