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  1. #1
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    Default Grinding lathe tools

    I typically grind all my lathe tools with a sharp knife edge, that is the way I do woodworking tools as well. I've seen in books that with some lathe tools, they round the edge and claim that it's stronger and gives a smoother finish. To date when I've tried I get no better results than with a knife type profile. I would say I'm doing something wrong, anyone know of any online videos that demonstrate this rounded profile, to my mind it sounds wrong that you would round over any edge but quite a few sources suggest it.

  2. #2
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    Default

    Quote Originally Posted by Tiger View Post
    I typically grind all my lathe tools with a sharp knife edge, that is the way I do woodworking tools as well. I've seen in books that with some lathe tools, they round the edge and claim that it's stronger and gives a smoother finish.
    I usually round the front vertical arris of a tool. It's meant to make the cutting point more durable and provide a better finish on the workpiece. Is this the rounding that you are referring to ? I think a sharp arris will wear faster and be prone to fracture.
    -- Steven Saunderson

  3. #3
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    Default Tiger

    As a seeker of truth take a trip to your nearest TAFE that teaches Fitting and Turning and look at this publication used with the courses, Fitting and Machining by Ron Culley, this book not only will explain the whys and wherefore of Lathe tools it will discuss in depth metals and so forth then you can make decisions re tool aspects to suit both the tasking and approach.

    Check with Ken( Neksmerj ) on the forum and draw down the Hercus Handbook that is in short a primer in tool sharpening and applications.

    So now you have two choices that will both cover your budget or enlarge your knowledge base with reference manuals that explain in detail why and how to cut and shape tools.

    There is a universal tool holder that has a guide jig to enable grinding by numbers to suit that tool holder,info in model engineering mags another valuable source of info at your local library as well as groups formed for the purpose of self help.

    Have fun and enjoy Peter

  4. #4
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    Default

    Hi Tiger,

    These links maybe of help to you?

    http://www.sherline.com/grinding.htm

    http://mmu.ic.polyu.edu.hk/handout/0102/0102.htm

    I will take some photo's at work tomorrow hopefully, in order to explain the difference between the two (sharp & radiused) toolbits. I presume we are talking about cutting metals of a sort?

    Regards
    MH

  5. #5
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    Default

    Assuming you are referring to the profile of the cutting tool, from a plan view perspective, razor sharp tools are intended to get into a shoulder with minimal radius.

    You will not achieve a fine finish if you are simply turning down a piece of material, unless you have a very, very fine feed rate, and you've got all day to stand there watching paint dry?

    If you think about it, what you are doing is effectively cutting a fine thread on the OD.

    For a nice finish, you need a nose radius of approx 0.5mm or bigger. Subjectively, hand ground HSS beats carbide tips, hands down for us novices. Try turning down a piece of square bar, and without warning, the carbide tip chips, and is buggered. There goes another few dollars. Carbide tips are perfect in CNC machines where all the parameters are closely monitored, and cutting fluid is abundant.

    As Penpal suggests, there's a lot of good info in the "Text Book of Turning" by Hercus.

    I can send you a pdf copy if you send me your email address. The quality is not as good as the hard copy book, then again, it's virtually free.

    Ken

  6. #6
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    Jan 2004
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    Mackay North Qld
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    Default

    Hi Guys
    In making a comment on the different nose shapes of HSS lathe tooling its important to think about the function of these tools and how they work. I see the lathe as a rotating vice and the tool as a sharp chisel to pare of the material sections that don’t belong there. The shape ,angle of approach, center height and tool clearances are all essential elements for success. Each tool and nose shape does a different job. Finishing tools are a different nose shap from roughing tools for example.

    While being nowhere close to being an expert on the subject, I would like to offer my somewhat different perspective on the preparation and use of HSS cutting tools. My background of course was as a boilermaker .Working for years along side of fitters and turners I was able to observe the use of HSS tools by these tradesmen.

    What is apparent is that these guys each had a toolbox full of different HSS cutting tool shapes which could be examined and then slightly modified by regrinding and shaped to the required work application. Later on in TAFE I also had access to fitters and the opportunity to ask them why they chose particular tools for specific jobs.

    Like any other skill, tool shaping and even learning the correct application for a particular shaped tool is a skill that must be developed. My interest in lathe work has only come as a result of the necessity to teach basic lathe operations to high school students over the last several years.

    Early on in my high school career, I ran into a gent who sells cutting tools for a living. Its more than just a living to him as he seems to have made a detailed study of tools and the chips they produce.
    He can look at the chip produced and tell you things like, if the shape and approach angle of the tool employed is correct. What I have gained from him is the understanding to look at what chip shape the tool is producing and work from there as a bit of a diagnostic.
    It is very satisfying to watch a kid drilling either on a lathe or sometimes a drill press and to advise him that the drill is cutting on one edge based upon the evidence of the chip or swarf ejected. To take that drill and regrind it to a state where it delivers perfect twin swarf spirals.Unfortunately not many want to learn something even as simple as this.

    Older fitters now tell me that true grinding of HSS tool shapes is slowly becoming a lost art. Hopefully a few amateurs such as our selves can delay this.

    I also want to echo the comments on the Hercus book and Tafe textbook on Turning and Machining -the best $80 or so I have spent this year.
    Cheers
    Grahame

  7. #7
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    Default

    Thanks for sharing your thoughts on this.

    Peter, I have the Fitting and Machining book, I'm now waiting for the movie to come out . It's very technical but authoritative.

    MH a picture or two would be great, maybe I'm rounding off too much.

    Ken, I'll send you some details a little later and Grahame there is a lot to this grinding metal lathe tools to get a good result.

    Now, I've also seen it stated that you should hone your tools, how do you hone a rounded surface effectively???

  8. #8
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    Default

    Thanks for the info and links.

  9. #9
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    Default

    Just give the top and edge of your tool a rub with a fine stone,it just takes off any little burr left from grinding.

    Make sure you have water or solubile oil handy so you can dip your tool into to cool it off when grinding. Try not to get it to hot.

  10. #10
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    Default

    Just another thing the nose radious you give your tool can also be dependant on your feed rate.

    I mainly use indexable inserts on my hercus but then i generally turn large items,so the rpm required for inserts is not really a problem for the limited rpm range of my machine.

  11. #11
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    Default Honing Lathe Tools

    I use a diamond file that is double sided, one side medium and one side fine from Mcjings. Works for me.Ken thanks for helping with the Hercus Manual etc.

    Peter

  12. #12
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    Default

    Hi Guys,

    I have just found a south bend scanned booklet on tool grinding. Well ! really I found it ages ago and could not remember where I found it second time round after originally reading this post.
    here tis
    http://www.akpilot.net/How%20To%20Gr...he%20Tools.pdf

    Its well worth saving to disk.

    Grahame

  13. #13
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    Nov 2004
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    Default

    Thanks, Grahame, that's a good link.

    Haven't found any online videos and not many commercial ones either, bit surprising given the complexity of the topic, would be good to find a range of different grinds for specialist jobs, anyway I'll keep looking.

  14. #14
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    Default

    Quote Originally Posted by Tiger View Post
    Thanks for sharing your thoughts on this.

    Peter, I have the Fitting and Machining book, I'm now waiting for the movie to come out . It's very technical but authoritative.

    MH a picture or two would be great, maybe I'm rounding off too much.

    Ken, I'll send you some details a little later and Grahame there is a lot to this grinding metal lathe tools to get a good result.

    Now, I've also seen it stated that you should hone your tools, how do you hone a rounded surface effectively???
    Hi Tiger,

    Sorry for no having posted any photos (images) yet but our digital camera is out of action. So the wife is going to borrow one tomorrow, so hopefully it won't be too long before I can deliver on that promise I made earlier!!.

    Btw, Ken although I wouldn't totally disagree with you about tipped tools they are just as good as HSS bits on non-CNC machinery, that is if the cut is consistent otherwise breakages will happen as you have found out to your cost. Today I was machining round mild steel bar with a tipped cutter and got excellent finishes. The secret is (as you mentioned) copious supply of coolant but a slow speed anything between 35 and 110 rpm and a feed rate that produces a continous curly piece of swarf even cuts as small as 0.2mm worked very well.

    Cheers
    MH

  15. #15
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    Default


    Quote Originally Posted by pipeclay View Post
    Just give the top and edge of your tool a rub with a fine stone,it just takes off any little burr left from grinding.
    Quote Originally Posted by pipeclay View Post


    Make sure you have water or solubile oil handy so you can dip your tool into to cool it off when grinding. Try not to get it to hot.

    Pipeclay, how do you give the top a rub when it has a top rake grinded into it, hard to get the tool to sit flat on the stone?


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