There are a few things to keep in mind. First, the overly religious argument about lapping is based on a total misconception, which is that it is being done to improve the accuracy of the ways. In fact, lapping in this context is not done to make the ways more accurate, but to reduce friction. Those that are highly correlated as "those who know" are mistakenly arguing against the process because it makes things less straight. They want the ways to be hand scraped, which is accepted practice, and in the end, would produce a better result.
HOWEVER, this is not why the IH Mills are recommended to be lapped. The weak link in the chain is not the accuracy of the ways, but rather their surface finish. Stick slip, and friction in general, make it very hard to operate the mills with tight gibs. Lapping reduces this friction, and by tightening the gibs in conjunction one achieves greater accuracy because the machine is less sloppy on the ways. See the note about increased accuracy another fellow got by being able to torque down his gibs more tightly with proper hex bolts instead of the plastic handles.
Is this newfound accuracy as good as one would get by having the ways professionally scraped in? Absolutely not. Is it a dramatically cost effective and good "bang for the buck" way to improve the performance of the mill without the expense and required expertise to hand scrape? In this case, those that "know" are the ones who've done it, and especially Aaron, and they almost universally report an improvement especially on those machines destined for CNC conversion.
In fairness, I have not yet performed the experiment on my mill, but I do intend to do so, and I'll take a battery of accuracy measurements before and after when I do. I'm willing to take the word on faith of Aaron and others that it's a good thing for two reasons. One, they're the folks that have experience with THIS PARTICULAR MACHINE. They are successful, aside from what the textbooks say would be better, at improving machine performance, and that is pretty objective evidence. Two, I did some interesting research.
Try going out on the net and looking to see what the material removal rates are for lapping. It is an extremely slow process to remove very much material at all, even when you have optimized the lapping process for as fast a rate as possible. Aaron's recommended procedure can't possibly remove enough material to seriously "ruin the machine" as has been seen, according to the figures for material removal rates I've seen for lapping. If you read his procedure, he doesn't recommend very many strokes at all for each grit.
With that in mind, it seems clear that it is nearly physically impossible for this "lapping" process to seriously impair the accuracy of the machine IF YOU FOLLOW AARON'S GUIDELINES! Of course your mileage may vary, and you need to tread carefully, but in fact I do not subscribe to the notion this ruins the machine, you never do this on engines, yada, yada. It's a good theory, but for this particular machine, friction in the ways can be terrible, especially on the Z-axis with the heavy cantilevered head.
So I'm going to lap, textbooks and experts notwithstanding. If I do ruin my machine, I should be able to measure to what extent and provide a cautionary tale for others.
Best,
BW  |