Looks like a harmonics issue. There are probably some loose/worn bearings in the headstock and or the gibs on the saddle are loose/worn.

Try a higher feed rate and/or deeper depth of cut.

Try making your final two passes like .003 for a finish cut

Try using some WD-40 as cutting oil.

The pattern is often called "gear tracks".  It took me a while to understand what is going on with these, but here is my explanation:  

If you look at the spacing of the marks, you will find that the major pattern is the same as the rack under the ways. The  patterns are due to the "noise" of the pinion and the rack, along with other "gear noise" in the apron, and gear box.  I call this noise, but you really  cannot hear it.  The meshing of the gears is not quite smooth, nor can it be with flat gears.  What is happening is the tool feed rate has slight changes in its rate (speeding up and slowing down) due to the gear engagement. If you look under high enough magnification, you will see a slight spacing difference in the tool track on the part. This is the primary cause of the pattern.  

One other thing about this pattern is that there are some very slight changes in diameter, but for most folks, you aren't going to measure it easily.  It will show up when you polish it lightly as you will better see which bands are a tad higher than the others.

ETA:  It is quite normal for this to show up on a fine finish pass, which .004"/rev really is.

Is this lathe driven by a long screw instead of a rack and pinion for feed travel?

If so, then the screw may not be straight and causing it to push the carriage up and down, or back and forth.  If there are gibs that you can adjust to minimize up/down or back/forth play may help. But, try to straighten the lead screw.

If you don't have those adjustments available and it is not lead screw driven, a different tool profile should help.  Personally, I have been disappointed with most insert tooling.  I prefer to grind my own.

I'd think that your compound is flexing under load.  Watch your tool closely for movement as the cut progresses.

Can you put the magnetic base on the compound, and an indicator needle on the ways, and watch the dial as it is feeding to try to determine if it is moving, and how it is moving?

Did you level the lathe when you installed it?

I would mark the leadscrew with a paint pen and or the handwheel and find the correlation between whats moving and the surface finish, likely something in the chicom lathe is not lined up or adjusted right and its rocking the carriage around. You can also grab the toolpost and pull back / push down while and see if the finish changes. Put a dial indicator between the carriage and one of edges of the flatways and push pull and see if something is rocking.

Properly leveling the lathe on a suitably rigid surface will return the ways in the same geometric condition they were in when it was ground. Level doesn't mean level to the earth, you just need to eliminate all the twist and a precision machinist level is the easiest tool you can easily access to do this. If do your alignment with a test part it can be hard to tell the difference between taper due to bed twist and taper from headstock misalignment. If you have a cockeyed headstock and the twist the bed to make straight parts you'll end up with the bearing surfaces only touching on the corners and it will rock and the surface finish will suck. Southbend used to only use three supports, two under the headstock and one at the tailstock, you might try loosening some of your hold downs. Your wood board might be twisting the little lathe.

It would not surprise me in the least if the contact between the carriage and the ways is poor even if its level/straight and you have what you have. Similar to how a grinder and paint can make a welder what he ain't, sometimes you end up having to use a lot of emory cloth when your equipment sucks.

This is true all true for a 8k lb lathe or a 80lb mini-lathe, the difference is there are so many other things wrong with the mini-lathes you'll never be able to tell.
Personal aside:
I have a 17x40 Whacheon in my garage that the previous shop owner said turned a taper. It was bolted to the floor and when I cut it loose to move it it jumped up. They had been using the leveling feet to try and get the taper out by pulling it to the floor. At my shop I didn't want to bolt it down as we are moving soon. Setting the 4 leveling jacks under the headstock I found that only one of the tailstock adjusters did anything. The Whacheon/Mori Seiki lathes use a huge cast iron one piece base with the lathe sitting on ground pads and bolted together. What I found is that being racking like it was caused the lathe to take a set.

Stock photo of a WL435 lathe, mine looks just the same:

Attached File


I didn't want to try and unbolt the lathe from the base as that had a lot of unknowns. Instead I made a weldment to bolt to the tailstock leveling jacks that effectively moved the rearmost leveling jack back 3ft behind the lathe. This also helped with picking it up several inches, Japanese machines are low and I'm tall. With the added mechanical advantage of the wider stance at the tailstock I could then twist the lathe back level using its own weight vs pulling down with anchors. This let me get the bed straight using a .0002/ft level. Then I found that the root of the owners problem was actually a misaligned headstock. I spun the headstock on the lathe bed using the provided adjusters and now it turns straight. I'm hoping that eventually the lathe bed assembly will flatten out over time. If it doesn't I'll bolt it down...

Don't underestimate how flopping machines are when you look sufficiently close.

Could the chuck be turning off center, or is the work not quite clamped evenly between the three jaws? I'm a total amateur, but that's what I would look at first, and you probably already have too. In for more expert opinions and the results of investigation.

What is your goal with the granite? Countertop granite isn't near stiff enough to offer any sort of "flat surface" that you would be able to reference in the way you're thinking. There is a reason surface plates are 6 or 8" thick in that size.

The proper way to check for twist in the bed was already mentioned above; a precision machinist level. Watch Ebay, especially for off-brand Eastern European stuff from mid century. I have a Polish level that puts Starrett master precision stuff to shame and I paid $60 for it on the bay.

Do the half it's stay engage when you just flip the lever down? IE do you have to push down and hold it? If not, I'd just stop doing that.