Lathe tool grabbing and related cutting issues.

[zeeprogrammer]

I was turning a bit of 12L14 steel. Nothing different than what I'd done differently before. I think the tool got grabbed and dug into the steel. Stalled the motor.

Reset everything and continued turning. Initially was getting a 'smooth' finish.
Was using power feed. Suddenly, instead of a smooth finish, I got a stepped finished. Several steps. Playing around with it, it looks like the tool keeps getting grabbed a little and digs in.

At one point, I would feed in .005 and it would cut deeper than I expected. The next .005 did hardly anything. It went back and forth like that several times.

Using a carbide insert.

Kept at it cause I was pretty good along and thought I could get through it.
As usual...last step, parting off. Stalled so bad the part moved in the chuck at a slight angle. So done.

I think I still don't have the compound slide gib right. With sufficient oil along the joint you can see it move if you lift it up and down. Looking (remembering) the gib, it seemed small (height).

I've played with this thing left, right, up and down...am I looking at replacing the gib?

Certainly, parting continues to be a heart stopper (or pooper maker) particularly with steel. I'd rather not 'have' to go to a rear parter (and this time there wasn't much in the way of chips before I had problems).

Any other thoughts?

I think the part is salvageable. I think there's enough there to cut off the 'parent stock' (hee) with my handy-dandy bandsaw. Then I'll see about what it takes to clean up. Still work-able if I can't. It's the bottom of a base.

Not much information here. I don't know what might be important.

Sorry to be any 'trouble' here...but I have that reputation ;D.

 

[Deanofid]

I don't know what kind of lathe you're using, Zee, but if you suspect the compound gib, then lock it when making your cuts.
Also, if your lathe is one of the import units, it may help to lap the gibs so they will put even pressure on the dove tails when you adjust them.

The sudden digging in problem could be because you have back lash that hasn't been adjusted out when you start your cut, or your tool needs to be repositioned, or it is dull, or, again, loose gibs.

When parting off, lock all your gibs except the one you are using to feed the tool, and make sure your tool is really sharp. Make sure the tool is perpendicular to the work. I would not feed with the compound, especially when parting, if you have a small lathe. Use the cross slide and lock the compound any time you can.

(edit) Forgot one thing, (probably more than that, really). Getting "steps" or scallops on the work piece is also sometimes an indication that the spindle bearings are not pre-loaded enough.

Dean

 

[Foozer]

I was turning a bit of 12L14 steel. Nothing different than what I'd done differently before. I think the tool got grabbed and dug into the steel. Stalled the motor.

two things cause that for me. the slide gibs loosen up and/or I forget to lock down the tailstock. More often for me its the tailstock ram lock i just dont give it quite enough OOMPH. lets the piece float around a few tho and she will grab just like you described.

Robert

 

[ozzie46]

Did you set the parting tool dead on center to the work? If it was even slightly off center it will cause problems. Your comment about not many chips would seem to indicate the tool was either not sharp or slightly below center therefor rubbing on the part instead of cutting. The other postings about locking things up are right on target

Just my 2 cents on the subject. I am just a newbe too and have run into the same problems. Learning to spend the time it takes with a diamond hone and a arkansas stone to get a razor sharp parting tool was my best achievement in parting ops. Resharpen often with a 7 X lathe.

I noticed when everything was right, turning the cross slide handwheel was almost effortless, but if the tool dulled or it was not centered you could feel the resistance.

If others with more experience than I see anything incorrect in what I posted please correct me.

If you have a 7 X lathe I have read that changing the spindle bearings to tapered roller bearings makes a great improvement to facing, parting and turning operations. I'm going to look into doing this to mine as well.

There are in fact numerous mods I plan on doing as soon as I finish my current builds.
One of the main mods will be tapered saddle gibs.

Man I never talk this much. Don't know what came over me.


Ron

 

[PhiberOptix]

Zee,

I agree with what everyone else has said above,

but just wanted to add

that some materials tend to grab more than others

in which case I turn the coolant on full

regards
Andy

 

[Maryak]

Zee,

Carbide inserts can appear tight but are sometimes loose in the tool holder. This allows the bit to swing about, altering the depth of cut. Check this and also that the holder is tight in the tool post.

Hope this helps.

Best Regards
Bob

 

[vlmarshall]

Well, he's cutting 12L14...does it get any easier-cutting than that? Like Ozzie said, make sure the top surface of your cutting tool is right on the centerline of the part. It sounds like it's not cutting until you really crank on it, so it could be too low, or too dull... and that you have a bit if backlash, or gib slop, in several places adding up.

Just a thought. Good luck & stick with it, Zeep.

 

[tmuir]

Check your carbide insert isn't blunt.

I had to change mine for the first time the other week.
I was trying to face off and end and it just wasn't working.
It was taking off more on the edge than the centre leaving me with a slightly pointed end.

I checked everything was tight, checked for play, all good.

When I looked closely at the insert I could see it was ever so slightly rounded over.
Changed the insert and everything was fine again.

 

[vlmarshall]

...or at least a chipped edge. I can't see ya wearing out a carbide insert on 12L, but setting the tool too low will give you tons of negative rake, which could have chipped the cutting edge, and would certainly require more cutting force, as well as trying to 'pry' the spindle up and away from the cuttter.
Pictures, pictures. ;D

 

[zeeprogrammer]

Wow thanks everyone. Loads of good help.

Thought a lot about this over night, and also talked with a friend this morning.
I think you are all absolutely correct. It's all those things.

Most of you will remember I started machining last Feb and have done only one (well two really) engines. Before the first engine I had similar issues and broke the lathe down, cleaned up, adjusted as I could, sanded and adjusted gibs, etc. Things were better.

I should have done the same before starting this engine. With more experience and knowledge I think I could have done a better job tweaking the lathe.

A quick measurement shows I can lift the compound slide up by as much as .007...you can see the gap between it and cross slide! It wasn't that bad before...I think that first big slam did something.

Moving the cross slide shows binding near my side...moves easy towards the far side. Nut needs adjustment.

Compound binds at the far left. The first time I sanded the gibs, it was on my desk. Probably not flat enough.

I haven't looked at the insert but I suspect it's damaged. I've chipped several already....probably pretty cheap ones. (Not that I'm sold on carbide inserts...I was using them partly as a test to see the difference between them and HSS.)

The parting tool not being sharp raises another question...when to sharpen..hm obvious answer is going to be 'when it's not sharp'...so let me try...how often (or after how much work) do you find yourselves resharpening tool bits (not carbide). Or do you simply hone as a matter of course?

The gib screws have nuts on them which makes locking them for cuts a bit inconvenient...oh wait...I tweaked the screws up to those kind with 'plastic' in them so they're self locking. I can remove the nut on the middle one and use the middle one to lock the slide. Right?

Spindle bearings not being pre-loaded enough scares me. What would I do to test that?

Yeah...the effortless crank turning...I certainly don't have that at some point of travel...and maybe too much at others. Learning what 'effortless' less is. Very subjective it seems.

Thanks very much all. This helps me a lot. Not just in what to do and look for but...thanks for the motivation and support.

It'll be a busy weekend...but I'll post results when I get there.

 

[tmuir]

I've got to a agree with you on insert tools.
I never use my insert parter, I use my HSS steel ones. I have 3 of different thicknesses and threy all work great, just every now and then needs a quick touch on the fine wheel on my grinder.

I've made a few HSS profile tools and they give a better finish than my carbide ones and my silver steel graver gives a near mirror finish.

I actually went and bought some more HSS tool blanks this week to grind a couple of tools and try them against my carbide tools, especially when I found out my carbide set I can't just by the bits that I need I have to pay $70 for a full set of 8, even though I will only ever use 2 of them.

 

[Deanofid]

A quick measurement shows I can lift the compound slide up by as much as .007...you can see the gap between it and cross slide! It wasn't that bad before...I think that first big slam did something.

Okay, .007" is a gob of slop, in my book. It could be it's just out of adjustment. If that's not it, check the gib to see if it's really flat. You can use a straight edge to eye ball it, or lay in on a piece of glass and roll it around looking for light under it. If it's bent, it may only be putting pressure on the dovetail in one place.
Lap it using wet-n-dry paper laying on a pane of glass until all mating surfaces are flat. If it's a brass gib, this won't take long. If steel, work at it.

The gib screws have nuts on them which makes locking them for cuts a bit inconvenient...oh wait...I tweaked the screws up to those kind with 'plastic' in them so they're self locking. I can remove the nut on the middle one and use the middle one to lock the slide. Right?

That should work. Adjust the screws on the ends and then use the middle screw for locking the gib when it's not in use.

The parting tool not being sharp raises another question...when to sharpen..hm obvious answer is going to be 'when it's not sharp'...so let me try...how often (or after how much work) do you find yourselves resharpening tool bits (not carbide). Or do you simply hone as a matter of course?

Do you know the "finger nail" test? To see if your HSS tool is sharp, run it across your finger nail. It should dig in with little pressure, and if you just swipe across the nail, it should bring up a little chip. This is good way to judge sharpness, but take care not to jam it into your finger!

I suppose we all have our way of doing things. I hone parting tools almost every time I use one. Just a touch on the stone to spiff it up a bit before I mount it on the slide for cutting. A parting tool is the most picky of them all, especially on a small machine. Get it sharp, get it square, get it level.

Spindle bearings not being pre-loaded enough scares me. What would I do to test that?

Don't be skeert! See what your manual says about it. If you don't have a manual, identify your lathe for us and hope someone with the same lathe will know how to adjust them. You can usually get some idea by chucking a piece of stock and letting it go about one inch past the chuck jaws. With an indicator on it, lift up on the chuck and see how much it deflects. Then push in and out on the chuck. You shouldn't be able to feel any play at all. Put the indicator on the face of the chuck and see what it does when you push in and pull out on the chuck. Shouldn't be hardly any readable amount of play. Tenths, maybe. If you're getting .001" or more, the bearings probably need to be snugged up.

Dean

 

[zeeprogrammer]

Thanks for the additional tips.

tmuir: I might not have been clear about the parting tool...it's an HSS 'knife' blade from LMS. At some point I have to grind and sharpen my own bits...I've been avoiding it up to now. In part because I want to make an engine...not a tool. Short-sighted I know.

In any case...I have little confidence when it comes to free-handing stuff. I've seen some interesting posts on making jigs/clamps/holders for grinding tools. I hope to look into that shortly. I'll have to set up the grinder properly too.

Dean: Yeah I think that big bang meant something moved quite a bit. (Not that the lathe didn't need adjustment anyway.) Finger nail test is a good tip. Always hard to know when things are right when there's little or nothing to compare to. As for the spindle...it's a mini-lathe 7x14 (HF, Grizzly, ToolsNow, Cummins, and so on.) The manual is little more than a pic with names for things. I haven't looked at the manual but looking at the lathe I don't see any way to adjust the spindle. I'll do the test you suggested. Just a quick hand shove makes me think it's pretty solid. No...I think the issue is around the saddle, compound slide, and cross slide...needs a lot of work around there. I hope I didn't bust something.

I'll keep the thread posted.

I'll try and take pics...but camera has been absconded with by other family members to take pics of first grandchild. They apparently don't understand what's important. :big: The child will grow despite us. While I, without my lathe, will languish.

 

[Deanofid]

Zee, we don't want you to languish. I don't have this type of lathe, but there are a number of owner websites that tell quite a lot about it. Check this guy for starters:
http://www.mini-lathe.com/Default.htm

And there is a Youhoo group that probably has many members that can tell you all you want to know;
http://groups.yahoo.com/group/7x12minilathe/?yguid=339832710

Dean

 

[mklotz]

In any case...I have little confidence when it comes to free-handing stuff. I've seen some interesting posts on making jigs/clamps/holders for grinding tools. I hope to look into that shortly. I'll have to set up the grinder properly too.

Wagner's music is far better than it sounds and free-hand grinding is far easier than it appears. Next time you buy metal get a length or two of 1/4" square keystock or just plain 1/4" square steel. Cut off a piece about the same length as an HSS tool blank. Decide a priori on a shape you want to grind on the end of your ersatz tool blank. Some suggestions:

an end that looks like a cold chisel or a big screwdriver tip
a hexagon
a triangle

Don't think about anything other than your intended shape and get grinding (safely - no gloves, good face/eye protection). You'll be amazed how quickly your hand-eye system will begin turning out something that looks remarkably like your goal.

After you have a bit of confidence in your ability to grind shapes, try copying by eye one of your commercially ground bits. Don't worry about precise angles and all that nonsense; just grind until it looks about right. (There's a lot of latitude in those angles for our purposes.)

Repeat these exercises about three times with sessions separated by a day or two. Save your efforts from each session and compare them at the end. You'll be able to see your progress.

 

[tmuir]

Thanks for the additional tips.

tmuir: I might not have been clear about the parting tool...it's an HSS 'knife' blade from LMS. At some point I have to grind and sharpen my own bits...I've been avoiding it up to now. In part because I want to make an engine...not a tool. Short-sighted I know.

Is this the type you are using?

http://cgi.ebay.com.au/NEW-PRO-T-TYPE-PARTING-TOOL-LATHE-CUT-OFF-TOOLS_W0QQitemZ170376877018QQcmdZViewItemQQptZAU_BnI_Woodworking_Metalworking?hash=item27ab40d3da&_trksid=p3286.c0.m14

If so they are dead easy to sharpen.
If not I recommend them
If you are only using it on brass you don't need any top rake and just need to sharpen the front so the bottom has rake backwards.
The good ones are wider at the top than the bottom so you don't need to put on any side rake.
Most important you set it at centre height.

I have 3 of these in holders of different thicknesses with the smallest being 1/16 inch which is great for undercutting the thread on bolts to allow them to screw right up.

 

[doc1955]

Reading this thread I would bet that your spindle needs a little more preload on the bearings. If you spindle has not enough it is next to imposable to part anything off and you will get chatter in turning. If you put an indicator on the spindle and what I did to check it was to move tails stock up and put pressure on headstock with it the indicator should hold steady. We had this trouble several times in my 35 years in the tool room and it is easy to fix.

Good luck
Doc


PS in sharpening a partoff blade make sure you do not over heat it in sharpening keep water handy and keep it cool if it shows any sign of discoloring it will not hold and edge and will dull quickly.

 

[zeeprogrammer]

Dean: Yeah...the mini-lathe site was one of the first I came across. I'll be reviewing that shortly.

Marv: Thanks. And however long it takes me...you already know that I'm going to work on making my own tool bits. As for Wagner...I have no real favorite...too many great ones...although I can say that Carmen is my favorite opera. Too bad it was ruined by that silly TV show. I used to play it in the morning to get me going. (Don't ask me anything about classical music...my problem is I remember the music...or the story...I can't seem to remember titles, authors, etc.) Kind of lousy.

tmuir: I think yes they're the same or very similar. But only similar. Your comments make me think I have some learning to do. I have 3. 1/16, .04, and .03. Same holder.

Doc: Thanks for the tip. Not sure about spindle being the problem. At least, I don't think it's the major problem 'du jour'. Not to say it needs adjustment...but I think the bigger problem is the compound slide...certainly I can see a large amount of play there. But I need to check everything now.

 

[tmuir]

tmuir: Your comments make me think I have some learning to do.

Don't worry so do I.
My brother in law asked me today if I could turn a part that will involve me turning a thread on the lathe. Thats something I wasn't planning on learning how to do for a while yet.
I've got so many other things I need to learn before hand, but isn't that all part of the fun?

 

[joeby]

Zee,

I don't have any experience with the type of lathe you have, but I do have a 109 and a 12x36 Atlas, neither of which are considered overly rigid machines.

A couple of things that need to be in the back of your mind when using these smaller machines for parting:

1. Part off as close to the chuck as you possibly can. I leave just enough out of the jaws to let the toolholder clear the jaws.

2. Sharpen the parting tool on the end only, if they are the commercial blades, the side clearance is already there. You can grind a slight angle on the end so that the right edge of the tool is ahead of the left edge, that way your part is cut off clean and the "pip" will be on the end of the bar.

3. Make sure you have the tool as much over the center of the cross slide as is possible, not overhanging the left side. This will help keep your cross slide from tipping under tool pressure.

4. Make sure your parting tool is on center and square to the spindle. I bump the side of the parting tool against the chuck face (spindle off, of course) before tightening the toolpost.

5. Keep the tool overhang to a minimum. If you are parting 1" material, you only need 9/16 - 5/8 of parting tool sticking out of the toolholder.

6. Run a lower spindle speed.

7. Use cutting fluid or coolant. I use sulphurized thread cutting oil, messy and kind of smells but works well.

8. I try to avoid using the three jaw if I need to do a lot of parting off, especially on larger diameter work. The four jaw supports the work much better than the three jaw.

9. If you are parting brass, try stoning the front edge of the parting tool to make the cutting edge a little blunt. Works the same way as "dubbing" the cutting edge on a drill, preventing it from pulling into the work.

I hope some of this helps, some has already been mentioned, all good advice.

Take care of the machine problems first though.

Kevin