When you are considering waterjet cutting services you should consider what kind of edge quality that you require, or at least would like for your project. Many waterjet cutting companies will give you a #1 or #2 edge quality as they cut faster and since time is money they are cheaper than a better edge quality would be.
This is a littler different than most other conventional processes are. In Plasma, Torch or Laser cutting there is a cutting speed that is normally used that will give an acceptable cut and that speed really isn’t deviated from a whole lot so the edge cut quality normally is about the same. Slowing down doesn’t give a significantly better edge and speeding up will quickly get to the point to where it will not cut through at all, so there isn’t a lot of point in changing the cut speed.
In conventional machining you want to run your cutting tool at the speed/feed that will give a clean cut without tool chatter which will dull that tool quickly at best, and can have other ill effects up to and including breaking the tool off, either damaging or scrapping the parts. So, there isn’t a lot of room to vary the cutting speed too much from the optimal speed/feed or you will end up with an unsatisfactory part finish.
In waterjet cutting you can vary pressure somewhat and abrasive flow which will have some effect but the biggest effect beyond these changes is simply the cutting speed itself. Waterjet cutting is simply a controlled erosion process and since the tool is very flexible then the cutting head can actually go fast enough that the stream will trail the cutting head by a considerable amount. This gives you striations in the material and the faster you go the more pronounced these marks will get and more curved back they will get as well giving a rougher cut the faster you go.
Many waterjet cutting companies will not bother to worry about what your parts or going to end up being used for and whether they would be better if cut slower (#5) giving a nicely finished part right off of the waterjet machine once cleaned up. Not all parts will be suitable as finished parts and will require additional machining in order to hold the specific tolerances, edge finish, or other features that can not be done on the waterjet so a mid range edge finish (#3) is great and will save money if there isn’t a valid reason to cut to cut with the better edge finish.
Occasionally there is a reason to to use a #2 or even a #1 edge quality but cutting faster gives a very rough edge especially on the bottom or exit edge of the cut so we prefer to avoid using them for several reasons some being listed here:
- The jagged edge is very sharp and will cut you when handling if you don’t use extreme care
- The rougher the edge the more size variation you will get in the parts requiring a larger tolerance
- The more material you will have to leave if you want to use another process in order to ensure that it will clean up
- Faster cutting increases the risk of the waterjet stream not cutting clear through the material creating wormholes possibly losing the part
- The jet almost constantly kicks back while cutting creating a huge mess of the machine, causing excessively high wear
The #5 cut will be a very smooth cut which will have a finish that appears to be a smooth metal edge that has been sand or bead blasted with an 80-120 grit abrasive. It will appear a little different than the original surface finish of material. The normal surface finish is quite often very compatible with the waterjet cut edge as they compliment each other but do look enough different to add some contrast to the parts from a cosmetic viewpoint. It will be smooth enough that you can pretty easily polish it to a shiny surface by hand or with small power tool if desired.
The #3 cut is the mainstay of the waterjet cutting industry as it is the mid quality. You can achieve this edge quality with a fairly low risk of kicking back into the material if you have an abrasive clog during mid cut but will hold a reasonable tolerance pretty easily and is a good value for many cutting needs.
We have a $100 minimum lot charge on most jobs but quite often in order to give our customers the best value for their purchasing dollars we will actually give them a #4 or #5 edge quality even though they don’t ask for it which gives them a very nice finished part and they can see what the waterjet machines are capable of so that the next time they may be more likely to request the better edge. Many waterjet shops quote the job to get it in the door and just assume that you want the parts cheap and quality doesn’t matter and don’t bother to ask how you would like them cut. Then, if you specify that they need to have a nice edge they will not tell you that it will cost more and when you get the invoice you discover that you are not paying the quoted price at all. We would rather give you a much better part, for a slightly higher price, saving you a lot of additional work in order to get a finished part. If you want a rough cut at a possible lower cost, please let us know and we will be happy to oblige you.