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Thread: Hole not round

  1. #1
    Join Date
    Dec 2015
    Location
    New Jersey
    Posts
    36

    Default Hole not round

    On the Shopbot (PRSalpha 96-48) at my makerspace, I'm getting holes that are not round. The picture below is about 1.5" diameter. I cut it with a 3/8" end mill. Any suggestions as to what's causing this?

    Attached Images Attached Images

  2. #2
    Join Date
    Oct 2000
    Location
    Willis Wharf, VA
    Posts
    1,716

    Default

    My first step when looking for cutting problems is to power up the tool and then grab each moving part...both ends of the gantry, the YZ car, the nose of the spindle... and shake it to see if you feel any slop. Since it's in a makerspace my first guess is worn out pinion gears, but they could also be loose on the shaft or not tight in the rack.

  3. #3
    Join Date
    Aug 2011
    Location
    Wilkesboro, NC
    Posts
    97

    Default

    I found when I was running my router with a climb cut on small holes at high feed rate, my holes looked like yours. I had a little slop in the machine like bill.young just talked about and the climb cut pulled the router a little before the drive motors could compensate.

    I switched to conventional cut for the holes and took out some of the slop in the machine. Plus I slowed down the feed rate some. Not so slow that I burned the spoilboard, but not superfast.

  4. #4
    Join Date
    Dec 2008
    Location
    Diamond Lake, WA
    Posts
    1,679

    Default

    Did you make the hole using the circle tool or is it an imported file? Lots of times, with imported files, circles are chopped up into lots of straight line vectors that mimic a circle. If that's not the issue, make sure you V-tracks are really clean and there are no nicks in the rail. Second, like mentioned above, check to make sure your machine is nice and tight in all directions.

    Another thing is to check you feeds and speeds. If you speeds are to slow for the feed, you will flex the bit more. If the feed is to slow for the speed, you will heat up the bit and shorten its life span.
    Don
    Diamond Lake Custom Woodworks, LLC
    www.dlwoodworks.com
    ***********************************
    Life is not a journey to the grave with the intention of arriving safely in one pretty and well preserved piece; But to skid in broadside, thoroughly used up, worn out, bank accounts empty, credit cards maxed out, defiantly shouting "Geronimo"!

    If you make something idiot proof, all they do is create a better idiot.

  5. #5
    Join Date
    Dec 2015
    Location
    New Jersey
    Posts
    36

    Default

    I did grab the spindle and gantry and try to move them to see if there was any play, I didn't notice anything, but I'll do it again. I have noticed a difference between climb and conv cutting. Basically for the circle, the odd shape remains, but it's mirrored. I also tried to cut some square slots (1" x 3/8") with a 1/4" bit. The short sides were angled, so it looked like a parallelogram. This was with a climb cut. I tried again with conv cut and it was much butter but not perfect.

    I'm cutting with 0.001" to 0.002" chip load

  6. #6
    Join Date
    Dec 2015
    Location
    New Jersey
    Posts
    36

    Default

    I took a closer look at the shopbot and it turns out the pinon gear on the y-motor was a little loose. I tightening the set screws and it's working MUCH better now.

  7. #7
    Join Date
    Mar 2013
    Location
    Memphis TN
    Posts
    861

    Default

    You might volunteer to replace the pinions as that is the surest, simplest and cheapest way to restore the tolerances to a SB. The pinions probably last no more than two or three hundred hours before wearing out. They are the soft part of the equation and meant to wear.
    ShopBot Details:
    PRS Alpha 96x60x12
    4hp Spindle
    12" indexer
    Aspire
    Rhino

  8. #8
    Join Date
    Dec 2015
    Location
    New Jersey
    Posts
    36

    Default

    Thanks, I'll do that

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