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One observation is that if you can measure your position accurately then you can correct your inaccurate screw to machine a more accurate screw. So an inaccura
by YZF 6y ago
One observation is that if you can measure your position accurately then you can correct your inaccurate screw to machine a more accurate screw. So an inaccurate, but repeatable lathe, can make a more accurate screw. I know that when you order a ball screw you will typically get a compensation curve with it, which lets you position yourself to better accuracy than the thread on the screw .. though presumably that's not enough to machine a better screw, otherwise they'd do that ;)
- petertodd 6y agoThe trick there is figuring out how to actually do that compensation in the pre-CNC world. I've seen references to cams used in certain screw-cutting devices. But not a detailed description of how exactly those cams worked or how people were actually measuring the error in the first place back then. > though presumably that's not enough to machine a better screw, otherwise they'd do that ;) These days it's probably cheaper to just program the compensation curve into your CNC controller than to actually build a better screw! The really accurate machines often use separate distance encoders anyway, rather than rely on a ball screw that's being stretched and compressed by both load and temperature effects during use.