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Thread: Slipping bit

  1. #1
    Join Date
    Dec 2012
    Location
    Strathfieldsaye, Australia
    Posts
    116

    Default Slipping bit

    I have the ShopBot Desktop with Z height kit added with a spindle (not router).

    For some time now I've had issues when performing a profile cutout. It's somewhat erratic, but on occasions the bit will slip down about 0.5". The bit is a 0.25" sipral upcut bit. I have no problems with other bits (0.125" spiral upcut, ballnose etc), only the 0.25" spiral upcut. During the execution of the profile cut out, the bit drops and starts making deep cuts.

    What I've tried:
    I've measured the diameter of the bit, and it is consistent with a new, unused bit of the same make and model. I've swapped the collet for a new, unused one. I've made sure everything is blown clean and clear of any dust. I don't insert the bit so far that any part of the flute is inside the collet, nor does the top of the bit pass beyond the top of the collet. Previously, I've tightened the collet nut the same as I would for other bits. I have also tightened it with greater force, trying to ensure a better hold, but still the bit has slipped.

    Other than swapping the bit for the new one, I've no other solution.

    Has anyone else experienced this? Suggestions?

    My good friend Scott would probably say it's because everything is upside down in Australia. He may be right

    Thanks

    Graeme
    Desktop, 1HP spindle, Z-upgrade
    Aspire 8.0
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Australian software developer and trainer - Delphi, C#
    Mobile development

  2. #2
    Join Date
    Apr 2013
    Location
    Kennebunkport, Maine
    Posts
    3,994

    Default

    With friends like me...who needs enemies Graeme!

    Sounds like you've done Most things, but I should have paid more attention when those two crib boards went bad on you....musta been Something going on?

    More for Newbies than you, and will probably get yelled at by people I respect, but here goes a copy/paste of my e-mail to you.






    Hate to say it good buddy, but you've probably fried both collet and bit?
    Called a "Catastrophic Failure" in Shopbot lingo, but VERY carefully inspect cleaned bit at collet end, and look for ANY discoloration/change of appearance/horizontal marks.......
    If ANY of those are there, bit TOAST!
    Most likely your new collet as well, as they both had to spin to lose a half inch!

    As a bike mechanic and growing up with motorcycles.....worn sprockets will deform chain...IF JUST chain is replaced, it will strip sprocket FAST, and ruin chain as well(usually drive sprocket on motorcycles...and smallest sprockets on freewheel. Regular chain replacement and cleaning is needed BEFORE any deformation!!
    Same thing with collet nut race/spindle/collet/bits.

    I THINK the bit might have become toast the first slip....and maybe the same with collet...and then just replacing one(and not both ruined both?)
    ANY discoloration or galling?

    When was the last time you cleaned your collet cone?
    (Your best solvent acetone/at least denatured...then cone up a paper towel soaked with it and spin spindle by hand ALL the way up.
    Use as many paper towels as it takes to come CLEAN!
    THEN do the same with a q tip.
    Collet nut/collet/and bit should be cleaned also to see if any gunk comes off. AND horizontal "Shading" is indication it's worn, and TOAST!
    They DO make felt collet covered cone cleaners of wood for the correct taper ...use paper towel over felt!...or make your own

    Did you clean off Gunk collets are shipped with to prevent corrosion?

    This is pretty good...skimming it before coffee even 1/3 done;

    https://www.cnccookbook.com/getting-...collet-chucks/

    I always seem to use downcuts for profile cutouts, so haven't had a bit slip.
    BUT then I blow collet/nut/spindle cone with 90 psi EVERY bit change, AND brass brush the bit EVERY time with Bladecote(Bostich) before it gets put away.
    More so that EVERY time I grab a bit I KNOW it's clean and tip has been inspected. I get burnt out sometimes, and just easier for me, and now second nature.
    MIGHT come from working on an old Pratt-Whitney Tape-O-Matic for my Dad for 2 Winters...as he and my brother were maintenance drill sergeants?

    Going to post this on forum anyways...as WAY too many people don't do daily or weekly maintenance.

    Hope it doesn't sound too harsh Graeme
    IF you're lucky.....people will LAMBAST me for being a control freak

    Looked briefly for good pic of a "worn ER-20" collet, but need more coffee for search words apparently
    Your friend,
    scott
    Scott Plaisted
    2013 Desktop/spindle/VCP 9
    Maine

  3. #3
    Join Date
    Jun 2004
    Location
    Springfield Mo
    Posts
    807

    Default Lock tite

    I use a bit of medium strength Loc-tite on the shaft of the bit when I put the bit in the collet. It dries overnight. Seems to help.
    (no lock tite on the collet threads)

    I have a bunch of collets for a PC router... so much easier to just change out the entire collet / rather than inserting bits each time.
    The decimal point seems to be the most important on the z axis... x & y not so much....
    ShopBot... Where even the scraps and things you mess up and throw away are cool....

  4. #4
    Join Date
    Mar 2013
    Location
    Memphis TN
    Posts
    673

    Default

    If you're using an ER25 collet, then it's almost impossible to over tighten it using the standard SB provided wrenches (unless you're the Hulk). Be sure your collet and collet nut are absolutely clean and make sure your collet nut has no fractures. The collet should snap smartly into the nut and not fall out. If it does, the nut has failed and needs to be replaced. You should replace the collet nut every 100 hours or so regardless. They are $40 from SB. I haven't found a good source of quality collet nuts outside of SB.
    ShopBot Details:
    PRS Alpha 96x60x12
    4hp Spindle
    12" indexer
    Aspire
    Rhino

  5. #5
    Join Date
    Jun 2013
    Location
    Pasadena, CA
    Posts
    962

    Default

    I had that problem occasionally with long 1/2" diameter bits (i.e. 6") when the vibration and leverage worked the nut loose over long hours.
    I have since replaced all my collet nuts with the ball bearing type. They don't create friction with the collet when rotating and I never had slip problems since. Also easier to turn loose.
    Not sure anymore where I bought them but they are like these: https://www.maritool.com/Tool-Holder...duct_info.html
    Box Joint, Dovetail, Guilloche and MazeMaker Software Here

  6. #6
    Join Date
    Dec 2012
    Location
    Strathfieldsaye, Australia
    Posts
    116

    Default

    The Desktop collet is ER20. Examining the top of the bit, it has striations around it. I guess it's time to bin it. It's been my favourite profile cutout bit for a long time. I guess it's past it's prime. I'd never switched to a new collet since buying the machine. 100 hours sneaks up on you, and is not difficult to achieve. I think it's time for a clean start - bit, collet and lock nut. Will order today. Seems the safest thing to do. I'm annoyed I forgot about the ~100 hour life of a collet. It's one of those things I used to know. Interesting about the ball bearing collet nuts. Had not come across those. Will investigate further.

    Thanks all for good advice. Will take a while for order to reach Australia. I'm reluctant to buy the parts from Shopbot, as the shipping is more than I"m willing to pay, even though it would arrive sooner. This isn't my day job, so I can afford to wait.
    Desktop, 1HP spindle, Z-upgrade
    Aspire 8.0
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Australian software developer and trainer - Delphi, C#
    Mobile development

  7. #7
    Join Date
    Jun 2013
    Location
    Pasadena, CA
    Posts
    962

    Default

    Quote Originally Posted by Coogara View Post
    ........ I'm annoyed I forgot about the ~100 hour life of a collet. It's one of those things I used to know. Interesting about the ball bearing collet nuts. Had not come across those. ......
    I am somewhat sceptical about the 100 hour rule (other than overly proactive maintenance). There are no moving parts in operation so why should they wear out? I would rather believe if somebody said "only 100 tightening cycles".
    I check my collets once a while for runout with a dial gage but I guess some of them surely have 1000+ hours including a few broken bit events but still without any runout or clamping problem.

    The advantage of the ball bearing collet nut is that the tightening torque is 100% applied to the thread and does not need to overcome the friction to the collet (and no twist applied to the collet itself, only axial force). I do need to soak the nuts in paint thinner and spin the bearing with a hand drill maybe once a year to free them when getting stuck.
    Box Joint, Dovetail, Guilloche and MazeMaker Software Here

  8. #8
    Join Date
    Dec 2012
    Location
    Strathfieldsaye, Australia
    Posts
    116

    Default

    I imagine '100 hours' is a worse case scenario (and maintaining best condition). A bit like luxury car maintenance replacing certain things (globes) at specific intervals to avoid unexpected failure. If one can afford it, and collets are not too expensive, then I guess it's okay, but how many people maintain a strict maintenance schedule on collets, I wonder?

    I did read about ball bearings getting gunked up over time, so I appreciate the comment regarding a good soaking. I'll keep those in mind, but for now, to keep the cost down, I've stuck with Techniks collet and nut from AllIndustrial. 50% cheaper shipping to Austrlia than ShopBot store.

    Thunder rumbling today, so staying out of the shop. Don't want a mini power loss in mid cut, on top of this issue.
    Desktop, 1HP spindle, Z-upgrade
    Aspire 8.0
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Australian software developer and trainer - Delphi, C#
    Mobile development

  9. #9
    Join Date
    Jun 2013
    Location
    Pasadena, CA
    Posts
    962

    Default

    Ah found the place where I bought them: https://www.arceurotrade.co.uk/Catal...Bearing-Type-B
    Pretty good deal for GBP 8.16 incl. VAT but unfortunately out of stock at this time.
    They shipped direct to the US no problem and modest shipping charge so I guess they would ship to Australia as well.
    Box Joint, Dovetail, Guilloche and MazeMaker Software Here

  10. #10
    Join Date
    Jan 2008
    Location
    Hobby-Tronics, Chiloquin Oregon
    Posts
    1,217

    Default

    Great thread. Thanks for the posting about the bearing collets. Russ
    AKA: The Train Guy

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