[Biff]

Sorry not a CNC question but I could use some help...

I'm just a hobbyist - no real education in machining except some high school classes. I have a B2227 and I get by OK for what I need to do. I can make parts accurately enough, get nice finishes, do some threading, though I wouldn't want to pay me by the hour. By a long shot the hardest operation on the lathe for me is parting off and I've had a real bugger of a time with it tonight so I think It's about time I got it figured it out.

Primarily I'm machining aluminum. I use the BusyBee parting blades (3/32" x 5/8") and their holder. When parting I get nasty vibration which results in either snapping the blade (I buy them in 3's because I snap so many), or the blade jams and rips the part out of the chuck usually launching it right at me, or if I'm lucky it just sticks and the drive belts on the motor start slipping. I've wrecked a lot of parts along the way. I've tried redressing the cutting edges on the grinder but it doesn't really make much difference over the stock grinding - assuming I'm doing it right. When parting I get nasty vibration - everything on the lathe bench starts dancing. I only extend the cutter as much as I need past the holder and use lots of lube and I've tried a few different kinds with no different results. I've tried different speeds and feed rates. I've tried adjusting the edge of the blade a little up and down of center using shims and not much difference. A fast feed rate always results in a snapped blade or jammed tool so I work slow. I advance the cutter a thou or two and let it shave and wait for the vibrations to subside then advance again and wait. I do that a few times then stop for a bit, which seems to help. It takes easily over an hour to part a piece off because I don't want to smash it and wreck it.

This seems like it should be a simple operation but I'm having a lot of issues. Any advice would be welcome!!

Thanks.

[chuck_hobby]

Are you sure the parting blade is perfectly perpendicular to the workpiece?
Also, how extended from the toolholder do you have the blade?

I should ask what diameter parts you're turning rather than assume it from the extension length, above.

Parting can be tricky but in just aluminum it sounds like you're having a hell of a time. Something ain't right. HSS parting blades, 1/8 or 3/32 pretty much what you're using, are what I use also, last time was from Enco I think. Cheap and easy, nothing special.

Best of luck!:wave:
Chuck

[wildwestpat]

Hi Biff

Suggest you reverse the parting tool action so that when it snags and starts to dig in it is lifted away from the work rather than plunging further into the work. (Think about the tool tip arc as it tries to plunge into the cut and you will become an advocate of the reverse running or rear tool post for all parting off operations as well as for some of the more difficult materials! Also try using a lubricant such as white spirit, WD40 or similar)

To do this you have two options firstly use a rear tool post for the parting off tool which must be perpendicular to the axis of the lathe and continue to advance exactly perpendicular to the lathe axis as well as having the cutting edge exactly on center height.

The second option requires a chuck that is bolted not screwed on to the lathe mandrel i.e. permits the lathe to run in reverse. The reverse rotation is then used to mount the parting off tool up-side-down with the tool cutting edge exactly on centre height and perpendicular to the lathe axis as for all parting off operations.

By using either of these reverse turning action methods the tool tip will be lifted away from the work and thus avoid the massive dig in that pulls the job out of the chuck. (This reverse tool positioning also works for conventional turning of difficult materials.)

Other things to think about are the clearances at the tool tip. The HSS tool out of the box requires the front and top clearances grinding to suit the material being cut as well as leaving the pip / breakout on the scrap side of the work. Aluminum will require these angle to be set correctly. That is the tool front face slopes back to the head stosk if the bit being parted off is the finished job. The back rake wil requuire adjustment to get satisfactory cutting as these HSS tools come with only the side clearances ground on each side. Check that the clearances exist and that the tool is not contacting the work by rubing further down than the side cutting edge. The tool mount needs to be clean and free from burs but check the vertical clearance by trying a very light face turning with a new out of the box HSS tool prior to grinding the front clearance and a bit of back rake.

The only other advice I can offer is to advance the tool into the work with a firm and deliberate action as a diffident feed can encourage chatter as can a slow rotational speed. The machine will have natural resonances which raising the rpm wil help avoid exciting as will keeping the tool and work overhangs to a minimum.

The use of insert tooling is well worth considering if you are going to do a lot of parting off and again the up-side-down tool helps but is not normally required with the insert tooling as the angles are all correctly set provided the insert is intended for the material being cut.

Hope this helps. Regards Pat

[photomankc]

I never had a lot of trouble with HSS parting of aluminum so I think there is a strong possibility that something in your setup is off. Look carefully at the height of the tool and be sure it is right on or just a hair high. Be 100% certain that the tool is perpendicular to the axis of rotation. Just a tiny bit off can lead to rubbing and binding as the tool goes deeper.

Chatter would occur at times when I was parting AL but nothing like that. I found a couple of things to be very true. New, sharp tools worked best (and I can't grind for @#%#), and going super-slow on the in-feed often makes chatter worse. Now when parting steel it became a whole 'nother ballgame. HSS blades were just no fun at all for me. I eventually picked up the Glanze insert type cut-off tool from Grizzly and cut-off is now a breeze more often than not. The inserts are almost ever-lasting in aluminum and last for many many cuts in steel too. The geometry is all good to avoid lots of rubbing. I don't think I'll ever purchase another HSS cut-off blade. That said you still have to pay careful attention to tool height. Too low and it can get pulled under when closing in the center and bad stuff ensues. Too high and it digs in with the slightest provocation and bad things can ensue.

Same rule applies though with the carbide cut-off. If you baby it, it will moan and groan and make life miserable so you have to get a pace going and keep it going through the cut. Should just be hissing along making curls. Once it starts to chatter it can be tough to get back into the cut and get it to stop.

[Biff]

Are you sure the parting blade is perfectly perpendicular to the workpiece?
Also, how extended from the toolholder do you have the blade?

I should ask what diameter parts you're turning rather than assume it from the extension length, above.

If it's not perfectly lined up it's pretty damn close. I suppose I could put the dial gauge to it to see if it's off a smidge. ATM, the piece in the chuck is 2.5" O.D. X 6" long, I hollowed out the end to 2" I.D. and about 2" deep so I'm effectively parting off a short piece of 2.5" O.D./2" I.D. pipe. I have about 0.5" of blade sticking out of the holder.

Pat,
I actually happened to overhear a conversation at BusyBee about a guy praising how much better parting was using a rear tool post. I always thought I should make something up to do that. It never occurred to me just flip the parting blade over and run the lathe in reverse... Sometimes I'm dumb.
Thanks for the idea!

I'll go through the setup again tonight and recheck to make sure everything is perfect, and try the flipped cutter too and let you know how it goes.
BTW yeah I use WD-40 for lube often. Funny you mention using it, I thought I'd get lectured about that. I find the aerosol can with the plastic tube on it makes life easy for me and my lathe is in my house so the smell of it is actually kind of nice vs. some other lubes when they smoke a bit.

[Fastest1]

Don't be surprised this is a very difficult process. The advice given is spot on. But I too buy my blades in bulk and experience problems in various materials even after thinking I have that particular material figured out.

[HuFlungDung]

Check what exactly is holding your carriage down before you do upside down parting. There is precious little but a few bolts, even on a good sized lathe. If you have an accidental pileup, it could wreck something pretty bad. Big lathes have a fair amount of mass in the carriage which helps hold it down on the bed, but a little lathe carriage has not got this characteristic so the parting forces (which are dependent on material and blade width and rake angles) are the same no matter what size lathe is being used.) I've never needed any upside down parting tricks to make an inserted tool work. All I can see the upside down tool accomplishing is serving as a sort of damper for a machine that is out of adjustment. But its not the proper way to direct cutting forces into the bed of a typical lathe with plain ways.

How much slop does your spindle have? Is your chuck any good? Wallowed out 3 jaw chucks are notorious for looking like they hold something, but really, they don't hold it securely at all. Whatever slack there is in the slideways that the chuck jaws move in, translates into lifting of the jaws. This typically means that the jaws hold tight towards the back, and looser at the front. It may even be possible to slip shimstock underneath the front of the jaws when the chuck is tightened.

The cure for this is to rebore or regrind the jaws with a preload applied that tilts them outwards as if they were in use, so you can straighten up the bore of the jaws.

One way to detect how good your chuck is holding is to put a nice round piece in, fully engaging the jaws, and about 6 or 8" hanging out. Snug the chuck up as per usual torque. Put a dial indicator on the far end of the bar. Take a soft mallet and tap the side of the bar near the end. See how easily it deflects into wobble mode. This is not a centering test, this is a holding test. IF the part barely moves off no matter where you hit it, then the chuck is holding well. IF it moves .03 or .06 out of wack very easily, then the chuck jaws need the servicing prescribed above. (Lift the indicator stylus off the part before smacking it!).

Once the jaws hold firmly for their entire length on the part, then you have a hope in hell of parting without extreme vibration.

I'd throw HSS parting blades in the scrap bin, except that they work very well in brass, bronze and cast iron Get an insert tool for superior performance. But having said that, the insert tool is not going to fix the problems that it sounds as though your lathe is having.

Also make sure that the gibs on the compound are snug. It should be difficult to crank the compound back and forth. This is something you might have to adjust from time to time, tighten for parting, loosen for taper cutting with the compound rest.

A lot of cheap lathes have setscrew gib adjustments. Those are crap because they continually come loose or worm their way into the shim. You'd be better off the remove the setscrews, and place shimstock behind the gib to fill the available space and thus custom fit your gib to the dovetail. You might have to scrape the rough machined surface inside the dovetail where the setscrews poke through, so that you can get a full length of shimstock in there. (I went through this exercise when I used to have a Palmgren millling attachment on my lathe. It worked sweet after this alteration).

Then put the setscrews back in to keep the gib from slipping out of the crack.

[around]

Biff,

Pat stated "The second option requires a chuck that is bolted not screwed on to the lathe mandrel i.e. permits the lathe to run in reverse. The reverse rotation is then used to mount the parting off tool up-side-down with the tool cutting edge exactly on centre height and perpendicular to the lathe axis as for all parting off operations."

Your B2227L has a threaded lathe mandrel. If you try and part with the lathe running in reverse you run the risk of the chuck unscrewing. This would not be good!

Cheers,

Adrian

[M250cnc]

Biff,

Pat stated "The second option requires a chuck that is bolted not screwed on to the lathe mandrel i.e. permits the lathe to run in reverse. The reverse rotation is then used to mount the parting off tool up-side-down with the tool cutting edge exactly on centre height and perpendicular to the lathe axis as for all parting off operations."

With the parting tool upside down mounted at the rear you do not need to run in reverse.

Phil

Sent from my HTC Desire using Tapatalk

[wildwestpat]

Hi Biff

Follow the advice about making sure the gibs are set correctly in all slideways. There is a lot of good advice on the 7x10 lathe gib adjustment which can be applied to any lathe. A rear tool post is well worth constructing if there is room on the cross slide to accomodate it. If make or buy a tool post that operates directly from the cross slide with out the compound as this will improve the ridgidity.

I suggest you face off a bar with a normal lathe tool then check the parting off blade against the new faced off bar. The blade side should just kiss the surface along its entire length if not the it is not perpendicular to the lathe axis at that distance from the chuck. Also check if you have not done so that the headstock is lined up with the bed. If you need instruction google lathe headstock parallel testing.

Hope you soon get a good clean partoff action.

Regards

Pat

[Dougal]

I used to have big problems parting on my 9x20 lathe, but recently it's all been working perfectly. I can even part stainless where before I was having biting issues even on plastics.

What I did was pull apart the tool-post and check all the faces. I found both loose bolts holding the base on the tool-post and faces which were raised around holes from tapping of threads.

I stoned the faces flat and torqued up the bolts, now it's parting better than I ever though possible, even with a blunt HSS tip that is 3mm wide. Can't wait to get some real parting tips now.

[LeeWay]

A little chatter goes a long way. I used to have trouble parting on a 7/12 lathe that used an aluminum QCTP. I could actually see the post flexing under load. I switched back to the OEM post and was a bit better, but gibs were still inducing chatter. I ground the tool with a steeper angle and raised it just a hair above centerline. That is when my trouble evaporated.
I built a new lathe and never had any trouble at all with the parting tool.
The moral is any leniency in the tool at all will result in poor performance. It must be as rigid as possible to work well.

[lordjw]

You could try tightening your lathe bearings slightly

Check which bearings your lathe has. For chatter free operation you should have tapered roller bearings. Cheap lathes can have ordinary ball bearings which will cause chatter under stress.

At the picture below two part tapered bearing on left and regular ball bearing on right.

Cheers!

Julius

[Biff]

I went over everything with a fine tooth comb and found the cross slide had a little wiggle in the ways. Taking out that slack helped a little but didn't solve the problem. The chuch seems to have a pretty good hold on the piece too. There wasn't any movement with some moderate hits but I didn't try really smashing it with my hammer, if you can call it that. It's just a baby 4 or 6 oz mallet with rubber on one side and plastic on the other that I use for alignment purposes. The indents the chuck left in the aluminum are consistent as well.

However I was just able to get my live center into the part I was trying to part off and that made all the difference. Parting went like butter with a nice consistent curl coming off and the nice hissing sound. Zero vibration or chattering. FWIW I also tried parting off right next to the chuck thinking maybe I was trying to part too far away but that had no effect as well.

AFAICT I've ruled out any slop in the ways causing the problem, tool height and alignment, being to timid about tool feed, etc. Whatever using the live center fixed is what the problem is. Would that point to the bearings? (either bad bearings or not preloaded properly?)

Thanks for all the input!!
Ryan

[Dougal]

Hi Ryan

Yes that would suggest the bearings are worth looking at.

[wildwestpat]

Hi Ryan

Looks as if you have found the source of your problems. The bearings are either on their way to the scrap box or they need to have the pre-load increased. Look at the parts list to see what type they are. If they are not sealed check that they have a little grease in them and take care not to let any bits get in to there. The pre load is adjusted on loct lathes by a threaded collar that has groves cut into it to take a 'C' spanner which is locked against a similar one when the correct loading has been obtained. If your lathe has thisa type of adjustment then you will soon get the hang of the adjustment. Make sure the threads are clean and oiled then you can feel the spring as the bearings tighten down as a reaction on the 'C' spanner. Do check that the chuck can be rotated freely as making the bearings too tight can cause excessive heat to build up. Much depends on the type of bearing and the quality. Some times simple deep row ball races are used to save on costs and these can give satisfactory service but the axial loadings including the pre-load capabilities are modest compared with other types designed to handle larger axial loads in addition to the radial load.

You might find that listening to the bearings using a screw driver as a stethoscope will identify bearing faults. Rotate under power - the sound of a bearing that is failing is a noise that is very distinctive. Some very large machines monitor bearing noise automaticaly to identify need for replacement before failures cause expensive problems.

Have you put a set of indexed tools on your nice to have list along with a rear tool post - lends and excuse to sift through ebay!

Regards - Pat

[fragger6662000]

I have always had problems parting with HSS blades and it is all dependent on the geometry of the tool and the blade and wear of the tool. Ally is pretty horrible to part as you get built up edge tool wear where the material sticks to the tool then breaks off removing material from the tool with it. WD40 is good for a lube but setup is everything. i have just bought a Glanze parting tool as said before. And i have to say it is night and day better than the HSS blade. The parting inserts are really good as the geometry cause the chip to be narrower than the blade so it will not rub and bind in the slot.

Here is a video that i have done.

Parting test run VIDEO

As you can see this is one of the 7 13 lathes and the only mod is tapper roller bearing in the main spindle which is a great improvement to carry out.

My short experience with this tool is that it is sensitive to centre height 0.1mm above or bellow it does not perform well. same with it being square to the axis. from the video you can see the the second cut i tried to increase the revs and it was not happy.

I feel that the key with everything is confidence if you have a good setup and confident it will work. Parting seams to sense fear! The confidence will allow to to get into the cut and allow to to continue pushing tool to maintain the good cutting conditions. reducing the feed will cause reduce chip thickness and lead to vibration and built up edge and poor chip clearance.

my recommendations would be

Inserted parting blade (£30 with decades of research and fancy coating)
Supported work piece
Rigid machine
Tool on centre line
CONFIDENCE
WD40 not essential
Good feed and speed which is related to the confidence
PRACTICE PRACTICE PRACTICE PRACTICE PRACTICE

[lordjw]

I had exactly the same problem as you. No matter what cutting tools you use, no matter what cutting speeds you try, no matter how well all is aligned and fixed the lathe always chatters when parting off.

Cheap lathes have regular ball bearings which cause this. I did modification for my minilathe and replaced crappy ball bearings with proper tapered roller bearings. After that I had chatter free parting operation.

Replace your chuck bearings or sell the lathe and buy a new one with proper bearings.

Cheers!

Julius

[LeeWay]

I don't doubt that tapered rollers would be better. I built mine using some standard roller bearings from VXB. I use the same ones in my mill and have to replace them every year on it. It runs all the time where the lathe only sees maybe a couple hours a day. They are cheap bearings. Maybe $20 per pair. The rest of the lathe is linear bearings and ballnuts. That probably had=s more to do with my good results than the bearings. I feel that even though these bearings are cheap replacements, they are higher quality than comes with a lathe head. I also use a t-shape cutoff tool rather than just straight. The straight oness flex a lot more than the T-shape.

First one on this page.
McMaster-Carr

[pp7]

I ran into similar problems when I was parting large diameter rod on my G0602 lathe. I was having to part off 5 inch diameter aluminum 6061 rod (after boring). I made a parting tool out of HSS (on a grinder) which caused a lot of problems when I dove into the aluminum over 3/4 inch depth. One way to do it is to first lock the slide, then use the fine travel adjustment to widen the groove back slightly back and forth as you dive toward the material. Although this works, it is a bit time consuming for my taste. The blazing fast method I have grown to prefer is to mount a $12 harbor freight 4 1/2 inch hand grinder to my tool post (I made a special tool), put in a cutoff blade of your choice, turn the lathe on (in reverse) and grinder on (wear a good mask and goggles) and dive in as fast as your heart desires.

Disclaimer: Not responsible for accidents or injuries.