Ballscrews end bearings

What about Berg? They were the source of choice for an experimenter/engineer I once dealt with.

Reply to
daniel peterman
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As a rule, you cannot bolt on accuracy to a machine, it is built in from the begining of the manufacturing process. In other words, a Bridgeport (new or properly reconditioned) is capable of holding .0005 tolorances (per OEM specs) in the hands of a skilled machinist - adding precision ground ballscrews and bearings (which are available) will not make this a precision boring mill. An example - chuck a .0005 or .0001 indicator in the spindle and lightly deflect the quill (not the tool holder), you will see at least .0005 deflection on a new machine (factory spec for quill to housing fit is .0005), extend the quill out

4" and you will probably see in excess of .001 deflection. Next check the spindle runout. Spec says .0003 on a new spindle, typically you will see .0005 runout or worse. Now put a dial indicator (all that is needed here) and mag base on the back vertical column and put the indicator on the back vertical edge of the table. Lightly deflect the end of the table front to back. You will probably see .003 movement or better and did it repeat back to zero, probably not. Putting precision ground ballscrews and precision bearings on this machine will help with your accuracy, but certainly not make it a machine capable of holding .0001 tolerances.

The bearing industry has come along way since the early days. Today there are two basic classes of bearings Class 3 (ABEC 3) and Class 7 (ABEC 7). Most every bearing bought today (from the wheel bearings in your car to the bearings in your ceiling fan) are class 3 (ABEC 3). Class 7 (ABEC 7) bearings are usually angular contact bearings used in precision applications. There is a class 1 (ABEC 1) usually a Chinese brand roller type and are considered "throw aways" (foundries use these alot). Class 3 (ABEC 3) most common - roller, tapered roller, pancake and angular contact as well as other types. Class 5 (ABEC 5) a slightly used class mostly seen in Japanese imports but still made by some US companies and usually angular contact. Class 7 (ABEC 7) super precision grade, usually angular contact. Class 10 (ABEC 10) this is ultra precision grade and includes ceramic bearings used mainly for high speed applications 20,000 RPM's on up.

Reply to
Dermako

You're right, of course. I was concerned about giving away what little I have, bolting on *less* accuracy with the upgrade.

I'm finding out more than I thought I cared to about screws and nuts. THK has a lot of info, albeit weirdly organized and difficult to navigate. Anyway, even non-precision rolled screws, grade C7 and higher, have less axial error than I expect to notice, about 30 um/300mm running length (or something in that range). I haven't run numbers yet, but thermal expansion and axial deflection from applied and induced loads might be as high or higher. They talk about heat control measures of all things in their literature.

Non-preloaded nuts have about .0005 backlash; preload nuts by definition have 0 backlash. 0 has a nice ring to it, and I'm back where I started: rolled screws and preload nuts from mass marketers. (Heh. Not WalMart.)

The only question left is whether it makes sense to install precision bearings at the ends. I suppose it does, or will at some point, but the price is prohibitive for hobbyists. With linear motion rails priced as they are on eBay, maybe the last project for the Grizzly will be its replacement.

So, do you think bolted aluminum slabs will be rigid enough? Cast iron? Rolled steel sections?

Thanks for the reality check.

Reply to
Mike Young

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