Bukito Idler Pulley Bracket / Synchromesh (fits OpenBuild V Slot Rails)

by codemite Sep 2, 2014
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I've been worried about my idler brackets since I got my Bukito, and was planing on designing this later today. Thanks for saving me the trouble! Can you put both sides on the Bukito, and do you think it's worth it?

I've modified the set. This is pushed from 5.5 to 6mm of thickness. It has an impact shield now as well as better geometry.

This one is strong enough that you don't need it on both sides. I believe the problem with putting it on both sides is that the V-wheels on each of the axis chassis will hit into the back of the opposite side because it's longer than the original. You will also need another spacer and a longer pulley bolt if you want to double it up. The mechanics of doing that won't work out well. I am working on a version that will have a bearing shield on the front to protect the bearings from frontal impact. It got hit and was almost knocked off the table today. I want to stress test this mod before putting them up. If you want to make it stronger bump up the fill to 50% or more to give it a little more strength. I found that 40% fill with the honeycomb worked out to be a good balance.

You shouldn't have two different ones. The X and Y idlers for the Bukito are identical pieces.

At first, you would think that. The original had a laser cut insert at the end that can be put into either side. This new design has the OpenRail grooves printed into the backside so you can't change sides.

On the Y- axis the bracket has to be on the back side of the rail pushing the syncromesh downward or the platform will hit the bearings. On the X-axis the bracket is on the Left side, opposite the extruder housing and must be down or the v-slot wheels will run over the syncromesh cable. If you reverse them then you will have a double problem.

I made that mistake on the first version. I made two which are opposites. Also, they can also be paired together on either side of the rail to make a very strong double bracket for a bearing for general purpose use with OpenBuild v-slot rails. .

I'm afraid you're wrong. I'm the one who designed the Bukito, so I think I know what I'm talking about.

The way you have the Y axis idler mounted is wrong. Your sychromesh cable is misaligned and the tension on it will change as it moves, which will introduce nonlinearity into its movement and fatigue the sychromesh and the plastic pieces, reducing their life. The Y bearing needs to be situated 3.5mm above the center-line of the upper rail on the Y axis beam or correct alignment, which should allow the carriage to roll over the top of the bearings (but not come in contact with them) at its extreme. The bit of plastic you added sticking out around the bearing is a problem, and the carriage will hit that, which is why the original part wasn't shaped that way.

Thanks. I get what you mean. I found that out the hard way. I needed to make a quick replacement to get me back in operation ASAP. I wanted to beef it up a bit because I travel allot in rugged areas. (Afghanistan). This design worked fine for the Y-axis replacement but when I printed another to make a matching set for the (good) x-axis, the synchromesh ended up too high due to the extra re-enforcement around the bearing. In order to keep that design It was just easier to make a mirror version copy for the x-axis. This seemed more suited to my goal and saved me time. I'm sure most don't need to go this far with it but traveling is the reason I purchased it over other choices. I take it with me into environments that other printers just wouldn't survive. My goal is just to make it more rugged and survivable. I want to keep it around a while.

By the way.. I think you did a fantastic Job with the design! I'm really happy with this unit. I see allot of hard work and thoughtfulness in the layout and see that you will likely go further with the design. I am going to expand that section a bit more and make an impact cover to protect the mesh cable and bearing from a frontal impact. It was hit once already today when someone was moving equipment around. Almost knocked it off the table. That would not have made me happy.

Here's a question. I'm in a very high dust environment. I know the Delrin wheels can deal with it easy enough. I have a filament filter running as well. My question is do think this dust will have any impact on the exposed circuit board or should I consider making an enclosure for the electronic component?

Glad you like it!

If you want to reinforce the bearing, I would do it by making the part thicker (taller, in the printing orientation). You can inset the screw heads so that the part can get thicker without needing longer screws. You can also add partial covers around the bearings, but the Y bearing really needs to be sticking up (3.5mm above the center line of the V slot) with the top exposed, and no reinforcement extending higher than the top of the bearing.

The components on the circuit board are passively cooled, so dust shouldn't be a big problem there, and I would worry more about ambient temperature. There are fans on the extruder motor and the hot end, both of which will pull in a lot of dust, so you might want to filter those inputs. Apparently, all of the PC case modders say that cutting a square out of a pair of pantyhose and stretching it across is the best way to keep dust out of fans. Covering the circuit board with the same thing to keep dust off of it while still allowing airflow couldn't hurt, as long as you find a way to mount it so that it is stretched (if it's not sheer, it won't allow airflow from the convection currents).

I've made changes to the original. I've cleaved off the obstruction and squared off the geometry. The geometry now sits below the threshold of the bearing for the y axis. I've also added an impact shield version as well as mirror copy of each in case others want to use them in their own OpenBeam projects. The previous version was sitting at 3.9mm off center so It's been corrected to 3.5mm. Thanks for your suggestions.

Is that 3.5mm from the center line of the v-slot to the center line of the y-bearing?

Yes, the center of the screw holding the bearings is offset 3.5mm from where the center line of the V-slot passes it (if you extend that line out past the end of the extrusion).

It's just carton packing tape. I modified it's surface after it was applied to the platform. I had a shortage of blue tape. I don't have access any hardware stores where I am. So, out of necessity, I played around with what I did have access to. I found that using Scotch or ULINE clear packing tape(the wide kind) ,some spray trim adhesive, old plastic ID card or Credit card, talcum powder, and a fine porous kitchen sponge(3m yellow scrubby). I've been able to get several uses out of it. It works surprisingly well. The steps I used are as follows:

First clean the plate with rubbing alcohol.
Apply the packing tape pressing out the bubbles as you go. You can peel it off and realign if needed.
Spray the end of the plastic card with a little bit of adhesive spray and spread it very thinly over the tape using the ID card as a scraper.
While it's still a bit tacky I use the dry sponge and put talcum powder on it then rub it into the surface of the build plate.
The fused in talcum powder helps you lift it off the plate easier. If you not, You will be pulling off the tape after each use. The talc powder should be rubbed in with the sponge after a short pause. Blow off the excess.
After printing I get one of the edges lifted using a fine thin flat tip metal object like a screwdriver and use the plastic ID card to scrape off the rest of part little by little.

I've been able to reuse it several times. It took a bit of practice to get the technique right. The trick is to get as thin and smooth of a layer as possible but you don't have to be 100% covered, just enough to bind the skirt and brim.

Yes, I'll take your suggestion of counter sinking the bolt and thickening up the part. I'll try a letter "L" shape for the bearing shield so that it doesn't rise above the bearing top on the Y. It should function as well for the X. The pantyhose idea is good for the fans. I will try to build a stretch frame around the electronics and ruse the existing stand offs as a snap on mount point like they use in green houses and tents. That may work out. I'll re-label send this current design as a General Purpose OpenBuild V-Slot Idler pulley mount and go with the straight cut for a Bukito specific ruggedized bracket.

Nice update. BTW, what is the clear tape you're using on your platform? I've experimented with a lot, but I haven't found any good ones that are colorless like that.