# surface finishs



## drsorey (Jul 27, 2014)

Newbe discussion needed.
Surface finishes
I have a sb heavy 10 and a set of 3c collets that i want to use.  A spindle adaptor would really be nice.  I have a taper attachment and have gotten the taper pretty much spot on and can get what I think is a relatively clean surface finish.  
I used cold rolled steel, turned it using a high speed bit, very, very lightly filed it, polished it with 400 grit paper, but still has a slight "ridging" that is very even but is certainly not polished. 
Question? 
Is cold rolled steel ever going to get a better finish?
Should I go to a finer grade of paper, at the risk of loosing the taper angle?
Is a smoother finish going to increase the "grab" of the SB taper?
I would really like to hear some of the more experienced guys thoughts.

Thanks
D Sorey


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## Tony Wells (Jul 27, 2014)

Self-holding tapers should be as smooth as possible for maximum grip. I believe I would recommend using a coarse paper first, backed by a file or similar flat tool. This should get rid of any "ridges" present. Then you should check the taper with a indicator and your taper attachment. It's likely to have been changed a bit by the first "polishing". You can correct any error as you progressively go to finer and finer abrasive. 

"Cold Roll(ed)" is a term commonly used to identify a material, but in reality it is a method of processing many steels. Typically, we find what most are calling "cold rolled" to be a 1018 or 1020 steel. Is is not capable of being hardened by quench and temper, but can be case hardened. As far as machining qualities, there are much better steels to get a nice finish, and 1018/20 is difficult to cut a fine finish directly with conventional tools. Most of us who would use it either try to avoid applications where it needs a high polish, or give in to machining it at high speed with carbide tooling and finishing with abrasive.


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## DMS (Jul 27, 2014)

CRS is notorious for being hard to get a good finish on. Some things can help, in particular, nice sharp HSS tooling, some cutting oil applied on the finish pass, and a generous nose radius on the cutter. You may also look up the "vertical shear tool". It's a fairly simple cutter grind that gets a really good finish. It will only take a couple thousandths off though, so you need to remove most material with another cutter.


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## drs23 (Jul 27, 2014)

Cold rolled just doesn't finish pretty in my experience. You've done everything that I've done to get the finish like you're looking for. I would use a rougher grade of emery cloth to begin with though. I start with a file to get the burrs or whatever the correct term is knocked down then 180 then 320 emery cloth and call it done. I guess you could go as far as 400 and down but I've not tried to win a beauty contest with the part. I just like it to be presentable.

Of course your choice of cutting tool along with the infamous speed-N-feed selection will go a long way to having a 'cleaner' part to begin with.

Hope this helps a little.

Dale

edit: I see DMS replied with probably a better alternative while I was typing. I'm going to give that a try as well.


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## Thoro (Jul 27, 2014)

Try a vertical shear tool ground from hss. It is extremely easy to grind, and will only shave up to 3 thou maybe, but may help you out with your finish on CrS and hrs. Google vertical shear lathe tool and look at images.


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## Ray C (Jul 27, 2014)

In addition to all the correct information provided by others, you will always get ridges in the finish when feeding the cutter by hand.  When metal cuts, there is a high level of pressure right at the interface between the material and the cutting edge and if the bit does not move with perfect "constant velocity" it will leave ridges in any place where the bit moved too fast or too slow.  It's not humanly possible to move the bit by hand with perfectly even consistency.  Only gears and lead-screws driven by the motor (or a CNC controlled set of motors) can do that.  -And thus, you will always have those ridges.

This applies to hard and soft metals alike but, it might be less noticeable on harder metals...


Ray


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## Mark_f (Aug 4, 2014)

I have made several MT 2  and B&S #9 tapers. I cut them with the compound as I don't have a taper attachment. I also have to pick up the taper and cut it in two stages to get the length as the compound only travels around two inches. I use what you all call cold roll and I get it from scrap dealer or lying around. I cut with HSS bit and the lowest speed on my South Bend ( lathe. My finish cut is always .001" or less. Then I polish it with 400 grit paper. They fit good. I put the B&S taper in my spindle by hand, it sucks right up and I have to tap with a mallet to get it out.

Mark


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## hermetic (Aug 5, 2014)

All of the above is correct and good advice, but also remember that the finish on the work is a direct reflection of the finish on the tool. In other words, if you are grinding your own tooling and the grinder leaves vertical striations on the tool, you will also get these on the work. If you use HSS and grind them yourself, use a fine stone, then finish with a slip stone, and check them with a magnifying glas. The better the polish on the tool, the better the polish on the work. Using commercially made tooling/carbide etc will only work if your machine has a rigid enough set up to handle the feeds neccasary to get a good finish with carbide. Remember, carbides main advantage is not its hardness or sharpness, it is iys ability to remove large amounts of metal and run HOT without loosing its hardness. This only works well with the rigidity found on industrial lathes, that is, after all what it do.
Phil

- - - Updated - - -

Mark_f
              Excellent work on those tapers, they look awesome, and if they fit that well, I think they are "near enough" Well done!
Phil,
East Yorkshire


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## mattthemuppet2 (Aug 7, 2014)

In addition to the shear or contrary finishing tool, a bit ground with a large nose radius can be used to take those ridges off. It'll leave ridges of its own I guess but much smaller and wider. It's another option


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## JR49 (Aug 7, 2014)

mattthemuppet said:


> In addition to the shear or contrary finishing tool, a bit ground with a large nose radius can be used to take those ridges off. It'll leave ridges of its own I guess but much smaller and wider. It's another option



Once again "For all the beginners here" (maybe I'll start using that quote to start all my questions) what do you, or anyone more knowledgable, consider a LARGE NOSE RADIUS? Thanks, JR49


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## mattthemuppet2 (Aug 8, 2014)

JR49 said:


> Once again "For all the beginners here" (maybe I'll start using that quote to start all my questions) what do you, or anyone more knowledgable, consider a LARGE NOSE RADIUS? Thanks, JR49



ah, sorry  I don't think there's really any kind of rule. No nose radius would be just the point from 2 sides being ground, a small nose radius would be if you just knocked of that point with a stone or hone and then up from there. The point really is that the radius of a large nose finishing bit would have to be 2-3 times larger than that on the bit you used before it. It won't remove a lot of material as the cutting edge is huge by comparison, but it should nicely shave off the imperfections left by the previous bit, especially if you run it at a higher rpm or slower feed than before.


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## NEL957 (Sep 1, 2014)

Something I like to finish my HSS is a 4" x 36" belt sander with a wore out belt on it to polish up my cutters. Just be careful to not drive the point into the belt or you will have a disaster. When I do mine I will lock them up in a machinist vise, never had a problem.
Good Luck
Nelson Collar


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## John Hasler (Sep 1, 2014)

JR49 said:


> Once again "For all the beginners here" (maybe I'll start using that quote to start all my questions) what do you, or anyone more knowledgable, consider a LARGE NOSE RADIUS? Thanks, JR49



"How to Run a Lathe" suggests a 1/64" radius for a roughing bit and 1/32" to 1/16" for finishing.


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## NightWing (Sep 2, 2014)

It helps to remember that when you are turning with a sharp pointed tool, you are actually cutting a very, very fine thread.  Adding a nose radius will definitely help eliminate the "thread" you see.


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## chuckorlando (Sep 2, 2014)

A large radius on a cutter is really pretty dang small ahaha. My 9x20 lathe is rigid enough to use carbide and get a sweet finish so I would think most machines can get a good finish from it. It's the high rpm on small stuff that would concern me not the rigidity so much. The largest factor I have found in finish is feed rate. If I see marks I slow it down. Provided the tool is good and material will finish ok.


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