RE: [CAD_CAM_EDM_DRO] Ball screws
Recently ran into a case where very cheap bearings were using "Case Hardened" or surface hardened balls and races. Look the same, under very light loads perform the same BUT they are not the same. By the way, did I say they were really cheap. Running in a metal saw these failed in a week or so with the back of the blade slicing into the outer race of the bearing. When replaced with conventional bearings and run for a comparable amount of time there is no sign of a groove or wear , just a shiny band where the blade back is running.
I have designed a lot of specialty machined used in our factories over the last 40 years. Depending upon the application, I have used Acme Screws, Acme Screws with counter loaded nuts, rolled ball screws, precision ball screws and ulta-precision ball screws up to 4" in diameter and 27 feet long. The trick is to determine what quality (= price) you need and don't over spend. No sense putting an Ball Screw on a hopper that levels to 1/2" or and Acme Screw on an axis that must repeat to +/-.002 in 10ft (didn't say accurate). Either way you will eventually be disappointed.
As was well stated, "you get what you pay for". The trick is determining what you really need pay for. Precision ground ball screws might be a little bit of over kill on a wooden frame router for example. Good rolled ball screws or even Acme Screws could keep you happy for years. On thing that will not make you happy is frequently failures and replacements
nitewatchman
From:
CAD_CAM_EDM_DRO@yahoogroups.com [mailto:
CAD_CAM_EDM_DRO@yahoogroups.com ]
Sent: Tuesday, June 03, 2014 7:03
PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO]
Ball screws
I have owned lots of "quality" lower price items and now am able to afford the "overpriced" big names.
You can kid yourself all you want, there is a difference. With Chinese stuff it is usually not how it works when new, it is how fast it needs replacement.
Buy cheap, buy twice. There is a reason it is cheap.
That is not to say that for a specific use the cheaper item is not a good choice, just to point out that there is nothing for free. Better materials, better heat treat, better balls. It all adds up to more money. But for a hobby machine that might only get 100 hours of use a year cheap is probably a great solution.
Tim Goldstein
A2Z Corp