PDA

View Full Version : what should i change ....



davidh
12-21-2009, 11:48 PM
i am turning an unknown material shaft thats about .750 dia. using a tool steel cutting tool, turning at 400 rpm, and a dept of cut of .100 or so and at the slowest feed my lathe will turn. (this is a decent tool room 12 by 24 american machine) im getting a wave of metal just ahead of the tool, just like im pushing the metal ahead of my cutting edge.

i have the little curls coming off at one setting, and longer curls coming off at other settings, and of course at higher speeds/cuts the curl is blue hot.

i have adjusted the height of the tool, re-sharpened and modified angles a bit and increased/decreased the feed speed and the rpm of the material. it still does it. altho the amount does vary with different settings.

the tool is sharp and yet the surface of the cut also leaves a bit to be desired.

this has happened using a cheap carbide cutters on other materials and other speeds and feeds too.

what is this caused from ? or what should i check to see if its not as it should be.

the end results are acceptable as the job is getting done but im trying to learn how to solve some of the dumb problems that keep the project from being really good. . . . .

the older we get, i think, the more time we have to question things . . . . . .

im too old to go to school plus my adhd leaves me with lack of ability to concentrate for any length of time.

help ?

Ken_Shea
12-22-2009, 12:00 AM
David,
Too many variables to give absolutes but I would sure try decreasing the DOC and see what that does.

Also 400rpm seems on the low side for .750 diameter.

And of course the metal being an unknown can always be a problem when things are right.

Do you have any quality carbide cutters to try?
Ken

Blue swarf is not always a bad thing if they are turning blue after they leave the material which is an indication that the heat is being carried away.

Carld
12-22-2009, 12:07 AM
Have you done a file test? Does the metal seem to be harder than other steel you get good results on?

If your talking about a ridge type ring that is right at the circumference in front of the cutter then I have seen that often. I have never worried about what is causing it but some times you can use a cutter with a slight leading angle rather than a square shoulder cut. If you have a V nose cutter try that and see if it works.

If your taking a .100" DOC that means your taking .100" off each side and reducing the diameter .200" at one pass. That seems to me to be a very heavy cut for that size lathe and may be why your pushing metal ahead of the cutter.

EDIT: I agree with Ken, you should be using carbide for such a heavy cut.

Wrustle
12-22-2009, 09:13 AM
Hi David,

Does your cutting tool have any type of chip breaker ground into the top? If you're just using a HSS blank that you've made into a cutter, it is usually flat across the top and would need some sort angle ground into the top. It's kinda difficult to diagnose with just the little info you've given us.

Also, I can't imagine you're taking off .200" total at only 400 RPM with a HSS cutter. You should be running at a minimum double that speed, but I suppose without coolant and the tool being HSS it would burn it up pretty quick, but .200" sounds like alot and we don't know how long a cut you are taking.

Is the material a cold finish.....smooth/semi-smooth greyish in color, or hot rolled, rough texture and a dark oily looking finish.

Also, check it with a magnet. It would rule out 303, or 304 stainless, which would give you problems as you describe. 400 series is magnetic, but would cut a lot better.

Let us know some more details if possible so we can be of better help.

Happy Holidays!
Russ

airsmith282
12-22-2009, 10:08 AM
if your using HSS cutters and no coolent you go as slow as possible but usually 300 to 330 , carbid 330 to max 550 but usse cutting fluid when past 300 rpm , take cuts of about 10 thou to 15 should be ok, i have turnned alot of 300 series steels and lots of unknows that were hard as hell and sometime you need to soften the steel if its to hard then reharden it after, ..

99% of the speed and feed charts are all pretty much bs when it comes to guys in the home and not in the industry thoes numbers do not apply and we have to compensat for our low end no industrel stuff as they call it,

Carld
12-22-2009, 12:47 PM
On a lathe his size he should be able to take a DOC of .050" @ .005" feed in CR or HR steel with HSS or carbide. Neither he or we know what kind of metal he is trying to machine.

.010-.015" DOC is for little toy lathes.

davidh
12-22-2009, 06:23 PM
thats what i thought. this is a sheldon 13, tool room lathe. strong and heavy.... more later tonite.

Machinist-Guide
12-22-2009, 06:53 PM
I see this issue when turning case hardened pins. The hard case rolls over like a big burr ahead of the tool bit.
Just a thought. Speeds & feeds, rake angles, could be the culprit also.

Oldbrock
12-22-2009, 09:50 PM
Check your front clearance. Sounds like you have too little, should be about 5 to 8 degrees, 3 for the finest feed you are using. Peter

Carld
12-22-2009, 10:58 PM
Sheldon 13, hmm, under the right conditions you should be able to cut .100" DOC. You must have a piece of hardened metal. Even CR or HR may push a little ridge at times, especially if the tool is a little dull, not set right or don't have the right front clearance.

The heavier the feed the more leading edge clearance you need.

beckley23
12-23-2009, 06:16 PM
You may not have enough horsepower for the cut. IIRC, the 13" Sheldon is a 1HP machine, unless you have the R model which will have a higher HP.
Harry

beanbag
12-23-2009, 06:23 PM
The times I have gotten that ridge in front of the cut, I switched over to a sharper and higher positive rake insert, which fixed the problem.

philbur
12-23-2009, 07:17 PM
Tool steel for me is high carbon steel. If this is what you are using then you need to keep the temperature way down with flood coolant, or take very light cuts. Blue chips or even a bit of smoke will kill the cutting edge instantly. Tool steel for lathe tools is normally tempered at around about 200 degrees C.

Phil:)


using a tool steel cutting tool, turning at 400 rpm, and a dept of cut of .100

outback
12-24-2009, 04:50 PM
That burr ahead of the tool happens to me all the time.

Try slowing the RPM down and a shallower depth of cut.

Coolant or cutting oil often helps.

Don't believe you mentioned the feed rate.

Personally, I don't like pushing a small lathe real hard regardless of the country of origin. 13" is a small lathe in my opinion and that is what I have in my garage.

Outback

Carld
12-24-2009, 11:59 PM
Hmm, what Harry says, 1hp may only pull .050" DOC. I don't worry about a ridge forming in front of the cutter, to me it's just what happens sometimes. I just file it off when I am done.