I am new to metalworking, and am struggling with my new lathe (9x20?)to achieve decent surface finishes on steel parts. Currently I am working with bright mild steel, but have just ordered some EN8, EN19 and SS304 to do comparative tests. I do not have the ability to flood cool the job, I am considering adapting to flood coolant system for use with soluble oil. Is this worthwhile?
I am cutting with a Korloy insert tool, 50 m/min speed and 0.1 mm/rev feed, which is conservative.
I use a little lathe a lot too. Sometimes the parts come out like chrome, sometimes they look like they'd been sandblasted. The difference is usually the steel. You are obviously using British terminology -- in the US we call BMS "drill rod" and it actually makes quite a difference what kind of drill rod I turn. To get a good finish, I mean.
I really doubt it's your coolant.
I have never heard of Korloy. I'm not going to bother converting your units to make sense to me. I'm assuming you've looked up the right speeds and feeds. You can try sharpening a HSS bit and using that. Do your roughing cuts first, and when you've gotten down to where your machine can handle a rounder nose, use a tool with its actual tip stoned to about 1/32" radius (that's 0.79375 mm radius) and use a fine feed. Coolant IMO mostly has two functions: it lengthens the amount of time a cutter stays sharp, and it lowers the friction path for chips leaving the cut zone. Both of these can affect finish somewhat, but not nearly as much as cutter topology and correct speeds and feeds.
One more thing. Are you positive you aren't getting chatter? The modern 9x20 lathes are very light machines, and it's got to be tough controlling chatter on them. If you look very closely at the turned surface under a strong light, do you see what look like facets on a gemstone? If so, your machine is chattering and you can work on trying to control that.
Is your tool post 'ROCK SOLID'.. If your cross slide has a compound on it and you are not making threads.. get rid of it... make or buy a tool post that mounts directly on the cross slide and is as big and massive as possible.
I have an import 9x20 and the compound was a joke and was next to useless for regular work, let alone cutting threads... I replaced it with a pretty massive 4-way (about twice the size you'd expect on a machine this small) and it works GREAT! I can make better threads just plungeing in parallel on the cross slid than I could with it.
The lesson that should have been learned here is carbide should have long ago been abandoned in favor of HSS and proper tool geometry. Carbide is a miserable failure on small machine tools--------the only success it typically enjoys is the incredible ability to allow the operator to avoid learning to properly sharpen cutting tools. I hardly think that's a good thing.
A comment on surface finish. Mild steel, which appears to be the topic of discussion, is amongst the worst of materials to machine in that it loves to tear. Only when carbide is employed along with a high surface speed and proper depth of cut and feed will it cut otherwise. The addition of lead to steel makes it machine beautifully----so if you'd like some success with surface finishes, try machining some of it. Your metals supply house could provide you with proper designations.
304 stainless is ugly to machine, but tends to cut with a good surface, assuming you have a sharp tool, and don't run it too fast. If you're intent on using carbide, be certain you do *not* use a C5 or C6 grade. C2 is the proper grade, and it makes a serious difference in tool life and success. Better yet, for a small lathe like you have, a properly ground HSS tool with positive rake and a chip breaker is even better. If you'd like to machine stainless that is fun to cut, buy 303 either S or Se, each of which are free machining, unlike 304. It cuts with a clean surface, although not quite as shiny as does 304. 416 is also a free machining grade, and is capable of heat treatment, should you have need.
I mostly use HSS toolbit because they work for me. I remember one time I was machining 4140 and have a tough time of it. My experienced machinest friend told me. Sharp HSS with a surface speed of 50 and lots of lube. I use that combination for most steels with good success.
Machining garden varity CRS will make you buy 12L14!
That is correct. Drill rod is *not* a mild steel by any stretch of the imagination.
Probably the nicest machining steel is what is labeled 12L14 here in the US -- a lead alloy to improve free cutting, and low enough carbon so it is not particularly tough (or hardenable) anyway. What it is *not* good for is weldability, from what I understand.
What I *don't* remember is what the UK calls hot rolled steel. (Could they call it the same as the US?)
That would have been my suggestion as well. As for where -- it depends on how much length you want. There are several on-line metal vendors who will sell you short pieces at premium prices.
But -- if you are willing to purchase (and have the ability to store) longer pieces, try to find a local steel vendor and buy it in 20 foot lengths (I think that is the standard length.)
EBay auctions offer small pieces of lots of interesting steels and other metals, but the shipping can be a killer, as most metals and alloys are quite heavy.
And -- if you are part of a local metalworking club, group purchases are a possibility. Either with new prices for the long stock, or with some eBay auctions which are lots just too large to be within the reach of a single bidder.
We have one member of our local club who specializes in what he calls "stolen chickens" -- which are often things being gotten rid of by his previous employer (before he retired). He still supplies such things, and they appear a the meetings, often with a feeding frenzy.
There was a lot of hex 12L14 on eBay a year or two ago for which we got together a list of who would commit to buy how much, and once we had enough subscriptions, the buy was made. Since he is retired, and has both a pickup truck and a trailer, he was able to drive some distance to pick up the metal, and brought it back to distribute it. The size was just the maximum hex which would fit through my 12x24" Clausing's spindle with the 5C collet drawbar removed, so it worked out quite nicely for me.
Perhaps you can get together a similar club activity.
What we have (better use commonly) here (Germany) for free cutting is:
9SMn28k and that would translate to 1.0715 The leaded equivalent would be:
9SMnPb28 (or 11SMnPB30) translates to 1.0718
But to my knowledge, you only get round stock in free machining.
What you call drill rod, is a bit better than what we call (in Germany) "siver steel", the quality of the Brits silver steel is unknown to me, but I guess it is either yours, ours, inbetween, or even worse:-)). The code for the Kraut-silver-steel is 1.2210 (or 115CrV3). A tool steel for _cold_ work.
The stuff you get here (easily, as always) as CRS*) is
EuroNorm. Hmmph. I have an Aussie customerr whose aussie engineers use EN material specs on their drawings, as well as metric stock sizes. I am constantly asking permission to use commonly available material grades and sizes. I have yet to find an American material vendor that even knows what euronorm is, much less is willing to cross reference.
For you guys working smaller machine tools, 12L14, 1215, 11L17, in stainless, 303, and brass, 360. When permissable, the only way to fly. Costs more, but performs.
The new(?) USPS Flat Rate box would be a great opportunity for an eBay seller. For $7.70 he could ship the 11" x 8.5" x 5.5" Flat Rate box full of steel anywhere in the U.S. Theoretically, that could be 145 lbs of steel. The USPS says "no weight limit", but I wonder. Oh, wait, there's also an 11-7/8 x 3-3/8 x 13-5/8 Flat Rate box that's somewhat bigger. Same $7.70. Bob
You've noticed that 12L14 has already been mentioned a few times. It's not the only free machining mild steel, however. There are others, commonly known as screw stock, or material for screw machines. 1213 and 1215 are two more numbers to keep in mind. These two are resulphurized and rephosphorised to improve their machining qualities, and contain no lead. They are rated @ 136% for machinability, based on 1212 @ 100%. 1018 has a machinability of only 78% as compared to 1212, so it's clear that these materials are far superior for machining, although they may suffer in mechanical areas. They are not recommended for parts subjected to severe fatigue stresses.
In addition to 12L14, there is another leaded material, 11L17, which is a high manganese alloy. It has good machining qualities and can be carburized, in spite of the small amount of lead in its makeup. 1117, without lead, isn't quite as good for machining (rated @ 91% based on 1212 as 100%), but is still far better than 1018.
If you require a tough material with excellent strength, but don't want to heat treat, consider using Stressproof (1144 Hi Stress) or Fatigue -Proof. These materials have excellent machining qualities, along with tensile strength far superior to the other materials. Stressproof and Hi Stress have a tensile strength of 100,000 PSI, and Fatigue-Proof is greater at
140,000 PSI. All of them are rated at approximately 80% machinability as compared to 1212 @ 100%. These materials cut very well, without tearing, and tend to cut better with HSS than carbide, at least from my personal experience.
Where? Large supply houses have them. I used to buy from Jorgensen Steel, now known as EMJ.
*Any* 400 series of stainless is heat treatable. The advantage of 416, assuming it fits your needs, is it's free machining, which is the reason it was mentioned. 440 is nothing short of a bitch to machine, so I don't recommend it for fun projects, very unlike 416. 416 is the best of all the stainless alloys where machining is concerned. It's rated @ 110%, with
1212 rated 100%. By contrast, 440C is rated @ 40%.. As I said, it's nothing short of a bitch.
Sadly, none of the free machining steel or stainless grades are recommended for welding. 1117 can be welded with mixed results according to Jorgensen's stock list. You should consider their use only when no welding is required.
Thanks for all the good advice. I have some work to do sourcing equivalents in South Africa, but our steel industry is fairly good. I know stainless 303 is available on order. I will collate all the info and the results of my experiments an post it when completed. Seems I will have to learn to grind HSS, damnit....