Finish Cut On Steel

[vigsgb]

How do you get a nice finishing cut on steel on the mini lathe?

I can't seem to get a nice smooth finish without throwing some wd40 and 600 grit wet dry paper on the steel shaft.

I am using autofeed and at every speed it seems to cut with a fuzzy rough texture.

I wish I could easily control the auto feed speed but it is fixed unless I change gears. Right now I am running factory 20, 80, 20, 80 gears as suggested and it seems the feed is too fast for the spindle speed.

Any suggestions would be appreciated :0)

 

[Maryak]

The 1st thing to understand is that a feed rate is still actually cutting a thread, albeit a fine one.

With this in mind the cutting face of your tool bit needs to be wider than the rate of feed.

Finish cuts are light cuts and should be no more than 0.005"

Hope this helps

Best Regards
Bob

 

[rhitee93]

Some steels are hard to get a nice finish with. The low carbon rod stock I occasionally buy at the local farm store seems to tear more than cut and leaves a fuzzy finish. 4140, on the other hand, seems to machine beautifully.

The tool tip is the biggest factor for me. It is much easier to get a nice finish with a tool that has a generous radius at the tip than one that is pointed.

 

[danstir]

I don't know if this will help, but it was not that long ago that I started using a lathe and I found that I was using to slow a spindle speed. I did this thinking the slower I went the better it should come out. Finally in frustration I started trying a higher spindle speed. This along with repeated practice in making a HSS tool bit with the proper nose radius and I finally started getting decent finishes. Still not mirror bright but close with little sanding to get there. Oh, and I was also using pieces of steel from things from my junk pile and that didn't help either. I finally went and bought some cold rolled steel and that worked a lot better.

 

[vigsgb]

I am using factory sharpened HSS on 1018 steel from a local Metal Mart place.

Should this machine well?

 

[ShopShoe]

vigsgb,

Are you using the older mini-lathe with high/low spindle speed selector or the newer model with better motor and all-electronic speed control?

I use the older one and if you select the "high" speed for the spindle with the speed-control "gearshift" the leadscrew will then advance more slowly relative to each revolution of the spindle. You then can then lower the motor speed with the speed-control on the switch panel.

Of course, you will now have less torque and the finish will still depend on:

--the type of steel
--the diameter of the stock
--the composition of the tool (HSS or carbide)
--the shape of the tool and how it is set to "attack" the stock
--the sharpness of the tool
--whether you are turning, boring, or facing

There is no recipe for success with the mini-lathe. You can study what others are doing and what is recommended and develop your own set of procedures for certain conditions as they come up. As in all parts of this hobby, the more you do the easier it gets to make things right the first time and the easier it gets to think through the steps of a project and the easier it gets to troubleshoot problems.

My own experience matches what rhitee93 said: 1018 is difficult, 4140 is better, 12L14 is wonderful, the stuff from the hardware store is all over the place and generally difficult.

My beginner experience with "factory sharpened HSS" was dreadful. In my first week I started grinding my own toolbits and started getting much better results. I spent an evening grinding a toolbit, trying different cuts, then re-grinding it to a new edge and trying again. There are many excellent tutorials on toolbit grinding on the web.

--ShopShoe

(And apologies for being long-winded today)

 

[rhitee93]

I'd have to agree with shopshoe. A sharp HSS tool with 1018 steel is not going to result in a great finish. If you spend some time grinding a slight radius into the tool tip you will see a difference, however you probably won't have a lot of success with finish until you get to something a bit more machinable. 12L14 was mentioned, and I agree it is nice to work with.

 

[vigsgb]

vigsgb,

Are you using the older mini-lathe with high/low spindle speed selector or the newer model with better motor and all-electronic speed control?

I use the older one and if you select the "high" speed for the spindle with the speed-control "gearshift" the leadscrew will then advance more slowly relative to each revolution of the spindle. You then can then lower the motor speed with the speed-control on the switch panel.

Of course, you will now have less torque and the finish will still depend on:

--the type of steel
--the diameter of the stock
--the composition of the tool (HSS or carbide)
--the shape of the tool and how it is set to "attack" the stock
--the sharpness of the tool
--whether you are turning, boring, or facing

There is no recipe for success with the mini-lathe. You can study what others are doing and what is recommended and develop your own set of procedures for certain conditions as they come up. As in all parts of this hobby, the more you do the easier it gets to make things right the first time and the easier it gets to think through the steps of a project and the easier it gets to troubleshoot problems.

My own experience matches what rhitee93 said: 1018 is difficult, 4140 is better, 12L14 is wonderful, the stuff from the hardware store is all over the place and generally difficult.

My beginner experience with "factory sharpened HSS" was dreadful. In my first week I started grinding my own toolbits and started getting much better results. I spent an evening grinding a toolbit, trying different cuts, then re-grinding it to a new edge and trying again. There are many excellent tutorials on toolbit grinding on the web.

--ShopShoe

(And apologies for being long-winded today)

ShopShoe -

Thanks for the information I do have the older model with the Low High gear and when I try to use High gear the motor cuts out and does not run. I think it is because there is a load on the motor from the 4" chuck that is tripping it. Not sure if I can adjust that somehow but looking into it.

I guess when I ask for free machining steel that must mean 1018 to them. Next time I will see about getting 4140 or the 12L14

Thanks for the information.

 

[Charles Lamont]

Nobody has yet mentioned cutting lubricant. What are you using?

 

[Clockguy]

Is 12L14 anything like Leadloy?? JL

 

[vigsgb]

Nobody has yet mentioned cutting lubricant. What are you using?

I had been using tap cutting oil or WD 40 for lubricant.

 

[vigsgb]

I am going to try some 12L14 as soon as I can get back to the lathe.

 

[Axel]

To get a nice finish the requirements are the same as when u want to get an accurate cut. The tool must be sturdy and the work must be clamped so it can be cut w o vibrations. And u must have a too that is of high finish, use a diamond hone to polish it with. This is all there is! But using a lathe islike playing the Blues, u got to have the feel for it, and nothing beats experience. Few things I learned over the years:

The last fine cut can be with a different feed, that will often help.
The last cut can be made with a rounder tip tool with more rake.
It's a good idea to experiment on a peice b4 doing the real job, to learn how to get a good finish.
Ethanol is great lube for aluminum
Use the tailstock center as much as possible.
Abrassive cloth sheds alot of particles, clean up after your done!

 

[ShopShoe]

Clockguy,

I am not sure that Leadloy and 12L14 are interchangeable terms. I do think they are at least close. Someone once posted a link to a chart that compared the terminologies used worldwide and I can't find it: Perhaps someone else can furnish that.

Charles Lamont,

I try dry, then WD-40, sometimes tapping oil (Currently "Tap Magic," but have used others in the past.) I only apply a little oil, trying not to fill the air with mist that I can inhale. I have considered building a mist system: I Miss Bogs's excellent discussion on the subject.

--ShopShoe

 

[gmac]

Here's one cross reference chart for carbon steel;

http://www.m3tubecomponents.com/images/Cross Reference of Steel Standards.pdf

I may have it wrong but I think Leadloy may be a trade name for a version of 12L14.

Cheers Garry

 

[ShopShoe]

Thank You gmac

--ShopShoe

 

[vigsgb]

I was wondering what the implications of breathing in WD 40 vapors, tap magic oil and such is. I am sure it cannot be good for a person.

I do have ventilation but I am sure that not all of the vapors or mist that is flying around goes up the vent and I am sure I have breathed in some of it.

Anyone have thoughts on this?

If you cut 12l14 with .010 to .015 thousands or less of a cut then the piece seems to stay cool and no need for any lubricant but does toxic fumes still come off the metal?

 

[purpleknif]

Been doin this for almost 30 years now and I have always found that too small a finish cut usually crates problems. Ever notice how your rough cuts look so nice? On my 7 x 10 I shoot for a .007 to .012 finish cut in aluminum. Then again with all the variables ( material, tooling rigidity, and so on) you just gotta try different approaches. That's why there's no one tool for every job. Its all part of becoming an experienced machinist.

 

[tomol409]

There is little doubt that a round ended tool will help to achieve a fine finish. But it should not be overlooked that it will also leave filleted corners. We are dealing here with models and sharp corners are the order of the day to achieve good fits. I prefer to use a sharp knife tool and to reduce the plan trail angle to the minimum. This the angle between the end of the tool and the workpiece, looking down in the plan view. Back and side rake should be higher -around say 10 degrees, with fine cuts, high speed, plus very slow feed rate. Free-cutting steel helps a lot and cutting fluid. For small work I often use a tiny, narrow parting tool set square, as the intimate contact seems to eliminate grooving and works well.

 

[lensman57]

Hi,

The best finish that I get is with a factory finish round nose tool. If your lathe can handle it try using a good indexable carbide tool, carbide sort of rubs off the metal rather than cut it but your speed and feed should be spot on. You could also try and experiment with a good HSS tool with a slight radius but angled towards the piece so it just avoids rubbing on the work, with some steels it works and gives a nice finish. Some steels such as silver steel do not give a good finish because of the composition of the steel and do require the use of an emery cloth to bring them to shine.

Regards,

A.G