Peter Wallers Robot Ramblings

[Roboteernat]

A few years ago, a collegue and myself designed a ceramic hot end. The best way to produce it would have been to compression mouldy it, and at the time we couldn't cost it out, although I worked for a company that sourced parts from ceramic molders in China. And soon the project went away.
The thin walled tube section is made from stainless heater is inside an aluminium block which has a high thermal coefficient, meaning it heats up very quickly, but stainless steel is very low, and this is what stops the heat from rising. This is them screwed into an aluminuim heatsink, to spread any heat that is passed into it through the stainless steel to keep it cool, hence the fins. It's ok on hour long print, but now things progressed to hours and hours long printing, the fan helps this.
The stainless steel is the key point. A ceramic block would stop heat transfer very well, and compression moulding will give you an exact seal around the threaded section tube into the heater block, but in this situation the ceramic is just replacing the aluminium block, so a pointless task. We looked into a ceramic tube section, but didn't get far with the designs.

[peterwaller]

I wasn't proposing to replace the aluminium block with ceramic just the stainless steel tube.
Trevor came up with a sample of PTFE tubing that goes up to around 280 and I just fitted that and am printing the spinner test sample at 265 C on a bed of 100 C.
While I had it stripped down I checked out the size of the ceramic tube and it is just about perfect being only 0.1 mm smaller in diameter than the stainless.
It fits into the existing head though I will need toe be careful with tightening the retaining grub screw and I thought I could glue the aluminium block to the ceramic tube using the glue below which works up to 1200 C.
http://www.ebay.co.uk/itm/1-x-HIGH-TEMP ... 1093590083

[Roboteernat]

Yeah, we started looking at the threaded section, but didn't get far, this was in the time J-head hot end came out, and was based on the v3. The screw tread on the tube in ceramic meant that there would have had to be 2 screwing cores in the mould, hence the cost and giving up at that stage.

Look forward to hearing your results

[peterwaller]

Had a quick play with the ceramic tube idea and did a rough test on the heat conductivity although it may not be that representative depending how good the contact of the temperature probes were with the tube.
Any way I placed my soldering iron and one probe in one end of the tube and jammed another probe in the other end with a bolt.
The Iron end was registering 350 C and the one the other end just 75 C which seem to stabilize after a few minutes.

That fuse was a slightly smaller one than I eventually settled on as the 1.25 inch fuse at 5.84 is a good fit into the printers head which is 6 mm.
The block I am using is the slightly later one for the BQ Prusa i3 mk2 which is tapped right through at M6.
I left the nozzle in the block and drilled out the thread above it to 5.9 mm drilling in far enough to give a slight counter sink to the back of the nozzle to help guide the filament through.
Then using high temperature glue from ebay glued the heater block onto the ceramic tube but with a 24 h cure time I wont know how good the bond is until tomorrow.

In the mean time the new PTFE tube seems to be working well and on advice from the very helpful people at Polymaker I am now printing the PC-MAX at 265 C on a bed at 110 C and it seems to be printing very well.

[Roboteernat]

Sounds good Peter, looking forward to seeing the results tomorrow.

[peterwaller]

It actually started printing but about halfway through a massive 6 min print the head fell off the ceramic tube.
I will have a more careful try at bonding it on again tomorrow and maybe add a grub screw for good measure.

[peterwaller]

Even 2 grub screws weren't enough, unfortunately trying to use a standard heater block there is only about 5 mm of the ceramic tube to fix it to, so I will have to rethink the design a bit at least I now know it can print.

[Roboteernat]

Sounds like it is a potential idea then, we didn't get as far as testing our ceramic screw insert design, but there we go. Perhaps a design would need the screw so that the forces of the plastic ectruding wouldn't push out the tube. I will try and find my old storage from my prev work and upload some images of the designs we came up with. Perhaps it needs to be restarted?

The fear of the grub screws is if too tight it could shatter the fuse case, will see if I can find anything suitable and run some tests if I get the chance.

Nice investigations you did tho

[peterwaller]

Just completed a rebuild of Defiant using mainly the PC-MAX polycarbonate filament for the chassis and lifting arms and just the scoop in Alloy 910.

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One thing that slightly surprised me was that the Polycarb was about 10% heavier so I had to introduce some weight saving measures in the chassis.

Here is a comparison of a HI ABS (bottom) and a PC-MAX chassis (top) after going a round with Anticyclone.

As you can see the ABS de-laminated but the Polycarb stayed intact.
I still think the Alloy 910 is the better armour and printing at 250 C on 45 C plate as opposed to 265 C on 110 C is much easier to use but when it comes to thin load bearing parts like lifting arms the polycarb wins out.

[peterwaller]

Back on the extruder front I have decided to look at some larger ceramic fuses to see if they are suitable.
For some obscure reason they don't quote the internal diameter but on the off chance they are usable I have ordered some 10 x 38 mm and 14 x 51 mm.
Hopefully they will be thicker walled and stronger unfortunately they are in China so could take a while to come.