I recentely disassembled the headstock on my 12" Atlas lathe to install a new drive belt.
I'm now getting some extremely rough cuts with both SS and brass stock, and quite a bit of vibration during the cuts.
If I put side pressure on the 3-jaw chuck that I'm using, I can feel a slight side-play that I'd estimate to be a least a couple of mils, so I'm suspect that the problem is excessive play in the Timkin headstock bearings.
My problem is that I've tightened the ajustment nut on the headstock shaft as tight as I can get it, which doesn't seem to be tight enough since still the shaft sideplay still exists.
Am I doing something wrong, or do I need a new set of Timkin bearings? Is something possibly locking the headstock shaft so that the proper Timkin bearing tension cannot be achieved?
To make matters worse, when I run the lathe in backgrear, it runs just fine except that there is a slight clanging noise that appear to be from the step pulley.
I suspect that when I reassembled the headstock, I did something wrong, but I can't seem to locate what it might have been.
I've got a guess. I think there is a spacer that is supposed to go on after the rear inner race, before the gear, before the threaded collar. If you left out the spacer, the threaded collar will bottom out on the threads before it presses the inner race against the outer. Or, you may have put the collar on after the gear, and the spacer is jammed against the key that is supposed to be roughly in the middle of the gear.
Harry, I'll bet you left a spacer out, or put it on the inboard end of the bearing.
There's an awful lot of takeup possible on an Atlas headstock. If you can't take up the slack, the bearings must be bottoming out on something (on the spindle) before they seat in the headstock.
I agree. Sounds like you have a shimming washer in the wrong place. The headstock should be shimmed to zero end play. I envy your Timken bearings. My Atlas still has Babbit, but it works fine. Bugs
Yeah. My baby Atlas has Timkens, but my old F.E. Reed has babbitted headstock bearings. The only thing I found I needed to keep them in good health was to install larger oil cups, so I didn't have to remember to keep them good and wet.
The little cups that came stock are only good for about two to three hours of run at low rpms before they run dry.
This is a little off topic, but after having done that once about 30 years ago, I switched to those "Power twist" belts that are made in sections. You don't have to take anything apart on the machine. The one on my Atlas 10" lathe has been there for 8 or 10 years now with no problems. A couple of months ago I upgraded my old ford backhoe from a generator to an alternator and had to change generator drive belt. If I had have used a regular one piece vee blet, I'd still be out in the shed amongst a pile of tractor parts. The Power twist belt worked there, as well.
LLoyd, I found the problem. It turned out to be the key on the gear the headstock gear that drives the threading drive was improperly seated, and blocked that shaft tension adjustment nut in its travel. I used my rawhide mallet to drive the key into its slot, and then the adjustment nut was not blocked and could do its thing. The problem vanished. No play in the headstock now (that is, less than 0.0001 inch).
My current challenge is that the majority of cuts I take are not entirely smoothe, but feel threaded. I believe that this is due to the carbide cutting tools that I'm now using, and I also believe the solution might be to grind a few HSS cutting tools with rounded ends. I remember going thorough this excise more than 30 years ago, but that's been so many years ago that I don't remember the solution required to get a very slick and mirror-like cut which I would like to do, but if I recall corectly it involved the use of a rounded end cutting tool. (I also recall that when we had a tools that would do this, we stashed them away and literally guarded it with out lives.)
Any suggestions that exclude use of a tool-post grinder?
If the shaft feels "threaded", there are some possibilities.
#1, feed rate is much too fast, or spindle is turning much too slow and you are actually threading.
#2 Gibs are loose on slide, apron, compound etc.
#3 Work piece sticking out too far
#4. Tool nose way way too sharp and is cutting into the work rather than shearing along the work.
When I first started making chips, I used to get this all the time, with an old Logan 10" lathe. And for all the above reasons.
This might help:
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I tend to run between 800-1000 rpm on vitually anything under 2", using HSS tooling Steel, aluminum etc. Then adjust my feed rates to match. A good start with a basic cutting tool is .005-,007 per revolution, YMMV of course.
If its a steel I know well, or aluminum, I may crank it up to
2000-3000 rpm depending on many things, using carbide. With a decent carbide bit, I tend to run my steel chips so they come off the work piece colored brown or straw colored, or even up to blue. When roughing, I mostly run blue chips. Shrug..while I like machining..standing there all day making tiny cuts is like watching grass grow. Most of my lathes are filled with high sulfer cutting oil, so I often run the blue chip speeds and feeds with oil flooding the cutting zone.
With some steels and a negative rake tool in a rigid lathe, Ive been known to burn off .02 per rev and in aluminum with a big radius on the cutting tool and still getting a good finish. But such is usually only for hogging off material fast.
This may not be possible with your lathe. Some are stiffer, more powerful than others. Shrug.
One thing a lot of people dont know about, which I strongly recommend, is to take a socket head cap screw of the proper size and replace one of the center gib screws on both cross slide and compound slide.
When taking a heavy cut, simply tighen them down a bit, particularly the compound.
Oh..I tend to sharpen most of my HSS bits on a belt sander. Shrug..gives me a good "grind" and is easy to tilt the table down to your 10-12 degrees and get proper relief, and simply turning it gently and quickly will give you a good radius on the tool nose.
I am NOT a machinist, nor do I play one on TV. But Ive picked up a few tricks learned in CNC production shops that often translate to home shop usage on lighter machines.
Gunner
Rule #35 "That which does not kill you, has made a huge tactical error"
Sounds like your tools are ground to a sharp point. That's alright for (some)shouldering, but not very good for smooth surfacing cuts.
Radius the points a little, and make your last cut fine enough to barely pull swarf.
Your longitudinal feed might be too fast for the radius that is on the tools, too. For a smooth cut, the actual "cuts" of the tool point must overlap about 30% or more.
Make a chip cutter with a slightly rounded lead edge and flat trailing edge. Set it to about 1/2 to 1 degree of horizontal relief. With the correct feed, speed and lubricant you can almost get a mirror finish. Bugs
In particular, most lathes with a quick-change gearbox (not sure about yours) have two forms of longitudinal feed available:
A) The usual, using the leadscrew as is used for threading, engaged by closing the half-nuts.
B) "Power feed" -- the leadscrew also has a keyway cut down its length, which turns a worm gear inside the apron. This gear either turns the handwheel on the carriage for a particularly fine longitudinal feed, or turns the crank for a smooth cross-feed. (This is determined by the position of some form of lever.)
If you have this, it should be used in preference to the halfnuts to minimize wear on the threads of the leadscrew. Also, the feed from the power feed is noticeably finer than that produced by the half nuts, which are truly designed only for threading.
The feed rate changes with the selected thread pitch, but in all cases, the feed is finer than the thread pitch. As examples, I'll give the coarsest and finest settings on my Clausing quick-change box:
TPI Lead Long Cross feed feed ------------------------------------------------- 4 0.125" 0.0367" 0.00017" 224 0.00446" 0.00065" 0.00016"
As you can see, at all settings, the power feed gives much finer feed than the threading half nuts. (By a factor of about 3.4:1 on this machine.)
All of Gunner's other advice is good, too -- I just thought that as a new lathe owner, you might have missed the longitudinal feed (if it is present on your Atlas -- it is not on my tiny 6x18, which really does not get used these days.
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