Rough turning with HSS?

[Flynth]

I'm exploring various ways to rough turn parts. I have carbide insert holders and I use them as intended (fast sfm, high feed etc). I have some hss blanks which I ground into a number of form tools, or grooving tools. I also have a couple of monster hss blanks (20mm or 3/4 in) and I'm wondering about the most effecient way to rough turn with them.

So I'm starting this thread to ask people doing machining with HSS only what strategy do you use for rough turning? Please say what lathe you have and what max speed, depth of cut and feed do you use?

According to the book I read and my lathe manual one is supposed to take the biggest cut possible during roughing. However being used to carbide the cuts they suggest look way too big.

For example. The manual says the biggest allowable force on the toolpost is 600kg (its a fairly small lathe 12in by 40in length with a 7kW motor, bronze plain spindle bearing and 1200rpm max speed). There is a chart in the manual which claims I should be able to take 3 sq. mm cut at 25m/min-75sfpm in mild steel(at a feed of 0.2mm that's 15mm depth per side! - that's 20thou feed and over half inch depth of cut. Insane!)

I never tried such huge cuts. The biggest I did is probably quarter of that and I could see some flex in the compound, the support etc. Did people in pre-carbide era really routinely take huge cuts like this? Is anyone still doing it that way?

I'm very interested if anyone does.

 

[Eddyde]

12x40 isn't really a "small lathe" at least from a hobby perspective. And 7kW! that's a lot of power, I would think it could indeed, take some deep cuts.
HSS is often overlooked, many seem to think carbide is the only way to go but that simply isn't true. A well sharpened HSS tool will often leave a better finish on most metals and you can grind a tool to any shape you need.
As far as maximum feed and speed, that depends on a lot of variables, I usually never calculate the F&S I just go by feel, keep pushing it till it starts to indicate strain, then back off a bit.
I learned on HSS and use it for much of my work.

 

[markba633csi]

Depends on the material too- 1/2" DOC isn't insane for aluminum but for steel maybe so

 

[pontiac428]

According to the book I read and my lathe manual one is supposed to take the biggest cut possible during roughing.

Yes, but to what end? Is it better to save time for production, is it better for the tool, or do the scrap buyers pay extra for a certain kind of chip?

 

[Ulma Doctor]

Tool shape , material to be worked and machine rigidity will ultimately determine the DOC’s

For goofs I sharpened a 1” HHS blank for my 2040 lathe and made 1/2” to 7/8” cuts in 1215 steel without much problems .
1215 is pretty much free machining so that really wasn’t a feat of engineering.
The shape of the tool was a knifelike, with higher cutting angles

 

[rabler]

I have a 9000lb Monarch 612, 25x50 1500 RPM, originally a 20HP motor but I removed that to make an RPC and use a 10HP in the lathe. And some 1” sq hss blanks. But as a hobbyist, other than testosterone satisfaction, extreme cuts are just asking for trouble . Big hot chips ain’t fun, and the high torques involved mean things go sideways more dramatically when a chuck isn’t tight enough, etc.

.100 doc (.2” diameter) on .020 feed is about my upper limit on mild steel, and that’s extreme for me. I use 100sfpm for steel, 200 for aluminum as easy to remember starting points w/ hss and adjust from there.

 

[Flynth]

12x40 isn't really a "small lathe" at least from a hobby perspective. And 7kW! that's a lot of power, I would think it could indeed, take some deep cuts.
HSS is often overlooked, many seem to think carbide is the only way to go but that simply isn't true. A well sharpened HSS tool will often leave a better finish on most metals and you can grind a tool to any shape you need.
As far as maximum feed and speed, that depends on a lot of variables, I usually never calculate the F&S I just go by feel, keep pushing it till it starts to indicate strain, then back off a bit.
I learned on HSS and use it for much of my work.

My lathe originally was made with a 3.5kW motor
A previous owner fitted a 7kW one (no idea why). It seems small compared with others I see in videos and on forums, but it's certainly not a mini lathe

So far I may gave been too conservative with my hss cuts as it took probably 4 times to rough with hss what I could do with carbide. Strain is relative right? I guess I need to learn what is acceptable.

Depends on the material too- 1/2" DOC isn't insane for aluminum but for steel maybe so

I'm talking about mild steel with the numbers mentioned.

Yes, but to what end? Is it better to save time for production, is it better for the tool, or do the scrap buyers pay extra for a certain kind of chip?

To save time during roughing. For me the best part of the hobby is design, finishing, assembly, also roughing unless it takes too long. If it takes ages I prefer to speed it up. With carbide I have a working method, but I'm exploring alternatives, because I do like the idea of the independence HSS brings. Also I like grinding my own tools.

Tool shape , material to be worked and machine rigidity will ultimately determine the DOC’s

For goofs I sharpened a 1” HHS blank for my 2040 lathe and made 1/2” to 7/8” cuts in 1215 steel without much problems .
1215 is pretty much free machining so that really wasn’t a feat of engineering.
The shape of the tool was a knifelike, with higher cutting angles

Do you remember what surface speeds and feed did you use? Did the cut feel like it was really straining the machine? (not necessarily in HP, but in rigidity)

I have a 9000lb Monarch 612, 25x50 1500 RPM, originally a 20HP motor but I removed that to make an RPC and use a 10HP in the lathe. And some 1” sq hss blanks. But as a hobbyist, other than testosterone satisfaction, extreme cuts are just asking for trouble . Big hot chips ain’t fun, and the high torques involved mean things go sideways more dramatically when a chuck isn’t tight enough, etc.

.100 doc (.2” diameter) on .020 feed is about my upper limit on mild steel, and that’s extreme for me. I use 100sfpm for steel, 200 for aluminum as easy to remember starting points w/ hss and adjust from there.

Interesting. You have a much more rigid machine than me I think, but similar in power. Going by the feel I too use the same speeds/feeds with HSS. For contrast I use the same doc/feed with carbide at up to 350sfpm.

I wonder if there is anyone that actually uses slow monster cuts, or everyone thinks as you said it's asking for trouble. Of course work holding is often the limiting factor.

The other day I had a 3in diameter by 5in long piece chucked in a 3 jaw, supported by a live centre with a morse 2 shank in a morse 3 sleeve in my tailstock. But it was some special strong steel so any attempt to take a cut deeper than 40 thou caused the piece to move in the jaws. The tiny morse 2 shank of the live centre just flexed with every rotation. It didn't help much. That's one of the reasons I try to use a morse 3 dead center as often as possible. I upped sfpm to 360, and the feed to 20 thou and I just kept taking such shallow passes with carbide. It didn't take long.

Likely with HSS I would have to take similar doc and feed, but with 100sfpm if I went by feel. Perhaps that's what it is and it's one of the reasons production moved to carbide.

Having said that I have no difficulty in getting the most of HSS on the milling side. For end mills of 10mm or less I always prefer carbide (for speed and rigidity), but for larger tools I like the reliability and toughness of HSS. I did manage to snap a 16mm HSS end mill recently unfortunately (in a Chinese mini mill too, the head swivel let go during a cut pulling the cutter into the work). I also have a big milling machine. A 4k lbs Heckert Fw250 horizontal mill. For lots of material removal I really like large horizontal hss cutters. The material removal rate is probably lower than my 10mm carbide end mill, but it sure is satisfying to watch. Hey, perhaps I can even get a better price for my chips?

 

[Flyinfool]

For the lathe I am nearly all HSS.
I have a Jet GH1340.
It all depends on the part you are making.
If the finished diameter is fairly small and/or long then a very deep cut to final size with a very slow feed is the way to go.
If the part is a big Dia then a shallower depth of cut but much higher feed may be appropriate.
When roughing steel I often take cuts of .25 deep per side, with a feed of .020, RPM dependent on diameter and material. You must keep a real close eye on the chips, and stay well away from the danger zones, as they can hurt you bad in an instant.

When roughing is is also imperative that your cutting point is as close to the center of the tool post as possible for maximum rigidity.