Small problem turning brass


Results 1 to 12 of 12

Thread: Small problem turning brass

  1. #1
    Registered
    Join Date
    Sep 2006
    Location
    Netherlands
    Posts
    7
    Downloads
    0
    Uploads
    0

    Default Small problem turning brass

    Hi,

    I'm a beginner (hobbyist) lathe worker and I've just started my first project, the pedal engine from Bengs.
    I've turned the first part, which seems the easiest to me. The problem is that at the end of the cut, there is a bump of material appearing, which of course ruins the dimensions (see photo).
    How can I prevent that? And what can I do about it now?

    I used a hard metal bit. Speed was about 2000 rpm (I can't go faster). The (turned) diameter is 5 and 4mm. Feeding by hand.
    Every pass I stopped a little to early, except for the last pass, which was up to the right dimension and I then retracted the bit while running, to finish the end.

    Small problem turning brass-img_0433-jpg

    Any insights are highly appreciated.

    Regards,

    Remco Poelstra

    Similar Threads:


  2. #2
    Member awerby's Avatar
    Join Date
    Apr 2004
    Posts
    5728
    Downloads
    0
    Uploads
    0

    Default Re: Small problem turning brass

    It looks like you're pushing the metal around rather than cutting it, which upset that bur on the end of your journal. That might be due to your tool's lack of sharpness, incorrect grind for the material, or a "built-up edge" on your tool tip; here's what Wikipedia has to say about that: Built up edge - Wikipedia, the free encyclopedia

    Brass cuts a little bit differently than steel, so you need to sharpen your tool differently to cut it effectively. The tool generally wants a zero to negative rake for brass; zero means that the edge presented is square (90 degrees) a positive rake is somewhat acute while a negative rake is a little bit obtuse. Here's an article that talks about this in more depth: Basic Lathe Tool Grinding

    [FONT=Verdana]Andrew Werby[/FONT]
    [URL="http://www.computersculpture.com/"]Website[/URL]


  3. #3
    Registered
    Join Date
    Sep 2006
    Location
    Netherlands
    Posts
    7
    Downloads
    0
    Uploads
    0

    Default Re: Small problem turning brass

    Thanks for your post.
    It's not good if I've to learn how to grind my tools first. I've received just enough material to get the model build.
    The current tool is perfectly clean, so it's probably not due to a built-up edge. It does have a slight positive rake, so I think I've to flatten it a bit then. How deep must this flat region be? Just the sharp top off?
    Do you guys have tools for each of the different materials? Or do you grind them each time?

    Regards,

    Remco



  4. #4
    Member awerby's Avatar
    Join Date
    Apr 2004
    Posts
    5728
    Downloads
    0
    Uploads
    0

    Default Re: Small problem turning brass

    If the only problem area is positive, you should be able to cut it off if you're careful. It's hard to describe exactly how to shape your tool (study that article I sent you), but if you're new to this (or even if you're not) it helps to get enough material for several tries. As well as grinding, it's often necessary to use a sharpening stone to refine the faces of your tool after grinding. Tool-grinding is a big part of lathe work, and yes, you need different-shaped tool bits for each different kind of material, as well as for different angles of approach, different tasks, and different stages of an operation. You end up with piles of these things...

    [FONT=Verdana]Andrew Werby[/FONT]
    [URL="http://www.computersculpture.com/"]Website[/URL]


  5. #5
    Registered
    Join Date
    Mar 2014
    Posts
    19
    Downloads
    0
    Uploads
    0

    Default Re: Small problem turning brass

    Turn the larger diameter after turning the small diameter. Won't have that 1 burr atleast. File would deal with burr on the hex. If you are doing more of these, check that the tool is on centerline. If it's above you maybe be rubbing the material mostly and causing that burr. Post a picture of the cutting tool.



  6. #6
    Member
    Join Date
    Feb 2009
    Location
    usa
    Posts
    6028
    Downloads
    0
    Uploads
    0

    Default Re: Small problem turning brass

    Looks to me the tool is above centerline.



  7. #7
    Registered
    Join Date
    Sep 2006
    Location
    Netherlands
    Posts
    7
    Downloads
    0
    Uploads
    0

    Default Re: Small problem turning brass

    I've fixed the burs by re-turning the larger diameter again and filing of the outer burs. It looks quite acceptable now, for a first part.
    I've verified the height of the tool using the tailstock center. It looks to me it's OK, but it might be a very very small amount of. I assume that even a very very small amount will ruin the piece?
    I've a few last operations to perform on the brass, then I can cut it off and the rest will be scrap, so I can do some tool height and tool shape tests then.



  8. #8
    Registered
    Join Date
    Nov 2011
    Location
    usa
    Posts
    16
    Downloads
    0
    Uploads
    0

    Default Re: Small problem turning brass

    As a general rule I try to turn the smaller diameter first both to minimize burring and also to maintain the rigidity of the part. In other words if you were turning the whole thing down to 1/4" (6.35mm) diameter and then went back to reduce the diameter at the end often there isn't enough strength in the 1/4" (6.35mm) portion to hold the part rigidly. It may deflect instead of cut causing tapers, chatter and otherwise poor finish. Also, when you reach the shoulder on the last pass it is good practice to back the tool straight out from the part creating a nice flat and clean surface on the face of the shoulder. One last thing I want to point out is that most carbide insert lathe tools have a 60 deg. angle at the cutting edge and you should usually have it turned so that the cutting face of the insert has a slight angle away from the face you are cutting to thus leaving a small bit of stock on the part to skim off as you back the tool away from the part.

    Moldmaker extraordinaire running many machines at B&D Machine, Inc. Tolland, CT.


  9. #9
    Registered
    Join Date
    Sep 2006
    Location
    Netherlands
    Posts
    7
    Downloads
    0
    Uploads
    0

    Default Re: Small problem turning brass

    I've a few more of these parts to make for the model, so I will try the small-diameter-first approach.
    I did back the tool straight out on the last pass, it's one of the few things I do remember from the lathe courses .
    Quote Originally Posted by chrisgraf2 View Post
    One last thing I want to point out is that most carbide insert lathe tools have a 60 deg. angle at the cutting edge and you should usually have it turned so that the cutting face of the insert has a slight angle away from the face you are cutting to thus leaving a small bit of stock on the part to skim off as you back the tool away from the part.
    Uh, I have no clue what you mean with this. Probably a shortcoming in my English.....

    Remco



  10. #10
    Registered
    Join Date
    Nov 2011
    Location
    usa
    Posts
    16
    Downloads
    0
    Uploads
    0

    Default Re: Small problem turning brass

    Your English is great. I am just bad at explaining things. I'll try to post and image. My first attempt on this forum.
    Small problem turning brass-lathe-tool-jpg

    A poor image but if you click on it it will be viewable.

    Moldmaker extraordinaire running many machines at B&D Machine, Inc. Tolland, CT.


  11. #11
    Registered
    Join Date
    Sep 2006
    Location
    Netherlands
    Posts
    7
    Downloads
    0
    Uploads
    0

    Default Re: Small problem turning brass

    Cool, thanks.
    Do I need to make sure the slight angle is as slight as possible? Or a bit larger? My tool has a bigger angle than the one you've drawn, so both angles are always very small. I've to be careful to make sure there actually is a slight angle.
    Small problem turning brass-img_0434-jpg

    Last edited by thoru; 01-15-2015 at 02:55 PM. Reason: removed duplicated image


  12. #12
    Registered
    Join Date
    Nov 2011
    Location
    usa
    Posts
    16
    Downloads
    0
    Uploads
    0

    Default Re: Small problem turning brass

    I believe it's mostly to assure that you are cutting furthest with the leading edge and not with the part of the cutter that is farther away from the center line of the part. Another lesser concern would be that too great an angle may tend to pull the part into the cutter, taking a deeper cut as you put force along the cut. This second concern is more important with a dead sharp cutter like yours. Many parts require a sharp corner but if that is not a requirement, most cutters have a radius at the cutting edge. This provides a better surface finish and a more even pressure in both directions (along the length of the part and in towards or away from center line).

    Small problem turning brass-lathe-tool2-jpg

    Moldmaker extraordinaire running many machines at B&D Machine, Inc. Tolland, CT.


Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

Small problem turning brass

Small problem turning brass