New assembly question

I've started assembling a Tantillus from self-sourced parts a week ago and have a couple questions. Even without the X or Y motors connected, the carriage movement seems very stiff. So stiff, in fact, that moving the carriage by hand pulls the 5/16" rods through the bearings and breaks the printed corners. (It's a LC case with printed ABS corners.) Installing the motors and connecting the gears seems to confirm that the entire assembly is too stiff, as turning the motor gears by hand causes all sorts of sticking and lurching. The lurching can be resolved by further tensioning the cables, but I imagine the carriage sticking would ultimately cause print artifacts.

Diagnosis and fixes: I've carefully cut the plastic bushings (printed from natural PLA) so they run smoothly across 5/16" rods. I suspect either the carriage bearings are sticking, despite applying white lithium grease, or there's an alignment problem. If the XY ends were somehow twisted, I would think they'd naturally align during squaring and tensioning.

Having never seen a live Tantillus, how stiff should the movement of the carriage bearings be on their 8mm rods? I'm guessing it's pretty smooth when correctly assembled.

Is there any special alignment process I should use during XY assembly?

Is ABS acceptable for the corners, or will they simply flex too much under lateral stress from the bearings?

When the entire assembly is correctly assembled, aligned and tuned, is loctite still needed to hold the 5/16" rods in their end bearings (as I read in the forums), or will they rest comfortably without adhesive?

Thanks!

They should not be that tight but right after assembly it is common that they are a little tight.

On a machine that is broken in I can move the head really easily by hand.

On the printed case there is hole at two of the ends where the rod can poke out and it relies on the fact that the bars do not move length wise.

One possible issue is the carriage assembly. If the little plate that holds the hotend is too thick or too thin it will cause the rod spacing to be off and that results in binding.

If the bearings are too tight on the cross bars it can be an issue. With cheap bearings 1 out of every 100 seem to be way too tight (almost have to hammer it on the rod).

When breaking in a machine I have recommend to lubricate the outer rods. not needed but can help.

I have attached a break in gcode file that you can run on the machine that will exercise the X Y assembly.

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Excellent information, thank you.You've given me a couple items to check.

Of note, I had to 'thin' the acrylic carriage plate with a sander to fit the Mk-V hotend. It originally measured around 5.6mm thick. Is 6mm the proper thickness? I can print a spacer if necessary to create the right offset between the rods.

Edited 1 time(s). Last edit at 07/09/2013 01:40PM by robster34.

No it is supposed to be 3mm thick. So that would be the reason you are having issues.

I do not mind that others sell parts for Tantillus. I actually expect it. But I would think that they would have at least built one before selling parts. The fact that they sell the kit with the wrong parts means they have not built one, they do not know how to assemble one and they can not perform any type of quality control as a result of not knowing how it goes together.

I guess this should be a warning to others looking for parts that they should ask the people selling the parts if they have ever built a Tantillus. If not be sure to stay away as it needs to have all of its parts just right.

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robster34 Wrote:
-------------------------------------------------------
> Of note, I had to 'thin' the acrylic carriage
> plate with a sander to fit the Mk-V hotend. It
> originally measured around 5.6mm thick. Is
> 6mm the proper thickness? I can print a spacer
> if necessary to create the right offset between
> the rods.

Nope, it should be 3mm acrylic. It's thinner than the 4.6mm groove, but the mid will clamp the top of the J-Head to the bottom of the top carriage once it's tightened. PM me if you want me to pop one in the mail, as I have a couple of spares.

I find that there are a couple of things that keep the XY from moving smoothly by hand. Proper cable tension like you mentioned is the top. Getting the gears lined up for even rotation is another.

The least obvious is to disconnect the motors from the electronics board while you're hand-testing the XY. When you move the motors by hand, they generate a voltage across the coils. If they're connected to the electronics, the snubber diodes on the stepper drivers rectify this enough to backfeed the power supply. If I move an axis fast enough, it provides enough power for the electronics to kick on and enable the stepper drivers. This actively brakes the motors and causes the axis to stop moving briefly until the power supply and filtering caps run dry. The end result is that the axis stutters as you move it quickly, as if the bearings are grinding or sticking to the axis.

Edited 3 time(s). Last edit at 07/10/2013 03:10AM by pokey9000.

Thanks again guys. The carriage works much better once I milled the carriage plate down to roughly 3mm thickness. The X-Y movement seems smooth as silk now.

The acrylic supplier also offered to immediately ship any replacement pieces that need to be made out of 3mm material for me.

robster34 Wrote:
-------------------------------------------------------
> Thanks again guys. The carriage works much better
> once I milled the carriage plate down to roughly
> 3mm thickness. The X-Y movement seems smooth as
> silk now.
>
> The acrylic supplier also offered to immediately
> ship any replacement pieces that need to be made
> out of 3mm material for me.


Glad you got it worked out.

I really hope others have not tried building a machine with a 6mm hotend mount and given up because they could not get the movement to work correctly.

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