Differences in sizes of parts, nuts and bolts???

[Nando]

Hi all,

Bringing this up here to see if anyone has noticed the same issues.

It's two separate issues:

1. Differences in parts sizes between "original" and bQ:

Picking release 2.3 there are two sets of parts the ones from the main branch and the ones that contains some changes made by bQ.

While  I would thought those to sets could be interchangeable they actually aren't (or at least not all parts are).

I like parts from both sets but hadn't paid much attention to the sizes and dimensions of both until now when I had to change a part and of course decided to go with the ones from bQ as they share the IPT (Inventor files)... I hate OpenSCAD.. i truly do... :D

See bellow what I mean, center part is bQ STL and right one is Carlos STL.

The hole position is not the same, and when trying to use the parts from bQ the holes wouldn't align with the bed. (I haven't checked but bQ bed holes must be closer together in the bed)

(Left to right: Mine changed part, BQ Part, Carlos Part)

The second thing you'll notice is the hole diameter and that takes us to second issue.

2. Nuts and bolts holes dimensions.

When I printed all the parts for my cyclone I noticed the holes were too big for M3, it would fit but with a large tolerance and I needed up using a odd measure. M3.5.

Not sure if anyone noticed the same?

Using the image above again the reason I had to update the part was for that, I wanted to use M3 in my new bed and decided to "fix" the part.

The one I made (left) uses 3.4mm for the hole, that is a decent fit. If you look at the other ones the holes is much bigger. IT works well if you use M3.5 bolts and nuts but that is not what is listed in the BOM file.

To try and understand why is this, I decided to look into SCAD files... and I struggled to understand anything...

Still I found the following, the default config states a screw hole tolerance of 0.4mm.

Default_config.h

---

// --- Tolerances ---

Y_threaded_rod_Tolerance = 0.5;

Y_linearBearing_pressureFitTolerance = 0.5;

PCB_holder_tolerance = 1;

axes_Xsmooth_separation_tolerance = 0.5;

X_threaded_rod_Tolerance = 0.5;

Z_linearBearingHole_tolerance = 0.25;

Z_radialBearingHole_tolerance = 0.25;

LinearBearingPressureFitTolerance = 0.4;

screwHoleTolerance = 0.4;

Z_threaded_rod_Tolerance = 0.5;

---

So this wasn't makign much sense as the hole size was much bigger than 3.4mm, so I looked further into the libs and noticed that by default it also had 0,4mm.

standard_parts.scad

----

include <MCAD/nuts_and_bolts.scad>

module hole_for_screw(size=3,length=20,nutDepth=5,nutAddedLen=0,captiveLen=0,tolerance=0.4,rot=0,invert=false, echoPart=false) {

----

I assumed that at some stage in the code both get added together making a total tolerance of 0.8mm that is way too much and would create the sizes that I see fitting M3.5.

So I change the tolerance in the Default_config.h to 0 and tested and magic happened. 

The resulting hole size matches with the one I updated using Inventor.

My updated part on the left and the new one generated in scad with 0 tolerance on the right.

Decided to write and send this email to see if more have encountered these two problems and if there is any reason for using such high tolerances in the parts?

Finally the fact that the two sets of parts may not be 100% compatible (bQ and Carlos) should be flagged in the instructions to avoid confusions.

I suspect I need to redo all my parts to just one set as I may have other problems that I didn't realized when I assembled it. For example my X gantry was to stuck and wouldn't move well, I suspect now it may be due to me mixing two parts, X carriage from bQ and side panels from Carlos causing the rods to not be at the same expect distance.

Cheers

- Nando

Sent from my Sinclair ZX81