Metal Lathe Surface Finish

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I bought a used ENCO 3 in 1 lathe/mill/drill two months ago and have been busy learning to use it.  Having worked around machinists in an aviation repair depot I am somewhat familiar with the process of metal turning.  I have been practicing with some steel rod, specifically the stakes used to set concrete forms.  I am having problems getting a decent surface finish. I have been trying different feeds and speeds, depth of cut, and various cutters ranging from carbide inserts to HSS pointed and radiused, at, below, and above the centerline of the shaft.  I keep getting a finish that is similar to that of a phonograph record, that is, grooved and rough to the touch. I have been turning dry and with cutting oil.On another board it was mentioned that sometimes cheap steels will "break away" rather than shear.  Anyone else have experience with this and have a solution?Steve
Reply:Try again with a piece of decent steel. the bar you are using seems to be the trouble, set the tool to centre height,Lincoln SP-170 MigHypertherm powermax 45Lorch T220 AC/DC TigButters FM 215 synergic MigKemppi 180 adaptive mig RULES ARE FOR THE OBEDIENCE OF FOOLS AND THE  GUIDANCE OF WISE MEN.
Reply:Get some W-1 or O-1 drill rod & try it.  You will like the way it finishes.  If your using carbide, it needs speed & heat to give a great finish.  Chromed rods from Home Depot aren't the ones to use as this steel will just groove like a phonograph.Even round bar from the local steel supplier will turn better than the stuff from Home Depot.MarkI haven't always been a nurse........Craftsman 12"x36" LatheEnco G-30B MillHobart Handler 175Lincoln WeldandPower 225 AC/DC G-7 CV/CCAdd a Foot Pedal to a Harbor Freight Chicago Electric 165A DC TIG PapaLion's Gate Build
Reply:You are setting yourself up for a disappointment trying to turn that stuff. Find a known grade so that you can set the proper rpms on your lathe. Good starting point for low carbon steel would be 90 surface feet per minute.Take (90 x 3.82)/dia in inches.  This formula will give you the rpms recommended. Find the closest matching speed on your lathe. If you are stuck between 2 speeds, pick the lower one.Next, buy some HSS blanks and learn how to sharpen them. Google "grinding lathe tools" or something. You might spend $4-6 on a 3/8" bit and you will get hundreds of grinds out of it. Forget the brazed carbide tools you see offered.  Put simply, you are better off with HSS (the brazed ones are usually duller than a good HSS grind).This should be a start.
Reply:Try some different material , even aluminum. If you have the right speed/feed you should get a really nice finish on that. With mild steel it likes to dig in a little at some spots. For the cutter you want it to be just a little bit below center. Use the live center in the tail stock to line it up.Another solution to fix the finish would be to run emery cloth across it+ scratch pad , that should fixer up.
Reply:Inexpensive pre-sharpened carbide is rarely correctly sharpened well enough to give a good surface finish on anything but maybe aluminum.  Get a hand full of 3/8ths or even better 10 MM HSS tool blanks and hand sharpen them using the "Tubal Cain" methodss from You Tube fame.  Insure that you dont overheat the tools while shaping, and hone them with a stone when they are sharp and properly shaped and you will end up with a very nice almost perfect finish on your material.  A well sharpened and properly honed HSS bit will deliver an almost perfect finish on mild steel and aluminum on the first or second pass.  Relief angle and tool to holder angles are critical, but as long as they are close and uniform the actual degree measurement is a little less important than the correct profile (a couple of degrees off on a well sharpened tool is OK).  Some steels like a little less relief for chip breaking and some like a little more, so experiment and find that sweet spot for the material you are using, there is one if you will take the time and find it.  And just as an aside,  underfeeding and underspeed is just as bad as over speed and over feeds, find the sweet spot and all will be good.  Good luck, hope this helps get you going in the right direction.BobI'm spending my Kids inheritance, I dont like him that much anyway!!!!!!Enuff tools to do the job, enough sense to use em.Anybody got a spare set of kidneys?  Trade?
Reply:Thanks for all the great pointers, fellows.   You confirmed pretty much what I expected.  Some of these steels of unknown composition give you all sorts of headaches for various processes except for bolting or riveting.  I have some HSS bits as well and a Tormek water cooled grinder so I can put a great finish on whatever I sharpen.  What made me suspicious of the metal was that I had ground HSS to various configurations and was still getting the same results.  A bastard file and emery cloth was the only way I got any kind of finish. Nice thing about HSS is that used bits aren't very expensive and many are ground already.Thanks again.Steve
Reply:There's no need to wet grind HSS.  It needs to be heated to a dull red before losing its temper (unlike ordinary tool steel). If you just use a bench grinder and dip in the water cup when its too hot to grip, you'll be fine.Yes, forget the carbide.  Just learn to sharpen a good profile.Oh, and I tend to use cobalt alloyed cutters.  The steel is in the same family as HSS, but has even higher heat resistance, which keeps its edge longer (especially when cutting stainless), for not too much more money.
Reply:If you are getting grooves, try using a bigger radius on the tip of your tool bit and a finer feed per rev.  The steel you are using is probably most of the problem.
Reply:Originally Posted by stevewmI bought a used ENCO 3 in 1 lathe/mill/drill two months ago and have been busy learning to use it.  Having worked around machinists in an aviation repair depot I am somewhat familiar with the process of metal turning.  I have been practicing with some steel rod, specifically the stakes used to set concrete forms.  I am having problems getting a decent surface finish. I have been trying different feeds and speeds, depth of cut, and various cutters ranging from carbide inserts to HSS pointed and radiused, at, below, and above the centerline of the shaft.  I keep getting a finish that is similar to that of a phonograph record, that is, grooved and rough to the touch. I have been turning dry and with cutting oil.On another board it was mentioned that sometimes cheap steels will "break away" rather than shear.  Anyone else have experience with this and have a solution?Steve
Reply:I tried this approach using a triangular carbide cutter and upped the speed 250% from the 90 sfm calculation.  It gave me a great surface finish so maybe this is the trick. I tried it on the stake rod and some mild steel bar stock as well and got equally good results.    I tried it with a freshly sharpened and radiused HSS cutter and got the same rough finish.  Again, thanks for all help,
Reply:http://en.wikipedia.org/wiki/Speeds_and_feedsIt's not the best reference but a decent primer. Also, you don't say how much stickout or length of material you have project past the chuck jaws. If, for example, you have 12" of 3/4" material between centers, you could be experiencing some deflection in the middle of you cut. Additionally, on a lot of the 3 in 1 machines I've seen the toolpost sits up higher than on a typical lathe and could cause some spring action. Point being, there are a lot of variables in turning steel or other materials on a lathe. Sounds like you are making progress.
Reply:Dunemetal, I have been using less than four inches on 1" stock and doing anything longer between centers.  I have a quick change toolpost and have been using automotive type feeler  gage material for shim stock.  The tool post and cross slide seem pretty rigid and I have taken all the backlash out of the contact surfaces.  The only slop is in the lead screw threads of the cross slide.  If the slides themselves are too loose, the weight of the handle on the will cause the pull cause the lead screw to back out a little.  Increasing the friction improves that.I may be dealing with a carbon rather than mild steel as someone suggested.  That would require a higher rotational speed.  (90 bs 80 - 130 sfm) so that could have contributed as well.  Now that I have figured out carbide, at least in this case, I need to play with HSS to try to get the same results.Steve
Reply:I finish ALL my turning within .001 of finish and then use 80 grit emery cloth with the lathe on Hi Speed to get those polished finishes.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Originally Posted by stevewmDunemetal, I have been using less than four inches on 1" stock and doing anything longer between centers.  I have a quick change toolpost and have been using automotive type feeler  gage material for shim stock.  The tool post and cross slide seem pretty rigid and I have taken all the backlash out of the contact surfaces.  The only slop is in the lead screw threads of the cross slide.  If the slides themselves are too loose, the weight of the handle on the will cause the pull cause the lead screw to back out a little.  Increasing the friction improves that.I may be dealing with a carbon rather than mild steel as someone suggested.  That would require a higher rotational speed.  (90 bs 80 - 130 sfm) so that could have contributed as well.  Now that I have figured out carbide, at least in this case, I need to play with HSS to try to get the same results.Steve
Reply:You hit the nail on the head here.  I grind a chipbreaker on the brazed carbide bits and try to take the last cut at 0.010" depth and something like 0.007" feed per revolution for most non cosmetic stuff and it looks great.  A bonus is that the chips are easy to clean up.Also, check to make sure you're using C6 carbide.  C2 is supposed to be for interrupted cuts and nonferrous. Originally Posted by dunemetal2.  Sometimes it is tempting to try to "sneak" up on a final dimension, in this case a diameter. Some guys will get within .008" and then try to take .003; .003; then .002. At this depth of cut, you sometimes get just a rubbing which leaves a fuzzy finish. It is also a function of the particular alloy, the grind/sharpness of the bit. A lot of the brazed carbide bits don't cut real well on these smaller cuts.
Reply:Great feedback and discussion - I appreciate the good tips.  Most of the tools I have are from the previous owner and most are the brazed/silver soldered type.  I noticed right away that the carbide tended to chip off so I plan to stay away from them.  Ditto with the replaceable inserts for source but they seem to work far better than the fixed carbides.  I bought a few used HSS bits but haven't taken much time for complete regrinds, only sharpening.  I haven't really tried to work down to specific dimensions.  I ran a precision measurement lab at the aircraft depot and am used to holding tight tolerances with my wood cabinet making efforts so I am expecting these skills will transfer pretty well to metal. Wish I had some of that depot stuff, shadowgraphs, coordinate measuring machines, surface finish machines, precision rotary gages, hardness testers, and so on.  Cutting to various depths and measuring the results is a good way to check things out.
Reply:thanks for the idea on those concrete form stakes - they are dirty cheap and a good size to toy with. Only comment I didn not see aded the the useful info so far is to try using auto feed if you have it, though I think some of the responses assumed you are using it.miller syncrowave 250hobart handler 140home made 400 amp engine driven in progress...