View Full Version : beautiful finish on lathe work

Alistair Hosie
11-04-2004, 05:15 PM
I suddenly while practicing with my lathe noticed that the finish was second to none.
I was getting instead of a finish needing a light emery-ing a finish which was beatifully smooth.
The ony thing I can think of was That I had reset my lathe height slightly ( an old boy told me to try it slightly below centre) anyway I set this at centre and was cutting with a new indexable tool with a carbide point and a very slow speed about 125rpm's and in backgear taking a very light cut a fraction of a mm whare did I go right'?
I had used more or less this set up before but the mirror finish was not this good.
I ask this because I should like to repeat it again and again this is the forst time on a lathe I have ever witnessed sutch a smooth finish.Give me some tips guys. Alistair

11-04-2004, 05:24 PM
Were your previous attempts on a different lathe? Perhaps your new lathe is superior in rigidity and tolerances. Light cuts for me and fast spindle speeds with a finishing tool work.

11-04-2004, 05:46 PM

You should not be using the backgear except for slow heavy cuts. With carbide you should try to stay over the recomended cutting speed for that grade of carbide that you have and the material that you are cutting. In general. high surface speeds will result in superior finishes, Since your Smart & Brown has both the balls and the brawn to handle nearly anything you can throw at it, try to use the higher speeds more and you will get better results.

Alistair Hosie
11-04-2004, 05:48 PM
god bless you laddie hey Thrud is here http://bbs.homeshopmachinist.net//biggrin.gifAlistair

Alistair Hosie
11-04-2004, 05:51 PM
Dave the reason I am doing backgear is that in spareys book he reccomends most amatuers to use backgear.However I will try faster speeds but till I get used to it I like slow feeds is that ok to use with high spindle speed?I prefer to take my time and not have it all go suddenly cut to finish cut in a few seconds as I like to take it easy at the moment so that I can stop it in good time before the saddle runs into the chuck Alistair

11-04-2004, 06:03 PM
Are you using a different steel or material?

Alistair Hosie
11-04-2004, 06:40 PM
no just the same the only thing I can think about is lighter cuts and changed the centre height slightly tinker,but the finish was magnificent

11-04-2004, 06:51 PM
Dave: Welcome back ! What Alistair neglected to mention is that his part is 12" diameter, giving around 400 SFM http://bbs.homeshopmachinist.net//biggrin.gif

Seriously Alistair, what diameter is it and what material?

[This message has been edited by nheng (edited 11-04-2004).]

11-04-2004, 09:56 PM
Well Alistair,on lathe work things change constantly,as the diameter of the part decreases,the cutting action of the tool changes.So does the finish,the chip form and the surface feet per minute.

Dave!Dave!Your back!!!Whooopie!!!!!! http://bbs.homeshopmachinist.net//biggrin.gif Finally a guy who understands artsy fartsy posts! http://bbs.homeshopmachinist.net//biggrin.gif

11-05-2004, 11:33 AM
Congratulations! Please let us have information on the insert that has given this finish.

Paul Gauthier
11-05-2004, 11:51 AM
Dave welcome back, hopefully you will be staying for a while.

Paul G.

11-05-2004, 12:01 PM
Sounds like you are giving a burnish to the part due to the slow speeds, if it works for you burnish on. Carbide likes very high speeds and feeds, that is why the production environment uses it (time is money). JRouche

11-05-2004, 12:30 PM
Welcome back Dave, Alistar should know not to question your wealth of knowledge. I have mised your post and only hope you can get back on a regular basis. I will be in Edmonton/Spruce Grove in two weeks bow hunting. Would love to meet you in person. Getting back to the thread most people read from the "old school books" on turning. The new inserts are really made for CNC and high speed turning. The manual machine operators need to speed up both their sfpm and their feed. It makes for less work hardening in modern alloy materials. Manual operators need to be quicker at the controls. I have learned this the hardway more than once.
God speed to ya Dave..eh

Alistair Hosie
11-05-2004, 02:05 PM
Just using cheap little set of made in India cutters wjich have carbide removable tips cutting small 11/2 " cylider but what a finish normal medium steel at around 150 rpm's in backgear came up like a mirror.Alistair

Allan Waterfall
11-05-2004, 03:57 PM

If those are the triangular TCMT tips,then 1&1/2" needs to be going about 580 rpm.
A Myford will get a super finish with HSS at about 200-250 rpm.
Try to turn something to a definite size and get a better feel for what you are doing
Next time you get some new tips,try the Sandvik,but I prefer HSS for 98% of what I do.


[This message has been edited by Allan Waterfall (edited 11-05-2004).]

Lynn Standish
11-05-2004, 04:54 PM
FWIW, I think I read on some posts on another board about a year ago that carbide is normally run at high speeds, and doesn't work well on most HSM lathe speeds. But... I think there were a couple of posts that said carbide would also work at very low speeds -- which defeated the purpose of using it to increase production.

My own experience roughly parallels what Alstair experienced, i.e. turning fairly slow often results in a better finish, especially on 1018 CRS. In addition, I have used carbide tooling to single point true up threads in 4140 rifle receivers. I was afraid to run the 16 tpi inside threads blind under power, so I turned the chuck by hand, and they came out with a beautiful finish.

11-05-2004, 06:46 PM
Alistair, I'm very happy to hear you're having some good experiences while practicing with your lathe. Continue on as you are - try different metal materials, different speeds, feeds, tools, etc. Enjoy it to the max, revel in it, wallow in it, and when you feel you're ready to make something, go for it. By the way, since your last post on Thrud's condition and the number of people who said they would pray for his return.... I don't believe its a coincidence that Thrud returned.

11-05-2004, 07:07 PM
Alistair mentioned Sparey's book and it is one that I refer to often. Like you I am in the practice stage with my new lathe (the new model 10X22 King) and having lots of challenges. Sparey mentions that you can get a high finish by setting the tool to rub. He doesn't go into any detail on this, but I suspect he means you would turn the tool into the work a bit so that more of the end edge is contacting the work. Perhaps you did this by accident?

I have tried this and got a horrible squeal, crazy harmonics on the work, and a panicky grab for the shut off switch (still not used to locations for all the controls). Guess there is a trick to it, like all machine tool operations.

[This message has been edited by dmcdonald (edited 11-05-2004).]

11-05-2004, 07:23 PM
WHen he says rub, I think he means, set the tool height so the relief angles on the tool actually are not enough relief? I guess so it rubs, causes a burnishing effect?
That horrible squeel is chatter. Finishing tool, the radius of the cutting tool is such that more of a cutting edge is contacting the work then a normal turning tool, and you take very light cuts with it.