1018 Finish Cut

J

Jim1946 SB9"

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Hi everyone.
Well I have started my first project on my 9" SB. I am struggling with surface finish I am cutting 1018 and want some pointers on finish cuts. At this time I still have lots of material to remove but would like to figure this out before I get to my final dimension. I have been reading about feeds and speeds but have yet to try power feed as I am not sure what feed rate to start with. Any advice about 1018 would be appreciated.
 
I guess on a 9'' SB I might start with a 0.005 feed and a 0.010 DOC (Depth of Cut) and see if produces the desired result. In general a finer feed will give a finer finish. Play with the tool height and shape also. 1018 is not known to produce mirror finishes, too slow of a spindle speed or too slow feed will sometimes cause some galling at the tool point and produce a intermittent rough finish.
 
You've picked a material that is noted for being difficult to obtain a good surface finish. However it is common and inexpensive, most of us use it often. Insofar as feeds and speeds are concerned, it may be a trial and error process on an older lathe.

Start with a lower RPM and fine feed and experiment by gradually increasing both, noting the results. (Be sure to use a sharp cutting tool or any observed results aren't meaningful.)

If your lathe is tight and solidly mounted you might set your starting RPM at about 200 divided by the work diameter in inches, for steel workpieces and sharp HSS cutters. If you use carbide cutting tools, the RPM can be tripled. Again, this is for steel. Use cutting lubricant to extend tool life - unfortunately it won't help the surface finish on 1018 as it does on most materials.

You probably aren't at a stage of development yet to make use of this but for a precise, finely finished diameter in 1018, a HSS "shearing tool" does wonders. The depth of cut must be very, very small however, typically around .001/.002 to prevent wear on the cutting edge and the feed rate must also be very small, on the order of .003 IPR.

Oops, Jim posted while I was bumbling around with my own reply. His advice is always good :)
 
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When you finally get tired of cutting 1018. Try some 12L14. It’s a free machining low carbon steel with similar properties to 1018 but with some lead in it. It machines amazingly nice…Good Luck, Dave.
 
Thanks guys. I have been messing around just trying to learn how to use the lathe. If all goes well the project will turn out to be a cannon. But I think I started a little big for the 9". I have a few 9" deep holes to do on this project and wanted a decent surface finish. So I think I will just learn to get the taper cut and will probably purchase some of that 12L14 for the final product and maybe down size it a littl. This is all about learning, the finished product is in my future but it might take a couple tries. Learning is the important part right now. I will be reading about that shear tool as much as possible and see if I can get one of those made up.
 
As others have already mentioned 1018/1020 mild steel is not well known nor easy to get a nice finish on. If you are after final finish then I suggest stepping up to some more free machining steel, again, like already mentioned.

That said, I use 1018/1020 a lot because a lot of my work includes welding as well as machining. The 1144's, 12L14's are not conducive to welding so I have had to learn to work with mild steels.

I have found that HSS tooling seems to work best but carbide inserts work well also if you are willing to take off heavier DOC's. I will usually rough out down to within .011-.012", then take a .010" finish cut, leaving a thou or two to be removed with a fine file and/or emery paper creeping up on the final dimension. I will start at around 80 grit and end up somewhere around 400 or 600 grit final.

The last finshing with sandpaper takes some time and time is money, so I generally will cut with carbide inserts and take a lot of material up until the final cut.

Seems to work for me if finish is what is needed. Otherwise I will make the final cut with HSS and let the finish be if it is not 100% necessary to have a nice finish, but I don't like doing that unless the part is not going to be seen at all. Even then it is not something I really like doing. It just turns out to be a balancing act of form vs. function.

Mike.
 
Don't give up on the 1018 just yet, LOL, there's no need to use a shear tool to obtain a satisfactory finish. In fact, old-timers would probably lift their eyebrows at the use of this tool.

Conventional practice was to turn the work to about .002 oversize. The work was then brought to finish diameter with a file and emery paper. It sounds like a crude process but with care and patience good finish and accurate diameters can be achieved, as Mike noted.
 
Well I tried the Shear tool. All I can say is Wow it works. Very early in the process and still need to experiment with DOC and Feed and such but so far this Shear tool looks promising. Will probably still need a little emery cloth to finish but much less effort than starting with the ugly surface I had before.
 
I keep a set of files and sandpapers on my bench for this purpose. you can get close to a mirror finish but it is so random. This material I often think is not completely homogeneous when you start to really look at it. It's also very soft and dings easily.
 
I can only guess at the diameter of the work that you are doing, a 9" Southbend lathe leads me to believe that it is less than 2" however. If using inserted carbide tooling turn the spindle up to it's maximum speed, rough at around .020-.035 DOC at .008-,015IPR feedrate, finish at max RPM at .005 or so DOC at .003-.006 IPR feedrate with flood coolant using positive rake tooling with a maximum 1/64" nose radius tool. This should get you in the ball park
Good Luck
 
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