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Thread: Upgrading questions...

  1. #11
    Join Date
    Apr 2011
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    California
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    3

    Default Gearbox

    I have prt alpha with the ASM911's - would like to add gearbox - anyone have a source for buying - not making - thanks Scott

  2. #12
    Join Date
    Sep 2006
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    Garland Tx
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    Scott

    The only over the counter gear boxes I know of are the ones Randy D. gave a link to earlier in this thread... Those have a backlash of 6 arc seconds. I don't know what that means in terms of CNC, but I've been told it's 12' over 3000 miles. I'm in the process of installing belt drives I bought from another ShopBotter, this was the best solution for me.

    SG

  3. #13
    Join Date
    Jan 2004
    Location
    , South Jordan Utah
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    1,693

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    There are easy ways to make your CNC router "sing". Some of the eariler Shopbots used stepper drivers that are inferior to the stepper drivers available today. That should not be suprising. Most of "yesterday's" electronics are inferior to today's electronics.

    I prefer to use Geckodrive stepper drivers when "upgrading" a stepper motor/stepper driver system. They make reliable products at an affordable price.

    I also like to use belt-drives instead of gearboxes. Belt-drives are bulky, but they are simple. It's far easier to replace a $20 or $30 component than it is to replace a $250 - $800 stepper/gearbox. If you have room, investigate using a belt-drive before spending a lot of money on gearboxed motors. I tried both. Although the upgrade motors offered by Shopbot to replace the motors that came with my PRT-Alpha were a bargain, when compared to the cost of buying those same motors directly from Oriental Motor, they cost many times more than it cost to add a belt-drive to the original motors. Cut quality was NOT improved with the gearbox motors when compared to the belt-drive motors.

    Sometimes we forget that a CNC router can easily cut DelRin and other "plastics" that are required with belt-drives. Why not improve the cut quality of your machine if you can do it for $150 or so per axis? Belt-drives are not rocket science. Anyone who can cut dovetails can cut the parts for belt-drives. Measure carefully and you'll do just fine.

    If you need a little advice, email me at miker@xmission.com. I'm old and I'm feeble, but I try to answer emails in a timely manner.

  4. #14
    Join Date
    Sep 2006
    Location
    Garland Tx
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    I finally got my belt reduction boxes installed... The Y car gave me grief! I finally had to remove the Z axis to get clearance enough to get my hands and tools in there. I think the close quarters was because I have two Z axis' and they are located at the outside edges of the car rather than one in the center.

    I've never had transfer rate issues even though I have only had a 42% transfer efficiency rate. After having to triple the unit values I had to clean things up and do it right with a powered hub. Now I'm at 72% and everyone is happy!

    I haven't cut anything yet... hopefully tomorrow, after I square up both Z's. It's also time for a new spoil board. It's hard to imagine how different the Bot sounds now! It really sounds quiet and smooth... I think the biggest difference may be that the motors are now essentially isolation mounted and no vibration is transferred from the motors to the frame.

    So far mechanically I'm very pleased with this route of upgrading. everything is solid and simple. I'll try cutting tomorrow.

    SG
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  5. #15
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    Apr 2011
    Location
    California
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    3

    Default Gearbox

    Steve does he make and sell them - would be interested in purchasing a set - thanx- Scott

  6. #16
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    Sep 2006
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    To anyone interested...

    My source was Mike Richards... He is not in a situation where he can make more drives, but is willing to discuss them If anyone wants to contact him off-line (miker@xmission.com).

    Also Dave RosenBleeth has a set of plans he sells.

    SG

  7. #17
    Join Date
    Jan 2004
    Location
    , South Jordan Utah
    Posts
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    If you already own a Shopbot and if your controller puts out step and direction signals (as opposed to CW/CCW signals) and if your controller can output a pulse stream 3X faster than it does now, you can convert your machine to use belt-drives.

    The advantage is 3X to 4X more torque (depending one the pulley ratio that you select). My PRT-Alpha without a gearbox, output a little less than 600 oz*in of torque. That's the same as 37.5 lb*in of torque. The 7.2:1 gearbox Alpha motors are limited to 80 lb*in of torque. That's a significant improvement. Those 600 oz*in motors become 1,800 oz*in motors (50% greater than the 7.2:1 motors). That's even more of an improvement.

    The disadvantage is bulk. Look carefully at the photo that Steve posted. Did you notice how the body of the belt-drive hangs below the rack? That reduces clearance on the Y-Axis. That was not a problem to me, but it may limit the type of work that you can do. Another disadvantage is that YOU have to design and build your own belt-drives. It is not hard, but it may take a try or two before you get it the way that you want it. I designed four different models before I was satisfied.

    Send me an email off-line if you have questions. (miker@xmission.com)

  8. #18
    Join Date
    Sep 2006
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    Garland Tx
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    I thought I'd post another image of the reducer actually on the Z axis... The arrow shows my actual loss of Z axis to be less than 1/2". Fortunately I had 12" to start with!

    I wrote a little program to air cut a 36" diameter circle increasing the speed until I missed steps. At 7"per Sec I started noticing little hiccups, and serious problems at 8. I figure if I cut at 6ips or less I can keep the resolution selection switch at 1000, however after reading old posts, people have reported no significant degradation in cut quality after setting the resolution to 500. Just a reminder... jog speed is not the same as cutting speeds.

    I tried my first cuts on a logo Thursday night with horrible results! an examination of the belt drive installation revealed I had failed to tighten the set screws on the pinions after I aligned them with the rack. I was able to sleep that night knowing I could fix the problem... I woke up early Friday AM with a sore elbow and an arm the size of a watermelon (slight exaggeration). Subsequent doctor visits reveled a torn blood vessel, long story short... I've been banned from the shop and life in general and haven't been able to try my hot rodded bot!

    Hopefully today!

    SG
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  9. #19
    Join Date
    Sep 2010
    Location
    Brooklyn, NY
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    47

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    Steve, I'm sure some of us are waiting for a report on your arm and Oh yeah, your belt drive results...how's it going?
    -RC

  10. #20
    Join Date
    Sep 2006
    Location
    Garland Tx
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    Roney and all...

    Sorry to keep ya'll at the edge of your seats! Those of you who know me personally know that I walk with a cane and a limp... My ShopBot crafted canes are nice but the limp has been getting real bad. The issue with my arm turned out to be a fracture suffered from a fall... to make a long story short, I get a new hip Wednesday the 19th.
    Understandably my shop time has been limited... However, I'm very pleased with the cut quality I'm getting now. The testing I did earlier by air cutting a three foot diameter circle to determine maximum possible cutting speeds apparently was not a legitimate test. All was fine until I tried V-carving a detailed logo... the bot was not happy. I had to reduce the pulse count from the driver from 1000 to 500 (remember it's an Alpha). My initial results were very exciting but things seemed to slowly deteriorate... Close examination showed that the set screws on several of the pinions had worked loose... New set screws with a locking compound seems to have brought back the initial excitement! Cuts I did today in HDPE are the best I've done in plastic on the bot. The recurring corporate logo that prompted the desire to upgrade has text in it about 1/8" tall... I believe a recent batch I did reached the limits of the substrate rather than the Bots abilities.

    In conclusion... I'm not reverting to pre belt-reduction any time soon! Also, if you're designing your own and can get set screws that use something larger than a 5/64" Allen wrench, you'll possibly avoid some issues I've had.

    My surgery rehab days include plans to edit an article on "hold down methods" similar to the one I did on "router bit basics" more on that latter in another thread!

    SG

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