Thread: How to achieve that polished look

Polishing is not a problem,alot of people will polish the last little bit to size.

If finish is important rather than a tollerance,polish it until your happy with the finsh,you could start with a course emery and finish with finer,I find 80 and 240 work well,a little bit of oil on the job as well as the emery works well.

As for vibration you DONT want it.

The WOBBLE should be eliminated,leveling the base will solve that problem,the lathe needs to be leveled first before opperation.

Using the tip of the tool will achieve a good finish as well as using a tool with a reasonable nose radious,slow speed and feed with constant coolant will give good results.

At times the material being machined will have a big effect on surface finish,the harder/tougher the material generally the easier to get a good machined finish,for example a piece of high tensile bar will machine finsh better than a piece of mild.

When I was teaching machining at a college in the US (I was the senior instructor in charge), obtaining a great finish was always so hard for the students (ages 19 to 55). If I remember correctly, the steel we used was "1015". It was very hard to obtain a high finish at any speed, in fact it was the most difficult operation to do. All the usual methods were tried and all failed. The cutting speed for roughing out was 80 feet/min. and the finishing speed was 100 feet/min. The diameter of the job was 1.250 inches. All the cutting tools were made from HSS. No carbide was ever used as it was considered far more important to have the students grind and shape their own tools. By doing this way, the students learnt how and why to shape their tools for the best performance.
I finally went back to the methods I had used over many years of building steam loco's and all kinds of things. I reduced the final cutting speed to the slowest speed the lathe would run, about 30 rpm. The tools were sharpened with about a 1/32 Rad. on the cutting point and the job was flooded with the "milky" soluable oil/coolant. The final cut was no more than 4 or 5 thou deep and the feed was set to the slowest available.
The other instructors watched a student performing the final cut in this manner and asked me why was I letting the student/s run the lathe so slow. Production in industry demanded "speed" and slow was unheard of. I took the instructors over to the lathe/job/student and showed them the finish obtained by this method. It was like a mirror!! And there were no tool marks to be found. Sure it was slow but for teaching and training, it was unsurpassed. The slow speed was only used for the final cut and the results were fabulous. It is essential that the tool be ground and shaped as good (read perfect) as possible and the cutting edge be honed razor sharp on all surfaces.
This is a method that works. It wont be found in any outside machine shop as it is of course, far too slow. But for all those who make "stuff" at home, this offers an excellent way to success when only HSS tools are available. Not everyone has an engine lathe with five horse power, inserted carbide tips and ceramic tooling in his/her garage that they use to churn out parts in mass production. The above description is for those who have time on their hands and want a super finish that is dimensionaly accurate. You don't have to drive your lathe at the "normal/required" speeds as set out in theory. Never be afraid to try something different, you just might be surprised at what you can do. As Pipeclay has stated, there MUST be no wobble or vibration of the lathe/part.

Thanks for the replies . Interesting Kody about the 1015 steel.....I will give that method a try. This is about the best I can get . It's just mild steel, as to what grade it is , I think its bright . The speed was about 700 , the tiniest cut was taken. Feed by hand. BTW that is the oil I use on the headstock bearings - I have asked the 'experts' and they all say a thin oil is the way to go..never use heavy oil or grease MIKE

Originally Posted by Kody

When I was teaching machining at a college in the US (I was the senior instructor in charge), obtaining a great finish was always so hard for the students (ages 19 to 55). If I remember correctly, the steel we used was "1015". It was very hard to obtain a high finish at any speed, in fact it was the most difficult operation to do. All the usual methods were tried and all failed. The cutting speed for roughing out was 80 feet/min. and the finishing speed was 100 feet/min. The diameter of the job was 1.250 inches. All the cutting tools were made from HSS. No carbide was ever used as it was considered far more important to have the students grind and shape their own tools. By doing this way, the students learnt how and why to shape their tools for the best performance.
I finally went back to the methods I had used over many years of building steam loco's and all kinds of things. I reduced the final cutting speed to the slowest speed the lathe would run, about 30 rpm. The tools were sharpened with about a 1/32 Rad. on the cutting point and the job was flooded with the "milky" soluable oil/coolant. The final cut was no more than 4 or 5 thou deep and the feed was set to the slowest available.
The other instructors watched a student performing the final cut in this manner and asked me why was I letting the student/s run the lathe so slow. Production in industry demanded "speed" and slow was unheard of. I took the instructors over to the lathe/job/student and showed them the finish obtained by this method. It was like a mirror!! And there were no tool marks to be found. Sure it was slow but for teaching and training, it was unsurpassed. The slow speed was only used for the final cut and the results were fabulous. It is essential that the tool be ground and shaped as good (read perfect) as possible and the cutting edge be honed razor sharp on all surfaces.
This is a method that works. It wont be found in any outside machine shop as it is of course, far too slow. But for all those who make "stuff" at home, this offers an excellent way to success when only HSS tools are available. Not everyone has an engine lathe with five horse power, inserted carbide tips and ceramic tooling in his/her garage that they use to churn out parts in mass production. The above description is for those who have time on their hands and want a super finish that is dimensionaly accurate. You don't have to drive your lathe at the "normal/required" speeds as set out in theory. Never be afraid to try something different, you just might be surprised at what you can do. As Pipeclay has stated, there MUST be no wobble or vibration of the lathe/part.

Kody
I also was taught this method about 55 yrs back.It does not seem to be well known these days.
It was called a "Water Finish" & used the methods you describe so well.
We could even use hardened carbon steel toolbits honed to a razor edge as well as high speed steel. Some old hands reckon the hardened carbon steel could be honed to a sharper edge, & was good for this method of finishing.
A few years back I used this method to finish turn the journals & crankpin of a crankshaft for a no 7 Bolton steam engine. The finished size was to be 0.437" dia & as you say, the finish came up like a mirror. The crank shaft was made from black mild steel plate, machined from the solid.
The engine is still running great !
Its a slow method of finishing,but precise, & a mirror finish, like no other method.
Thanks for outlining what could be a forgotten method of turning to obtain a finish.
regards
Bruce

Question: Using that slow rpm and feed method. Does the tool have normal side rake ? And, is any back rake needed ? 1/32 is a fine radius , could be difficult to grind freehand MIKE

Hi Mike,
An easy one to try is the shear tool bit, it is said to give great results
Vertical Shear Bit

And there is a bit of talk about it here just recently
Sneaking up to final dimesions good ... Bad ... Or ugly. - The Home Shop Machinist & Machinist's Workshop Magazine's BBS

Dave

I will just point out that with the vertical shear bit you don't have the top of the tool set on centre hight, you set it so it is around the centre of the tool. Once that spot gets a bit blunt you can move the tool up or down for a clean sharp edge.

Dave

hi this is how i was tough to get a good finish during my apprenticeship.Come to think of it commercial pressures were hardly mentioned. We just lost points for going over time on a job. Some times instead of a radius tool id us a honed flat tool like a parting tool.very boring when there was a long cut. Like kody said it worked

Originally Posted by Kody

When I was teaching machining at a college in the US (I was the senior instructor in charge), obtaining a great finish was always so hard for the students (ages 19 to 55). If I remember correctly, the steel we used was "1015". It was very hard to obtain a high finish at any speed, in fact it was the most difficult operation to do. All the usual methods were tried and all failed. The cutting speed for roughing out was 80 feet/min. and the finishing speed was 100 feet/min. The diameter of the job was 1.250 inches. All the cutting tools were made from HSS. No carbide was ever used as it was considered far more important to have the students grind and shape their own tools. By doing this way, the students learnt how and why to shape their tools for the best performance.
I finally went back to the methods I had used over many years of building steam loco's and all kinds of things. I reduced the final cutting speed to the slowest speed the lathe would run, about 30 rpm. The tools were sharpened with about a 1/32 Rad. on the cutting point and the job was flooded with the "milky" soluable oil/coolant. The final cut was no more than 4 or 5 thou deep and the feed was set to the slowest available.
The other instructors watched a student performing the final cut in this manner and asked me why was I letting the student/s run the lathe so slow. Production in industry demanded "speed" and slow was unheard of. I took the instructors over to the lathe/job/student and showed them the finish obtained by this method. It was like a mirror!! And there were no tool marks to be found. Sure it was slow but for teaching and training, it was unsurpassed. The slow speed was only used for the final cut and the results were fabulous. It is essential that the tool be ground and shaped as good (read perfect) as possible and the cutting edge be honed razor sharp on all surfaces.
This is a method that works. It wont be found in any outside machine shop as it is of course, far too slow. But for all those who make "stuff" at home, this offers an excellent way to success when only HSS tools are available. Not everyone has an engine lathe with five horse power, inserted carbide tips and ceramic tooling in his/her garage that they use to churn out parts in mass production. The above description is for those who have time on their hands and want a super finish that is dimensionaly accurate. You don't have to drive your lathe at the "normal/required" speeds as set out in theory. Never be afraid to try something different, you just might be surprised at what you can do. As Pipeclay has stated, there MUST be no wobble or vibration of the lathe/part.

Originally Posted by morrisman

Question: Using that slow rpm and feed method. Does the tool have normal side rake ? And, is any back rake needed ? 1/32 is a fine radius , could be difficult to grind freehand MIKE

Mike the important thing to remember about the radii on cutting tools particularly tools for finishing is that the cutting edge should span a distance greater than your feed rate. Not particularly good at explaining things but for example with a feed rate of 30 microns per rev
your tool needs to span 40 or more in order to not get that thread type pattern left on it. Rake angles are normal otherwise.

Probably clear as mud but I hope you can make sense of it.
Garry

I read Dave's links . Most of them on that forum seem to prefer the 'sneaking up' method. It depends, as one said, on your particular machine and how it is set up and the material you are turning . All down to experience . Mike

In the past I have done a Wet finish, basically a HSS flat tool, with a small nose radius, slow rpm and feed. FLOODED with coolant. feed was based on the 1/3 principle, ideally in 1 rev you would cover 1/3 of the flat tool length. The cut depth was based on 1/3 of the nose radius. rpm was 1/3 that of normal for HSS, The flat was no longer then 3mm. I can't remember the correct term is is top rake or chip breaker or something, but you only grind away perpendicular to the cut face and not along... if that makes sense, so that you get full contact with the flat on the job. Watch for chatter!!