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Long 8mm ACME screw

Discussion in 'CNC Mills/Routers' started by CNC77, Mar 8, 2018.

  1. CNC77

    CNC77 New
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    Hi

    Anybody here who have sucessfully run the openbuilds 8mm ACME in 1500mm length?
    i have two 1500mm i have been thinking about trying on my cnc router, but i hear manny on the forums having problems on even shorter lengths, but is this do to the screw beeing slightly bendt during shipping or is the screw simply to thin? I also see most builds compress the screw, but i think pulling tention on the screw would prevent wipping.

    Anny ideas?
     
    #1 CNC77, Mar 8, 2018
    Last edited: Mar 8, 2018
  2. Gooshpoo

    Gooshpoo Veteran
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    I was going to run 1500mm screws but they where just 2 floppy. you would be better off with 12mm acme rod.If they have a dip or slack they will cause problems if there not both the same.
     
  3. CNC77

    CNC77 New
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    This is my first CNC router and its a 1000x1500 workbee, i need this size for its intended use. If belts is the only option without big modifications how reliable are they? GT2 or GT3? On the workbee the belts run inside the cbeam hold down by the mini Wheels, anny idea if it is room to run the dubble/stacked belts modification?
     
  4. Giarc

    Giarc Master
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    There is room to run the double belts. Many people have done that with their Ox CNC routers.
     
  5. Kevon Ritter

    Kevon Ritter Veteran
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    What's the machine purposed for? If you built it heavy, then you may want to keep the idea of using screws. You can get 12mm screws in up to 12mm lead. You can get 1/2" up to 1/2" lead. The other option would be ballscrews, but that starts getting pricey. If you are just cutting lighter woods and other relatively light material, double belt it.
     
    Mark Carew likes this.
  6. CNC77

    CNC77 New
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    I will use it to cut aluminium and wood so it would be best to use screws. I have lookt in to cheap 1605 ballscrews from China, but it look like manny have problems with bendt/wipping screws.

    I would really like to give the 8mm a try because i allready have two 1500mm long screws that came With the router and my plates are ready for the 8mm screw. If i desided to use the 8mm i would use the SMW3D R7 tensioning method that involving placing the lead screw bearings on the OUTSIDE of the plates and pull tension on the screw instead of compressing the screw like on most other screw driven builds like the sphinx and others. But i need the machine up and runing and dont have the time to Waste on sulutions that is guaranted to fail. On the other hand i really would like not to have to do a bunch of custom plates and modifications with the time and money involved in that. So anny input from you guys is welcome!
     
  7. Kevon Ritter

    Kevon Ritter Veteran
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    You'll just be stuck running at relatively low feedrates. Whip is a result of rotational velocity.
     
  8. CNC77

    CNC77 New
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    So you think the accuracy wil be good and that i can run the feedrates needed for both wood and aluminum but as an example might have problems jogging across the table at high rapids?
     
  9. Kevon Ritter

    Kevon Ritter Veteran
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    I'm just pulling numbers out of my rear, but I don't know if it would do more than 1000mm/min. Even cutting with small (3mm - 1/8") end mills can require higher feeds in sensitive materials. Unless you're cutting foam or materials that don't care about rubbing (not sure there are any others), you won't be able to use a larger (6mm - 1/4") end mill due to low chip loads. Aluminum is fine at lower feeds if everything else is setup appropriately.

    With an 8mm lead (travel, not diameter), 1000mm/min is 125rpm. 2000mm/min is 250rpm. At 1500mm/min, homing takes 20s per 500mm of travel.

    A belt will easily hit much higher feeds. I came up with my own design based around this general length requirement. I went with a 15mm HTD-3M belt. I haven't actually built the machine or tried the general design as of yet though.
     

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