Sunday, January 24, 2010

making Mendel element on Welding tip and Torque test video

An in focus picture of the shorter Extruder with long wedding tip made in December.

Here is the New longer Peek insulator with the shorter welding tip.

The insulator anti twist securing hole drilled out read or a 3mm screw.

With the screw fitted and a bevel to aid the alignment of material being extruded this was made using the tip of a 22mm flat wood bit.

The brass inserts were removed from a standard plastic 3A chocolate block attached to my last 7 ohms of cotton covered nichrome wire.

The red cable is attached to one end of the element and taped to the Peek insulator using 200C heat resistant Kapton tape its ready to wind the element.

Element wound ready for the Black wire end of the element to be taped up.

Taped up twice on the long Peek insulator.

The end on view now with a K type thermocouple slid in under the layer of Kapton tape its the green wire.

Last months heated barrel looked like this before the high temprature black self amalgamating tape was put on.

Now for my second Video where I miss getting the scale showing 2Kg for the second or third time each time destroying two foot or more of ABS welding Rod as the splines eat it up as it starts to slip and yes it had already stated to slip by the time I got the camera to focus on the digital scales Ahhhh. We decide to give up before we had got any more frustrated by trying to film it.

Testing the new splines shaft in my perspex clone of the Mendel extruder block with 3mm ABS gave a maximum of 2kg of pull measured before the ABS starts to be eaten away by the splined shaft.

Now we know that Wade has achieved 5.5kg of pull without slippage.

So whats was the difference.

Nophead is using the AKA47 "worm" pulley. It is 15mm OD, ~13mm ID using an M4 tap

And has suggested halving the ID to 6.5mm and using a M3.5x0.6 tap with an OD of 10mm

The other difference is both Wade and Nopheads extruders have a spring tensioner to control the pressure of the grip.

Where as the standard Mendel extruder has the pressure set by setting up the gap to be 2.5mm between the bearing and the splined shaft using a drill.

I tried using a 2.4mm drill this had no effect on the grip.

Using the AK47 "worm" pulley makes a lot of sense as it will be gripping more of the ABS.

So tomorow that will be my next Job.

Many thanks to Nophead for all his marvelous pioneering work on extruders and extremely detailed blogs.

Not forgetting AK47 and his great "worm" pulley blog entry the next task is to make a new acrylic block tat can incorporate the "worm" pulley


Wade Bortz said...

Nice work - I love the video! I was just thinking I should make a video of my pull test too.

I'm messing around with a home made worm gear next as well; I think to get higher pull forces we need to grip more of the plastic filament at once, so a larger diameter pinch wheel should help, and Nophead's worm gear pinch wheel should be even better.

Unknown said...

i really like that worm drive design it seems like a good way to go, though i think it would be allot better if the parts were more redly available though. but i will try to learn what i can from it. i was thinking more planetary gearing myself

Anonymous said...


There is a variant of a sun gear arangment (originaly developed for radar rotor drives) that works something like a harmonic gear arangment.

If you split the anular gear into two annular gears but make one the output drive and one tooth less than the other half you can get very large reductions very efficiently all in a single stage.

Anonymous said...

sorry for sun gear read planetary gear

Unknown said...

Back from a 3D scan of my heart full of Radiation for 24 hours..

Midges daughter not allowed to visit as she is expecting.

Have lost the brass blank I made yester day for he worm drive. N idea how or where so making another one.

@ Wade
What are you using if its not a worm gear to get 5.5kg of pull?

@ Dissidence
I know I kinda messes up my plan to make a Mendel that any one can build without special parts.

Regarding drilling out the welding tip. I think this can be done by drilling it out in 0.5mm steps without needing a lathe the same for the Peek insulator. Instead of fixing the peek with circlips 2 small screws at the top going down into the length of the peek using an extra piece of MDF will work.

@ AK47

I machined the Brass at 1600-2200 RPM it seemed to cut OK at that kind of speed is that the kind of speed I should have used?

The blank I made was 11mm long 10mm diameter I had cut a 2mm wide grove ready to cut the worm thread into. Dose that sound about right?

I may try using some tiny 10mm gears I got from Farnell. they have 48 teeth 13 in a quarter (4 x 13)- 4 or the Conrad coupler that is 7.78mm with 8 teeth a 1/4
(4 x 8) -4 = 28 teeth

I may try tapping a Conrad gear into a worm as well.

Any other sugestions as to how to make this drive gear easily I will try.

Any Idea as to what is the optimum pull force required to have a Reliable stage 1 extruder.

By stage 1 I mean an extruder that extrudes 0.6mm good enough to make things like a more complex extruder body and gears + replacement parts.

Unknown said...

I like the design - simple and seems to match my own experience with welding tips. I've just got some kapton tape so I should be building a nozzle very similar.

Nice photos - very clear. Good use of the brass connectors for the nichrome too.

Unknown said...

Hi Renoir,

yea its taken me some time to figure out how to get auto focus working on close ups.

I set flash off flower option on. I then move the camera position until it manages to lock its focus. I still throw out 25-50% of pictures though still end up out of focus.

Digital camera auto focus firmware/software seems to need a little more work.

Better than film though just a need manual focus/auto focus override.

It was Nophead who suggested Welding tips a long time ago.

The simplicity of it appeled to me as I have made the original MK1 extruder tip using 6mm brass drilled out by hand before I had a lathe. Cutting the thread in it was a nightmare. That was why I liked the welding tips with their pre-cut thread and 0.6mm hole right through.

It means without a lathe you can hand drill the hole out if you step the drills up 0.5mm at a time. The drills follow the 0.6mm hole.

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