What Scanning Head Should I Get?

cheesiechanman ,
I can't offer any advice on a type of scanning head to get. I only have experience with the Renishaw SP25. There are lots of pros/cons of the Renishaw vs Hexagon probe systems to consider. A good place to start would be to see what it would take to upgrade your machine with either. It might be a costly ordeal or a quick swap out of a few components depending on the type of controller you have. From there you can weigh the pros/cons of each. On paper I'd say the Hexagon probe has more to offer, but I have met people who have worked with both and still prefer the Renishaw probes.

Main benefits of Scanning (for me)
- More points = better outlier removal and filtering. Even if you don't use filters on the scan data, more points means that outliers and form errors have less impact on the average measured values.
- More points = more data for profile/form measurement.
- Scanning is generally faster. It may take a little longer to program, but if you have a lot of parts to check, you can save a lot of time scanning. It depends on what you are measuring, but for the parts I measure it is about 3 times faster than touch points.
- Less form error. There is no lobing effect to worry about. I used to work in a mold shop that used SP25 probes but never scanned with them. They just used it as a touch probe. They chose it just for it's accuracy and durability. They had another CMM that used a TP200 which is a TTP that uses strain gages to reduce the lobing effect. The accuracy of that probe is quite comparable to a scanning probe, but I'm told it is pretty delicate and can't support the same sort of probe lengths.
- Supports very long probes. With the SP25 you can have probes up to 400mm long that are still accurate within tenths. I sometimes use a probe that long on our bigish 15-30-10 machines. It is a little tricky not to hit things as the head whips that thing around. Even having a more reasonable 100mm long probe can be really nice after using a machine that only supports 60mm probes.
- You can use really short prehit/retract values. A TTP works best when you have enough prehit to accelerate to the full touch speed. An analog probe will take a hit on the return stroke, so it isn't as much of a problem. I used to work with tiny parts and often used a prehit of 0.005in to get inside small grooves and slots. Seems very applicable to your spline measuring.

Main disadvantages of Scanning (for me)
- Calibration takes forever. With the SP25 it is about 3min a tip angle. There are ways to make this go faster for tips you use regularly, but you just can't beat the calibration speed of a TTP. I'm told that the Hexagon probes are much better about this and only needs to do the long scanning algorithm for one angle, the rest are faster.
- Touch points are slower. When you use an SP25 to take normal touch hits it takes something like twice as long. It seems agonizingly slow if you are used to a TTP. Some probes support fastprobemode which are more like TTP hits, but you loose some accuracy.
- Probe module is bigger/longer. If you are using a small CMM, it reduces your usable measuring volume if you need to measure all sides of a part with different probe angles. And, sometimes having a 25mm body width can seem kind of bulky if you are used to a much narrower TP20 body.

I'm sure there is something I'm forgetting to mention but I've gone on long enough. As far as how hard is it to learn to program scanning on your own, not very hard. I know you have already done some scans with a TTP, so you already figured out the hard stuff. To do the same with an analog probe just means using different settings and checking different boxes. A lot of auto features have scanning options that can make simple shapes really easy. Even if it takes you a while to get comfortable with scanning, you can still program normal touch points in the meantime.

cheesiechanman ,
I can't offer any advice on a type of scanning head to get. I only have experience with the Renishaw SP25. There are lots of pros/cons of the Renishaw vs Hexagon probe systems to consider. A good place to start would be to see what it would take to upgrade your machine with either. It might be a costly ordeal or a quick swap out of a few components depending on the type of controller you have. From there you can weigh the pros/cons of each. On paper I'd say the Hexagon probe has more to offer, but I have met people who have worked with both and still prefer the Renishaw probes.

Main benefits of Scanning (for me)
- More points = better outlier removal and filtering. Even if you don't use filters on the scan data, more points means that outliers and form errors have less impact on the average measured values.
- More points = more data for profile/form measurement.
- Scanning is generally faster. It may take a little longer to program, but if you have a lot of parts to check, you can save a lot of time scanning. It depends on what you are measuring, but for the parts I measure it is about 3 times faster than touch points.
- Less form error. There is no lobing effect to worry about. I used to work in a mold shop that used SP25 probes but never scanned with them. They just used it as a touch probe. They chose it just for it's accuracy and durability. They had another CMM that used a TP200 which is a TTP that uses strain gages to reduce the lobing effect. The accuracy of that probe is quite comparable to a scanning probe, but I'm told it is pretty delicate and can't support the same sort of probe lengths.
- Supports very long probes. With the SP25 you can have probes up to 400mm long that are still accurate within tenths. I sometimes use a probe that long on our bigish 15-30-10 machines. It is a little tricky not to hit things as the head whips that thing around. Even having a more reasonable 100mm long probe can be really nice after using a machine that only supports 60mm probes.
- You can use really short prehit/retract values. A TTP works best when you have enough prehit to accelerate to the full touch speed. An analog probe will take a hit on the return stroke, so it isn't as much of a problem. I used to work with tiny parts and often used a prehit of 0.005in to get inside small grooves and slots. Seems very applicable to your spline measuring.

Main disadvantages of Scanning (for me)
- Calibration takes forever. With the SP25 it is about 3min a tip angle. There are ways to make this go faster for tips you use regularly, but you just can't beat the calibration speed of a TTP. I'm told that the Hexagon probes are much better about this and only needs to do the long scanning algorithm for one angle, the rest are faster.
- Touch points are slower. When you use an SP25 to take normal touch hits it takes something like twice as long. It seems agonizingly slow if you are used to a TTP. Some probes support fastprobemode which are more like TTP hits, but you loose some accuracy.
- Probe module is bigger/longer. If you are using a small CMM, it reduces your usable measuring volume if you need to measure all sides of a part with different probe angles. And, sometimes having a 25mm body width can seem kind of bulky if you are used to a much narrower TP20 body.

I'm sure there is something I'm forgetting to mention but I've gone on long enough. As far as how hard is it to learn to program scanning on your own, not very hard. I know you have already done some scans with a TTP, so you already figured out the hard stuff. To do the same with an analog probe just means using different settings and checking different boxes. A lot of auto features have scanning options that can make simple shapes really easy. Even if it takes you a while to get comfortable with scanning, you can still program normal touch points in the meantime.