Contraptor

Hello !

This will be the thread for the contrapteur mini-cnc project.
The goal is to make a complete replica of the mini-cnc, but using metric parts.
The good thing about the mini-cnc is that it uses all contraptor parts, so translating it's part is basically translating contraptor.

So to start, we need a frame with about the same dimensions as the contraptor mini-cnc.
Here bellow is a draft, conversion has been made the following way :

• For short parts, use parts with the same number of holes.
• For long parts, use parts about the same length.

Picture :

It ends up looking very much alike.
Some things may need to be changed once we start adding the moving parts, we'll see then.

So now that there is a frame ( in sketchup ), what is needed next ?

• Sliding elements : design already started in the big-cnc project, raw aluminium square tube easily available.
• Linear bearings : TBD, main problem is here is that aluminium channel is hard to find. Could be made by shortening U profile legs.
• Linear rails : design started in sketchup, same problem with aluminium channel.
• Coupling nut clamp and Lead nut mount : TBD
• Shaft mount : easy, will be made with laser cut holders, see discution
• Belt clamp : easy too.
• Motor mount : design already started in the big-cnc project, from square tube cut in half, with rubber vibration isolation.
• The rest ( parts column ) : TBD, but lots of progress already done for the big-cnc project

Picture of a first draft :

Documentation : 

• Wiki page ( under Metric version )
• Sketchup file to be uploaded to 3D warehouse
• Build log with pictures
• Trying to document it as well as the original mini-cnc

Any comments/advice is super welcome !

Update.

Added : 

• X and Y rails
• Z sliding elements
• X , Y and Z stage
• Ball bearing mounts

Modified :

• At first I used the new version of the Z axis, but it turns out with 20mm there is not enough room to fit a pulley inside an angle, so the pulleys needs to be bellow. Ended up with a mix of the two.
• Diagonal bar
• Linear bearings now fit correctly, that was tricky

Next steps:

• Design the coupling nut clamp, it'd be nice to find a way to do it like the ball bearing mount ( stacked lasercut parts ).
• X currently uses angle-14, angle-16 makes it larger than the contraptor mini-cnc, but is a more standard size. Needs testing.
• Ask ( doing it right now ) if it would be possible to attach the table to the Y stage using two-sided tape or something like that … would increase working area.
• Add the last ball bearings, threaded rods, pulleys, belts, and then motors.

Picture time !

Also, it's now on Google Warehouse for easier download.

Update.

Happy new year !!

Worked on the elements today, not everything is finished yet, but it's beginning to look like something.

Ball bearing mount :

• 
• Put the holders on the inside of the angles
• Put the screw holes closer to the bearing so that the bolt heads hold it in place ( forgot to repeat on the angle, todo )
• Added a bit of empty space to leave space for a bolt head when attaching the angle

Motor mount :

• 
• The rubber plate is now in two parts to accomodate the circle shape at the front of the stepper
• Still missing the 3 angle holes

Lead nut mount :

• 
• Hegagonal plastic plate is for holding the lead nut
• Round plastic plate is for closing the element ( prevent back/forth movement )
• Has room at the bottom for the bolt head

Lead nut mount for sliding element :

• 
• Made similarly to the other lead nut mount, but but with a shape that centers the lead nut in the sliding element, and room for bolts to secure it to the sliding element.
• Will be reworked so that the lead nuts and the bolts are horizontally aligned, will reduce the size of the plastic plates.

Added all these modifications to the contraptor mini-cnc machine.

Pictures : 

Todo next : find out what's todo next.

Update.

Made a few modifications : 

• The motor mounts are now lasercut parts, this is mostly for simplification and price reduction.
• All of the axes now use the sliding element. It is a new version of it, with a single length : 40mm, and all the inside covered with UHMW-PE. Hopefully it is also a more simple version, but it needs testing.
• The table is elevated by 20mm, it will be put on 4 adjustable rubber+screw+screw-handles-things, for super easy adjustment of the table ( up to about 1 or 2mm ) . The screws will be in a place where they do not stick out of the table ( by using 2 tables of 4m thickness on top of each other ) , so 100% of the table area will be usefull. Also needs testing.
• All of this gives a bigger working area : 320x220 mm ( more than A4, yeee ! ).

Pictures :

Design update.

Working on a contrapteur version of the contraptor sliding-element for use in the mini-cnc.

Here is how it looks in sketchup :

The version on the right is for use with UHMW-PE extrusion, the whole element is coated with plastic, and the angle is in contact with the element on all the surface. It needs to be extruded, so it's suitable for mass-production, but difficult for DIY. It may also be 3D-printable.
The version on the left is closer to the original. It uses two UHMW-PE pads ( instead of 6 ) but works similarly. It can be made with the contraptor mini-cnc and a dremel, that's what was tried here : 

The material is a cutting table from the mall, it's the only UHMW-PE that could be found locally ( EDIT : in fact not UHMW-PE, probably just HDPE, does not slide as well ). It was 9mm thick, close enough to the 10mm in the design.
Here is how it looked in Cambam : 

A note on cutting UHMW-PE : It was difficult to find a bit to cut it with, finally ended up with one with a teethed ball at the end.
Cutting too much at a time ( DepthIncrement, used 0.25 ), too fast ( CutFeedrate, used 250 ) or cutting only one track ( used 3 ) led to plastic accumulating in the tracks, then after a while melting and causing chaos.
Could probably be solved by using some sort of fan/extractor.

After running in about every mechanical/software problem you can have, two days later, here is the first successful cut : 

It fits in the metal tube ( think it's steel, there was no aluminium at the hardware store ) : 

And the angle fits in it : 

It fits, but in that state ( closed square ), it would be difficult to adjust ( too stiff, no bending ).
After playing with it, here is what seems to work best :

This way it slides well, and the angle is held well, and it would be adjustable with screws.

Next steps :

• Drilling another plastic pad
• Drilling a metal square tube
• Try them together

Update : unable to cut another part, the cutting bit is "worn off" ( big plastic blobs form around it ), waiting for others to come in the mail box.

Update.

Plastics received, tried using them on the mini-cnc, a few pictures :

PTFE sheet 20mm and 3mm :

Polypropylene sheet 2mm and 4mm :

UHMWPE 10mm and 20mm ( it's actually called RG1000, but they say it has the same caracteristics at a lower price ) :

First thing made was the UHMWPE parts for the sliding elements, cut from the 20mm sheet … that went well :

Result : they fit the angle perfectly, and they slide very very very very well. Very impressive. Next step for this element is to make the aluminium part ( cut/drill the square tube ).
The very good thing with cutting UHMWPE is that it does not melt easily the way the other plastics tried do, makes everything easier.

Second thing are the lead nut holders. They are supposed to be made with a lasercutter, but they can also be made on the mini-cnc … it just takes a lot more time and noise.
Not finished on that, it's very difficult to find the right settings, as the polypropylene melts very easily, but here is a picture of so far :

The cut with 3 parts at the bottom went well, the parts fit nicely.
At the top it is cutting all the parts for a complete nut holder at the same time. That second cut went bad shortly after the picture due to melting causing missed steps missing more melting …

That's all for this time, I'm away on a trip for a week, more melted plastics after that :)

Quick update.

Not much time for working on this now, and probably for all march.
The Polypropylene melts too easily to correctly drill the parts in it. Just ordered acrylic sheets ( pre-cut to 150x200mm, will make things easier ). Also a few other plastic types to try including HDPE.

Update.

Tried replacing in the design another metal part from the contraptor mini-cnc, with one that can be made on a lasercutter or on the mini-cnc itself : the dremel mount.

Not much to say, just a picture :

This should also work on the contraptor mini-cnc, so as the contrapteur mini-cnc does not exist yet, I'll maybe try it on the current machine first.
A definitive version will probably have more rounded angles.

Update. With progress !

Received the lasercutter, had to change like half of the parts, including all of the electronics, but since a few days I'm able to make cuts that are close to correct.
It's controlled by grbl, so it works fine with GCODE generated by cambam for the mini-cnc, with just a few little adjustments.

About grbl, to get the lasercutter to work, I had to fix a bug in it, in the process I had to read it's code several times : it's awesome ! It really should be contraptor's "official" firmware.

So the first part I worked on is the lasercut lead nut mount.
It's contrapteur's equivalent to contraptor's lead nut mount.

Here's how it looks in cambam :

The hexagonal shapes are what holds the lead nut ( M6, 18mm long ).
The "screw head" shapes at the bottom of the parts are what hold prisoner the heads of the M5 screws. These are used to attach the finished element to the rest of the contraption.
The circle shapes are what "begin" and "end" the stack of parts. They maintain both the lead nut and the M5 screws "trapped".
Finally the 4 holes in each part are for 25mm M2 screws, that hold all of the stack together.

Here is how it looks fresh out of the lasercutter :

It's still attached to the acrylic sheet with "holding tabs" : 

They easily "snap" out by breaking the holding tabs, and then need just a little bit of cleanup : 

Then we stack the hexagonal parts around the lead nut :

Then the two M5 screws "slide" in :

Now the two "closing" parts are used to close the stack, trap the lead nut and the two 5m screws, and the M2 screws are used to hold it all together :

It can then be attached to a contraption and move around a M6 leadscrew : 

In the end, it seems to work good. I can't wait to use it for real in the mini-cnc.

More to come soon !