Build times are a critical evaluation tool. Afterall, what is the point of purchasing an RP machine if it is not "rapid". Often, sales people are not provided with accurate build times. In other instances, they have been told to "shave time off the build times" they have been provided for a benchmark. "Just tell the prospect it took half the time, they never verify it".

Always require a guarantee that the build time for the parameters and orientation your benchmark part was built with.

Check for clauses regarding material strength specifications. While a clause stating that machine parameters must be set a certain way may be reasonable, clauses specifying part orientation are not. Most designers do not design products based on feature orientation in a RP or 3D printing system.

Try to determine how the specifications were derived. Were they simply taken from supplier data based on a more generic use, or were these specifications based on actual testing of the material in the RP/3D printing process? Design some simple samples or a sample with features covering several orientations, and have the samples built. Then do a simple manual test to verify if the system meets your needs.

Accuracy is not a simple specification to get an "accurate" answer. Some RP/ 3D printing systems require post curing or strengthening processes. Typically, these processes negate any accuracies of the actual machine. What is important to the end user, is the "total process", or end result.

In a perfect world, accuracy can not be better than half your resolution unless your parts are designed for the resolution. For instance, if you have a machine which is building in .01" layers, you should not expect accuracy to be better than +/-.005" unless your part is designed in such a way that all Z dimensions are multiples of your layer thickness. Do you know of designers who design products in accordance with their RP machines? WE DO NOT.

Stated accuracy should be reasonably achievable and repeatable regardless of build location within the build envelope and regardless of the relationship of your part dimensions to the machine resolution.

Many processes require extensive post processing before you receive a finished part. Some have fast build speeds, only to disappoint the user with slow post processing. Some are just plain slow all around. Others require steps which there is no legitimate control over the process, such as post curing with UV lamps, or dipping the part in chemicals to make the part strong enough to touch.

It has recently come to our attention that several technologies claiming to be capable of completly curing thier parts on the machine, actually require post curing apparatus (PCA's) for fully curing. SLA is well known to require this, but flash based technology requires this too, as their are geometries which do not fully cure internal areas. Accidently break a part which is not fully cured, and you end up with a toxic mess.

It has come to our attention that occassionally, the on-line clearing houses may come up with an unbelievably cheap price.

You may be familiar with this strategy from your local "Big Box" store or supermarket. It is called a "Loss Leader". The idea is to give you a price which is likely way below cost. The smaller RP service bureaus obviously can not afford to take losses, so they can not compete.

The hope of the online clearing house is that the next time you need an RP part, you will skip the little guy and just go directly to the clearing house site. Thats when they will make up their profit - after they have you hooked.

The best way to overcome this is to take advantage of the Loss Leader, but don't let yourselves be sucked into their game plan.