turning 4140-w-small lathe
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  1. #1
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    I have a small 9"X23" chinese lathe and am trying to turn/face some 3" round 4140. I am very new to this and have gotten tow here I can turn about .010 at a time-w-carbide but cannot seem to be able to turn-w-HSS tools. I try and shape/sharpen my own tool bits and shape the HSS tools-w-similar profiles as the carbide. My lathe will only go down to 125 rpm. Is this still too slow? According to a formula I got it should be about 77 RPM but man this really seems slow.

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    HSS tools need more clearance and top rake angle than carbide to get them to cut, you really need to get a book that shows you how to grind them.A good one every machinist should have is the Machinist Ready Reference, it's about $25 and tells you exactly how to grind the bits.

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    Here's a link that might help...

    http://155.217.58.58/cgi-bin/atdl.dl...24/Ch7.htm#top

    Scroll down until you come to the section about cutting angles for HSS tool bits.

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    I could not navigate to this link.
    I will get the book that was recommended.
    Is HSS OK for 4140

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    You didn't state what condition your 4140 is. Annealed or heat treated makes a big difference. If you are getting OK results with carbide, stay with it. If you want to use HSS, you must learn the proper way to grind and sharpen it.
    Some people don't understand why their tool worked fine cutting soft stuff but is terrible with steel.
    Find someone to mentor and show you how to do it. Some things are tough to learn on your own.
    Good luck.
    Les

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    One more site - click on link below:

    http://shopswarf.orcon.net.nz/turntool.html

    I use HSS to turn 4140 annealed and 4140 HT on a 9" South Bend and don't have any trouble at all.

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    Mike - thanks a ton. Have you by chance got a picture of a cutter that you have shaped for facing?
    The 4140 I have is annealed so I understand it should not be too tough on the HSS.

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    Challenger, I don't have a digital camera so can't post any pictures.

    Take a look at the following site. I think this information will get you a good start on grinding a tool bit that will work great for you.

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

    You might get a little frustrated at first, but before you know it, you'll be able grind tool bits very easily. So KEEP at it!

    By the way, I recommend that you don't buy any pre-ground bits - their too expensive and you will never learn the fundamentals of cutting tools.

    Mike


    [This message has been edited by Mike Burdick (edited 04-04-2003).]

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    from a novice that has done a little grinding of my own tools, the Sherline page is the best. Has easily understood examples that you can really see what they are trying to say in. Very well done I'd say.

    You are right - it is hard to learn and I think the reason it is so hard is the poor drawings that make it really difficult to understand the viewpoint and the angles involved.

    The drawings of the tool in the grinder really tell it I think.

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    I sharpened a bit as per the shealine site and there was aome improvement however I am still a ways away from being happy-w-the lathe or perhaps my ability. I am trying to use the profile of the right hand cutter in the document to face my stock but it doesn' twork very well. It leaves a rough finish and there seems to be too much heat. I am running at 250RPM

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    Challenger,

    Try facing from the outside to the center, your bit won't need as much clearance as if you were going the other way. Also try this: Grind the bit so that it has a sharp point and reduce to lowest feed rate. If it cuts okay, but leaves a rough finish, then round the bit's point a little and try again. I think Sherline's site suggested just "break" the point a little. Which is good advice.

    When you grind the bit keep this in mind...the cutting edge is the only thing that can touch the metal, anything else will cause rubbing and prevent the bit from cutting the material. Also, the steeper the back rake the less power needed to cut the metal and therefore less heat will be generated.

    Please don't get discouraged....I'm sure you'll figure out the problem and it most likely will be something very simple.



    [This message has been edited by Mike Burdick (edited 04-04-2003).]

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    I will try a steeper angle on the rake. I understand this to be the angle on the top of the tool. I have the cutter feeding into the stock from outside as I have never had any luck going from center outwards. I have about a 10 degree angle on the face that will be closest to the end of my round stock and I angle my tool post so it enters the face of the stock at about a 10 degree angle. The other ground face of the cutter is ground off the front of the HSS square and ends up a little less than 90 angle from my first angle. Then the top of the cutter is "hooked"-w-about a 7-10 degree angle. I am thinking you are saying to make this top face or hook steeper? I am having a bit of trouble understanding how this sharp edge will peel off metal but I will try it. On another subject I hear the words "chip breaker" refered to from time to time. Can you explain a chip breaker bit please?

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    250 is too fast for 4140 using high speed tooling.Watch your cutting edge.Is the color changing from silver to a brown or blue? If so you are burning it up.Also put a lite coating of cutting oil on part.

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    I have not had a chance to go at it again but hope to on Mon. I will try slower. The cutter has not changed but it did produce blue chips so I know too much heat was there. I hope to have a machinist friend take a look at my attempts. Is there supposed to be a rake on the top of a facing cutter? Right now the cutter is raked from high to low on the top but is straight from front to back. In other words there is still the "factory" edge on the top/inner edge. If I remove this edge and just have the point left I will have to reshape/grind an entire new cutter profile if it goes dull. Otherwise the cutter edge will no longer be on the center of the stock.
    Can anyone explain what the term "chip breaker" means?
    Howard Christian

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    Howard,Im not very good at explaining things as others are but Ill try.The chip breaker is any means of disturbing the metal flow over the tool surface.They are usually ground into the tool and shaped as a mini ditch or such.This causes the chip to flow into the "ditch" and make it change its flow direction quickly causing the chip to break.Kind of like a break wall in a large body of water.Water hits it and goes from a wave to spray.Not a great example.
    The older carbide insert tools had a beveled pad that sat on top of the insert and forced the chip to turn up quickly causing the chip to break.
    How about picturing an ice cream scoop as it is drug through the ice cream.The chip breaker preforms in the same manner and is shaped in a simular way. Hope this doesnt confuse you. As I warned you I dont explain things clearly as I would like.:> )

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    I understand completly and your explaination was good. Is the chip breaker essentially for avoiding the large spring like metal that comes off cuts? In my short and not very succesfull experience I have noticed these long springs of waste to be quite a problem and it would be easier to have small chips just fall to the bottom.

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    yes, chipbreakers are very important, a friend of mine almost had his leg cut off at the calf from a spiraling chip. CHIPBREAKERS A MUST HAVE!!

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    Slow down your rpm. Your formula is correct, around 75 rpm. If you think this is too slow, increase your FEED rate. Heavier feed will help break up chips, as well as look like you are getting somewhere.

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    I'm curious why you would post on a 12 year old thread? D

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    Quote Originally Posted by Don Nielson View Post
    I'm curious why you would post on a 12 year old thread? D
    Because I was looking at "New Posts" . . . I guess the new software still has a few bugs, as a 12 year old post should not have been found under this heading.

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