Sunday, 7 December 2014

Linear Carriages

I have started printing the linear carriages and the first batch have turned out well.   They are designed to have 2 x LM12LUU linear bearings fitted, which are clamped by the means of 4 x M4x16mm cap screws and 2 circlips on  each bearing to stop it moving up and down.  They were printed on my Up Mini at a resolution of 0.2mm, fine quality and 1/4 fill to keep the weight down. I will say though, make sure the part is printed with teh pockets for the balls facing upwards and if facing down, even with smart support the pockets are not radiused correctly.

I  am using GT2.5 open ended belts so the carriages are designed to grip both ends.  I printed and tried a few integrated belt gripper designs before I settled on the one below.  It is made so the belts pass over each other and are secured so the ends pull from the opposite side of the carriage, pulling the print layers together, not apart like it would if each belt was attached from the top and bottom.  This is important especially if the chamber is heated as I don't want any delamination of the part.   This also means I don't need to worry about too much belt tension breaking anything.   A 6mm  long piece  of 1.75mm filament is pressed into the eye where the belts fold over and becasue the teeth mesh together they cannot pull out. I yanked on both belts really hard and there was no movement so I am very happy.

carriage with belt fitted and securing nuts and bolts

close up showing the belt fed into the carriage and the small pieces of filament
locking the end loops

The belt grippers are located dead centre between the linear rods in both the x and y direction so there will be lateral forces on the bearings from the belt pulling the carriage up and down.   This also means that the steppers are mounted off centre to keep the timing belt centered to the carriage.

Like the end effector each carriage has a 10mm diameter N42 magnetic ball JB welded to it.

Complete carriage assemblies fitted

close up of the
 carriage assembly with bearings fitted

Friday, 5 December 2014

End effector and hot end fabrication and assembly

Well I think the design is pretty much finalised so I have started to machine and print parts and assemble them.

First up was the hot end.  It was cut from a single piece of alloy bar on my lathe and then the 5 mounting holes drilled on my mill. I still need to machine the stainless heat break and alloy heater block however which is planned for this weekend.  I am still tossing up making my own extruder nozzles but for the cost it would be just as easy to purchase them.

cutting heatsink grooves with parting tool

Tapping the M6 thread for the pneumatic fitting and heat break

Drilling the holes using the mill with DRO and the circular pattern function

The next task was to print the end effector on my UP Mini printer.  I ended up using the fine print speed, 0.2 layer height and 1/4 fill just so the sockets for the magnetic balls were nice and accurate. I have modded the heat bed on my Up Mini so it runs at 80ºc which stops parts warping.  I also used the new Verbatim filament and am very happy with the results.  The raft and supports came away from the printed part quite easily.

My design uses six N42 10mm diamter magnetic balls that are glued into the effector sockets with JB weld. It must be said however that this process was harder than expected and if I was to do it again I might use plain ball bearings and magnets in the rods.  The reason for this is the magnetic balls are just so strong.  Even at 60mm apart then will attract eachother as can bee seen in the video below and if you get too close they will jump out of the sockets and stick together

As you can see as soon as soon the balls are put in place their poles align and if one is rotated, the other moves.  This is important to remember before scuffing the magents so the JB weld has something to stick to.  What I did was place the magnets and marked their tops with a niko pen, then scruffed the oposing side with some 240 grit emory tape.  I was only able to glue magnets at a time however and needed to wait 24 hours for the glue to set before attaching the next ones.   I also found I need to wrap the magents that had already been glues with a tissue befoer gluing the next becasue if the next ball to be glues jumped out of the socket, it could hit the already glued ball with enough force to break the glues and knock the ball from the socket.

The effector was prepared by scuffing the socket with emory, drilling some 1.5mm holes so the glue had a little more to key into, then cleaned both the socket and balls with isopropyl alcohol

end effector sockets scuffed and drilled ready for the balls to be glued
Once all the balls were glued, the hot end, fan duct and 40mm fan were attached using M4 bolts and nuts.  This ensures a nice stong attachment that will not come loose or flex which will increase the overall accuracy of the printer.  Weight wise the complete end effector weighs 135 grams 

 I have also designed and printed a twin extruder end effector but have not made the hot ends yet.  It is the same footprint as the above effector which will make the tuning much easier. I also disigned adaptors for the E3D-V6 hotends just in case I didn't have time to make my own. An adaptor was also designed for the singel extruder above.   Again the aim here is to make things as rigid as possible.

end effector with 40mm fan and dual coling duct attached

More parts have arrived, including the 6mm alloy plate, carbon fibre rods and the 30x30 extrusion for the frame so lots more to do.

Will post more soon.

Monday, 1 December 2014

Verbatim 1.75mm ABS filament quick review

A few weeks back i purhcased some of the new 1Kg Verbatim 1.75mm ABS filament form RS components to see what it is like and I have to say I am very very happy with the quality of the filament and the print results.

The filament is made in Japan and comes vacuum packed in plastic then packed in a cardboard box which is great as it protects the filament properly.  Dimensionally the filament I tested was spot on 1.75mm with no variance on the spool I received.  The 005000-812 black filament prints with a nice high gloss at 235ºc extruder temperature and the supports and raft were nice and easy to remove from the print,   something I have struggled with other generic ABS filaments.

The 53mm spool core diameter is bigger than most so I designed and printed a reducer with a 22mm bore so I could use my standard spool holder on my printer. The .stl file for it be found here 

So all in all I will continue to use the Verbatim ABS.  I have some other colours to trial but if they work as well as the Black, I will not be dissapointed.