Still Not Right...

[cdhknives]

After what I thought was properly seating the new bearing race, finishing assembling my headstock, and making some test runs, I was trying to do some serious work today.

http://www.hobby-machinist.com/threads/drilling-hardened-steel.36275/

While plunging a 1/4" 2 flute endmill I had issues. Besides requiring a lot of pressure, it started to chatter all of a sudden. On close inspection, the cutting edge chipped out. I tried again using the side to walk the hole over. SNAP!

While taking the mill out I felt the spindle shift. It had developed several thou end play. ??? I tightened the preload collar and went to work again, figuring it was just the left race not seating fully. New mill. Grabbed into the work and seized the mill...stalling the whole lathe. Now over 0.050" end play has appeared! Another mill trashed. This tiem I broke out the plastic deadblow hammer and whaled away on the left end of the spindle (yes I had a thread protector!) several times, I got over a full turn on the collar before end play disappeared, and I'm really worried!

No signs of any other trouble. I think maybe the left bearing race was in a bind previously, instead of seating square, and it finally straightened out and settled into place when I put it under a working load...but I'm a little concerned. Is there something else I need to be looking at???

 

[Rangemaster1]

Well, at least you got a hole in the knife blade.

Why don't you take some pics of your setup so we can see what you've done.

It sounds like you solved the problem. What are your concerns now? Is everything well lubed?

 

[Rex Walters]

Sounds like BillH50's advice not to use an endmill was sage.

I've still got a lot to learn about machining, but, frankly, trying to mill hardened steel with "a lot of pressure" and whaling away on a precision machine with a dead blow hammer certainly sounds like exactly the wrong approach.

If I understand you correctly, you used an endmill in the chuck of a lathe to try to bore your new hole (on first read I thought you were using a milling machine). You also recently replaced the bearings in your lathe. I know nothing about using an endmill to cut a hole in hardened steel (I simply wouldn't even attempt it — I'd most likely use a grinding burr to do much of anything with hardened steel).

Replacing spindle bearings in a lathe I do know something about (I replaced the bearings in my Logan just a few months ago). At no point should a dead-blow hammer be involved! With precision machinery and bearings you want to press, not pound. Since turning a lathe on end and putting it into a hydraulic press isn't feasible, the trick I learned on the Logan lathe forum is to make a ghetto horizontal press. Get yourself to the hardware store and buy some threaded rod (say 5/16"), a handful of corresponding nuts, various short lengths of plumbing pipe and fittings (preferably metal, but PVC will do in a pinch) of varying diameter (something large enough to fit over the nose spindle), and a bar of, say, mild steel.

Before you take the old spindle out, turn a couple of bushings with an outside flange for each end of the spindle. You want to locate the 5/16" threaded rod in the center of the spindle. Let's say your lathe is designed such that your spindle removes to the right (the tailstock side of the headstock). After removing all the collars and fittings so the bearings are free to be pressed out, you'd place the bushings in each end of the spindle, insert the threaded rod through the length of the spindle, and find appropriately sized pipe segments to apply pressure to the right places. The idea is to use the nuts to gently and continuously press out the spindle from the headstock. You can generate an incredible amount of force with just a nut on a threaded rod. The short lengths of pipe are to provide bearing surfaces for the pressing.

Here's a picture from "dadhills" on the Logan lathe forum showing how things go together for removal (reinsertion is basically just reversed):



If I were to do it again, I'd actually turn some "pipe" segments that are precisely sized for my lathe instead of using plumbing pipe that wasn't quite exactly sized to fit the various bearing surfaces I needed to press upon. When you reinsert the spindle with the new bearings already on the shaft, it's important that you only apply pressure on the outer races. Keep torquing the nut until the bearing is fully seated.

Gentle taps with a dead blow hammer are great for tramming a vise or the head of a vertical mill. Whaling away with one to remove a lathe spindle is a good way to damage a good machine.

Good luck.
--
Rex

 

[jererp]

Wacking spindles once or twice with a dead blow hammer to seat the bearings was a common practice when rebuilding spindles on the factory floor where I was a manufacturing engineer. First time I saw it, I was shocked as well. But they explained to me that if they didn't do this, the bearings would seat themselves the first time a load was applied. Those spindles would run 24 hours a day, 7 days a week, holding tolerances to acceptable capabilities.
Just saying.

 

[wa5cab]

One thing seldom mentioned is that the Atlas Technical Bulletin on the headstocks is written as though the bearing cone is a push fit on the spindle. As everyone seems to find when installing a spindle with either new or original spindle bearings, this isn't the case. From various descriptions, it seems to be from a light to a moderate press fit. This isn't any particular problem with the right hand cone as you can press it on prior to beginning the installation. But the left hand one is another matter. So finding the zero end float point can be a little tricky. But even with a dead blow hammer, I wouldn't hit the end of the spindle directly.

Several years ago, I made a tool to among other things remove the 3MT x 2MT adapter from the spindle. It was made from a piece of 1-1/4" dia" aluminum a little longer than the spindle. The majority of the length is turned down to 3/4" dia. The w-w/4" dis. head doesn't normally touch the left end of the spindle but with nothing in the taper, it will. It would be safe enough to pound on the tool head without any risk of damaging the threads on the left end of the spindle.