Page 1 of 2 12 LastLast
Results 1 to 20 of 33
  1. #1
    Andy_paul is offline Cast Iron
    Join Date
    Aug 2005
    Location
    Texas
    Posts
    293

    Post

    Ok, I'm no master machinist. I'm self taught and have been doing pretty well in my home shop for the past 5 years. My biggest weakness is finding the center of a round part, and accurately drilling bolt circles, boring etc. I have trammed the head of the mill to within a thou or two. I always use a center drill, and for some reason, I always end up with holes that are off by .005-.01. I have a cheapo co-axial indicator, and I suspect it may be the problem. Its big, bulky and I always have to take the knee way down to have the real estate to use the darn thing. I'm all open to hear some better methods of how to find center.

  2. #2
    smallshop's Avatar
    smallshop is offline Diamond
    Join Date
    Jun 2005
    Location
    North Central Montana
    Posts
    4,442

    Post

    A "thou or two" may not be good enough. If you move your table to a different spot to drill than where you indicated your part at you get projected error. also,Try a test indicator in an indicol rather than your co-ax it will tell you if your co-ax is cheesy or not. I recommend Interapid.

  3. #3
    mill hand is offline Senior Member
    Join Date
    Mar 2006
    Location
    usa
    Posts
    188

    Post

    do you have a digital read out on your mill?
    are you locking the table down?

  4. #4
    Andy_paul is offline Cast Iron
    Join Date
    Aug 2005
    Location
    Texas
    Posts
    293

    Post

    Yes, I do have a dro on the mill. Would it be necessary to lock the table with a very small spot drill? The DRO never shows more that .0002 movement. I think my problem lies in the centering of the part.

  5. #5
    Forrest Addy is offline Diamond
    Join Date
    Dec 2000
    Location
    Bremerton WA USA
    Posts
    9,047

    Post

    Andy, does your mill have a horizontal spindle?

  6. #6
    Join Date
    Dec 2003
    Location
    suburbs of Ann Arbor, MI, USA
    Posts
    11,851

    Post

    Couple of suggestions...

    -use vee-jaws for a better grip on the part (4points of contact instead of 2)

    -use a singlepoint test indicator...the coax relies on a mechanism and precision alignments and fits therein. I am a fan of Interapid's offerings in that category.

    -use a 120 deg spotting drill rather than the center drill...cups the drill point better IMHO and just as rigid

    -lock table & saddle gibs as suggested...noting any change in the DRO readings and compensating appropriately.

  7. #7
    willbird is offline Banned
    Join Date
    Jul 2005
    Location
    North(very) West(very) Ohio...near exit 13 on OH turnpike
    Posts
    3,714

    Post

    On the center drill, if you use one, and I understand why, they are short, rigid, and common in the shop, so only use it to SPOT, then it is a 118 degree spotter, all is good, don't drill deeper than the drill point, and surely don't drill deep enough to actually start to get a center. I elarned how bad this is for the following drill in harder materials, the tips of the flutes start cutting first and get chipped, it cannot be good for the drill in softer material either is my thinking.

    Do yourself a favor, spoil yourself and buy an interrapid incicator, I bought a .0005 and aquired a .0001 over 20 years ago, the .005 has been repaired once, otherwise they have served me faithfully ever since, their only downside most of us machinests never see is they are effected by strong magnets, so guys that only grind don't use them...turning on a 6" permag chuck will damp .0003 tir out of an interrapid...didnt belive it until I was shown it by a man with far more experience ID grinding than me.

    Other than that hands down they are the nicest deal going, a guy turned me onto them back in 1984, so I guess it has been 22 years...I was 19 then hehe, 41 now, still on that same indicator.


    It comes to mind your mill may have some "lost motion" somewhere, so with a good indicator you can dial in, and come back to 0 on the DRO from differant directions and see what ends up happening. Also I have never seen this, BUT your quill travel may not be square to the spindle bearings, I cannot imagine how that could happen on a good machine, but you can check for it.

    Bill

  8. #8
    gbent's Avatar
    gbent is offline Diamond
    Join Date
    Mar 2005
    Location
    Kansas
    Posts
    4,559

    Post

    What Willbird said. Never move the knee after picking up location. Learn to tram head dead nuts on a 6" circle.

    When the head is not trammed dead nuts and you move the knee, the location changes. If you are out .004 on a 6" circle, and you move the knee 3" after removing your co-ax, you are now off .001 on location.

    In addition to the Interapid, get an Indicol that will attach to the spindle with a tool in place. This will allow you to use your indicator at any time. The easier it is to use, the more often you will use it. Also, get a couple of small mirrors to read the dial when its facing the column. Sticking your neck around back gets old very fast.

  9. #9
    Andy_paul is offline Cast Iron
    Join Date
    Aug 2005
    Location
    Texas
    Posts
    293

    Post

    Forrest, no I dont have a horizontal spindle, if I did, what were you going to suggest, out of curiousity?

    I guess I will have to spoil myself and get a good interapid indicator and an indicol.

    I did not think about the knee changing the position of the tram, however, I was aware that the quill would throw you off, for example, if you tram the head with the quill retracted, and make your cuts with the quill extended several inches. It just magnifies your tram error, correct?

    Thanks a lot for the input guys, I am going to hit up ebay shortly and try to find a decent indicator.

    I would love to work in a real shop for just a few weeks, I know I would pick up so many "good habits". Being self taught, I think I have taught myself some bad habits, and I need someone around to slap me out of them

  10. #10
    cruzinonline is offline Hot Rolled
    Join Date
    Apr 2006
    Location
    Savannah, Georgia
    Posts
    911

    Post

    The reverse also works, if you tram your mill with the quill fully extended, then the accuracy is higher when retracted.

  11. #11
    willbird is offline Banned
    Join Date
    Jul 2005
    Location
    North(very) West(very) Ohio...near exit 13 on OH turnpike
    Posts
    3,714

    Post

    Horizontal machines at times have "droop" to the spindle, I have seen it more than once on boring mills, really it is usually a gib on the Y axix that is loose, the end result being that the Z axis does not move parallal to the spindle centerline.

    Andy you strike me as a guy that can walk AND chew gum both at the same time, you will learn things and re-think methods over time, bumping elbows with grizzled old bad smelling machinests/tool makers/millrights will allow you to pick up more faster...we gots some of those here so your gonna learn lots, and pretty fast

    Bill

  12. #12
    Peter S is offline Titanium
    Join Date
    May 2002
    Location
    Auckland, New Zealand
    Posts
    3,962

    Post

    Andy_Paul, it sounds like you are doing OK.

    Tram your head over the largest circle you can swing (ie the width of the table). Use a dial or finger indicator and read directly on the table surface. No blocks, rings or anything else required, all will introduce error.

    Personally I tram the head without locking the knee, because I almost never use the knee lock at any time for the work I do.

    Centre you workpiece with a finger type indicator of some sort, the result will be right, whereas it sounds like the Coaxial type are not always trustworthy.

    You can even use a plunger-type indicator if that is all you have, and if you have enough room. The magnetic base will stick to your drill chuck and away you go. Sounds clumsy (it is) but use what you have.

    I don't take much notice of the suggestions about not moving the knee, sometimes you have to. Try not to, ie plan ahead.

    It sounds to me like you are getting a reasonable result for drilled holes. Use a new centre drill and a new, good quality, drill. Make sure you ease the centre drill in, using high revs, cutting oil and clear often.
    Same with the drill, slow down to correct speed, cutting oil, clear often.
    Don't use re-sharpened drills on a job like this, keep yourself a good set for jobs like this.

    I disagree with the idea of only dimpling with a centre drill. Make a decent centre in my experience.

    Maybe you need to start thinking about boring your holes if you want exact locations, but this will slow you down a lot, single point cutting is a another (harder) skill to learn!

  13. #13
    Andy_paul is offline Cast Iron
    Join Date
    Aug 2005
    Location
    Texas
    Posts
    293

    Post

    I dont mind .005 or so, but when you are lining up 4-40 and 6-32 threads, sometimes you have to drill the hole out larger to align all the holes to threads in the bolt circle.

    Thanks guys

    Tonight I am going to recheck the tram and try again.

  14. #14
    dirty old man is offline Stainless
    Join Date
    Apr 2005
    Location
    Griffin, GA
    Posts
    1,195

    Post

    I have never seen an Indicol, so I took a look in my catalogs today and found the Indicol, also, in KBC cat.,I found a new one from SPI, but it IMO, misses the boat inasmuch as as you must remove the tool from the collet/holder/chuck.
    Enco has an imitation rig that sells WITH INDICATOR, for a good percentage less than the Indicol W/O INDICATOR. Is the Indicol worth the difference?

  15. #15
    eKretz is offline Titanium
    Join Date
    Mar 2005
    Location
    Northwest Indiana
    Posts
    2,786

    Post

    I wonder that Forrest wasn't inquiring because he was thinking about the effects of indicator sag.

  16. #16
    Davis In SC is offline Titanium
    Join Date
    Sep 2005
    Location
    South Carolina USA
    Posts
    3,001

    Post

    I once had a guy working for me that had a Blake Co-ax. He scrapped quite a few parts before I made him stop using it.
    Unless the quill is in perfect tram, you are changing the center location, if you move the knee up or down, after you indicate the center of the workpiece. Error can be even more, if there is any wear or play in the knee gibs.

  17. #17
    Join Date
    Apr 2005
    Location
    Benton, IL USA
    Posts
    4,570

    Post

    One reasone most everyone recommends the Indicol + Interapid combo is that you can mount your tool and indicate the ID of OD of your part for centering. I have a Blake Co-Ax and do use it for some jobs, but 90% of my work gets centered with the Indicol + Interapid.

    Enco has an imitation rig that sells WITH INDICATOR, for a good percentage less than the Indicol W/O INDICATOR. Is the Indicol worth the difference?
    The Indicol is 1000% better than the knock offs. Biggest difference is that the Indicol stays locked while the others don't. It's a $50 investment that will last a couple of lifetimes of daily use.

  18. #18
    Join Date
    Dec 2003
    Location
    suburbs of Ann Arbor, MI, USA
    Posts
    11,851

    Post

    The Interapid method (and DRO) seems to work for me. This 3pc stack of casting, new bearing race and seal ring were all located by 1/4" dowel pins reamed .001" undersize in the casting and .001" oversize on the steel elements, done on a garden variety Bpt.

    The assembly slipped together with a minimum of fuss despite 3 different setups.


  19. #19
    rimcanyon's Avatar
    rimcanyon is offline Titanium
    Join Date
    Sep 2002
    Location
    Salinas, CA USA
    Posts
    3,274

    Post

    One more thing to try:
    put a cylindrical square on the table, and use an indicator to check whether the z axis is parallel to the square's axis. It could easily be that your z axis ways have excessive wear and its time to rebuild.

  20. #20
    Join Date
    Nov 2005
    Location
    Maryland
    Posts
    6,759

    Post

    Enco has an imitation rig that sells WITH INDICATOR, for a good percentage less than the Indicol W/O INDICATOR. Is the Indicol worth the difference?
    The laws of economics haven't changed. You get what you pay for. If you buy cheap chicom junk, then your work is going to be cheap chicom junk. I have more respect for myself.

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

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