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View Full Version : Parting is such bitter sorrow/Grizzly update



Tyro 001
11-01-2007, 10:56 PM
I had a 36" long 1 5/8" dia piece of CRS chucked in my 13" x 40" lathe (Grizzly 4016). The outboard end had been turned down to 1 1/4". I had also bored a 1/2" hole through the center. I had it supported on the outboard end with the steady rest, which was about 8" from the end; and with the follow rest right at the point where I was doing the parting operation. Everything was tight, I had lubed the points on the stead rest and follow rest; and there was no vibration. I was parting off 1/2" wide "doughnuts" and had parted three of them when the parting tool grabbed the work and all hell broke loose. I managed to get the lathe stopped before any serious damage was done; but I broke the top casting of the steady rest, and completely ruined the follow rest. The good news is Grizzly had the parts in stock, and the total for the steady rest top casting and the follow rest body casting came to $102.00, including shipping. I guess the good news for all of us is Grizzly does seem to stock parts.

I've had quite a bit of trouble with the parting operation and I gather it is something of a problamatic operation. I was parting at 70 rpm and 0.0012 feed rate. I had aligned the tool post using a dial indicator, which indicates to 0.0005". Although I had the parting tool dead on at the front and back, I had noticed there was a 0.002" bow in the blade where it passed through the middle of the tool holder. I was unable to correct the bow; but I hoped since it was in the middle of the toolholder it wouldn't make any difference. I was aproximately 1/4" into the cut when things went down hill. By the time I got the lathe stopped the afore-mentioned lathe parts were broken and the 1 5/8" CRS was bent and sitting on top of the parting blade. The tool post and blade are Dorian and they did not flex at all. Once I opened the chuck and released the 1 5/8" CRS, it snapped back to its original shape with no visible distortion.

A manufacturer, who doesn't want his comments attributed to him and who uses CNC equipment, told me he thought I was running too slow, with too light a feed. He told me he parted off 4'' dia. Al at 500 rpm and with a feed rate twice to three times what I was using. He felt I should be able to part the 1 5/8" CRS at least at 200 rpm. My books all say rpm should be about 1/3 of the recommened rpm for turning the same piece and feed rate should be slow. I think 70 rpm is close to 1/3 the recommened turning speed. I'm getting tired of being showered with broken bits of cast iron and steel. Anybody have any suggestions?

Bruce Griffing
11-01-2007, 11:01 PM
Make sure the cutting edge is slightly below center rather than on center.

wierdscience
11-01-2007, 11:09 PM
You didn't mention what type parting tool you are using.I assume you are using inserted carbide if so what about lubrication in the cut?Are you using coolant,cutting oil what?

C - ROSS
11-01-2007, 11:09 PM
Part off as close to the chuck as possible, crank the speed up, don't support the outboard end. I use the chuck as a guide for aligning the parting tool, usually run about 300+ on smaller sizes and then some slower for larger stock, sfm is what counts. I feed by hand, it takes time to acquire the feel. Also use cutting oil on the cut I judge it by the sound, if it's making too much noise squirt some more oil.

Ross

Tyro 001
11-01-2007, 11:13 PM
The cutting tool was HSS, not an insert type. I was using 20 wt motor oil as a lubricant.

wierdscience
11-01-2007, 11:37 PM
The cutting tool was HSS, not an insert type. I was using 20 wt motor oil as a lubricant.

Heat is your enemy then,flood coolant will work better than motor oil.When I setup a HSS parting blade I indicate the blade itself and not the holder.Many times those blades are a little less than straight when out of the box,they depend partly on the holder to keep them straight.The blade needs to run straight in so the sides don't rub.

Your friend running CNC has several advantages you don't including rigidity and constant speed turning.His RPM can ramp up and down continuously as the diameter shrinks so he is always maintaining the exact feed/speed.He's probably also using an inserted carbide parting tool the geometry of which makes a big difference.

Your speed is limited by two main factors,one your cutting tool(HSS) and two your steady rest,niether will tolerate high speed for very long.

An inserted carbide parting tool would help,but I believe coolant would help even more.

Rich Carlstedt
11-02-2007, 12:09 AM
I am confused, Were you parting off to the right of the steady rest ?
Or were you in the middle of the bar?
What I think you are saying, is the bar was so long, you used a steady rest 8 inches from it's end, then to the right of that, you had the carriage with a follow rest and were parting off there.
If you were between two "rests" then that is the reason for the crackup.
As the tool exerts pressure, the bar will close....closest to the operator and BANG
In a parting operation, support must be to the LEFT of the tool and close by
Machine controled feed is more constant and much better for parting operations

Rich

tattoomike68
11-02-2007, 12:15 AM
Slow feed will let the tool rub, get hot and chip weld will get ya. More feed and lots of oil.

Joel
11-02-2007, 01:43 AM
I would go roughly 200rpm and .002 or so using power feed. Keep the feed up when parting!

Renegade
11-02-2007, 02:05 AM
Do you have a band saw?
In a shop with manual machines it's faster to turn OD bore ID and then saw the pieces a little long, then face to the required thickness.

Norman Atkinson
11-02-2007, 03:04 AM
Tyro, this is an old war horse. It is trundled out time and time again. Understandably so, I add.

An old Brit cracked the problem and wrote about it. It was G H Thomas in his Model Engineers Workshop Manual. Tee is the publisher.

Basically, the parting tool is mounted on the back of the saddle with the lathe running forwards. The tool is exactly on centre height but is angled at 7 degrees to do the top clearance. That means that furure re grindings only means a lick at the front of the tool. The top of the tool has a vee ground in it. 140 degrees is recommended. Lots of cutting fluid is needed.

Now think about where you have got to. The tool will plunge in cutting a ribbon of swarf. But the ribbon will curl up because of vee ground in the 'top' and will not jam( which is what you did)
Being upside down, the swarf falls down by gravity and doesn't build up. Also, the wear of the saddle etc lifting up and down is minimised.

I hope that this helps.

tattoomike68
11-02-2007, 03:18 AM
Many machines use un upsidesidedown parting tool.
Screw machines do it alot, they are parting off parts in 2-6 seconds, half way fancy parts too.

I will tell your thier other secret to parting fast....

Is a 1/2" pipe blasting oil on the tool at 100+ PSI. no kidding.

My advice is dont be shy putting oil in the cut.

Jim Hubbell
11-02-2007, 03:30 AM
In learning to part off on an Atlas bench lathe, I have picked up a few ideas. First is support. Always as near as possible to the chuck or other support. Second is RPM. When parting ferrous slow is the way. If it does lock up the crash is not as horrendous. Al and brass may be parted at much higher speeds as noted earlier. Third is lube/coolant. I don't have flood coolant so I drip tap matic or some such directly into the cut. Good results. Feed rate is kind of feel/listen. I feed so that the chip curls into a "watch spring " and the tool does not scrape. If possible I use the " cathead " for support rather than the chuck. There is one or two pictures at this site.
http://picasaweb.google.com/shopm8

R W
11-02-2007, 05:51 AM
Do you have a band saw?
In a shop with manual machines it's faster to turn OD bore ID and then saw the pieces a little long, then face to the required thickness.

Have always used a power hacksaw (don't own a bandsaw) in this situation,
and then used the same method as quoted above, it is much easier than using
a parting tool.
My experience with parting tools is that the are only to be used when nothing
else can be used.

ptjw7uk
11-02-2007, 08:55 AM
not wishing to pinch this thread but I just had a look at Jim Hubbell's pictures and the one showing Truing an old chuck has me a bit confused.
In an old chuck the wear will be in both the jaw teeth and the scroll itself and the idea of grinding the insides of the jaws would be OK if you could hold the jaws apart against the thrust of the scroll(not sure if I'm explaining this right) as if you had gripped an object as in the picture you are surely relying just on gravity or your hand (missing in oicture)

Peter

Carld
11-02-2007, 09:44 AM
Tyro, I see several problems with your set up.

Parting done to far from the steady rest.

Follower rest may have been running on the part being cut off rather than the uncut shaft.

Spindle speed and feed to slow.

Engine oil!!!!!!! You didn't really use engine oil did you? You need to use cutting oil or flood water based coolant on a parting tool.

Why didn't you hack saw the turned down piece off and chuck it in the lathe and part the pieces off. You can part off close to the chuck and move it out after parting two or three pieces that way.

Since you turned down less than 8" and drilled it at the end of the steady rest you could have sawed 10" off the bar. Then chucked it up and turned it down with a live center in the end. Then drilled it and fliped it around and sawed or parted off the large end and started parting off the pieces. It's not a good idea to use a steady rest unless there is no other way. Steady rests have problems of their own.

Jim Hubbell
11-02-2007, 01:53 PM
ptjw7uk, you are correct, which is why there is a flat washer held at the rear of the jaws.

Lynn Standish
11-02-2007, 05:03 PM
The replies have all been good advice, but you stated "the 1 5/8" CRS was bent and sitting on top of the parting blade". Are you sure your parting tool was exactly on center or a couple of thou high? It sounds as though the CRS may have tried to climb the tool, which is usually caused by the tool digging in and deflecting downward even further. This might also be caused by an inclusion of some sort of hard material in the CRS (it happens) that snagged the tip of your parting tool.

Even so, I second the comments about not using steadies or live centers in a parting operation and doing a parting operation as close to the chuck as possible.

lane
11-02-2007, 08:52 PM
THINK ( lots of cutting oil ) Thats the secret.

oldtiffie
11-03-2007, 02:53 AM
Its quite in oder to use other tools and methods in conjunction with a conventional parting-off tool if it suits you. The intent is to part one bit from another.

I quite often use the band-saw to finish off the parting/separating - just depends on the job.

Good tools and rigidity are required. I prefer low speed and high feed rates and as Lane says, plenty of cutting oil.

I won't part-off under power feed as I like to "feel" the job.

Others do just as well using their own methods as well. So there is no one right way for everything - just suit the job, the tools and the lathe at the time.

In this example, I have used an IFANGER parting tool which works well - right up close to the chuck and the short length in the chucked shoewd no sign of being torn out of the chuck. I went is as far as the tool could then I welded the "off-cut" to a bit of RHS, put it in the band-saw and cut it off - easy.

http://i200.photobucket.com/albums/aa294/oldtiffie/Part-tool1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Part_off4.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Part_off8.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/IFANGER_TOOLS1.jpg

I hope it helps.

Paul Alciatore
11-03-2007, 11:42 AM
RE: the motor oil thing. You really don't want to use motor oil for a cutting fluid. It has additives and is optimized for, well, use in an engine. Fancy that. One side effect of using motor oil is that with prolonged use, it will leave a stain on the machines. If you want to use oil as a cutting fluid, you can buy various weights of oil in gallon or larger containers for about the same or lower prices as motor oil and it will have fewer side effects.

But there are oil based cutting fluids that would work much better. And then there are water based fluids that are much more economical.

One thing about a parting operation and cutting fluid is the difficulty of getting the fluid to penetrate down that 1/16" or narrower crack to where the cutting is actually taking place. A viscous motor oil may never get there even if there is a steady stream of it. This is probably why a high pressure stream is used in one of the examples above. I would think a low viscousity fluid would be better.

Another consideration is the rigidity of your tool holder. You don't mention the tool holder you were using. Probably the worst one would be a lantern post, Armstrong holder, and an extended, narrow blade. All the elements can flex and when that happens you get binding or the work runs over the tool.

I am not an expert on this, but I would agree with the comments about faster speed and feed.

And of course, DEAD SHARP. You did stone the tool before the operation to touch it up, didn't you?

x39
11-03-2007, 01:42 PM
In addition to the aforementioned suggestions you might consider using a four jaw chuck. An independent four jaw chuck has considerably greater gripping force than a three jaw scroll type, so if the work does tend to grab, it will be less likely to slip in the chuck and precipitate a crash.

Tyro 001
11-03-2007, 02:26 PM
Thanks for the replies. In answer to your questions:

1) I was using a Dorian Quadra Post. It didn't appear to flinch at all; nor did the cut off tool, even with the CSR sitting on top of it.

2) I was using the motor oil because it was handy, and I have a bunch of it in unopened bottles. Since none of my vehicles use this type of oil; and I don't have any other use for it, it was essentialy free. I prefer to use oil based lubricants since the shop is unheated and I've been told they water based stuff not only will freeze, but it can get some nasty microbial growth, which can be a pain to clean up. Any suggestions (what to get) here would be appreciated.

3) The steady rest was 8" or less to the left of the cut, ie. I was cutting off to the right of the steady rest as seen in the link Jim Hubbel provided. The follow rest was exactly behind the cut off tool, not to the left nor the right; however, since the follow rest "button" was wider than the groove, it is entirely possible it was bearing on the out-board end of the piece being cut off, thereby causing the crash.

4) I was using a HSS cut off tool not a carbide insert type. I think I will switch to the insert type if for no other reason than to get better cleareance and to eliminate tool grinding.

5) Putting the cut off tool on the saddle is something I've considered, but haven't quite come to grips with how to do it. Aviemron, I assume the parting tool is held at a 7 degree angle with the nose up and tail down?

6) I've figured out how to tell if my turning tool bits are at center height, how do you tell if the cut off tool is at center height? I've been using the tail stock center and a magnifing glass to gauge the height of the tool. Is there a better way? Is it better to have the tool at, above, or below center height? I've been shooting for exactly center height.

Thanks all. As usual, it's a pleasure to study at the U of HSM.

wierdscience
11-03-2007, 10:35 PM
FYI,Koolant King and a couple other brands of water soluable coolant are very good.They don't grow bacteria and they don't freeze down to about 0*f.Since I have been using Koolant King I have never had a problem with bacteria and our shop gets up to 100f and 90%humidity in the summer,perfect for bacteria growth.

Even if you do have some get funky smelling every so often it is still well worth the hassle.Better finishes and longer life from your tooling are the benifits.

Hope this helps.

Mcruff
11-03-2007, 10:56 PM
For a part this small in diameter I would use HSS steel with about 300-400rpm. Motor oil would be fine for this and I have done it hundred of times. As for staining, straight sulfer oil will stain far worse.
You can use a standard center gage to tell if the cutter is above or below center by a visual test.
http://www.littlemachineshop.com/Products/Images/480/480.C391.jpg
Just press it up against the round part and then put your tool against it, if the top of the gage falls toward you the cutter is bleow center if the top of the gage falls away from you the cutter is above center. This is how they taught apprentices in the shop I served my apprenticeship and the instructors when I was in trade school.

Bruce Griffing
11-04-2007, 08:58 AM
As to above, on center or below, see my original post. It should be slightly below. That way if the tool deflects, it results in a slightly lighter cut rather than a heavier cut that would occur if you were above center. Cutting above center is not a stable operation unless you can guarantee no deflection at all.