# Turning 3/16" Mild Steel



## RVJimD (Jun 11, 2015)

Hi guys,

I am turning down some cold rolled steel and having trouble with it wanting to crawl up on the tool.  I am starting with 3/16" rod and only need to take off about .025".  If I try to take it all in one pass it crawls up on the tool and bends it at the chuck.  The parts are 1" long and I chuck it as close to that as possible.  If I take  two or three passes I can get some of them finished.  I was thinking I would be able to do them in a single pass...  I need them turned down just enough to fit inside some brass tube.  Not sure there is any better method of I am just stuck making several light cuts?

I am stuck with reducing the size vs using a stock size because of the parts they mate up with, otherwise I would use tube and shaft that matched.




Jim


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## Rex Walters (Jun 11, 2015)

Fair warning: I'm a complete novice and really don't know what I'm talking about, but I thought I'd share my experience anyway.

Are you taking 0.025" off the diameter or off the radius? Hand ground HSS tooling or inserts? By "crawling up on the tool" do you mean the part is deflecting away from you (from tool pressure) or actually deflecting upward (which I suspect might mean a dull tool that isn't cutting well).

I only use hand-ground HSS tools. For thin rods, I usually have more success by taking larger bites than small ones. Taking a cut of 0.010" to 0.020" (radially) ensures more on-axis load from tool pressure than radial load. Trying to take off just a thou or two is much harder since the part will just deflect. That is, with more depth-of-cut it feels that you're pushing more on the end than you are deflecting the part side-to-side.

The success factors for me are: collets, freshly sharpened and honed HSS tools, and an optivisor to see whether I'm really on center and cutting the way I want.

One inch really isn't that short for a 3/16" mild steel rod, but I did recently learn a neat trick for reducing much longer thin rods. Say you're making a long thin bolt or pin where the head is, say, 1/4" and the shaft is 2" long but only 1/16" in diameter. Start with the stock in a collet with only a short length extended. Turn down the first half inch or so to size, then pull the stock further out of the collet to turn down the next half inch or so. Doing it incrementally this way ensures the thin section is always supported by the remainder of the stock.

Dunno if that technique might help or not, but it's worth a try.

Good luck.
-- 
Rex


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## tertiaryjim (Jun 11, 2015)

Can you support it with a live center in the tailstock ?


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## RVJimD (Jun 11, 2015)

Good points/questions Rex.  I am using HSS and I put it on the stone after I started having trouble and got it nice and sharp but didn't help.  I didn't want to do it between centers just to avoid the extra steps.  It doesn't need a hole in the end of it...  I am pretty sure I could shorten it up like you suggest and make that work.

I think I can get them made, but I was just checking to see if I was forgetting some obvious solution.

Jim


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## brino (Jun 11, 2015)

Rex touches on many good questions, tool type, sharpness, and tool height.....

one more question is what is your tool shape?

I like to shape the cutting tool so that most of the cutting pressure is on the side, you push the tool (and workpiece) more towards the headstock than towards the "back" of the lathe.

-brino


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## Silverbullet (Jun 11, 2015)

If you were using a turret lathe a box tool is your answer. The have a set up that will not let the rod deflect. If you had one you could use it in your tail stock or your compound with some modifications . Or just set up the follow rest if you have one.


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## higgite (Jun 11, 2015)

Jim, 

Some good points so far. I'm curious, what rpm are you running?

Tom


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## RVJimD (Jun 11, 2015)

It is good for me to ask a noob question occasionally , since I am most certainly STILL A NOOB.  

All the what and how are you doing this or that helps me remember stuff I would know if I had more experience.  I DO appreciate the help!

I am running about 500rpm.

I think one of Rex's initial point about shorting up the stock is my biggest trouble.  I am now pulling out about  3/8 at a time and using a cutoff blade and it is working great in one DOC pass.  Then when I get an inch turned down I can simply part it off and start the next one.

Here is the setup that is working fine.  I have about 15 of these to make and this isn't too bad now.
Thanks for the tips!


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## higgite (Jun 11, 2015)

RVJimD said:


> It is good for me to ask a noob question occasionally , since I am most certainly STILL A NOOB.
> 
> All the what and how are you doing this or that helps me remember stuff I would know if I had more experience.  I DO appreciate the help!
> 
> I am running about 500rpm.


Hi Jim,

I'm pretty much a noob, myself, but the rule of thumb I keep reading is to run mild CRS at 100-150 sfpm. For 3/16" rod, that's in the neighborhood of 2000+ rpm. I don't always follow the rule, but usually find that best results are with at least half of calculated rpm. Have you tried turning it at higher rpm?

You also might try taking lighter cuts on such thin stock, say .015" and .010" or 15/5/5. Hope this helps.

Tom


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## brino (Jun 11, 2015)

RVJimD said:


> Here is the setup that is working fine. I have about 15 of these to make and this isn't too bad now.
> Thanks for the tips!



Hi Jim, I'm glad you got something that works!

I found some 3/16 steel rod and tried a few myself. I started with about 2" hanging out of the collet (for worst case) and around 350 rpm(for no particular reason than that's where I left it!). I was never able to cut more than about 5 thou. radius (or 10 thou. off diameter) without the stock rolling up onto the tool bit. Even when it did cut, the stock ended up tapered; bigger away from the headstock because the rod was pushed away from the tool.

One inch stick out from collet was reasonable though. Changing to around 930 rpm did seem to help a little.



higgite said:


> the rule of thumb I keep reading is to run mild CRS at 100-150 sfpm. For 3/16" rod, that's in the neighborhood of 2000+ rpm.



Tom, the references I usually go by say 60-80 sfpm for cutting steel with HSS tool bit, so for 3/16" stock around 1200-1600 rpm.

-brino


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## RVJimD (Jun 11, 2015)

I noticed a bit of taper also.  Real evident if you are trying to get a nice slip fit inside a tube.  I was doing about half an I ch at a time with no problem.  I even did a few at one inch but I could tell I was asking for trouble.  I am using the cheesy  cold rolled stuff you get at the box stores so it is probably not as hard or ridgid as anything else.

Jim


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## higgite (Jun 11, 2015)

brino said:


> Tom, the references I usually go by say 60-80 sfpm for cutting steel with HSS tool bit, so for 3/16" stock around 1200-1600 rpm.
> 
> -brino



brino, good catch. I keep forgetting that some tables apply more to production machines and carbide tools. Maybe that's why half of recommended speed works so well for me and my HSS tools. 

Tom


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## Jester966 (Jun 12, 2015)

Why do you want to take a full depth of cut as opposed to several lighter cuts?  If it is about saving time, it seems to me that pulling the part out ~3/8 at a time wouldn't really solve the problem, even if it does cut well.  And, you would end up with "steps" (may or may not be an issue)

I would think that increasing the RPM and taking 2-3 lighter cuts would more efficient.


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## RVJimD (Jun 12, 2015)

I think my actual full DOC was only .015, I thought one pass seemed plausible, like it would have been on anything in a larger OD.  I was able to do it about 1/2" at a time with no problem.  I didn't notice any step at the continue point and the finish just a bit rough is a good thing since I will want to put a bit of grease on the shaft for lube between the shaft and the brass bushing.

Please keep in mind I am really absorbing a lot of this information and it is all valuable and sure to be used on future projects.

Jim


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## francist (Jun 12, 2015)

It appears you've got it figured out and it's working for you, that's the main thing. I'm no expert by any means, but I use the 3-times-diameter as a basic starting point for maximum stick out from the chuck unsupported. Sure you can stretch it, but it seems to be a good ratio for anticipating whether there might be deflection issues to watch for or not. Kind of prepares me for it, I guess is what I'm saying. 

It's also interesting that you're getting better results using your parting tool for the whole operation rather than a normally ground tool with a nose radius. But again, it's working so  that's the main deal!

-frank


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## Wreck™Wreck (Jun 12, 2015)

To much unsupported length and not the best choice of tool, also too slow on the spindle speed.

I would leave only 1/16" clearance at the chuck (set a carriage stop), use a live center and a 35º diamond insert tool with the smallest nose radius you have to clear the center.
 At a minimum 2000 RPMs, .008-.012 IPR feed rate to rough leaving .004 for finishing at .004-.006 IPR to finish, 2 passes and part off.

2000 RPMs is 33.3 Rev. per second, 1" at .oo8 per rev. is 125 revolutions, divide by 33.3 SPR and you have a 3.7 second cycle time for the rough, twice that for the finish pass, That is 12 seconds of cutting time, figure 10 seconds to change to the parting tool, 5-10 seconds to part off.

Good luck


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## Rex Walters (Jun 14, 2015)

Hi, Jim. Sounds like you've got it figured out, and I'm glad the tip to only extend a bit at a time helped, but I think the slow RPM and parting tool aren't making your life any easier. 

I'm definitely still a noob as well, but I recently started taking speeds and feeds a lot more seriously with much better results because of it. Basically slower speeds are for heavier roughing cuts, and faster speeds for shallower finishing cuts, but you still want to be in the ballpark for your material. At 500 RPM you're only getting around 24.5 SFPM (about 1/3 to 1/4 as fast as you should be turning). Since you only need to take 0.025" off the diameter, you're basically just making a finishing cut. The references I use (laugh) say around 60-80 SFPM for roughing cuts and around 100 SFPM for finishing cuts on plain carbon mild steel (as they say, that's the great thing about standard references — there are so many to choose from!).

A center would, of course, help prevent deflection, but on such a small part it seems unnecessary. On really long thin rods you need a follower rest anyway — a steady rest still lets the part bend in the middle) — or continue to use the "step and extend" trick you're using now. The "three times diameter" rule of thumb says no more than 9/16" should extend from the chuck, but I'm pretty sure you could get away with even a full inch extended as long as you take off the full amount in one pass with a sharp turning tool (per my earlier comment: more axial load that way and less radial load).

I bet with a freshly ground turning tool, 3 or 4 times faster RPMs and taking the full 0.025" off the diameter you'll get much, much better results. I'd feed by hand, but if power feeding on my Logan I'd use the slowest or next slowest feed (0.004" or 0.008").

By *far* the best article I've ever read on sharpening HSS tool bits is Conrad Hoffman's treatise on the matter. Really great article, well worth reading and re-reading several times — some great info there.

Lastly, can you adjust your 3-jaw chuck for runout (sta-tru back or whatever the trade name is)? Otherwise, unless you're really lucky, you've almost certainly got enough runout to make it hard to turn small diameters and take the same amount off all around. Small, precise stuff is usually best handled with collets, the 4-jaw (independent) chuck, or old-school turning between centers. I only use my 3-jaw for rough and ready larger turning jobs. Buying some 3C collets and a closer for my old Logan was one of the best things I ever did —  utterly changed my opinion on just how "loose and worn out" my lathe was.

Enjoy!
-- 
Rex


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## mattthemuppet2 (Jun 17, 2015)

do you have a tail stock center and steady or follow rest? I would be inclined to get the work piece well supported and turn down the diameter first using a very sharp RH HSS toolbit (don't use a cut off tool for turning). Get it close to diameter and then sand/ polish to the final dimension given that these will be axles. Then put your cut off tool back on, stick the rod the minimum distance out of the chuck to part off and crank them out. Go much faster than you think you should for turning and be very very careful to get your cutting edge on center to avoid the rod riding up onto the tool.


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## markknx (Sep 20, 2015)

Follow rest should fix this.


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## higgite (Sep 21, 2015)

I think he fixed it 3 months ago. 

Tom


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## markknx (Sep 21, 2015)

Ha ha I just got a notice on this yesterday.


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