# finish when turning



## pmdevlin (Dec 19, 2016)

Very basic question here, when I'm turning on the lathe, doesn't matter what material, brass, aluminium, the finish is very, well best described as scratchy.

I have just use a new index, doesn't matter what speed, by hand or using the auto feed (which is marginally better) the finish is poor, I then have to finish with different grades of emery cloth, which means the finish is then dull. I remember my mentor, when he turned, the finish was always crisp and perfect.

I am relatively new at this, until now, the finish wasn't that important, but now I need to turn some stainless shaft and have a nice finish as its for an rc project which needs exact tolerances, so I want a good finish.

Any ideas appreciated

thanks

Paul


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## goldstar31 (Dec 19, 2016)

Paul
       It is a well known saying but the finish is no better than the finish of your lathe tool.

As you are a newcomer, might I suggest that you read the remarks in Conrad Hoffman''s suggestions on his site.- Advance Tool Sharpening ?

There is a lot of blether about sharpening ALL the faces of a lathe tool. In fact, a lathe tool need only be honed for the Depth of Cut. It might be a few thousands of an inch! The rest of the tool is for all sorts of reasons like rigidity and cooling but it doesn't need to be honed. Use a cutting fluid if you want but I settle for the old fashioned lard oil for steel.

If you hone- and I don't write grind, you need a very fine stone. Perhaps Arkansas or a fine diamond one but you should aim in a reflecting your thumb nail in the cutting edge. If you angle your tool with less than 3 degrees to almost rub, you should create  the  finest steel wool which will crumble if rubbed between your fingers.

Does this help?

Regards

Norm


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## Hopper (Dec 19, 2016)

Quote : " I use a new index"

Presumeably you are using a small home hobby lathe. You may find High Speed Steel tool bits give a better finish. Most small lathes do not have the rigidity to do well with indexable carbide tools. Also good quality brand name indexable inserts may help, as may using the ground-finish inserts some manufacturers supply for turning aluminium etc. They work well on steel on small lathes.


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## pmdevlin (Dec 20, 2016)

Hi Norm,

thanks for reply. My concern would be actually sharpening the tool by hand, and losing any specific cutting angle. I realise we are in the machining world, but having to sharpen a new tool, is that common practise, have I naively expected too much. As I cut, I take only a very light pass all the time, probably nerves thinking I am going to jam the lathe! I have a very very fine polishing stone, maybe use that?

Hopper, yes hobby lathe, Ill try some hss bits that I have, thanks!

Paul


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## goldstar31 (Dec 20, 2016)

Hi Paul
            Thanks for your reply. As someone who never 'took up the tools as a job', I can understand your problems very clearly.
No one seems to explain that there is little or no difference in the various cutting tools in the workshop. Whether you are drilling a hole, milling or using a lathe, the same cutting action and the same demands are made.  A mill is only a drilling machine and a drilling machine is only a lathe turned at 90 degrees. Consequently, a cutting edge will work if it . is say 5 degrees or 7 degrees regardless of the machine. In a small amateurs shop you need a SHARP edge because you haven't got the rigidity and horse power to push metal away. In Production terms, such things are important. You and I are concerned  with using one tool to replace using a lathe and getting things to two thous oversize and then grinding the last bit to a 'mirror finish' The foregoing is 'old practice' but our tools are of that generation.
Further simplifying matters, you should be able to have a lathe tool which will remove the hairs on your arm - or laughingly, the pubic hairs on a flea! 

To get   a mirror finish, you can do it either by cutting followed by a succession of finer and finer abrasive grits or putting the mirror finish onto the tool and getting a tenth of a thous off a part with a honed tool. What you will not get- or I cannot, is a mirror finish from a lathe tool which has had a buffing from something which is not dead flat.

Apologising for probably telling you how to suck eggs, you can get surprising results with a flat topped lathe tool-having got the top mirror finished on a bit of dead flat plate or a bit of glass and then honing the cutting face. Once you UNDERSTAND just how little one needs, you can concentrate of adding the improvements.

I hope that this is constructive.

If you want me to try to explain how to get cutting angles with a cheap 6" double ended grinder, then ask

Cheers

Norm


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## django (Dec 20, 2016)

Always try to take at least .005" deep finishing cuts. Lighter cuts can result in the tool pushing away from the work then skidding on and then digging into the work surface giving a terrible finish. Hope this helps PS All other factors must right as well eg sharp tool on centre height, rigidity, speed and cutting fluid.

Paul


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## Niels Abildgaard (Dec 20, 2016)

Hello Paul

Can You show us pictures of Your misery?
Will help getting help for You


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## pmdevlin (Dec 20, 2016)

makes sense norm, especially the bit about not having the hp! Its a chester conquest, I got second hand a couple of years ago, but as time has passed, my expectations have increased, probably due to friends asking for that "little job" and its always that job that you want to do very well

I'm using (probably) cheap metal, with cheap indexable cutting tools. Today as I'm off work, I went rummaging through the tools etc I was gifted when my mentor passed away a couple of years ago. There are some hss tools (6mm I think) I don't even know which way round they go in the tool post, maybe Ill post a pic for you all to advise!

Django (great film by the way!) you are probably on the money here, scraping along is what I am doing, maybe I need to be bold and actually cut something on one pass!

Now I'm getting fussy with the lathe, I see it has play and slop that has developed, especially when parting so its probably time to give it some tlc, I don't even know where to lubricate it!


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## Charles Lamont (Dec 20, 2016)

django said:


> Always try to take at least .005" deep finishing cuts. Lighter cuts can result in the tool pushing away from the work then skidding on and then digging into the work surface giving a terrible finish. Hope this helps PS All other factors must right as well eg sharp tool on centre height, rigidity, speed and cutting fluid.
> 
> Paul



This is just not true. With a *properly sharpened* and set high speed steel tool, I can often take a cut of less than 0.0005" in decent material.


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## goldstar31 (Dec 20, 2016)

Charles Lamont said:


> This is just not true. With a *properly sharpened* and set high speed steel tool, I can often take a cut of less than 0.0005" in decent material.


 
This is quite achievable and seems to be now forgotten and better. It  is possible to get that 'barely perceptical swarf' which the old timers like Cleeve published.


Years ago, the late Jim Early and I tried to republish and were threatened with legal action by the then new owners of Model Engineer.

And a Merry Christmas to all our readers:wall:
​


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## deverett (Dec 20, 2016)

If you are worried about your tool sharpening ability, have a look at GadgetBuilder's Vertical Shear tool.  This can give a very good finish.
http://www.gadgetbuilder.com/VerticalShearBit.html

Dave
The Emerald Isle


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## goldstar31 (Dec 21, 2016)

deverett said:


> If you are worried about your tool sharpening ability, have a look at GadgetBuilder's Vertical Shear tool. This can give a very good finish.
> http://www.gadgetbuilder.com/VerticalShearBit.html
> 
> Dave
> The Emerald Isle


 
What rarely seems to be asked is 'How does one remove a tenth of a thous' when all one has is a lathe with thous engraved on the feed screw dials?  Obviously, moving a slide one division ie a thous, means that the lathe will cut TWO thous. Can we improve on what we have got? 

Well, I have lathes long past their sell by date- and arguably a bit shakey.

What can be done without a lot of effort to remove a gnat's cock of metal rather than 2 whole thous? I doubt that few of us have the gear to remove an exact tenth of a thous but removing that tiny dusting of metal is practical.

Whilst there is a mathematical formula developed out of the 6th proposition of Euclid, it is doubtful that no matter how clever we are, our machinery will fail us.  Well, like mine??????

However, the math or maths suggests that if we set the top slide over by 'about' 5 or 6 degrees, that whisker of metal can be removed by using the top slide only.

Does this help?

Norm.


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## Hopper (Dec 21, 2016)

> There are some hss tools (6mm I think) I don't even know which way round  they go in the tool post, maybe Ill post a pic for you all to advise!



You might get yourself a copy of LH Sparey's classic book "The Amateur's Lathe". It has the best illustrated rundown on grinding various HSS lathe tool bits that I know of. The rest of the book is worth its weight in gold too. Essential reading for every aspiring (and existing) lathist. 

If you are going to use a lathe, you need to know the basic principles of how it cuts metal. Might as well start now!

Also, on depth of cut with indexable carbide tools, often these will give a better finish with a deeper cut than with one of just a few thou. They seem to like a bit of work to do and not to be just rubbing on the job. But I find that HSS finishes better on my ancient hobby lathe that is not the most rigid or wear-free of critters.


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## django (Dec 21, 2016)

Charles Lamont said:


> This is just not true. With a *properly sharpened* and set high speed steel tool, I can often take a cut of less than 0.0005" in decent material.


 
What isn't True? Also Why would you even want to be taking half thou cuts when you can polish it off in a matter of seconds? Sounds to me like your not taking the right finishing cut in the first place? Maybe the old adage of measure twice cut once should be applied.


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## Charles Lamont (Dec 21, 2016)

django said:


> What isn't True? Also Why would you even want to be taking half thou cuts when you can polish it off in a matter of seconds? Sounds to me like your not taking the right finishing cut in the first place? Maybe the old adage of measure twice cut once should be applied.



It is not true that one needs to take a 5 thou cut to get a good finish. I know what I am doing. Well, sometimes. Evidently we work differently, which is fine.


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## django (Dec 21, 2016)

Charles Lamont said:


> It is not true that one needs to take a 5 thou cut to get a good finish. I know what I am doing. Well, sometimes. Evidently we work differently, which is fine.


 
I didn't say that you needed to take 5 thou cuts only try to to avoid the rubbing that can occur when using indexable tips especially on poor quality steel, that's all.


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## Blogwitch (Dec 21, 2016)

Try taking a 2 thou cut on something like Delrin and see what sort of mess you get, then try 20 thou and be amazed at such a great finish on the same material. That is mainly due to getting rid of the heat generated by friction, the shallow cut can't do it, the deep one gets rid of it in the shavings.

This is the same with most materials, a decent cut usually ends up with a good finish while shaving doesn't. The only time I have come across anything different is when I am boring on both the mill and lathe. 
I always try to do a fairly deep cut, say above 5 thou, sometimes a lot more, to get down to exact size.
This is with HSS BTW, with moulded tungsten, you will be very lucky to get a decent finish on a small machine with a shallow cut.

John


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## bazmak (Dec 21, 2016)

Never tried to take off  1 tenth thou,why would i.If you need great accuracy
then turn to +1 or 2 and polish off Simples


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## goldstar31 (Dec 22, 2016)

bazmak said:


> Never tried to take off 1 tenth thou,why would i.If you need great accuracy
> then turn to +1 or 2 and polish off Simples


 
I was following through the drawings of the Acute tool and cutter grinder and noted some tolerances were 'tight'. Whether these are needed to be held remains to be seen.

However, when it comes to boring, the expedient of 'papering' is difficult- to say the least. I recall several 'nasties' when boring cast iron for such things as the Quorn and the Mark 1 version of Versatile Dividing Head and- OMG- the Westbury mill drill when I split the bored casting. They nipped:fan:

Way, way before this, I was obliged to sample in tenths to do the statistical analysis - to set up production machinery. You know this three standard deviations from the mean malarkey calculations. Not everyone's cup of tea but I recall messing about with 'real' engines- the 12" to the foot variety when 3 thous meant - knackered!

Now where did I leave my 'guessing stick'?

Norm


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## bazmak (Dec 22, 2016)

agree Norman,i too had to work in tenths way back when we all did proper engineering.My point being that with home engineering and cheap chinese
lathes I have not yet nor do I see the see the need to work in tenths
If I need to make a cylinder and piston to better accuracy then I would do the bore and then the piston to suit. As an apprentice with unlimited equipment and measuring equipment its not difficult apart from failing eyesite and shakes
Merry Xmas


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## goldstar31 (Dec 22, 2016)

bazmak said:


> withequipment and measuring equipment its not difficult apart from failing eyesite and shakes
> Merry Xmas


 
Happily I'm on eyes that my late wife bought as my Christmas and Birthday presents. No cure for deafness and a wheezy pair of bellows, I'm afraid. 

At least, I still have enough puff left to wish you and everyone here a very Merry Christmas. May 2017 bring you all lots of workshop enjoyment.


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## Wizard69 (Dec 24, 2016)

pmdevlin said:


> Hi Norm,
> 
> 
> 
> thanks for reply. My concern would be actually sharpening the tool by hand, and losing any specific cutting angle.


Sooner or later you will need to grind and hone a HSS tool.    I really see no way around this as even if you use indexable tooling eventually something comes up that needs a special tool.  

In other words grinding your own tools is a basic skill in a machine shop.  As for loosing a cutting angle how would you do that?   If you cant judge the angle buy a protractor or other angle standards.  



> I realise we are in the machining world, but having to sharpen a new tool, is that common practise,


Yes it is.   For one things like drill bits leave the factory with a general purpose grind and it might not be suitable for your intended work.  HSS tool blanks of course are seldom ground to a cutting edge at all. 


> have I naively expected too much.


Maybe!   Lets face it every body is new to this at sometime unless they grew up in a machine shop.    However we really don't know what is wrong here.  Posting a video or a few pictures might help.  


> As I cut, I take only a very light pass all the time, probably nerves thinking I am going to jam the lathe! I have a very very fine polishing stone, maybe use that?


Most indexable tooling is not sharpenable!   

For HSS tooling you need a grinder and a variety of stones to grind and then hone the cutting edge.   


> Hopper, yes hobby lathe, Ill try some hss bits that I have, thanks!
> 
> 
> 
> Paul




By the way even though you need to learn to sharpen HSS tools indexable carbide can be very useful in a small lathe.   The trick is to buy the right tooling.   

Now all of this being said you need to have your lathe setup properly.   If the lathe is new it should be disassembled, cleaned and lubricated.     Reassembly should verify that all parts are properly fitted, gibbs adjusted and so forth. A close inspection of the tool post should be made.  After all of that the cutting edge of the tool must be on center.  

One other thing here proper spindle speed and chip load is a must!     Your post has me thinking you might be having an issue here.  Different tool geometries require different depth of cuts to work properly.  When looking up tool geometries on line id suggest using grinds advised for finish work.


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## goldstar31 (Dec 27, 2016)

Wizard69 is pretty much 'on the ball' so perhaps I can leave you to digest the information he gives!

Honing is where most newcomers express difficulty and if you do need experience, I would suggest that a jig might avoid rounding corners- which spoils things.

I would therefore commend you to a simple book like Ian Bradley's Shaping Machine and Lathe Tools book by MAP.

It is as old as tea, some of it is pretty dated and you may have to buy it second hand. Mine is 1976 and falling to bits but it gives a simple jig which ensures 110% results. 

Martin Cleeve in his Screwcutting in the Lathe book describes how he approached things. Nothing wrong in that whilst some of the ol(ish) ornamental turning books and articles describe something called a Goniostat or Goneotat which really old turners could hone so well that they could turn ivory and ebony as well as exotic hardwoods. All this dates back to Maudsley and Holapffel days.
You MIGHT get other suggestions but some of the work that these old people performed was truly mind blowing.

Cheers

Norman


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## joco-nz (Dec 27, 2016)

goldstar31 said:


> This is quite achievable and seems to be now forgotten and better. It  is possible to get that 'barely perceptical swarf' which the old timers like Cleeve published.
> 
> 
> Years ago, the late Jim Early and I tried to republish and were threatened with legal action by the then new owners of Model Engineer.
> ...



Norm - can you remember the issue(s) the relevant articles were published in Model Engineer?  I think I now have access to some of those very early issues through a club.  Still under copy right no doubt but I would be interested in reading the articles.

Cheers,
James.


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## kiwi2 (Dec 27, 2016)

Hi Paul,
             If you want a really good finish on the lathe I would suggest you buy a diamond cutting tool from Eccentric Engineering. Sharpening the HSS tools is easy using the holder which comes with it. There is only one angle to worry about. Using square tool bits gives a good finish but if you use a round one for the finishing cut it will give a mirror finish. It works well for wood as well.
Regards,
Alan C.


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## goldstar31 (Dec 27, 2016)

I have a copy- somewhere and I've just come home from Christmas visit to family.

As far as the index goes, it is in Volume 115 and Issue 2882 and called 
'Setting a Lathe to one ten thousandth'

Come back - if I can help further

Cleeve was an extremely talented writer. Not always accepted- like me





None of your blokes know another Antarctic Auster 7from 1949? If I can get travel insurance which is extortionate for an old fart of nearing 87, I guess that I'll be in North Island  in November.

Regards

Norman


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## BillWood (Jan 19, 2017)

kiwi2 said:


> Hi Paul,
> It works well for wood as well.
> Regards,
> Alan C.



Hello,

Could you elaborate on using tangential bits to cut wood please ? 
Do you put a rounded corner on them ?
Do you turn the bit around 90 degrees and use it as a shear tool ?

Bill


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## pmdevlin (Jan 19, 2017)

Hi all
many thanks for all the replies. Here is where I am at. Sharpening my own tools, well I was thinking if the cutting angle wasn't perfect I had ruined the tool. I have found some hss tools, and had a go, and was pleasantly surprised that the finish was better. On close inspection (these all came from a deceased friends collection) he had been making specific tooling no doubt for specific jobs. Can these be continually changed by me if I want to, maybe a silly question but do they lose strength?

Back to the indexable set I have, well now I realise they are cheap. A set of 5, £30 from the Northern engineering show would probably mean not that great now I have started looking around?
I intend to go to Doncaster this year, so will pick up some tools there, and some books, cant beat a good read.

What would I like to achieve? well my machining really is basic things for model boats and planes, simple fittings etc that cant be bought, searchlights, handles and the like, its much nicer to make you own, and because of scratched finishes I then spend ages with wet/dry and polishing cloths. I will post a video and some pics.

Machine is a Chester conquest, I am second owner, although when I got it some 6 years ago it had not been used. I have been deliberating what to do with it, over time (and not much use) the backlash and as I call it slop has increased, parting takes two cuts to stop it kicking back, and the cross slide has excessive play that I cant seem to get rid of. Chester at Deeside is half hour away, I have attempted to contact them twice since Christmas, they still have not replied, with the intention of asking do they do any courses, like Axminster do (in Warrington) or offer any sort of service/set up training.

So, its sort machine out, and touch/buy 

http://www.thedoncastershow.com/

I'm on a budget, I use 6mm tooling, can I have a shopping list suggestion please, I cut brass and cheap ally, occasionally plastics, machine will be sorted by then!

Many thanks for all replies and suggestions, pics to follow

Paul


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## kiwi2 (Jan 20, 2017)

Hi Bill,
            The normal diamond tool holder uses a 1/4" square section piece of tool steel. (First photo).
I replaced it with a piece of 1/4" round tool steel ground to the same angle as the square tool using the guide. (Second photo).
The orientation of the tool to the work is shown in the third photo.
An example of the finish quality is shown in the fourth photo. A log of wood was machined across its end grain. What is shown is the finish achieved by the tool - it hasn't been sanded.
Regards,
Alan C.


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## BillWood (Jan 21, 2017)

Hey Kiwi2 thanks for the details on the wood finish.

And now a question please, relevant to the OP's initial question

A concept I've bumped into a few times and never really understood is relationship between tip radius, feed rate and depth of cut for final finish.

I've sometimes seen things like this written in books and internet and my broad understanding is that the intention is to cut a "flat" mirror finish as opposed to a " corrugated threaded " finish.

_"Make sure the tip radius is slightly greater ? than the depth of cut and greater ? than the feed rate" _(Am guessing that this makes it impossible to cut a "thread")

As a relative newb my best finishes are always obtained by using a shear tool, or by using a knife tool set round to rub, or a tangential with a rounded nose - I have never been able to get a conventional round nose finishing tool to give me as good a finish as these other methods. Am sure that both the OP and myself and maybe others would benefit if somebody could point to a good book or website or maybe say a few words that would help to understand relationship between doc/feed rate/tip radius on a hss round nosed finishing tool. Sometimes I get my knife tool ground just right and can get a wonderful finish when set round to almost rub and like it says in the old Sparey/Westbury/Mason books can do 90% of my cutting with just the one knife tool.
_
*Thanks

Bill*
_


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## goldstar31 (Jan 21, 2017)

Whilst I agree with most of your remarks,  whatever you do on a lathe cuts a thread- of sorts. The only time that one doesn't is when the lathe is converted to a shaper.

However, however, a shaper tool and lathe tool take on the same configuration. Read ' Ian Bradley' if you doubt me.

As for rounded noses, you are actually lengthening  the cutting edge - which theoretically should require more horsepower.

Having 'cantered over the course' myself, you should also read Martin Cleeve on the subject where he removes then thousands of an inch.  Unquestionably, I do not have all the answers but the question of chip breaking tools comes in. Your excellent referees never got there as I doubt few had the tooling to do it.  Further, this mental difficulty of separating wood from metal seems to persist.

For an earlier generation, the same tools were used to cut wood and metal. If you read Holzapffel- and many more, they cut not only wood, metal and stone to machine bone and ivory. 

For my part, I used to cut lignum vitae with metal cutting lathe tools. The turnings were virtually brown grease and went to polish the result.

I hope my comments add to your interesting and well thought out discussion

Norm


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