Great information! A was facing similar issues with my lathe and was ready to scrap the entire thing, but saw this video and managed to trace the problem to the worn morse taper on the live center. 0.02 mm side to side play was enough to cause chatter. I put a dead center and problem solved! Thank you!

I think you would be able to make a video pointing out all the checks one should do before buying a lathe now you have had so much experience in the matter. It would be so useful 😊

@nheng6913

Жыл бұрын

Several forums such as homeshopmachinist and practical machinist have probably covered this in depth in the past but a KZread video would be a welcome addition. The critical areas are common to most "industrial grade" lathes such as this. The important thing to remember is the market to price to condition relationship. A machine will have wear if it's seen regular use. Judging how much wear is acceptable and in what areas is the most useful part of a guide. One thing I've found very easy to check is fluid levels. If the headstock has little fluid and actually had abrasives in it that you could feel, take a pass on that one (actually happened).

In addition to my earlier comment, I described a "following" steady rest. In this case we had a "leading" steady rest which would encounter a bulbous turning. A "following" steady rest would not necessarily do so since the cut has already been made. Make a short cut, apply the steady rest in a following position and then proceed with the cut and see what happens.

I think you should ditch the live centre in place for a normal one. I'm sure that would solve the chatter problem. Thanks for sharing

Old turners trick, balance the offset driving dog by adding nuts to the dog locking screw. It may be necessary to use a longer bit of screwed bar to accommodate the nuts required. It is better to use a face plate to drive the dog as weights can be added to the plate to compensate for dog and off set work. A dead centre in the tailstock will take the bearing error out of the rotating centre.

@grahamc887

5 ай бұрын

A good practical example of between centres turning. kzread.info/dash/bejne/ZmR_1byAmdzLp84.htmlsi=bzPSnQtQ09cwBszH

The DCMT insert you show is my favorite. This is the form of the Korloy uncoated, sharp insert for aluminum. Magnificent finish. It helps to always use a cutting lube from brush, drip or flow. For aluminum, many thin solvents work fine like kerosene, Starrett M1, WD40 and others. For steel, a cutting lube like Mobil Omicron (now Mobilmet, I think) works well. It is/was available in 1 gallon jugs.

@samuelfielder

Жыл бұрын

Machinists seldom explain why they have chosen a particular insert for a particular job. It would be helkpful if they did. I had DCMT inserts because of their pointy shape which I thought would result in less tool pressure on my Chinese minilathe. I usually use a neat cutting oil when trying to get a good finish on steel, but it is very expensive. I think it's Dormer Supercut. WD40 on aluminium. Mobilmet seems only available in UK in 208L drums costing over £1000.

If you are still using that worn out old chuck, turning between centres will be difficult/impossible. Take the chuck off, use a faceplate to drive the dog, and a centre fitted directly into the spindle nose. The scrap chuck needs to go into the bin, and when you have an accurate chuck, turn a 1" bar to the exact centre height, and use it as a gauge to set tool heights. Tipped tools will run at 1000rpm+ in something like your M300, as long as tool height is correct, and your chuck is accurate. For many jobs, though, a tangential HSS tool will be as good or better than tipped, and if you get one from Eccentric engineering, it will come with a sharpening jig, and uses 1/4 sq HSS, so is very cheap to use.

@nheng6913

Жыл бұрын

While driving with the chuck is problematic, the chuck wear doesn't really matter much. As long as the chuck is tight, you are still faced with three small contact points where the chuck holds the dead center. See my newer post regarding this. My solution has always been to grip small diameter parts with either aluminum flashing or business card (or even paper). This and a tight chuck seem to dampen many resonances caused by the tiny three gripping points. And I'd second the use of HSS in many cases, although I love several carbides for my work.

Excellent video. You discovered the steady. Unfortunatly there is no solution to turning long shafts, It has to be designed around by ensuring that the only machining is at each end, Excellent job as always

@samuelfielder

Жыл бұрын

Thanks. Bought the travelling steady as new old stock on ebay - quite expensive. Only thing that didn't come with the lathe.

There are many potential causes for the chatter. With one last and minor sales pitch for VFD drives (no, I don't sell them), they allow you to dial the speed up or down. They can allow you to move the overall "system" away from machine resonances. You can infinitely reduce RPM until the chatter stops. When turning a very fine finish, they can help you move away from any visible resonance visible in the surface finish, IF one should appear. ... Ok, no more VFD pushing 🙂 One thing to keep in mind with MOST carbide inserts is that they are not sharp and they really cannot be or the edges would crumble in production. This is worsened by the carbide coatings, which introduce even more of a microscopic radius at the cutting edge. The carbide is really designed to run at the feed rates and RPMs defined for the insert model and part number. They really depend on the FLOW of the material over the edge. This only happens at high speeds and feeds. In the recent past, I went through many different insert configurations, most with the same result. My favorites now are Korloy inserts for aluminum. These are uncoated and DO have a sharp edge and leave a beautiful, near mirror finish on aluminum. I also use them on mild steel with similar results and even with softer stainless (less tough) at lower speed and feed (half manual, half auto feed). For general turning of steel, I use larger triangular inserts with large nose radius. The best are older uncoated but some coated with small radius are ok, but no mirror finishes coming out of them. You could also go back to HSS where the world is at your feet. You can grind any standard or custom shape you need. Better finishes at less than aerospace speeds and feeds are easier. Before condemning the tailstock play (you have thrown the quill lock on, which helps) I would look at your dead center at the chuck. I have one of the wonderful Rohm set-tru chucks I've mentioned before but for any turning under about 1/2" diameter, I wrap a piece of aluminum flashing or even business card around the part and clamp tight. Why? The 3 points of contact from the chuck, ESPECIALLY on small diameter parts like this center, don't allow the mass of the machine to show through. Instead, there are many resonances of the part because of the three small contact points. These resonances are exacerbated by any length of stock in the spindle when turning the end of a bar. In your case, I suspect those resonances may be aiding your chatter because your driven bar stock has sort of extended the length of the driving end center. So, clamp the driving center with business card and tighten the chuck well. A few years back I lucked into a high quality spring loaded live center. I love this tool and use it exclusively now. Only on large, heavy parts would I go back to the live center. With the live center, however, be sure to apply adequate pressure from the tailstock before locking its quill.

@samuelfielder

Жыл бұрын

Yes, a friend told me he used polished inserts designed for aluminium to turn steel to get a good finish. I haven't tried it yet. They must have a higher rake. If you think a small dead centre in a 3-jaw will set up resonances, couldn't one avoid this either by turning a bigger diameter down to a point (one has to turn the point anyway to get it on-centre), or by using a 4-jaw? I feel that using a soft thing like a business card is introducing less rigidity.

@nheng6913

Жыл бұрын

@@samuelfielder The business card has worked well for me. When tight, it give three pressure points but leading away from those points you still have a compressed fiber area which I suspect has good damping properties. As I think about your quest here some more, I think you should ditch the chuck for this turning on centers phase. The whole spindle - chuck body - chuck jaws - dead center system is subject to resonances and they end up being audible. Try dropping RPM way down AND increase your feed a bit but do this slowly so you don't break any inserts. Soft aluminum roof flashing works well also and should help answer your fears about paper. While typing I'm listening to your comments on the live center and your desire for the longer one. Also heard the radius vs diameter comments. For a good use of money, consider a high quality DRO. It will make you smile over and over again. I installed an Acu-rite and had some high accuracy Heidenhain scales at my disposal at the time. For the cross slide, I used scales with 5 micron resolution because I was turning some critical adapter parts at the time. The longitudinal feed has a scale either 10 or 20 micron for size and cost considerations. With your quick change adapter and good DRO, you should be able to change tools and hold added error to a few ten thousandths or so. (sorry for the inch to micron flip flopping)

@samuelfielder

Жыл бұрын

@@nheng6913 Yes someone else took me to task for keeping the chuck in the set up. I need to do more experimenting. My lathe did come with an ancient DRO, a DIGIPAC 5 which senses movement using steel balls inside a cylinder (don't ask me how), but I took it off to do the refurb and have not bothered to reinstall it. Probably better to get a new one nowadays, but I can't throw more money at this lathe until I've taken a decision on tis fate!

Great video, I admire your patience, (although I bet a few profanities were off camera!) On my lathe, I have similar problems, albeit not so severe. I do have to 'work at it' to get long bar parallelism, usually finishing with emery. It really is a shame about the tailstock quill, the only answer I can see for that is to get the body bored out to clean up, and have the quill ground, then hard chromed to the new size, but I guess you knew that, you could lose the engraving though, depends how deep it is. You're making progress though, and I'm sure you'll get there, you don't seem to be the kind that gives up, cheers, Dave

When you apply a following steady rest to a bulbous turning as you had when you applied it will you get more pressure on the middle of the turning as you go down the turning. A second traverse where you had a slightly concave turning should yield less deflection caused by the steady rest and a better result. Each pass should show lesser deviation because there is less variance in the deflection caused by the steady rest. Ideally after a certain number of passes you should average them out and get a uniform diameter. Of course algebraic series sometimes diverge when we expect them to converge toward a minimum and we get worse results. It argues for a trial.

@samuelfielder

Жыл бұрын

Good point.

Any long shafts requiring high tolerance and finish always went to the cylindrical grinder, if you wanted to do something in the lathe you'd need to compensate and polish, even long shafts are usually stepped, and more often than not job pieces are not long items. You machine as far as you can go, remove the traveling steady then machine the chuck end and blend in

Rather than purchasing a new live centre, would angling your compound to 45' let you get your tool in easier; with that right hand tool at least.. would also save you having to get your quill out.

@samuelfielder

Жыл бұрын

I don't think so, that particular tool holder is just too wide to fit in there. I could have put it on the righthand side of the tool post, and avoided having to wind the quill out.

You should clean the morse taper 3 arbor with acetone and not touch it with your fingers before putting it into the housing for it. That goes for the housing also. Liking the content though thanks

Have you tried tried doing a true "between centers", i.e. removing the chuck and using a faceplate and a center in the spindle? It would take the chuck completely out of the picture.

@samuelfielder

Жыл бұрын

No I haven't. But unless you think the chuck isn't itself rigid enough, I don't see the advantage. I cut a true point on the bar in the chuck (as shown), so even if the chuck has massive runout it wouldn't matter.

Cross slide and compound slide Gibbs

The travelling steady should be behind the tool not infront

@samuelfielder

Жыл бұрын

Why so?

I bought 2 different sets of those centres on eBay & both went back as garbage. They're cheap & that's what you get but what annoys me is that both were bought from real UK sellers & they literally just repeat the Chinese bullshit!!!

Go buy a Skoda live centre. That 10 buck job you are using is crap! You can get them to run a bit better with FAG or SKF bearings