Arcol blog Just another RepRap weblog

15Sep/10Off hotend prototype one

I was quite excited about my new prototype. Interested in my findings?

Keep reading.

Im offering since months the improved rapman-like hot-end (still need to write an article about it),
but I wanted to try out a new design. I made this:

Other then the above mentioned features, it contains the following improvements:

  • three holes at the top, so the wires are going in an S-form, so harder to broke one of them
  • simplified nozzle tip
  • flared the hole with reamer

Seeking for the right fire cement

This was not easy. I have tried out more then 9 different brands, and finally prusajr sent me the right one.
The fire cement is black, can withstand 1200C, and dries the outher surface really quick.
If you bake the cement too soon(without waiting to dry it), it is prone to develope cracks:

Although this cement dries really fast, but takes ages to dry it completely. It is best to heat
up slowly the hot-end to fasten the drying process.
(Also disconnect the thermistor until the fire cement is not completely dried!)

It comes out of steam, and bubbles develops, if you are heating too fast
(also if you dont care, it is prone to crack while drying):

It is really painfull process. It is extremely hard to assemble the hot-end, so I started to hate by heart the
fire-cement thing. I dropped fire cement completely, my next design will not contain it for sure.

Comparison with my Rapman-like hot-end kit

I dont know how many people know this, but Im offering Rapman-like hot-end kits for sale since ages.
I will write an extended article about it.
It is rapman-like hot-end because contains the following improvements:

  • machined PTFE tube
  • simplified nozzle tip, also flared out


So I could compare my new prototype with this design easily.

Here is a comparison photo between them:

Its clearly shows that my design is shorter about 20mm.

Experiences and mistakes

1. First and foremost this big melting chamber didnt work out.
At first it is really easy to push the plastic, (and some comes out of the nozzle's tip), but it is harder and harder to
push it, as the melting chamber is filling up.

So this big melting chamber does not improve the hot-end, but makes things worse.

2. First layer of firecement is 1mm width in my design, while in rapman's its about 0.3mm.
It makes a huge differences. At the end my hot-end can be heated up (using standard rapman's electronics) up to 205C after 2 hours. While the stock one can be heated up until 250C for sure, and I use it at 244C when printing.

Also having a bigger melting chamber does require more power to heat up to the target temperature, maybe this influenced too the too cold final temperature.

Future plans

Making prototypes is a slow process. But I dont give up, Im still searching for the best design, and I already made the next version, and should be manufactured in two weeks. So please keep an eye on this blog.

I finish this article with some more photos for eyecandy. Enjoy!

Longueur comparison:

Nozzle tip comparison:

Nozzle closeup:

Comments (4) Trackbacks (2)
  1. Hi

    Have you thought of using Klapton tape instead of fire cement?
    You can buy it at the makerbot site. It is cheap, removable and works well.
    Also it heats up much faster than fire cement.


    Stephen George

    P.s. Good luck with the design

  2. Stephen: I could use it for the first layer. Maybe it would improve the final temperature too, as it is much thinner.

    For other layers I would avoid using it, as the heater wire what Im using is quite strong, so some force required to hold it.

    Anyway I abandonned completely the fire cement idea. Also Kapton should be tiring process too.

    The next prototype will be done in two weeks.


  3. I see two problems with this design.
    Because of the big melting chamber, one might not be able to pull the plastic up again because it will get bigger at the tip.

    Also the shorter hot-end and having the heater element higher up, might cause the plastic to melt/soften up to the top. I already have this problem with the standard Rapman design with PLA.
    Sometimes the plastic gets soft up to the upper end of the Hot-end forming a bulb on top of it. If this happens, i cant extrude any plastic, because it wont go into the Hot-end anymore.

  4. Domonoky:

    True and true. It is really hard to pull back the plastic, also it soften up in the PTFE tube. I needed to put the ptfe tube in boiling water to be able to pull the stuck plastic from it.

    I learned from this prototype, and I have finished my next one, which performs awesomely well. (my english is simply not good enough to say how awesome is the next design).

    Stay tuned.

    (also I will update this article with some more photo, because I disassembled that extruder, and you can clearly see all this problem from the plastic)