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01-09-2008, 10:56 PM #1
cut off tool - don't know how to use it
My cut off tool chatters even under an oil drip when cutting 1 inch round stock mild steel .
Chips come off, but no steady spiral of steel shaving.
Should it be on center or above center?
Should the tool have a relief cut on the sides so it does not rub as it cuts in?
Should it be ground down to cut thinner than the width of the cut off tool stock ?
Should the work speed be slower than for regular turning ?
Perhaps there is already a reference to this in past posts, but could not find it.
01-09-2008, 11:12 PM #2
I know this sounds like "we only work Thursdays" but what sort of lathe are you doing this with?
01-09-2008, 11:14 PM #3
The best luck I have had is to slow your spindle speed way down. I use the lowest speed on the back gear on my Sears Atlas. I try to center the tool on the work, and usually the action tends to pull it a little to the low side. Feed by hand as much as it will take, and use lots of cutting oil. dont just drip it on, but use a steady stream of it. I'm just an amateur, but it works for me.
01-09-2008, 11:23 PM #4
One rookie to another... We'll see how I do against the pro's
Should it be on center or above center? - ON center or slightly below. If you don't know how to test this, take a small ruler or any thin light straight metal and lightly pinch it between your tool and your work. It should stick straight up and down.
Should the tool have a relief cut on the sides so it does not rub as it cuts in? - Most cutoff blades have some side relief already ground in. You need good relief on the nose, and the nose should be slightly angled.
Should it be ground down to cut thinner than the width of the cut off tool stock ? - NO! If anything, the cutting edge should be wider than the rest of the tool.
Should the work speed be slower than for regular turning ? Hmmm... I don't think so.
ALSO - keep your tool overhang as short as possible. So if you are parting off a 1" piece, have only 1/2" plus a little bit sticking out of the tool holder.
ALSO, ALSO - make sure your tool is PERFECTLY perpendicular to the work. Maybe not that important on thinner work, but it gets to be a problem when parting off heavy stock.
Good luck, let us know how you make out. Post some pics of your setup if you still have trouble.
01-09-2008, 11:25 PM #5
You must include your lathe specs: size,etc. I'd suggest,without knowing anything about your lathe's size or rigidity,to not stick out any more of the cutoff tool than necessary to sever the bar you are cutting off. Also,make sure the cutoff tool is vertical. Sometimes the holder will hold the tool a little tilted so it rubs on one side. You did not mention how large,or what type cutoff tool you are using,or the type of tool holder it is in. the old fashioned cutoff holders that fit in the old lantern type tool posts are not very rigid. Specify all this stuff to get any kind of real help. Yes,keep the tool on center,or it will not fully sever the bar. Feed by hand if necessary unless you have a fairly large lathe. Cutting off is one of the most demanding operations for a lathe,especially small ones. Use slow RPM.
01-09-2008, 11:36 PM #6
On center or below
side clearance & relief preferred
rpms 500-1000 with minimum overhang of tool and stock from collet \ chuck.
01-09-2008, 11:48 PM #7
Is this one of those gawd danged HSS things? Remove the toolholder from the toolpost. Walk to the shop door with it in your hand. Open the door. Look for a bush. Throw the tool in that bush
Git one of those newfangled carbide insert cutoffs. 3/32 width may do, but 1/8" is more rugged.
BTW, if you need to part off brass or cast iron, go out to the bush and get your old partoff tool
01-10-2008, 12:17 AM #8
if using a lantern tool post , turn the rocker base upside down & shim if necessary to correct height ( center ) ..an openside block is even more ridgid ,which i now use.just a stud on a tnut /plate & a block w/cutr out for tool ..snug up the gibs ,particularly on light lathes....i ususally start w/ 1/2 or less normal sfm on late model craftsmn 12x36 .( cutting mild steel) ..if chattering does not stop as u start to seriously cut , drop the speed down ...& REMEMBER to feed in slowly at the reduced speed so u dont crowd the tool .....relief on front & sides ,as stated ,minimum overhang .,constant drip of dirtiest old engine oil i can scrounge for mild steel ( chip clearance is paramount ) ..if u cant get a stdy cut , u r most likely not on center /not sharp/no front clearance & it either wont cut or digs in ..... i use a slight top rake ground in w/ a large radius...cutting a V in the face of the bit helps tremendously ,minimizing chip clogging ,since u r not trying to dispose of a wide chip ( when u get to the point of v ,u r removing stock that has clearance around it ....) other helps in a deep cut are backing tool out & taking cuts on side of primary cut , to provide clearance..........there are other tool placements ( rear tool post , that some prefer)..
on the crftsmn , the power x feed is too fast for use , necessitating hand feed , at least for me ......
now after all that , a goosenck holder makes life a lot easier ....a shop made one on my 1895 14 in reed (1600 # ) is very forgiving ,since it will flex OUT of the cut rather than IN & a wreck...in fact i can turn a 60deg point on a one inch bar by plunging in a full width 3/8 flat bit w/out chatter at 140 rpm...it will flex down 1/8 in when needed, plainly visisble ...the armstrong gooseneck holders are not as flexible , but still forgiving ....
final thot is there is a serious learning curve on parting off ..each machine / operator has different parameters ( evidenced by posters using LOWEST speed possible & normal SFM , & neither of theses extremes comes close to suiting me )....
01-10-2008, 12:26 AM #9
Tool perpendicular to spindle... Did I mention to keep the tool perpendicular to the spindle?
Cut-off as close to chuck or collet as possible without hitting something.
stick tool out as little as possible.
If using a lantern toolpost, STOP using the lantern toolpost..... don't do any cutoff until you have stopped.
Slow may NOT be right..... faster rpm may be better, or worse. Gotta find the sweet spot. But slower OFTEN works.........
if a single phase motor on lathe, get used to chatter..... 3phase is MUCH better.
keep "on" the infeed, if feeding manually.... often a little heavier feed will stop chatter.... but too heavy will snap the tool, so watch it... its a "feel" thing if manually feeding.
Make sure all slides are properly adjusted as to the gibs.
Make sure the spindle bearings are properly adjusted.... bearing clearance will cause chatter you won't believe.
01-10-2008, 02:16 AM #10
Real close only one thing you left out, when having problems grind the cutting surface at an angle of between 10 - 20 degrees (nothing accurate). It should help if you are already doing all the other things you talk of. Also you might tighten up your gibbs for that operation then loosen after.
Let us know how it came out!
01-10-2008, 03:07 AM #11
Everybody hit on about every thing I can think of. My personal preference is not too slow on the rpm (I use about 200 or 300 with 1" stock on my 12x36) with slow feed. If you are parting off a long chunk you might lay a hammer handle or piece of wood lightly out at the tail end to kill any singing. You probably already know, don't put a center out there on the end in the tailstock, you'll pinch.
01-10-2008, 06:26 AM #12
The way I was taught
Back the compound so the tool post axis is behind the compound axis.
Depending on the lathe model tighten the(or one of the) compound gib lock set screw(s) snug.
Forget the hand fed stuff unless thats all you have, the power feed is there for a reason.
.003-.006 per revolution in most cases works for me.
You should be able to part most materials at the same speed as facing.
Grind your parting tool with a slight relief towards the chuck side so that
the piece that is being parted comes off clean with out a burr.
01-10-2008, 10:23 AM #13
Manchester or equiv.
I am Ox and I approve this here post!
01-10-2008, 10:56 AM #14
All good advice. Parting is one of the hardest things to do.
Heh... parting is such sweet sorrow???
Thankyew, don't forget to tip your waiters and waitresses!
All kidding aside, less-rigid lathes have a terrible time with parting off.
You can really increase your chances of success by increasing the rigidity of your setup. This means chucking the work as closely as possible to the chuck jaws so your cutoff tool will barely sneak in, cranking the compound back so the tool block is directly over the cross-slide to eliminate rocking, and as mentioned, tighten the gibs.
Also, consider making a tool holder that's just a dumb old block of steel with a slit pinch bolt arrangement -- that made a huge difference for me. The other benefit of this is that once you figure out the tool height, and build it into the block, it's always right.
One other thing to consider is that HSS parting tools need to be SHARP. I find that I get best results if I hone them pretty much every time I use them. Also, hone them so the front edge isn't perpendicular to the side -- have a slight point on the tailstock side. This will put the "nub" on the remaining stock, not on your workpiece.
01-10-2008, 12:30 PM #15
Humor is the best medicine,parting is such sweet sorrow,chit man.
I was wanting to say that at times more feed will stop chatter,BUTTTTT,this is a thin line that if crossed will wake you and your closest neighbor up.
sure seems like alot of good ideas above here.
01-10-2008, 12:57 PM #16
My first few attempts at parting were not very productive. I read all the advise from this site and still couldn't make it work.
Finally, an old machinist showed me how to check the spindle bearings. There was only slight movement but that adjustment made my lathe a pleasure to part with.
SCOTT (fabricator - wanabee machinist)
01-10-2008, 05:43 PM #17
Cut off tool
I can't believe you guys never heard of a spring cut off tool. Had a lot of trouble with a lantern toolpost with a standard cut off tool. But with a spring cut off tool in the same lantern holder its a piece of cake. Works with higher speeds and faster feed. I use a tooth brush dipped in Rigid black sulphurized pipe cutting oil just held on top of the cut. These spring cut off tools are very pricy new but peanut price on ebay. Not going to sell my bar or spring thread cut off tool, shaper tool and 6 other spring tools I have.
01-10-2008, 07:09 PM #18
01-10-2008, 07:23 PM #19
If using a small lathe (I have a Southbend 9) try turning the parting tool upside down. I find an older light machine tends to have a little wear in the headstock bearing. By turning the tool bit upside down and running in reverse the cutting forces drive the spindle down against the "rugged" part of the machine. Also remember chatter has 2 "normal" causes, both related.......RPM too fast or feed rate too slow. By the way I use a Phase 2 quick change tool post similar to the Aloris
01-10-2008, 07:25 PM #20