Problems turning steel

Wrong tool shape? Feeding too fast? Crap steel?

Is there any chatter or vibration when you take a cut? What is the depth of cut? When you get close to the size you want, do you take a light finishing cut (spinning the job faster and moving the tool slower)?

This any good ??

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-- Regards,

John Stevenson Nottingham, England.

Visit the new Model Engineering adverts page at:-

Height of tool (must be on CL of the spindle).

Put away the carbide tools and start with HSS. You will learn a lot and understand how to fix problems.

Nick

Ed, the site John has suggested is very good and you might like to have a look at this one it is very easy to understand and takes you through step by step.

You will find a good section on achieving the best finish but it is well worth reading through the whole so that you are confident your settup is OK.

For this diameter and using carbide tools the speed seems fairly slow. What is the shape of the tip? a slightly more rounded point may help. What is the depth of cut? Try a higher rpm, very slow feed and small depth of cut. Is the carbide tip OK, they chip easily on the cutting edge something easily overlooked when you first start turning (at least it was for me)

Make sure the tool 9cutting edge) is exactly on centre height close will not do. Are you using hand feed or power feed? Have you tried a different piece of steel, unfortunately all mild steel is not equal when it comes to the ease of machining. If the tip has a sharp point turn it slightly so that a greater area of the tool is in contact with the work when cutting, make sure that if you do this you only take very light (finishing) cuts otherwise the tool will chatter and with carbide chip the cutting edge. Ed I'm sure some of the experts will come along and give you some more professional tips but these all worked for me when I was starting out.

Best regards

Keith

A small radius on the nose of the cutting tool can make a big difference in getting a smooth finish, and a fine feed will help as well. The other thing to consider when using carbide is that you can't creep up on a finish like you can with HSS, and often being a bit more aggressive with your depth of cut will result in a big change.

Ed there is a picture here:

- does your finish look like the one on the left-hand side of the part?

Believe it or not this was the best surface finish I could get out of the heap of s*** Chester DB10G lathe I had for a short while last year. Sharp nose/radius nose - Carbide/HSS made no difference as the feed rate could not be set fine enough on the damn thing. Moving the carriage by hand would get a better finish, but only in patches as my manual feed rate varied.

The finish on the right-hand section of the 1" bar in the picture was cut on a Myford running at top speed (640rpm) with a carbide tipped tool and depth of cut set at about 0.008". However the feed rate was set to fine at something like 0.0035"/rev. The finest feed on the DB10 was about twice this.

Try and experiment a bit more with your speeds and feeds and see what your lathe does. What lathe do you have btw?

Peter

Thanks for all the advice - I have checked the tip, and that seems ok,

- It looks like I am not running dead on the centre, so I will adjust that tomorrow. I am going to look at the feed speeds again - Looking at the picture, I have something more like the left hand side of the pic.

WIll also check the feed speed and adjust the gears if needed tomorrow.

Thanks for all the info chaps - all very useful

Just coming to my mind: Carbide tips like to crack from time to time. I do not look at them (if I get a bad surface) but feel with my fingernail. I draw the edge of my fingernail along the edge of the tool (as if I want to cut the nail) and feel any cracks this way.

Nick

Also try centre drilling the end and running a centre in the tailstock for support. You don't say what lathe you have or size and 15mmØ by 50 mm out could be a lot for a small lathe.

-- Regards,

John Stevenson Nottingham, England.

Visit the new Model Engineering adverts page at:-

If that doesn't work then try to get hold of a length of free turning ms bar and see if the finish improves. I had some old miscellaneous steel bar from somewhere that gives a long stringy swarf and a rubbish finish whereas normal ms turns quite nicely on the same setup.

Hth,

Probably EN3B which is a commercial quality mild steel suitable for welding, I do have to turn a lot of this stuff. It is possible to get a good finish but you have to hit it hard, and quite high surface speeds. I would imagine a lot of smaller lathes wouldn't cope too well.

An example I turn a bush for a customer which is made from 35mm en3b, it has a 30mm section 9 mm long. This is turned in one hit ie 2.5mm depth of cut at 1000rpm, with a fairly heavy feedrate to allow the chipbreaker to work. Theres no way a light finish cut can be taken, it will just tear, unless cermet tips are used.

But one should realise finish does not have to always be like a mirror, as long as the material does not appear torn it's all down to personal preferance or in my case what the customer specifies. Lines are ok as long as the job looks bright.

Wayne....

I have lots of en3b too - it is horrible to turn, especially when threading. But it can be turned shiny with luck & a following wind.

Tips:

- use HSS as already said, you can grind it 'sharper' than carbide.

- a final finishing tool with a small (1/32-1/16" wide) flat ground on the tip like

the need for really fine feed by making thin, wide swarf.

- if you have a small lathe, don't lean on it, nor the bench/cabinet when finishing; the tiny distortion can make a visible difference.

HTH Guy

A very simple and always works method I use is to select a slow backgear speed and slow feed using suds. This will produce a mirror finish as long as the cutting tool has a small radius. Don't use carbide tips on a small lathe. HSS is ok but my preference is carbon steel which is harder at the tip than HSS but cannot stand hot cutting thus the reason for slow speed. It takes a little extra time but the result is worth it. Likewise when adding a chamfer to a mild steel bar, turn the chuck by hand to finish cut with suds applied and see the finish. Hope this helps...

That statement about carbon steel didn't get out of my head. Is it really that way (I guess, or you woudn't have said so)? What carbon steel are you using? Means, how much carbon? I would guess something like 0.7%. Or are you just case hardening some piece of steel?

Thanks, Nick

Remind me not to offer you a turning job hehehe....

500+ bushes in 3b would take a fair time in back gear, i can manage em in 40 secs each with a good finish ;-)

Yes it really is. As to percentage carbon in the tools I have which are ex Myford supplied I'm not sure but silver steel works equally well. My reference is from Tubal Cain book Hardening, Tempering & heat Treatment.In it he shows a graph of Vickers Hardnes no v temp. Carbon steel has 1000 hardness with HSS at 900 at 0 temp and both equal at about 250deg hardness 800.

But I bet you didn't do it using a Myford Lathe and used Carbide at high speed on a substantial production lathe. For me mass production is 6off and time is free! Who needs a job! Reminds me of a guy who supplied a 7-1/4" loco with an inaccurate wheel flange form. "Can't be wrong he said, I've had 250 sets turned on a CAD controlled lathe!".

Well not a myford. but a 2nd op capstan of similar size. But much more rigid. Some carbide yes.

Time is never free unless you're single lol.....

Hehe I was only kidding you know !

CNC even. I use those too, but only when the job warrants it. But true if your program is incorrect then the machine will faithfully produce a load of crap. So human error there most likely.

Wayne...

PS. This thread just reminded me. I have a lot of 7/8" and 22mm EN1a bar ends here(6-10" long), which although I can't give away (Seen the price of steel these days!!) I can let go for what the scrappy will give me. In fact today another 30 bar ends will be produced, so I have to do something abou the room they are taking up. Any takers?

[carbon steel makes nice finish]

Wow! Just coming up from the cellar: I shaped a rectangular hole in some BDMS. The tool was out of silver steel. I expected a desaster and I got a miracle. It didn't get dull and made a really nice surface.

Always something to learn ...

Nick

Thanks to Guy and Wayne for the informative posts re en3b it does sound like it might be the stuff I've got.

Cheers,