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Questions about doing a 4 foot C-Beam Linear Actuator

Discussion in 'CNC Mills/Routers' started by Marshalltjones, Apr 14, 2016.

  1. Marshalltjones

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    I noticed that the parts store doesnt have a 1500 mm acuator. Is that because 1500 mm is too long to prevent whipping of the screw?

    Also, do you know if you can buy the actuators with the new high torque motors?

    Marshall Jones
     
  2. Metalguru

    Metalguru Master
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    Yeah, I asked the store about it and they said it was because of the whipping issue. I found a seller on Ebay that has the exact same lead screw as the parts store, with the same plastic anti-backlash nuts, but in 8mm, 10mm and 12mm diameters. Might be able to make the 10mm fit in the C-beam. However, they said that the longest length they could get was 995 mm.

    I was thinking of making a support out of nylon that would slide inside the c-beam inner v-grooves and have a hole to support the lead screw. You'd have to have 2, connected by some sort of rod that held them half the length of the c-beam apart. One would go on each side of the gantry, and as the gantry moved back and forth it would drag the two supports with it. This way, the lead screw would be supported on the long side about halfway from the gantry, reducing whipping. But, it's kind of moot if you can't find longer leadscrew...

    As far as the motors go, just buy the actuator without the motor and buy the motor separately. BTW, have you seen the new toothed belt 2:1 reduction kit for the c-beam? Uses the standard motor, gives you twice the torque, twice the resolution, and is way cheaper than the high torque motor. Only half the travel speed, though...

    Maybe look on Alibaba for longer lead screws?
     
  3. Giarc

    Giarc Master
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    McMaster Carr has larger precision acme rods. They come in 6 foot lengths. Dumpster CNC sells anti-backlash nuts for the various threaded rods. Or, buy a block of delrin and take any access rod you have from that length and make a tap to make your own nuts. That is what I did. SO far, it is working just fine. I basically made a clone of the open builds anti backlash nut in 3/8" and am going to do the 1/2" next. The nuts I made will fit in the cbeam.
    [​IMG]
    [​IMG]
     
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  4. Metalguru

    Metalguru Master
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    Giarc | OpenBuilds

    How the heck do you make a tap for the acme screw Can you put up some pix?
     
  5. Giarc

    Giarc Master
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    When I get back from Atlanta I plan to build a newer / better 1/2" tap. I will do a quick tutorial if it works. Here is a picture of a 1/2 rod that I cut grooves in using a chop saw. I cut them at 90 degrees to each other. I cut down into the rod which was fastened to a jig I made and pulled it out. I then chucked it in a drill and ground down the end on a bench grinder. The 3/8" worked great (beginer's luck) but I can't find it at the moment. This 1/2" did not because I messed up a cut. I plan to use an abrasive blade in my table saw on the next attempt so I can control it better. Here is a picture to show the general idea.
    [​IMG]
     
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  6. Metalguru

    Metalguru Master
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    Nice, Craig! I'm going to have to try this. I might just whip up a jig for the table saw as well.

    I looked at Dumpster CNC, he has some good stuff, I really like the Delrin threaded couplers, and especially the threaded shaft collars with the internal thread, these are a great idea. They even have a little shoulder so you don't need the shim washer. But conspicuously absent are the 8mm threaded parts to fit the OpenBuilds lead screw. He has 6mm and 10mm, but no 8mm. I've always hated the set screw collars, they ding up the threads on the lead screw really badly. I'm going to shoot him an email to see if he can get the 8mm ones.

    I'm a little bit leery that Delrin is strong enough for this application though. I want to try some, but the lack of 8mm is a piss off. He does have the unthreaded ones, though.

    Come to think of it, this may be a perfect application for the homemade tap. Simply buy a smaller ID smooth bore shaft collar, and tap it for the 8mm lead screw. Hmmm, going to have to consult my tap drill charts...
     
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  7. Giarc

    Giarc Master
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    You could try to drill a homemade collar slightly less than 8 mm. Cut a slit in one side of the collar. Put the 8MN rod in it and put it in a vice and tighten it. Heat up the rod and continue to tighten the vice on the collar until you melt the thread imprint into the collar. Tap a hole through the split side so you can tighten it up so it won't move on the shaft. Although, if you make a tap, it would probably be easier.
     
  8. Metalguru

    Metalguru Master
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    Yeah, making a split collar is probably beyond my equipment capabilities. Besides, tapping Delrin to a 3mm thread for the clamp screw would probably not hold. I think the commercial ones have a metal nut insert of some kind...
     

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