Gravity – The delusive force

Why is gravity so weak? Possibly because its the sub-dimensional effect of a much stronger super-symmetric hyper-force. Maybe its because gravity is mediated by closed strings whereas the other forces are mediated by open strings. Either way, as well as being extremely weak compared to the other fundamental forces its also extremely  unreliable. Sure we stay attached to the earth most of the time, but when it comes to holding things down like the Y Axis of my OverlapStrap you cant rely on it at all!

To resolve this problem I added some reinforcements to the Y-Chassis so that it is clamped down in much the same was as the X-Carriage.

I had run out of alu angle, so I used fixit blocks instead, and also because it just illustrates a slightly different implementation of the same concept. I also got some scotch double sided tape as recommended and covered the acrylic bed with it. With these tweaks in place I was able to print belt-width-adjuster_1off.stl again, only this time I could remove it from the bed without breaking it.

The photo above is the bottom side that was attached to the bed, the top is pretty much the same quality as before. Then I got a bit more ambitious and decided to print something bigger belt-split-jig-bracket-universal_2off.stl

Sadly both of these failed. The problem this time is that being larger parts, they succumb to the effects of warping. The parts warped so much that the part came off the bed mid print, and the layers got completely misaligned. I have ordered the parts for a heated bed, and also ordered some PLA, as I understand warping is less of a problem with PLA.

Going back to smaller parts, my best print so far after alot of tinkering, and pain with reprap host came out much better than my first attempt.

On the left is the new print, and on the right is my first print for comparison. For reference, my settings I tweaked were:

  • Reduced Temp to 220°C
  • Increaced Filament Size to 0.85mm
  • Increaced Infill Size to 0.6mm
  • Increaced Layer Height to 0.4mm

Reprap Host – Gotcha’s

There are a number of “features” in reprap host that make it confusing to use. So much so that most people seem to have given up on it and now recommend either using Skeinforge or Repsnapper.

  • There are a number of “legacy” preferences, that at first look, you would expect can adjust things like the steps/mm however these settings are really edited by modifying the firmware
  • The MaximumFeedRateX and MaximumFeedRateY parameters do effect the feedrate, but only when using the axis jog dials. When printing, or using the Home button (in the same screen as the jog dials!) The firmware settings are used.
  • The Extruder control tab seems to start off with the extruder set to reverse despite the reverse checkbox being un-checked. You have to check and uncheck it to get it to be correct.
  • The feed-rate of the Extruder is constrained by the  Extruder0_FastXYFeedrate setting which would be expected, however its also constrained by the MaximumFeedRateX and MaximumFeedRateY Global preferences. This is quite annoying for me, because I have such a low feed rate (200mm/min) so if I want to use the XYZ jog dials I have to set the preference to 200mm/min, but then if I want to prepare the extruder by loading it up with filament, I have to remember to go and change all the preferences to 3000mm/min
  • By clicking various combinations of the ramp and switch heat on/off button the text on the button can say anyone of the following:
    • Switch heat on
    • Switch heat off
    • Switch heater off
    • Switch heater on

    Also because the ramp button does not properly change the up/down state of the heat button by playing around you can get various confusing combinations of state compared to the text that tells you what the state will be when you press it!

  • The Ramp button is only really needed for drying cement, (i.e. part of the extruder manufacturing process) Its really confusing to have this button on the tab at-all, especially in combination with the above feature.
  • The Layer height preference must be set the same for all extruder’s. If different settings are used for each extruder the software makes a calculation error and starts the print at Z4.0 i.e 4mm above the bed! This one caused me a lot of pain recently as I had no clue as to why the gcodes being generated would be wrong. it was only by chance that I ran reprap from the command line and noticed an error message saying that they were different, and luckily guessed that this was the cause.
  • The documentation suggests that by changing InterLayerCooling to false and setting Extruder0_CoolingPeriod to -1 that the machine will not return to the home position between each layer, however looking through the source code it is apparent, that it is impossible to disable Homing. The software needs to be fixed to achieve this.
  • Finally Reprap host is incredibly slow, its about 10x slower than Skeinforge, and Skeinforge is about 10x slower than Repsnapper, making Reprap host 100x slower than Repsnapper! I should think the reason for this is probably the use of TeMpOrY gcode files rather than using memory mapped files or something else. When I run reprap host, my system usually grinds to an unusably slow rate for 10 mins or so. Repsnapper generates gcode for the same file in a number of seconds.

Finally here is a screenshot of the wonderful Repsnapper (since I had never seen a screenshot before using it)

Welcome to the future.

Acrylic Bed

I was having trouble getting the first layer to stick so I mounted an acrylic bed. I had to move my Z end-stop up, so at the same time I mounted the Z end-stop on an adjustable riser, so that I could fine tune my Z offset.

With these two tweaks I was able to get a really good print of belt-width-adjuster_1off.stl

The trouble was that it stuck to the acrylic too well, and was near impossible to remove, in the process of removing it I completely wrecked the underside of the print.

I have been told that a good material to print onto is scotch blue tape, so I am going to try that next.

First Print!

Well I haven’t posted for a while, because I have been working on my Decking. As well as that though I have been finishing off the OverlapStrap, since my last post I have made several improvements, such as beefing up the X-Carriage

Improving the way the Thermal Barrier was fixed to the CrudeStruder. I also added the finishing touches such as mounting the end stops, wiring up all the (pre-assembled) electronics, and general finishing off needed to test everything.

Then this weekend after a lot of tinkering and a lot of help from Tonokip via IRC, I was able to print my own derived version of Nopheads Mendel Pulley which I re-designed in openscad.

It looks pretty ugly, but I am quite pleased that its roughly resembles the pulley that I was aiming for. It did however need some cleaning up, this is what it looked like straight of of the printer.

The problems I am having are

  • Getting the right setting for e_steps_per_mm
  • Getting the first layer to stick (I am currently printing directly onto MDF so no surprise)
  • Strings and crud attached to one side.
  • Detail level is too low. (The pulley is not detailed enough to have teeth yet so its not usable)

Stepper Motors

When I ordered my stepper motors sometime last year from motion control products I chose the cheapest model at £11.23 which was FL42STH38-1206A sometime afterwards I realised that these steppers have much lower holding torque than the recommended mendel FL42STH47-1684A-01 (25.5N-cm vs 43N-cm) however this was not a major problem since mendel requires that “Torque must be at least 0.13 Nm” which is 13N-cm, and well below the rated holding torque. It was only when I came to wiring the steppers up that I came across the next problem. The Generation 3 stepper drivers are for use with Bipolar steppers.

Wheras the steppers I had bought were Unipolar steppers.

Fortunately for me they were 6-wire Unipolar  steppers, and as you can see from the wiring digrams above you can just not connect the centre taps for the coils (labeled A and B above) and we have a bipolar stepper again.

More recently when I decided it was cheaper and simpler to use two steppers for my Z-Axis, I was a stepper short. This time I bought the SY42STH47-1684B compatible product from Zapp Automation for only £8.50 it has a holding torque of 43.15N-cm and is a 4-Wire Bipolar stepper. I am going to use this to drive the CrudeStruder, as I think it could benefit from the extra torque.

OpenSCAD

I have been hacking around with OpenSCAD. First I added an exponent operator to the language because I felt that writing pow(x,2) was a bit more cumbersome than x^2 . Then I added a few more operators like a component-wise multiply and component-wise divide I wanted these to make it easier to translate points so I could use them as datums. I even implemented an experimental rotation operator. Then I decided to get a little bit more adventureous. What I wanted to do was make the OpenSCAD editor have syntax highlighting. Investigating doing this using qcodeedit is on the OpenSCAD todo list, so I thought I would give it a try

I was quite pleased with the results and it wasn’t to complex to implement, QCodeEdit’s QEditor is almost a drop in replacement for QTextEdit. I created a wrapper which allows somone compiling the source to choose which editor they want to use with compile time flags. In fact, to disable QCodeEdit support all one has to do is uncomment out the line with

CONFIG += qcodeedit

in openscad.pro

EDIT: All the changes have been merged into the main github repository which can be checked out using

git clone https://github.com/openscad/openscad.git

OverlapStrap X Carriage

Here is the latest photo of my OverlapStrap I have made quite a lot of progress on the X axis Carriage. As you can see the basic idea is the same as the Z skates and Z rollers previously posted. Also mounted is the CrudeStruder. I feel like i am very close to getting things working, all the electronics all also ready they are just waiting to be connected up. I just need to re-inforce a few things, tweak a few other things, and hope that the whole thing comes together as planned.

OverlapStrap Fixit Blocks

“Fixit blocks” are the bread and butter for Bodgeit’s Repstrap Bertha and my own OverlapStrap design. They are convenient little fixing blocks sold by:

Unfortunately for people living outside the UK these blocks seem to be difficult to source. I am afraid that I also don’t have a solution for people wanting to buy these blocks from a supplier in their own country. However I am willing to re-sell packs of blocks via ebay, and ship internationally so if anyone is interested drop me an email. It seemed to me that also no one has drawn accurate drawings of these blocks for anyone who was interested in making their own. So here are the drawings below

The drawing is also available here as a DXF file.

Also for anyone trying to source these in other countries, here are some potentially useful search terms:
Modesty Block
Jointing Blocks
Knock Down Block
Knock Down Fittings
Fixit Block
Fixing Block
Cabinet Fixing Block
Viereck Möbelverbinder – German for: Quadrilateral Furniture Connector
Cupboard Connector Block

There is also something very similar, but not quite the same in the USA. I think in the USA they might be known as ‘Knock Down’ fittings/connectors.

OverlapStrap CrudeStruder

Sometimes you think you have come up with a simple design, but when you come to real-ise that design it turns out to be much harder than you imagined to make.

So I went back to the drawing board, and came up with something even simpler. This is what I have come up with, the crudestruder.

There is nothing really innovative about this design, its just a piece of MDF with mounting holes for a NEMA 17 and some 15mm copper pipe clips to hold on the thermal barrier. I used another short piece of 16mm PTFE rod with a 4.0mm hole to act as a filament guide. The pinch-wheel is just one of the standard mendel m4 bearings, and is held using a flange of aluminium that I cut off of my original stock of aluminium angle. This pinch wheel mount is held using the same m3 bolts that hold the NEMA in place. The top hole of the mount was cut into a slot to allow minor adjustment. I use a conrad electronics splined model car insert to provide grip on the drive shaft.