[wklove]

Hey all,

I am a new to machining so this may sound like a dumb question, but I would appreciate any helpful information. I am using a horizontal Haas lathe and I was wondering if after I finish a cutting pass on the diameter, if I jog the machine back in reverse, will that have any effect of the surface finish? Help or hurt it? What if I reverse it and then repeat it at the same diameter? Does it help or hurt?

I am doing some research on some related topics so I was curious if someone had some thoughts. I realized that when jogging it back in reverse, it does make some contact with the part and shaves off small areas here and there. Was just wondering if that is hurting or helping the finish.

I would really appreciate any links to studies or information on this subject.
Thank you!

[DMF_TomB]

if you mean if you backup the cutter without adjusting it so it no longer touches part it will in general leave tool marks.
.......all machinse deflect and bend some so even after taking say a 2mm cut if you were to not change things but run the feed again in general you will remove additional material.
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if i were taking a 2mm roughing cut i would allow for 2 more 0.2mm finishing cuts and would expect the first finishing cut to remove more than 0.2mm. i would expect the 2nd finishing cut to have to be less than 0.2mm because the first finishing cut sprung back or overcut.
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surface finish is often better with carbide tooling using higher speeds.

[wklove]

Yes, I meant that if I make a 2mm DOC along the cylinder/diameter of the part, then reverse it, and go back over it again without adjusting anything. So basically just rastering back and forth over the already cut surface while the workpiece spins. So that will leave unwanted tool marks on the finish?

I know there is no real reason why you would want to do this, but it is apart of what I am looking into.

[underthetire]

What kind of finish are you trying to achieve? I dont think its going to help with finish so much as size going back and forth. A lot determines finish, balanced chuck, type of machine, type of tooling, etc.. We turn to optics quality here, even a profilometer will screw up the finish, they check ours with some kind of laser. I also did a set up for a company that made medical imaging devices, had to hold better than an 8 on an internal contour of some OFHC in a production environment. Our finishing machines have hydrostatic ways, air bearing spindles, and special ground diamond tools. Temp control to 1/2 degree. Cant even flood cool the parts, the coolant can smear the chips across the face of the parts. The point of my long winded post is, "good finish" is a pretty general term.

[RICHARD ZASTROW]

Just to point out the obvious, if you cut toward the headstock (chuck) with a positive rake turning tool (insert) then reverse the feed direction, you will be trying to cut with a negative rake tool.

Dick Z

[flyinchips]

Now that we've all told you what we think. Go do it and observe. It is the BEST thing a newbie can do. You will learn more than surface finish if you just go and DO.
And while you're doing it, have fun!