Another 3 Axis Position System for a RepStrap

I found a pretty cheap, easy alternative to the bearings being used to hold the stages to the rails. I recently started making my own McWire RepStrap Frankenstien and used a "Sliding Closet Door" roller. It is also called a Wardrobe Door Roller. See the attached photo. It seems like it will work fine and can be had for fairly cheap if you look around.

good find! this is a prime example of how many eyes can make finding solutions and/or better parts easy.

a couple questions:

1. the arm bearing design is there to allow you to adjust it and tighten up the bearings against the rail so you dont get any play in the non-axis direction (for the x axis, this means the x axis wobbling in the y direction) how have these worked out for that, and do you have any play? I noticed they have elongated holes so hopefully you can use those to adjust it up to the channel

2. how much do they cost? if you use the cheapo (yet still really nice) skate bearings, they are $1 / ea. if/when the RRRF starts selling kits for this, we can probably get them for under that.

... some years ago i build a 3-axis cartesian basis for a ferrofluid-nanopositioner - this one was very small, flat and simple - maybe it's of some interest for another easy to realize repstrap ...

The foot-print is 18x12 cm (20x20cm with the overlapping knobs and the Z-'tower') and the possible way of 40x25mm wasn't so exorbitant too but as you can see in the second image, the XY-gliders have an extreme simple structure with ordinary brass-screws and a sort of velvet for high precision and slack-free driving.

The axes-knobs turns very light and the manual accuracy with the small knobs was in the 1-micron-area (better, than the resolution of the microscope).

I used this system under a video-microscope as 'coarse' positioner and then i drove the ff-nanopositioner, which had an accuracy of 0,1 micron and 500x500 microns travel-range in X and Y.

Tis kind of precise low-cost screw-gliders can be made in bigger scaling and with other soft tissue as counterpart for the screws too, so here would be no need for precise fixing and the motors could be small and weak too.

I knew, that our 'grandfathers' sometimes used roasted pig-skin in a similar way for performing a form-grip and lubrication for gliders in the same place ...

Viktor

Zach,

No play what-so-ever. Yes, you can use the two elongated holes to snug things up to the rail and I have had no problems with it. Of course, I haven't gotten the thing up and running yet so under "actual" use it may give some play. I doubt it though. The assembly isn't of the highest precision but it isn't sloppy, especially when tightened up to the rail.

Can't beat the skate bearings on price! These cost about $4 for a set of two but I did no "shopping around" nor did I look online. Costs can surely be found for less but probably not under $1 each. However, this is a complete little assembly so requires less build time. (I am assuming the skate bearings need an attachment. Is this true, I've never really looked closely?)

Question:

The skate bearings end up being metal on metal in this application, no? Does this affect performance or result in slip? The units I'm using are a semi-hard plastic and don't really slip much but I imagine that the coefficient of friction is greater. Don't know if it will be an issue either way.

Cheers!

Viktor,

Nice pics!

You said "a sort of velvet." What is it exactly. Is it actually velvet of just a higher quality?

The threaded rod looks like a very high thread/inch count. What was it? Can it be bought or does it need to be special made? Could one use a gearing system to drive a courser rod for the same or near-same precision?

Cheers!

Hi Demented Chihuahua,

... the threaded brass-rods i bought in the tool-store, it's a normal M5-threading - i only lathed the rods for inserting small ball-bearings with 3mm inner hole.

The 'velvet' was a synthetic velvet-like fabric, i used it only, because it was there

In particular you can use every fabric - it forms with time the form-grip for the threading.

You can define the friction and form-accuracy through layering more sheets, so you have a bit more compression between the plates, the fabric and the screws ...

Viktor

Edited 1 time(s). Last edit at 10/09/2007 02:08PM by Viktor Dirks.

Viktor,

I like the definable friction and form-accuracy ability. That is a very big deal. Imagine being able to do that with many parameters of a system and not just one! With a quick-built RepRap you could build mos things. Take a little more time and effort and install some optional control mechanisms and you can build much more valuable--commodity-wise--things on a finer scale. Think art and instrumentation. This is something future versions of RepRap should incorporate.

Cheers!

Hi Demented Chihuahua,

... if you havn't read this ( [forums.reprap.org] and [forums.reprap.org] ), then go through the threads and the links i posted - with a self-joining magnetic-joint-tripod i didn't have any work with aligning axes, inserting bearings, gears, belts or other stuff ...

You can imagine as fixing three linear drives on a basis-plate, fixing the three arms on the gliders and apply your dispenser (or my diodelaser) on the toolhead-plate, plugin - and you're ready for reprap!

I'm on the software now, so maybe in some months i can control every kind of noncartesic assembly and output calculated slice-coordinates, so i can play around with different kinds of 'self'-assembly structures ...

With a smaller tripod (e.g. 20x20 centimeters footprint) i can move and build with sub-micron-accuracy in centimeter-range, with a scaleup (for example 2x2x2 meters) and an extruder for centimeter-thick trays the same software could build macroscopic objects, as furniture or so, too ...

Viktor

Viktor,

A problem could be the scale up of the magnetic joints, yes? I haven't ever seen magnetic spheres larger than about 1 cm or so. Where would you get spheres big enough for a 2x2x2 meter reprap?

Demented

Hi Demented,

... spherical neodymium-magnets with 19 mm diameter are strong enough - i buy them here: [www.supermagnete.de]

For not so exact joints you can use normal ball-joints, they are often used in vibrating machines, can be bought in normal hardware-shops and the counter-glidings are from sintered metall or plastic ...

Viktor

How did you attact the bearings?? Are they just press fit into the bracket or did you do something else? I ask because I'm also in the middle of building a CNC machine based on the McWire Instructable and was planning on using a bearing to hold the free end of the threaded rod to stiffen things up a bit.

My initial use will be to route out rough shapes for pinewood derby cars. I get to teach my girls how to design in a cad program which should be fun In the end I'd like to wind up with something I can use to build the parts for a reprap in whatever form it evolves into.

hey william.

it would be much easier to show you in pictures, but until i can get into the lab again to show you, i'll just have to describe it. there are essentially 3 different types of bearings in my version of the mcwire design:

1. static horizontal bearings on the outside of a stage. these bearings replace the aluminum rail mounted to the bottom of a stage. you will want 2 on each end of the stage. they are easily mounted. you drill a 5/16" (or 8mm) hole, then mount the bearings with washers on each side, and a nut. i use a 3/4" length 5/16" diameter machine screw, and countersink it so the head is flush with the stage.

2. spring tensioned horizontal bearings. these bearings are the bearings mounted on an arm like in the mcwire design. i switched to using 2 bearings, and attaching a spring between them to keep the tension. its pretty easy as well. you drill 2 holes on opposite sides of the stage, countersink them, etc. you then make the bearing arms. the bearing arms should have a countersunk hole for mounting the bearings. to mount the bearings to the bearing arm, you simply use another 3/4" length 5/16" machine screw. drill a tiny hole to put a penny nail through, and glue it in place. once it dries, bend it at 90 degrees and this is where you will attach the spring to. once you have 2 of these, mount them to the stage, and you're good to go.

3. a further modification to the mcwire design i've made is to put vertical bearings in the aluminum u channel itself. that way, the acrylic stage rides on the bearings themselves, and not directly on the aluminum. this makes the gliding action *so* much smoother. i'm using 3/4" x 3/4" aluminum from McMaster, so there is a 1/2" wide space in the middle. i cut 3 pieces of 5/16" threaded rod to a tad bit over 1/2" long with a hacksaw. after that, i took the threaded rod, put a bearing on it, and sandwiched it with washers. then you have to force it into the middle of the U channel. in order to keep them level, i took the blade off my hacksaw, laid it flat inside the channel, then forced each bearing down into the aluminum channel until it touches the hacksaw blade. then simply remove the hacksaw blade, and marvel at your smooth rolling aluminum channel.

i haven't gotten to the Z axis yet, but its very similar. also, keep in mind that each of the bearing types all use the same type of skate bearing (technically a 608 bearing)

this weekend i hope to finish my machine, thoroughly document it with pictures, update the DXF designs with my most-recent changes, and get everything released on the net for you guys. i'd like to thoroughly document it so that its even easier to build!!!

... here i have some images from another 2-axis-positioner with a flatbed-structure and relative simply driving and assembly ...

Viktor

Sorry Zach, I must have responded to the wrong post. I was talking to Viktor, he posted some pictures of a small XY table that was hand driven and I liked the way the bearings appeared to be mounted and wanted more info.

I received some 'slick strip' tape in the mail I had ordered and put it on my version of the McWire machine and it does wonders so I'm hoping that I wont need to go to anything other than the aluminum channels as bearing surfaces. It will all boil down to how strong my steppers are as to wether or not I'll need to go to some kind of 'active' bearings for the tables.

Hi William,

... i fixed the bearings with cyanacrylat on the rods and in the mountings.

If i want a better stability, then most with pressing small dots in the aluminium around the bearings, so they will be compressed tightly ...

Viktor

Cool, sounds workable for my application. I have a bunch of bearings that have a flange/rim on one face so I can just glue it to the rod and then push it into a hole in the mounting bracket until the flange is seated.

So far I really like the McWire concept. I'm just adding a few mods to improve, in my eyes, the overall precision and ridgidy.

... have a SPAM-bot solved the image-code?

The lazy spam-bots use human backends:
[www.schneier.com]

Unfortunately, I deleted the message before flagging what user it was. I'll hammer them next time they pop their head up.

... damned! clever beasts (or spambot-programmers) - that means even captchas are obsolete now ?!?

I think we'll have to go straight to Voight-Kampff* testing.

Viktor, reaction time is a factor in this, so please pay attention. Now, answer as quickly as you can:

It

... hihihi ... i runs conform with subject 3

Viktor

I smile politely, then call the cops.
I saw a turtle once...

um...I don't get the change in posts? ???

Hi Demented,

... a spam-bot dropped in after William and Sebastien removed this posting, so it's even again ...

Viktor

Zach,

I was a bit in silence in the past few weeks, but I have been following your progress closely.

If Im right your status is more or less the following:
- you have improved the mcwire design, so it more wear resistant (teflon strip)
- you have migrated towards the ardour platform
- more smoother motor running

What is missing which is prevent the design actually functioning?
(the first goal is pen plotter, am I right?)

To put the long story short: I cant wait to have one.

Can we consider the design stable?
If so, can we manage somehow the postage to Hungary too?
(If its through the reprap store the better)

Is there any remaining problem to solve?

Best regards,
Khiraly

Hey Khiraly,

Yup, you're right. Basically the only technical thing remaining is to finish the firmware for the Arduino so that it talks to the host software and then does the right things. That is happening as we speak. I'll be posting results here soon hopefully.

Other than that the remaining hurdles are:

1. updating the lasercut drawings to reflect all the changes/updates i've made to my v1.0 design.
2. documenting the full assembly of a McWire Cartesian Bot.
3. creating the part kits and making sure every part specified is used.

so yes, its technically ready, but there is still quite a bit of work to do before i can offer the kits for sale on the store. know that i am working very hard to get this stuff done as fast as possible.

khiraly Wrote:
-------------------------------------------------------
> Zach,
>
> I was a bit in silence in the past few weeks, but
> I have been following your progress closely.
>
> If Im right your status is more or less the
> following:
> - you have improved the mcwire design, so it more
> wear resistant (teflon strip)
> - you have migrated towards the ardour platform
> - more smoother motor running
>
> What is missing which is prevent the design
> actually functioning?
> (the first goal is pen plotter, am I right?)
>
> To put the long story short: I cant wait to have
> one.
>
> Can we consider the design stable?
> If so, can we manage somehow the postage to
> Hungary too?
> (If its through the reprap store the better)
>
> Is there any remaining problem to solve?
>
> Best regards,
> Khiraly

Zach,

That's awesome. Thanks for all the hard work!

Demented

Thanks Zach for the update. Cant wait to put my dorty hands on the parts!