Roughing cuts in a 10K lathe

[MarioM]

Hi to all,
I am always a bit scared to put a roughing cut in my lathe, and would like to have some practical advise.
My lathe is a SB 10K, if I am making a roughing cut on a 1" CRS stock, 60 fpm and 0.010 feed, manual lubrication, what is the max. or the average depth of cut to be on the safe place and not wasting time using normal HSS tools.

Mario

 

[Stan]

Try and get a download or buy a copy of the famous book by Southbend "How to run a lathe".

IIRC it says that a lathe like the 10K will reduce the diameter by 3/8" on the roughing cut.

Edit: Just so there is no confusion - a SB 10K is a light duty 9" lathe. They were a very popular high school shop lathe.

 

[steamer]

Got a picture of the set up?

The bar is 2" long or 2 feet long?....ect
Between centers?

Makes a difference.

Dave

 

[steamer]

On a 2" long piece of 2" round free cutting steel, in a 4 jaw and backed up with a live center. my 12" Logan will take 3/8 on diameter with ease, 500 rpm and .005"/rev feed with HSS. It can do more than that actually....but why do I need to.

I would expect the same or very close from a Heavy 10.


Carbide should be run much faster that HSS....

Dave

 

[Ken I]

Like Dave says - it all depends - can the job take it - does the machine have the horses.

A rule of thumb for mild steel is 3 HP per cubic inch per minute.

Take your 1" bar @ 250rpm x 1/8" depth of cut @ 0.010" feed would give 0.859cu inch per minute or about 2.6 HP

Working backwards from say 1HP available then the depth of cut would be 0.035"

Listen to your machine - if it "groans" your approaching the limit.

Ken

 

[steamer]

I think leadloy might be a good bit lower than 3HP/cubic inch.....but the right neighborhood. My lathe is nominally 2HP.

I don't have a tach and it's a mechanical variable speed drive...500 is an estimate. It could have been 300....

Dave

 

[purpleknif]

That's why experienced machinists learn to "read the chips."

 

[Mosey]

My 10K has an automatic load-limiter.... the flat leather belt slips when I exceed a certain, comfortable depth of cut... about .050", with it's 1/2 hp motor.
I can still turn lot's of nice metal into junk pretty quickly.

 

[Maryak]

IMHO, as has been said already, it's a volume thingy...........speed, feed and depth of cut. Notwithstanding that, if you need to remove large lumps of metal, it's quicker to do it with a slower speed, a greater depth of cut and a coarser feed than the other way around. It's also kinder to the machine and the toolbit.

Having a geared head and a quick change feed box make this much easier to achieve than messing around with belts and change wheels if it's only a one off.

I personally cannot understand why nearly all the manufacturers of small lathes seem to think that 125 rpm is an acceptable lowest speed.

Best Regards
Bob

 

[steamer]

That's why experienced machinists learn to "read the chips."

YUP 6's and 9's and they better be blue your not making money!
;D

That's OK...I'm not MAKING money.... ;D

Sometimes its just nice to watch it make a cut....kinda like watching a camp fire...but hey ...that's just me.

Dave

 

[steamer]

So Mario, what brings you to these parts?....do you build model engines or involved in model engineering?

Dave

 

[rake60]

The tool in use also makes a major difference.

With carbide, I like to run 300 feet per minute.
Tool steel get a 200 feet per minute surface speed.

Depth of cut is dictated by the rigidity of the machine.
On my 9 X 20 hobby lathe at home, anything over .050" depth of cut has it chattering.
The 12 X 36 at work will go almost to .100" before it turns violent.

If you're not making blue chips on an industrial machine, you're costing the company money.
If you're making blue chips on a hobby lathe, you had better have enough money in reserve
to buy another hobby lathe.

Rick

 

[MarioM]

Thank you very much to all for your advise and information. I feel more comfortable know, and realized what was doing was not to bad.
The set up is a 6.5"stock with about 1.5" inside the chuck and supported with a live center. I was making cuts with a depth of 0.050" and seems to be OK, it did not groan and the automatic load-limiter as Mosey call it did not complain. I believe I could push harder.....but I would rather do another cut than spoil it.
3/8" for a cut really seems a lot to me......I prefer to watch somebody doing it before I try it......
Actually I am making a tailstock die holder for my lathe.......a long time wanted tool that it now finally seems to come to life.
Answering to Dave question, I just got involved with model engines a few months ago.......made my first Stirling and got it running with the group help. After this first engine I realized needed some extra tools to do jobs better and faster before start another project.

Mario

 

[steamer]

Glad to have you Mario!

and your right....no need to push it hard....just take another cut.

Dave

 

[steamer]

And I don't think I'd want to try 3/8 on diameter on a 6.5" part in my Logan either! :big:

Dave

 

[rake60]

I used to operate an old War Horse of a vertical boring mill at work.

One large bearing housing casting we worked with had 5" on a side of stock to come out
before you were even close to finish.

Roughing depth of cut was 7/8" at .045" feed.
The blue chips that were flying out of it were in the perfect shape of a 6
(or 9 depending on you point of view).

Those chips weighed a little over 1 ounce.
You certainly didn't want one of them to hit you!

That machine was so rigid, it would not chatter. It would stall if you pushed it too hard.
You had to work your way up to the maximum cut with one eye on it's amp meter.
When the meter was passing the amperage of the main fuses it's the electrical cabinet,
it was time to back it off a bit.

Rick

 

[steamer]

http://www.custompartnet.com/calculator/turning-horsepower


Here's a nice little calculator for determining the power for a given cut. Interesting....might want to plug in those parameters Rick....

Dave

 

[Dan Rowe]

The South Bend book "How to Run a Lathe" does not really have anything to say about the depth of cut. It does give the usual speed and feed charts but the depth of cut is not really covered in the text.

Here is a link to a 1914 book titled "Turning and Boring"
http://doit101.com/Lathe/lathe.html

Here is the direct link to chart of the experimental data compiled by Mr F. W. Taylor for speed feed and depth of cuts speed and feed for steel with 1.5 hours between tool regrinding.
http://doit101.com/Lathe/chapter2.html#Fnanchor_1

For rough cuts I only rarely use power feed. I run the lathe slow and feed by hand. With steel if the chips are straw colored at the tool bit I am happy. If they turn blue after they hit the chip pan you are fine. If they are blue at the tool bit back off the feed a bit to get back to straw. You can remove a lot of stock quickly and no calculations are required.

Dan

 

[Swifty]

I believe that eyes and ears are the best indicators of how the machine is going. As the others say, get the chips coming off right, straw color and chipping off nicely. If the swarf is coming off in long strands, the feed rate is too slow, besides being dangerous. The cut has to sound right as well. If the lathe is vibrating and sounding like it's struggling, back off a bit, either with speed or feed.

Paul.