Get sample parts cut before you buy
Watch over an operator’s shoulder while the part is made. Watch the part being made from drawing to finished part. If you can’t see the machine in person, at least have them videotape you making your part. It is important to watch the machine make your parts because that keeps sales people honest.
Carefully measure the dimensions of the part accurately. Check how well the corners come out, especially inside corners. The most difficult thing for an waterjet to do is an inside corner in thick material.
Look for “witness marks” on the part that indicate poor feed rate control, sensitivity to vibrations, or other machine problems. They may also be caused by deep scratches in the surface of the material, or the pierce point.)
Witness marks shown along the edge of the part
Test for repeatability
Repeatability is the ability to repeatedly make the same part to the same tolerance. It won’t help your productivity if you have to make the part five times before you get an acceptable result.
Check for repeatability by making several of the same part in different spots of the machine. Place them on top of each other and check how well they line up at the edges. Ideally, you should not notice any difference between the parts.
Measure the results
Always measure the results as accurately as possible. Some abrasivejets are high enough precision that you will not be able to see problems with the naked eye. Check critical dimensions around the parts, and see what kind of tolerance the machine can really do, and compare that with the manufacturer’s claims.
Don’t compare apples to oranges
Always take the same part drawing (or specifications) to different manufacturers and have it made from the same material so that you can compare the same part between the different machines. This lets you directly compare machining times, accuracy, and finish quality. The manufacturer will probably have sample parts that show off the features of their machine, but make sure they make your part also.
Don’t be fooled by Linear cutting rates:
Linear cutting rates–how fast the nozzle can cut in a straight line–don’t accurately reflect the parts you will make (unless you are cutting a lot of big squares of material). Don’t rely on this figure, however. For machining operations, you will want to slow the machine down significantly for higher precision and surface finish. Also, due to jet behaviors, it will also be necessary to slow the machine down for corners and radii to allow the jet lag to catch up, and give you a precise part.”
Rather than ask, “How fast will it cut 3″ (7.5 cm) thick aluminum?” ask, “How long will it take to make this particular part, and what kind of precision can I expect?” And don’t forget to make them prove it by having parts cut while you watch.
The speed range a machine needs
For abrasivejet machining, it is rarely necessary to go over 100 inches per minute (25 m/min). This is because your main limiting factor will be the cutting speed of the abrasive jet cutting process. You may want the machine to go a little faster than this during traversing, but the traverse speed will play a very minor role compared with the cutting speed.
For pure waterjet cutting, you will want to move much faster than this. If you do primarily water-only work, you may want a machine as fast as 300 ipm (76 m/min) or faster. If, like most machine shops, you only do a little water-only cutting, do not worry about maximum speed.
Consider operating costs
Find out in detail what it costs to run the machine, as this will determine your overall profitability. This is greatly influenced by the cost of consumables (such as electricity, water, sewer and abrasive), cost of spare parts (such as nozzles and pump seals), initial purchase price of the machine, and costs of labor. This number can vary significantly between manufacturers. Consider how many days of work each month it will take you to pay for the machine. Have multiple manufacturers cut the same part for you, then add up all the costs for that part. You will probably discover huge cost differences because of the efficiency of the path planning algorithms, the nozzles and pump used, and other factors. See Waterjet operating costs for more information on this.
Talk to customers who have the brand of equipment you are looking at
People who are using the equipment on a daily basis know a lot about how it works. Ask questions such as:
- What is their tech support like?
- Do they like dealing with the company?
- What surprises did they find?
- Do the manufacturers live up to their claims?
- Would they buy from them again?
If you are a potential competitor to the person you are talking to, they may give you bogus info. You probably want to talk to someone who is on the other side of the country. Likewise, go ahead and ask the manufacturer for references but also find someone who they don’t recommend for references.
Also note that people are generally reluctant to admit making a purchasing mistake and may try to convince themselves (and you) that it wasn’t really a bad investment. Talk to more than one customer to try and get an accurate portrait.
Look for legitimate bargains
You might be able to get the best price by buying off the show floor of a trade show, or buying demonstration units or beta prototypes.
It costs a lot of money to ship a machine. Manufacturers would gladly knock a few thousand dollars off the sticker price to avoid having to ship it back to inventory. This is a win-win situation for both you and the manufacturer. Be careful that you get the machine you need, however.
You might find that the machines on the show floor get sold quickly; therefore, you might try to buy several weeks before the show, and say that you want the show unit. Also, keep in mind that the show machine will probably get used during the show, so it may not be as new and shinny as a new machine, but it should be totally fine.
Take advantage of a slow economy
Consider buying a machine when the economy is bad. If you have the cash, this is a good time to get deals. Especially if the economy went bad unexpectedly, and the manufacturers suddenly find they have over-built, and have inventory. Don’t count on this, though. Waterjet machines sell quite well, even when the economy is bad. Often, people start looking for “new business,” when the existing business is slow. Ironically, for this reason, waterjets actually sell fairly well when the economy is slow.
Check for tax advantages
At times, governments offer big tax breaks when buying this kind of equipment. In the past few years, the US government has offered large tax advantages for purchasing equipment. Check with your tax advisor to see if you can take advantage of these tax advantages.
Documentation is important
At first you may not think that manuals and help screens are very important, but wait until your operator leaves, and you need to train a new one. Do you really want to spend $2500 to $5000 to have someone come out and train them? Therefore, documentation is more important than you might otherwise think. Good documentation is also very helpful for learning more than what is covered in class.
Ask to see the documentation and look through it. Does it make sense to you? Are there enough illustrations about how to do things? Does it clearly explain how to do basic maintenance (such as overhauling the high-pressure water pump)? Can you quickly and easily look things up?
Skimping on documentation is one way that manufacturer’s can save money and unless prospective customers insist on proper documentation, the incentive is for them to cut corners.
Don’t be fooled by horsepower
Remember, it is the HP at the nozzle that does the cutting, not the horsepower of the pump motor. If you want to compare apples to apples, then download the Waterjet Web Reference Calculator from the software section of this web site.
Buying ultra-cheap machines
There are a lot of cheap machines out there that are fine if you want to do crude work at a high cost of operation, such as a hobby in a garage at home to make trinkets for friends. Many of these are simply machines like plasma cutters that have been outfitted with a waterjet head. However, if you plan on making money with an waterjet, and want to compete, then it is important to buy professional level equipment that was designed for the task.
Controller choice is one of the top decisions you can make in terms of buying a profitable machine. By optimizing the tool paths through software it is possible to make tremendous improvements in both the speed and precision of the part. This can mean that low-power pumps and nozzles can compete with higher power pumps and nozzles in terms of speed, and do much better in terms of precision, and last longer and cost less to maintain. If you then take such a controller, and marry it to a powerful, well constructed pump and table—one that is designed from scratch for waterjet use—then you will have a high degree of capability. You will be able to things that your competition cannot. You will be able to make parts faster, and to higher tolerance, and with fewer headaches. If you buy a low precision machine with a bad controller, you will save money on the purchase, but pay dearly in the long run, if not sooner.
Here are some really bad features of the low cost machines, that will cost you money:
Bellows are not fully sealed
The bellows protect precision components such as ball-screws and rails. If the bellows are not sealed, abrasives will almost certainly damage these components over time, resulting in a machine that does not run well, and has little resale value.
Control software is not designed for abrasivejet machining
This will result in parts that take a lot longer to program, take much longer to cut, and are much lower tolerance. They may also have memory or other limitations that make it impossible to make complex parts.
Low precision components
This will result in low precision parts, making it impossible to fully realize the potential of the technology.
Low quality components
These will result in frequent and costly maintenance, as well as down-time and frustration.
Improper protection from rust
Machines that were designed for other processes such as plasma cutting, and then retrofitted with waterjet cutting heads, will have a lot of problems with moisture, and the abrasives.
Lack of key features that are useful for waterjets
For example, they may lack water-level controls, making it difficult to cut under water to reduce noise and splash.
Lack of support
The company making the machine probably does not have the resources to do it right. Therefore, they may also not have the resources to support the machine, or even be in business.
That said, if you just can’t afford anything better, then such a machine may still be fine to use for hobby cutting. You may want to consider buying a used machine instead, as at least then you are getting something that is more suited to the task.
Buying every option in the book
If you want to save money, then spend your money on a machine with a solid foundation that can be easily upgraded later. Unless you are getting exceptionally good pricing on accessories, then you may want to skip buying a “fully loaded” machine in favor of buying a more expensive, but also more solid machine that can be upgraded later.
Consider this also when buying expensive software. Once you have your machine and have worked with it a bit, you will be in a much better position to know if you really need the high-priced nesting or scanning software..
Training packages are well worth it in most cases, so ask about what packages the manufacturer supplies. With your machine you should get some basic training for free during the installation. Make sure to schedule time where your workers will not be interrupted during this training, though.
You should purchase additional training to be had a month or two after you have had some time to use your machine on your own for a while. It makes a big difference. Once you have had a chance to do things the hard way on your own for a few months, you will absorb the information from the follow-up training much faster. You may want to coordinate your follow-up training to be at the same time as your first pump rebuild, so that someone can be there to assist you for that at the same time.
If you buy a lot of accessories, be sure to buy additional training, and expect that the machine will take some additional time to learn.