Need some help understanding my cross feed

As I learn more on how to use my small 6 in atlas lathe, Im seeing something I dont understand. When I use my cross feed Im getting a real large swind in readings. I am expecting wear, but could there bee this much on it?

Heres some steel I used for this post. the cross feed is set at 0 on the marks.


Next I turned the cross feed to 10 and took a measurment.


So Im taking 10 on both sides and the cross feed is worn .005 apx? Sorry for the rough pick, best I could do with my phone.

Ok Vince, are you saying the cross feed dial does not match you dial ind? If thats the case there is no
more seats on the bus. lol Us with older machines or some imports thats life. Mine dont match either
thats why I use a dial indicator at least I can see that, I never go by my dials they are off by maybe
.004. or more, and its a South Bend around 1942 so I expect that.

Vince O

Your pictures show you taking a cut along the length of the diameter. I'm guessing what's happening is as you are taking a cut, all of a sudden your cross slide or perhaps top slide moved and started taking a deeper cut. So, with the tool bit out of the way can you move the saddle, or the cross slide, or top slide by hand? Even top grade new machinery has some slight slop or it wouldn't work, but older machinery of the Atlas class should not have that much slop. The abrupt amount of change in diameter suggests something came loose, the nuts that hold the feed screw, the cross feed nut, etc.

I don't know much about the Atlas and can't be more specific, others with more knowledge will be along and give more specific suggestions.

all the best

Olin

I'm not sure if this is your question but some cross feeds are graduated so that .001 could mean .001 on the radius or .001 on the diameter.

Gene

centers out of aligment? if not tighten the gibs on the cross slide and compound rest.

Just to clarify, you are taking a plunge cut perpendicular to the work, correct?

First thing first, make sure that your tool is exactly on center line, as being above or below can alter the depth that you cut. Make sure the work, tool, tailstock, chuck, etc, are all tight and running true.

When you go to make the first plunge, back the cross slide out, at least a full revolution or two, and feed it back in to remove the backlash from the screw. Feed back in slowly to touch the work, and set your zero. Then carefully feed in a bit, say 10 thou. Then, WITHOUT backing off the cross slide, move the carriage a little ways, say 1/2", then feed in another 10 thou, and make another 1/2" cut. Make sure to take fine cuts, with a sharp tool. When you are done, you will have an accurate way to check the cross slide feed. Measure the diameters with a micrometer, if you have one, and compare the difference.

When a leadscrew or its nut wears, it will not affect the distance traveled per revolution. The largest effect is the backlash, or free rotation of the screw or nut when you change direction. It is possible that one area of the screw is work more than the rest, as the worn areas, with thinner flats on the top of the screw gradually move to less worn areas with more material, but you would see this effect over several inches, not several thousandths.

-Cody

You also have a very long piece of stock and it's bending under cutting pressure. Need to be careful when cutting long, thin diameter stock. It will jump-up and climb on top of the bit -scare the pant's off you and break the bit.

Here's the order of things I'd check.

Another thing is that your tailstock might not be centered and that will cause you to cut a taper that could go from wide to narrow or narrow to wide depending on which way the tailstock is misadjusted.

You may have a lot of slop in the gibs.

It's also very possible your carriage is moving on the flat ways.

Your tailstock might me moving because it's not clamped down hard enough and it slides sideways across the ways.

The acme screws in the crossfeed could be worn.

The crossfeed thrust bearing (actually the crossfeed dial on an Atlas) might be moving when there's pressure against it (same thing happens on the compound dial).

The head could be misaligned.

The spindle bearings could be bad.


Ray

Ray C said:

You also have a very long piece of stock and it's bending under cutting pressure. Need to be careful when cutting long, thin diameter stock. It will jump-up and climb on top of the bit -scare the pant's off you and break the bit.

Here's the order of things I'd check.

Another thing is that your tailstock might not be centered and that will cause you to cut a taper that could go from wide to narrow or narrow to wide depending on which way the tailstock is misadjusted.

You may have a lot of slop in the gibs.

It's also very possible your carriage is moving on the flat ways.

Your tailstock might me moving because it's not clamped down hard enough and it slides sideways across the ways.

The acme screws in the crossfeed could be worn.

The crossfeed thrust bearing (actually the crossfeed dial on an Atlas) might be moving when there's pressure against it (same thing happens on the compound dial).

The head could be misaligned.

The spindle bearings could be bad.


Ray

Click to expand...

I agree, you have a long unsupported piece of stock. The more you cut, the more deflection you will get. The deflection will be the worst in the center and taper off the closer you get to the chuck/tailstock. A steady rest will solve that problem.

Ok guys thanks for the help. More the fact that I knew that my lathe is worn, just didnt know how bad maybe. I took some 1 1/4 stock, cold rolled, and took a measurement about 5 inches apart. I understand about the movement on the thiner stock, but Im not going to buy any more tooling for this lathe, other than some boaring bars. Im in the hunt for a larger one, so that when i find one under power Ill make some cuts to see how its worn.

I do know my centers are lined up, took me long enough to set it back up after taking the tailstock apart.

I tightened all the gibs

there is alot of "lash" on the cross slide by hand so Im guessing this is my delema.

For me the little lathe cuts well and straight. Now for you guys, LOL maybe not! But remember im learning and with your help I will get better or go broke trying!

Just off the head stock


Towards the tailstock


- - - Updated - - -

Oh and thats about 2 inches off the head stock and tail stock. 5 inches inbetween the measurments.

Smaller lathes can cut just fine. Some need more nursing as you go. In the case of a 6" lathe cutting a 2" bar -well, that's not really a fair fight. When I had a smaller, older lathe, my first "real" project was to make a PTO shaft for a generator. Best I could do was about a 10-15 thou DoC, less for stainless steel because you could literally see the compound flexing. By keeping the cuts very light, it would do OK.

Here's a rundown of things that happen when lathes wear out... These are common problems not specific to any brand of lathe but are more common on really old lathes that didn't have the benefit of hardened components. Some things mentioned are specific design flaws that could be be corrected if you're inclined to do so. NOTE: My purpose in telling you this is so you can check for these things and not drive yourself insane (like I did) when things aren't working when you think everything is fine.

On yours (if it's exactly like mine) you'll notice the acme screws in the crossfeed and compound terminate at the dials and there's a set screw that holds the dial to the acme screw. That set screw can and will move under pressure because it is that set screw that bears the brunt of the force on the acme screw during the cut.. Also, on units that have a lot mileage, the threaded brass cross-nut that the acme screw threads into can wiggle in it's fixture -and you'll have repeatability problems. Also, as the jib ways wear, you can't find a happy medium of having the jibs be snug and still allow free travel from end-to-end. You'll find repeatability problems as you make cuts and depending if the compound position puts the jib at a high or low spot or somewhere in between. Same thing happens when the main ways wear on the sides. When adjusted to fit near the headstock, you can't roll the carriage down to the end. If you adjust it to fit the end (which is not worn as bad) the carriage will drift all over the place as it gets close to the head. On units that had bad bellying in the ways, you encounter problems with consistent parallelism of the leadscrew. As the carriage goes over the low spot, the leadscrew pushes up on the carriage via the halfnuts and that causes additional wear on the halfnuts. EDIT: In addition to wear on the halfnuts, the uneven pressure on the carriage causes the infamous "leadscrew imprint" problem. On some of the older lathes, you'll notice the handcrank gear wiggles due to wear. When in autofeed, the crank naturally turns by itself and when it goes past center, it suddenly plops down with enough momentum to influence the carriage and a mark will show in the piece. On a worn lathe, you notice that the tailstock ram may not lock-up consistently at different amounts of extension. You will also find that on some models of lathes that do not have V-grooves, the tailstock relies on a tight fit on the inside of the way rails. The area about 1 foot from the chuck is usually worn the most so, it's not possible to adjust the fit to suite the entire length of the ways. Adjusting the TS, every time you move it out of it's comfort zone is time consuming. On older lathes, the mechanism that holds the end of the leadscrew to the gear that turns it might not be a solid method -and this will cause surface finish problems as the leadscrew floats around. If it's bad enough, you can see threads change pitch randomly as you make a thread cut.

I've probably missed a few but these are the things I can rattle-off quickly. BTW: I spent the better part of 3 years figuring this stuff out one-by-one, lump-by-lump, bruise-by-bruise.

Ray