Surface finish problems

[timh]

Hi i am having problems with turning steel on the lathe the surface of the steel looks like very fine threads. I am turning 1in. cold roll and have tryed hss and carbide with the same results any ideas? Also speed seems to make no difference.

[tattoomike68]

Cold roll 1018 is not known to be easy to get a good finnish on. I use a file and emory cloth to smooth it from an oversized state.

1140 stressproof is a dream to machine.

[toastydeath]

Try a small (1mm) radius tool, so it wipes away the tool marks at low feeds.

If you are using inserts, you should be able to buy an uncoated carbide insert with that kind of nose on it.

[SGW]

Minor nit, I think Stressproof is 1144, but yeah, in my experience it turns to a beautiful finish. Generic "mild steel" cold-rolled can be a colossal pain.

Grind up a HSS tool and stone the edges after grinding to get rid of the grinder marks...or use a fine grinding wheel. Stone a small radius on the tip, and see how that works.

[timh]

Thanks for the tips i will try them out and see what happens. Can you weld 1140/44 stressproof and how does it wear?

[Joel]

How much feed are you using and exactly what speeds?

[dalee100]

Hi,

Can you weld 1140/44 stressproof and how does it wear?

Personally, I think welding stress proof pretty much sucks. Being a "tool steel" it will harden and crystallize causing it to become brittle. It does have excellent wear characteristics though and machines pretty well. I go through a lot of it at work.

And yep, 1018 is hard to get a good finish on. If you need a high finish on 1018, I would suggest using a different finish method, (like tattomike68 suggested), or switch to a material that can give the desired finish without a second operation.

dalee

[BadDog]

Agreed, I hate turning "mild steel". It tends to want to get "fuzzy" due to tearing, and it's hard to get a good finish regardless of what you do.

I've had the best luck with negative rake tooling (and typically a minimum 0.030+ DOC), but that's on a Mori Seki I sometimes use. My home lathe won't run negative.

So I find I do best with a specially ground HSS tool. I use a regular roughing tool and screw the finish till I'm getting close, then switch to the "special" tool. It has a rather significant (deep and narrow) chip breaker with a sharp curve and providing a fairly high positive rake edge. The point has a small radius, at least a bit wider than the max feed rate I'll run it at, and all hand stoned with a diamond lap before use.

BUT, here is the key (I think). You have to reduce the clearance relief to near nothing. This is only a finishing tool and will not take more than ~0.010 to maybe 0.020 MAX DOC cuts. I often run it at less than 0.010, and it also serves as my "skim a thou or two" tool. Feed is not so sensitive, but generally slow since I'm looking for finish. The reason for the minimal relief is that it will want to suck into the material due to the high positive rake. Pretty much any positive rake tool (the most used by HSMs on light lathes) will want to suck in on the mild steel, and this is what (seems to me) causes the tearing. The small relief prevents that AND provides a sort of burnishing effect.

I've actually gotten some rather decent (enough to use as machined) most of the time. But sometimes I still have to go to the file and emery routine. Also, in this case, you don't want your typical lathe bastard to do the finish cut. It'll leave almost as a bad a finish. IMO, you want (and I use) a finer toothed single cut mill bastard and a modertely light touch, perhaps with either WD40 or other light oil. Optionally, I use chalk a lot. This will remove the fuzzies and leave a decent finish. Finally polish with emery if desired.

I do a LOT of "mild", and this is what I've come to believe is the best way given what little I know and the smallish antiques I have to work with...

[timh]

Thanks bad dog and everyone else i do need to be able to weld the part so i will just play around first and see if i can get a good finish.

[BadDog]

Oh, and on the finishing tool, you'll generally want to use some sort of lubricant (also a bit of a coolant) because the fine edge won't take much heat/friction. Light oil seems to work better for the really fine cuts. But I use dark sulfer for heavier cuts on steel.