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Strong OX

Discussion in 'CNC Mills/Routers' started by Hytech2k, Nov 28, 2014.

  1. slm222

    slm222 Well-Known
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    what do you feel the benefits are between the v rail and v wheels vs using the wheels that run in the slot?
     
  2. Hytech2k

    Hytech2k Master
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    Strength wise, not sure. I use v-rail to help keep dust and debris from fouling the track where the wheels run and effecting the quality of the cut. Plus since the v-rail is mounted more towards the outside of the extrusion less spacers are required to get the necessary clearance for the gear rack which equals better rigidity. I tried the original Ox design with the belt and wheels in the groove, it required a constant effort to keep it clear.

    Gerald
     
  3. slm222

    slm222 Well-Known
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    Ahh ok. I wasn't sure if it was for a reason like less friction
     
  4. Tom Allen

    Tom Allen Well-Known
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    I'm very impressed with your work and the details you offer. You are certainly a significant contributor to the forum.
    Wow, very impressed with the sturdiness of your machines. No flimsy stuff for you. I can see where the v-wheels are the weak link in the chain. If you had your druthers, what would you use to replace the wheels?
    Again, thanks for your work and time.
    Tom
     
  5. Hytech2k

    Hytech2k Master
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    Thank you for the kind words. The V-wheels do contribute to flexing quite a bit. I will probably redesign it at some point to use HiWin or THK linear rails. I wanted to keep this machine more affordable for the average user, linear rails add a lot of money to the build. I push this machine hard a lot just to see where the weak points are and what improvements could and should be made.

    So far i'll be satisfied just changing out the racks and steppers on the Y axis and installing new wheels. But I do see linear rails in the future for this machine and my Joes Evo.

    You should check out the build Steve Spenceley was working on, very rigid design.

    Linear Rail OX

    Again thanks,

    Gerald
     
  6. Robotbeetle

    Robotbeetle Well-Known
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    Gerald, I've been trying to ask how do you determine your feeds and speeds. I've been cutting aluminum and I could use what you know regarding this. Also, on my cnc router I measure at least .010 to .020 inches of displacement at the tool bit tip when I put a 5 lb load on it using a fish scale or luggage scale. Can you try this and tell us what amount of displacement for x and y you measure under the same load please. I can post a picture of this if you like.
     
  7. Hytech2k

    Hytech2k Master
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    Sorry about the absence. To be honest I never really became proficient cutting 6061. I was able to get to a point where it was working pretty well but I still wasn't happy with the results. The bit I finally settled on a .125 O-flute chinese bit. They seemed to work as well as the Toolstoday bits and Onsrud bits. Dry cutting didn't work as near as well as a mist. I'll have to pull up some old files for you and see what the feeds and speeds were that I was using.

    I am prepping to do a full tear down and rebuild of this machine, I have numerous wheels on the X cracked and/or split that need replaced and i'm also swapping out the Y gear racks to 20/20 1/2" wide racks with more powerful steppers. After I do the rebuild i'll be more then happy to check that for you. My machines a bit wore right now so i'm sure the numbers wouldn't be good. Just send a photo of exactly how you would like to check it and i'll do my best to accommodate..

    Thanks

    Gerald
     
  8. Robotbeetle

    Robotbeetle Well-Known
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    Thanks. I know it's tough to do a tear down and revamp the system. It feels like I have to completely rebuild an assembly four or five times for any small change. Of course it would help if I could just stop improving it.
    This is what it looks like when I test for deflection under a 5 lb load. The steppers are energized and I pull on the chuck with a luggage scale or fish scale. I measure both X and Y deflection under load with a micrometer and dowel pin to see if any improvements were made. Out of the four causes for bit breakage (chips clearing, bit run-out, heat, and deflection) deflection is the bane of cnc routers in comparison to typical shop mills.
     
  9. Hytech2k

    Hytech2k Master
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    Actually i'm looking forward to the tear down. I haven't had to do anything major except change all the Y axis wheels at one time, other than that it's been pretty solid.. The tear down is really to just do some routine maintenance and upgrades..

    I'll test mine when I get it back together and see what the results are. I was just thinking, isn't 5 lb's a bit much though for a side load, i'm not sure what your running for DOC but it's usually pretty shallow right, shouldn't be much side load on the bit I would think. Or am I missing something, just curious? Are you running the extreme wheels or the delrin? Also what size bit's are you running, O-flute or 3 flute?

    If you put the dial indicator on top of the gantry above your hand facing the carriage does it show deflection going the opposite way? Just wondering if the carriage is twisting/rotating due to wheel flex..

    I might just redesign the plates on mine for THK or HiWin linear rails, eliminate the plastic wheels all together, not sure yet, it's a pretty big expense for a machine that does nothing but cut wood...

    Send some photos over of your machine if you don't mind, looks like a great build i'd like to take a look..

    Thanks

    Gerald
     
  10. Robotbeetle

    Robotbeetle Well-Known
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    Well you're right. When I'm cutting wood I have no problems. My DOC for aluminum is usually .025 inches. I just wish my chip load was higher. It must be .0005 inches right now which is too low as far as anyone is concerned. The 5 lb load is just a standard I pulled out of thin air to know if I'm improving the slack or inherent deflection of the system. I imagine a standard mill has zero to half a milli-inch deflection under this load btw.

    I've been running extreme wheels but I've just switch to metal for the z axis. It could come down to how clean I can keep it too. For aluminum 6061-T6 and 5052-H32 I've been using 1/8" O flutes from drillbitsunlimited. Very cheap and still sharp. Based on experience I've had no excessive heating or anything.

    Speaking of which what size and strength are the springs that you use next to the steppers? I've had some unfortunate instances of the stepper gear getting kicked out of the rack's mesh in the Y axis.

    Back to the experiment, if we have data from before and after switching to enclosed linear guides then we would be able to understand if the improvement was justified. After all, the improvement would not be cheap but could contribute to longer tool life and worry free runs.

    I'll put more pics up when I get a chance.
     
  11. Hytech2k

    Hytech2k Master
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    You're most likely right about the deflection on a standard mill, but this stuff is no where near that quality. But I understand where your coming from, the more rigid the machine the better cut quality, tool life, etc.... Honestly with the wheels, I've never been a huge fan. I have always found deflection no matter what in amounts more than what I would like. I think switching to all hardened V-wheels would help immensely, but without hardened v-rails they would wear out way too fast. My other machine uses hardened V-wheels running on angle iron for rails, very rigid machine.

    I will find a way to measure the springs for strength when I disassemble the machine, I just picked them up from the local Home Depot if I remember correctly. I tighten mine down until all the backlash is gone then go about 1.5 turns more to pre-load the spring.

    Just wondering but how many wheels do you have on the X gantry carriage? Are you running the Ox style Z-slide, with wheels and such?

    I'll be more than happy to help out in anyway I can. I found another supplier for spur gears so hopefully all my parts will arrive shortly and i'll get started on the tear down next week..

    Thanks

    Gerald
     
  12. Robotbeetle

    Robotbeetle Well-Known
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    Here's another pic.
    I think the Y axis, which is in view, could use a few more wheels probably. I think most of the deflection was coming from the Z axis wheels originally. I'm about to tighten everything up and see if my improvements made a difference.
     
  13. JFAirplane

    JFAirplane Well-Known
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    Is having the stepper with a belt drive reducer help a lot ?
    Or is the addition of a belt system on the gantry might be better too vs a direct drive motor running on the gear rack ?
    thanks
     
  14. Robotbeetle

    Robotbeetle Well-Known
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    I don't know what you are comparing the belt drive to or how you are judging it. Why did I design it this way? Belt drives stretch and reduce accuracy significantly when the table is this big (4' x 10'). A very short belt has less stretch overall so for Z axis here it is negligible regarding accuracy. Also, if system elasticity is a notable figure of merit then flexible couplings probably offer the least value but are very convenient for other reasons. Although I've never measured it I believe that rack and pinion offers positional accuracy which is second only to ball screws and maybe chains. I hope I answered your question.
     

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