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• Minimizing backlash

  Stefan Lochbrunner • 11/28/2015 at 22:53 • 2 comments

  So far backlash hasn't really been a concern but the other day I had this idea that should help reducing it. It's similar to what was done in this machine which was recently featured on the blog where two nuts were pressed in opposite directions by some metal strips.

  It came to me when I had this threaded rod with those two standoffs laying on my bench along with a small box of misc parts among which were some springs. I was just sort of playing around with these parts wanting to see how far I could compress this quite stiff spring but then something interesting happened: The spring locked the two standoffs together pretty much eliminating the backlash, although it depends on how tight the spring is compressed. Of course, as it is the standoffs aren't completely locked, especially when the rod is turning fast but that's an easy fix.

  It's nothing revelatory but the way I stumbled upon it is somewhat amusing. As evidenced by the above example the general concept is a commonly known technique but the option of adjusting the pressure at any time makes for a nice feature.

• Some links

  Stefan Lochbrunner • 11/12/2015 at 13:35 • 0 comments

  • You might know the MIT Machines That Make project that spawned the Mantis CNC Mill. Some other projects of their's that I find relevant to mine are:
    • The PCBMill and
    • the Spindle.
  • Another project from Ilan Moyer, the maker of the above PCBMill, is the Magic Mill which is just beautiful.
  • The RepRap wiki has a lot of information on PCB milling as well

• Mechanical 'design'*

  Stefan Lochbrunner • 11/11/2015 at 16:54 • 1 comment

  *not really design, more like doing something and seeing what works/sticks. Problem: Metal doesn't stick.

  First attempt:

  I think you see what I was going for here:

  Read more »

• 'Spindle'

  Stefan Lochbrunner • 11/11/2015 at 16:39 • 7 comments

  Thought about using a rotary tool but I'm not sure if the machine will be able to handle it. For now the plan is to use a DC motor with one of those cheap self-tightening chucks (although that's not too different from a regular rotary tool):

  ---

  Update 2015-11-24:

  Some thoughts on how I'm going to mount it:

  The motor is attached to an angle and will also be supported further on the left. Probably with some metal or acrylic pieces and a hose clamp to pull it tight against the base plate. The 2nd angle on the right will be a support/guide for the bit. I don't have any 1/8" inner diameter bearings (or drill bits for that matter) that could act as low friction guide so I guess a hole will have to do; it remains to be seen how I'm going to make that hole.

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  Update 2015-12-23:

  I'm still waiting for the v-groove bearings and since I'd like to fabricate most of the next batch of parts in one go I haven't gotten too much done on this building wise. However, I did some tests on reducing wobbling of the bit. Initially the bit was off by about .5mm such that the very tip would move in a circle with a diameter of 1mm. I tried reducing it with a makeshift bushing but this had too much friction, causing the motor to slow down or even stall.

  Pushing on the chuck such that the tip of the bit would go towards the center approximately halved the wobble and by rotating the bit inside the the chuck got it to a point where the wobble is negligible. The problem is that this chuck holds the bit only on a slim ring where its jaws close and the end of the bit that is inside the chuck has some space to move around. In hindsight this is pretty obvious but I just couldn't resist when I saw this chuck on eBay. I guess this will have to do in order to finally get the machine running for the first time and I'll make some improvements once I'm there.

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  Update 2016-03-03:

  As I mentioned in the other log I had to reorder the bearings but now that the second order arrived I finally got back the motivation to continue work on this.

  I pretty much just implemented the ideas outlined above so this is how the spindle mount looks like now:

  I made some mistakes on the acrylic base plate since I rushed it a bit to get it done and see if this concept would work but those are primarily cosmetic so I could just make a new plate if I feel like it. I also still have to shorten the brass right angle pieces since they limit the machines range of motion a bit. Assembly of the spindle-mount/z-axis (shown below) was a bit of a pain because a couple of screws are obstructed - the ones under the motor on the metal angle, for example - but once done it seemed to work quite well. The optical flaws aside, the motor is mounted pretty sturdily to the z-axis so if I can get rid of the wobble of the bit it should work nicely.

• Endstops

  Stefan Lochbrunner • 11/11/2015 at 16:32 • 0 comments

  They are not integrated yet but these are some ideas:

  One of the ideas was to use buttons as endstops and mount them to the aluminium something like this:

  But since I also salvaged some of these optical interrupt switches from the printers it'd probably be a good idea to use these instead:

  Read more »

• Electronics

  Stefan Lochbrunner • 11/11/2015 at 15:33 • 0 comments

  The stepper motors seen in the main project image are salvaged from old printers. Maybe I'll write about them in more detail some other time.

  To control the motors I'm using StepSticks which are really cheap on eBay and easy to use and are in turn controlled by an Uno.

  As you can probalby guess from the image the Uno is running GRBL so nothing fancy here.

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