ROFL, McGyver certainly does have a lot of posts, he’s a copyright law expert, a scraping expert, a critic on most fronts, and I am sure a legend in his own mind. His work is so fantastic I know I personally lie in bed awake until late at night scheming how to steal his photos but my evil plans are foiled by diabolical watermarks. Drat! Getting back to the real issue and point of the thread,
Everyone is arguing about completely different things so of course they don't agree.
ChrisD's post is excellent, and should be read carefully by all concerned. He is mostly right, and frames exactly why the group's discussion is really about two completely different things:
- "I am a machine tool builder by trade"
Is everyone here also a machine tool builder? Well you're not, are you? Chris is, some others are, but most of those experts are not hanging around CNCZone wondering how to get their Asian mini-mill to perform better by scraping it in to a ten thousandth. They have skills, facilities, and budgets that are radically different than yours. If you have access to all that, you will get a better result too. If that doesn’t work for you, you need another plan.
Remember that there are all kinds of other things the builders can make the same argument for. They laugh at mills with 1600 rpm spindles, mills that use steppers instead of servos, mills without toolchangers or enclosures, and control software that can’t take feedback from a servo encoder into account just to name a few. The professionals live in a different world and are solving different problems. They are not trying to build CNC machines for a few thousand dollars. As I said, you need another plan because a lot of what you are going to be doing the Experts will shake their heads at.
We are not reconditioning machines that were once scraped to perfection by Hardinge. These machines have never seen a scraper, though they may have been scratched up by some other random piece of metal. Most have not been ground either. The ways are rough milled. The question is with limited skills and resouces, how do we make them "good enough?". Or perhaps not even that, "How do we make them better?"
- "If you think you are "reducing friction", okay, but if the damn thing has so much friction to begin with, it has more problems than lapping is going to cure."
Yes, absolutely, you are so right! These little imports do have a lot of problems, more than lapping will cure if we are honest. The average machine builder or professional machinist will throw up their hands, shake their heads, and ask why you are wasting your time on this junk! You can’t make these imports perform as well as a Mori Seiki by lapping the ways, nor by scraping either BTW. We are in violent agreement! But you can get a CNC mill that cuts to a thou or better very reliably. Not nearly as efficiently and quickly as a pro machine, but you don't care, because you're a hobbyist.
Here is the bottom line:
If you want to think like the professional, you wouldn't consider either lapping or scrapping. You wouldn't be fooling with these little imports. You'd buy a real machine, and likely one that is already running-- those same pros are also not dropping everything to learn how to scrape. There are pages of professionals posting about this, and you can go read that advice now if you like. Head over to PM and ask what they think about retrofitting a nice Bridgeport knee mill. Better, save the embarrassment and search—it’s been asked many times. They're going to tell you to forget about repairing or retrofitting. Plenty of CNC machines that still work great are for sale cheap in this economy. Go buy one and get on with your business.
If you’re not a professional, you are a hobbyist. It's all fine and well to have delusions of grandeur about scraping in your machine to a ten thousandth just like McGyver. Excellent! Maybe you are restoring some venerable old Monarch 10EE. Cool! If you've got the time and skill, go for it. But if you don't, you're going to need another plan. You are in search of shortcuts because you aren’t going to spend the time or money a professional would, and if you could you don’t have their skills. Get over it, there is no shame in that. You can still build a CNC machine accurate to a thousandth.
As for lapping, understand why we are lapping before you decide it can’t possibly work. It’s not about making anything straighter or crookeder whatsoever as Cruiser and I have both said. You don't do enough of it to “wear out” the straightness if you're doing it right. You're making 20 to 40 strokes with each grit and that's it. Experts should look up exactly how much material can be removed by abrasives with 20 to 40 strokes (hint, using machines, diamond grit, and optimal conditions you get 0.000029"/minute removal). You will find that the effect is not capable of moving a thousandth, or in most cases more than a couple tenths. I think we agree these machines were not accurate to tenths to start with?
Understand clearly why we lap and what the lapping process can and can’t do. Not all machines need it. Many don’t: no need to lap indiscriminately. But understand that if you're talking about an RF-45 of a vintage where the ways are really rough and you want to run the gibs very tight, then I will paraphrase Chris and suggest that you consider doing what someone who has the knowledge and experience of having done it has done. Lapping works. It is an improvement. If done properly, it does not destroy the accuracy of your machine, quite the opposite, it improves it.
In that case lapping is simply the moral equivalent of scrapers flaking just for better oil control and behavior. That’s all. If you’re a scraper, snowflake instead. It’s prettier and probably works better. Otherwise, look at it this way:
Lapping the ways takes a couple hours of an afternoon. If you succeed, your machine is better for it. If you fail, you spent 2 hours and now you need to scrape it in like the Experts suggest. That’s going to take a lot more than 2 hours, so what have you really lost? It’s probably taken longer than 2 hours to write all the posts in this silly thread. You will not suddenly make your machine more inaccurate if you don’t get crazy with too many strokes. The abrasive just can’t remove enough material for that to happen.
BTW, even if I wanted "professional results" on an RF-45, I wouldn't bother with the scraping. I would take the disassembled machine, fill all the cavities with epoxy granite, haul it to a machine shop, mill off the dovetails and put a precision guide surface, and then I'd mount a set of linear rails to it.
Scraping isn't the be all and end all either, but I'm sure that will ignite yet another controversy!
(nuts)
Cheers,
BW
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