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longrange
08-26-2003, 05:11 PM
pete and mike, my goodness these boys are real proud of their bearings a 50mm bearing costs 450$. everything is ready but the bearing, damn it was fun. I have a guy checking to see if a class 5 bearing will work.
Now pete (stepside) you know i never spit on anyone unless they deserve it, usually.
bearings of this size only come in mm, a 50 mm is something like 1.94 inches which is fine by me. this is from what they told me a precision aircraft bearing not something they have on the shelf, Im still looking.
stuart

Mike Burdick
08-26-2003, 07:38 PM
Stuart,

Yes, that's about the cost of those things. I apologize for not making that point clear. In my mind I was thinking of a "spindle extension" and did not want to compromise the accuracy of your lathe. I'm sure just an ordinary ball bearing will do just fine for you. If you need the accuracy later you can always go up in class.

If you want to go to the following link and type in the bearing you want. They should give you the tolerances and then you can decide what will work for you.

www.awbearings.com (http://www.awbearings.com)

No matter what kind of bearing you use, I think for your intended purpose the steady rest by John Stevenson will serve you much better than a traditional steady - and won't leave any marks on your work.

There is one other point I would like to make here. Just because a lathe has worn ways near the chuck doesn't mean one can't turn out quality work. Once the inaccuracies of a lathe are known, a good machinist can compensate for this. It is not often that a shaft (whatever) has to be turned down precisely along it's entire length. Most of the time it only needs small lengths (press fits for bearings, etc.) to be within a tolerance. So on these, don't rely on the dials, just measure each time you make a cut. Naturally, if your lathe won't meet your tolerance for the piece you're doing, one has to be inventive and figure a way to jump over the problem. Thats what makes machining fun!

I wish the more experienced machinists on the board would tell of the "quality" part they had to make on equipment that probably should have been tossed. I think most of us would have a new appreciation for the tools we have. And not to mention, we would sure learn some good tips.

Hang in there....Mike




[This message has been edited by Mike Burdick (edited 08-26-2003).]

Forrest Addy
08-26-2003, 08:00 PM
No, you don't want to use regular ball bearing in the business end of a machine tool spindle.

If you could see the trace of an ABEC Grade 1 angular contact pair where a potato shape wanders in and of a chart of concentric ring when each ring represent 0.0005" you'd never use them for anything but crude stuff like intermediate shafts for geared transmissions.

Spend the money and get a pair of ABEC Grade 5 or 7 angular contact bearings ground DU (duplex universal). Besides the pricey bearings run cooler and last longer at high RPM.

Stepside
08-26-2003, 08:48 PM
Ok--it is just money. Well maybe you don't need a class 7 bearing. What kind of speed are you going to be turning and what operations? Even if you are running that little SB wide open it isn't that fast. I think the class 7 is overkill. You could use a very well fit plain bearing with a decent lube system and get the results you want.

Longrange does spit, but it washes right out and isn't nearly as bad as my flatus.

So Longrange do you want my 9 inch steady or do you want me to help you build one using a plain bearing or what ?

I do agree that the best bearings you can afford would be the thing for a machine spindle that is really cranking the R's. Remember that your lathe is running in plain bearings and works just fine.
Pete

DR
08-26-2003, 09:34 PM
Guys,

When you need precision bearings do some shopping. Most bearing houses don't do much business in the precision grades so shop around a little.

Last time I needed a matched set of class 7's the quoted prices were all over the place. From $1800 down to $460 for the same set. The outfit with the $460 price had several sets on the shelf. The other places would have had to order the single set from Barden and were pricing at list or varying discounts off list.

wierdscience
08-26-2003, 10:20 PM
Angular contact class 7's,what size do you need?I have access to a few different sizes in matched pairs and singles most with pheneloic cages some with brass,these are surplus but brand new sealed packages,if I have the size you need you can have them cheap.

Thrud
08-27-2003, 12:35 AM
Stuart
for a steady like Johns any better grade (better than utility grade) will work just fine. The ABEC-7 or better or gr3 tapered bearings should be used in spindles for obvious reasons. If properly cared for (clean lubricant of the correct viscosity) and properly installed they will last a lifetime.

If you do ever replace your bearings the "trick" bearings to get are the ones with Silicon Nitride balls - these offer lower galling, higher rpms, less lubrication required (many new high speed spindles using these bearings with a light grease instead of oils), and 5 times the life of chrome balls.

Nearly all bearing failures are from improper installation, followed by improper lubrication. Other failures include mis-alignment, dirt, improper application, and at less than .1% material & manufacturing defects.

[This message has been edited by Thrud (edited 08-27-2003).]

longrange
08-27-2003, 02:21 PM
<font face="Verdana, Arial" size="2">Originally posted by Mike Burdick:
Stuart,

Yes, that's about the cost of those things. I apologize for not making that point clear. In my mind I was thinking of a "spindle extension" and did not want to compromise the accuracy of your lathe. I'm sure just an ordinary ball bearing will do just fine for you. If you need the accuracy later you can always go up in class.

If you want to go to the following link and type in the bearing you want. They should give you the tolerances and then you can decide what will work for you.

www.awbearings.com (http://www.awbearings.com)

No matter what kind of bearing you use, I think for your intended purpose the steady rest by John Stevenson will serve you much better than a traditional steady - and won't leave any marks on your work.

There is one other point I would like to make here. Just because a lathe has worn ways near the chuck doesn't mean one can't turn out quality work. Once the inaccuracies of a lathe are known, a good machinist can compensate for this. It is not often that a shaft (whatever) has to be turned down precisely along it's entire length. Most of the time it only needs small lengths (press fits for bearings, etc.) to be within a tolerance. So on these, don't rely on the dials, just measure each time you make a cut. Naturally, if your lathe won't meet your tolerance for the piece you're doing, one has to be inventive and figure a way to jump over the problem. Thats what makes machining fun!

I wish the more experienced machinists on the board would tell of the "quality" part they had to make on equipment that probably should have been tossed. I think most of us would have a new appreciation for the tools we have. And not to mention, we would sure learn some good tips.
thank you for your input mike it has helped a great deal and i have learned a lot. the more i learn the more i can pass on to my students. my lathe is not really that bad at all I have done 3 barrel replacements and two rechambers and they all shoot fine. I just have to lay a file on one end for a while, .002 over about 6" I was just hoping for perfection.


[This message has been edited by Mike Burdick (edited 08-26-2003).]</font>