PLA Bushing Best Practices

I am assembling my tslot tantillus and was running into some issues with the x/y ends and binding during assembly, problems I don't recall on my first tantillus kit from sublime ( rods and printed bushing were supplied).

Initial Setup:

I remade the x/y ends so that the bushing was integrated into a single piece, I am thinking this was a mistake as they may need some ability to deflect a little like bronze bushing holders do.

I am using 5/16" O1 drill rod from mcmaster car, the rods seems straight and the finish is ok certainly not polished.

Also my PLA bushings had a dull finish when printed from not being printed at a high temp. The PLA is also purple ultimachine and not translucent so may have more additives / filler in it to get the solid color? Maybe this makes them more tacky and less smooth.

I was also using the pla bushing of the metric version and not the sublime / thingiverse one.

Problem:

While the x/y ends slide effortlessly by themselves, when the 2 ends are attached with a rod I could only slide the assembly one direction ... it would not go back the other direction without a lot of effort. I tried making the x/y ends much looser on the rods but this didn't help.

First Attempt to fix the issue:

I ended up ditching the integrated bushing, I reprinted the x/y ends as they should be without the bushing integrated.
I then printed the bushing at a much higher temp to get the print surface shiny. I switched to the bushing stl from sublime also.

It seems much better now but will still bind unless the x/y ends are held very parrallel (not sure how much binding when deflected is normal).
I imagine when the spectra is install and things are square this won't be as much of an issue.

Other ideas:

- Polish the rods with polishing compound
- Use a different / clear pla
- Make the bushings a looser fit in the x/y ends
- Recheck alignment between the rod pairs (currently about .25mm from end to end).


Any ideas and best practices and how much binding should be expected with the full x/y / spectra assembled unfinished? Or things I should be doing to make it smoother?

Edited 2 time(s). Last edit at 05/15/2013 04:11PM by goopyplastic.

They do tend to bind really bad if the cables are not attached and the LM8uu's in the carriage are not broken in yet.

Natural PLA does tend to work better but I have used colored as well without problems.

Using the end of the rod to cut the inside of the bushing out as stated in the instructions does really help.

Adding some lubricant for the first while helps.

Making sure the 3mm laser cut hotend mount is the correct thickness matters a lot.

If you look at Igus's bushings and rods they recommend a rough surface and say to not use a polished one. I believe this is to reduce the surface area in contact with the bushing which in turn would reduce friction.

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Can you just use normal lm8uu's here rather than the printed ones?

Ben

plexer Wrote:
-------------------------------------------------------
> Can you just use normal lm8uu's here rather than
> the printed ones?
>
> Ben

No. The rods rotate and the bearings have races that run only length wise. If you rotate the shafts the balls either have to turn in place in the race and leave dimples or they don't turn and you leave flats on the balls. Either way the LM8uu is ruined and the linear travel gets rougher and rougher with each rotation.

They must be bushings of some sort. Brass, Bronze, Igus, Delrin, Steel or Printed all come to mind. Ultimaker uses Bronze. Ditto uses Delrin. Tantillus uses printed or Igus.

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If the plastic parts were modified would these be ok bronze bush ?

Thanks

Ben

plexer Wrote:
-------------------------------------------------------
> If the plastic parts were modified would these be
> ok bronze bush ?
>
> Thanks
>
> Ben

Yes but remember the outer rods are 5/16" and not 8mm because high precision 8mm rods do not fit in 608 bearings without a press fit.

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Ok I guess several options possibly, go with 5/16" rod, hammer 8mm into 608's or depending on hardness turn down end of 8mm to fit 608's?

Ben

I hammer hundreds of 8mm h6 rods into 608's for the Wade's idler in Mendel90 kits. They vary between loose and needing a good bash with a hammer or squeezing in with a vice but I have never needed to turn them down.

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nophead Wrote:
-------------------------------------------------------
> I hammer hundreds of 8mm h6 rods into 608's for
> the Wade's idler in Mendel90 kits. They vary
> between loose and needing a good bash with a
> hammer or squeezing in with a vice but I have
> never needed to turn them down.

Thanks for that I hoped it would be that simple

Ben

Started working on the xy ends in openscad to make them to be adaptable to different bushings.

Files attached if anyone would like to take a look and make any comments in case I've screwed up or if it's rubbish.

Thanks

Ben

Also note that assembling Tantillus with rods and bearings that need to be press fit could be a nightmare since the current design has you slide the rod through one bearing all the way to the other bearing on the other side.

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Still under the bushing topic, can I replace all LM8(S)UU with bushes?
I guess their lighter and make less noise as well, right?

colpaert Wrote:
-------------------------------------------------------
> Still under the bushing topic, can I replace all
> LM8(S)UU with bushes?
> I guess their lighter and make less noise as well,
> right?

I used printed ones in the carriage of first machine for a few days but they have to much slop. The carriage is really short in X and Y so it requires really precise (even tight) fitting bearings.

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This means I should really find high precision 8mm rods, right?
The drilled rods I got are just a tiny bit bigger than the 5/16" ones I got, to the point that they fit inside the 608 bearings.
Btw, the bushes I was thinks were printed but would also have a steel ring covered with PTFE (like this one [4.bp.blogspot.com] from Alain's blog [tantillus-br.blogspot.com.br]).

colpaert Wrote:
-------------------------------------------------------
> This means I should really find high precision 8mm
> rods, right?
> The drilled rods I got are just a tiny bit bigger
> than the 5/16" ones I got, to the point that they
> fit inside the 608 bearings.
> Btw, the bushes I was thinks were printed but
> would also have a steel ring covered with PTFE
> (like this one
> [4.bp.blogspot.com]
> AAAAAAAABD0/0tL57hbw7R4/s1600/20121008a-Bucha.jpg
> from Alain's blog
> [tantillus-br.blogspot.com.br]
> -do-carro.html?m=1).

Yes those are good for the outer rods but again I would use the linear bearings on the cross bars.

I would hold off on ordering higher precision rods until after you test fit linear bearings on the ones you have.

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