Tuesday, June 22, 2010

Lathe Free Resistor Extruder Heater

It may be early to post this, but I'm still waiting for my hardware order to come, so I have been playing with what I can. (also, I expect that once my hardware arrives, I'll be too busy to blog much)
I really like nophead's extruder heater design. I figured that It would be possible to build it without having a lathe on hand, so had a go.

The heater block is made from some scrap 22mm round-bar (It was a door handle in an earlier life). I cut the end square, and drilled the resistor and thermistor holes before cutting it to length. This allowed me to have a big handle for holding the bar straight in the drill press while drilling the off-center holes. I then cut it off to 10mm length and by sticking a 5mm diameter bit of round-bar in the resistor hole to hold it, I drilled the 5.5mm through hole for the nozzle and SS insulator. I tapped it to a tight tolerance (didn't open up the thread all the way), so that my fittings would be tight.

The nozzle is a .6mm MIG torch tip. It has M6 thread. I drilled it out to 3mm, then cut it off slightly longer than the bore. The exit hole is actually quite a bit larger than .6mm (sliding fit for mig wire), so I may close it up if I need to. I tried squeezing the end of the tip in a vise, but it didn't decrease the hole size, other than flattening it. Once I rounded the hole by squeezing around the circumference, the hole was not much smaller than original. I can melt the hole closed with my tig torch if needed and re-drill it to less than .5mm.

To work with the tip (and the isolator), I simply drilled and tapped a hole in some scrap metal and screwed the tiny pieces in to hold them.

The isolator was more trouble.. Having found some M6 threaded rod (BZP) at Ikea, I drilled it out to 3.3mm without effort... The hole stayed very close to center all the way though. This allowed me to believe I could easily do this without a lathe.

Not quite so easy was the SS threaded rod I then bought to make the isolator. I found with my cheap drill-press that I was not achieving depth without coming out the side of the rod. I even tried drilling in both ends, but that didn't help. For my last try, I kept rotating the fixture 180 degrees as I drilled, this maintained the hole more on center. I'm confident that I could do better, and for 1.5 euros for 1m of the threaded rod, it would be cheap to keep trying. Even though the top hole is slightly off center, I think this one will work fine. I tapered the bottom hole, using a tapered reamer like nophead did.

I pressure tested the assembled unit, and got no bubbles from the two threaded joints at 100PSI, do am hopeful that this won't leak (.... cold... not sure what will happen when it gets hot). The Copper nozzle deforms against the SS rod end forming a seal I think.
For the top, I intend to M6 thread some 10mm copper plate I have to increase the heat removal from the upper part of the isolator. I may dremel some material from the isolator just above where it enters the heater block if needed. I'll put a layer of PTFE between the block and the copper heat channel. I have a nicely sized aluminum heatsink from an old PS that I intend to use forced air cooling on with a 40mm fan. Silver grease between all the necessary bits should keep the heat moving where it's supposed to.
Because the block is circular, I should have no trouble drilling a bit of PTFE rod to fit around it as an insulator, I just need a 22mm drill..... I may try gooping it up with the high-temp gasket maker that I'll use to insert the thermistor and resistor.

So, in short it is possible to make a resistor block extruder heater, with SS isolator and mig nozzle with only a drill press and some hand-tools. I think it's much easier to drill SS than to run a die along it, so starting with threaded rod seems logical if you can drill more or less true. Mig tips are cheap, and if I want a smaller hole, it's quite easy for me to close it up.

The tools I used for this are not exceptional.. A cheap and nasty Chinese drill press, an M6 tap, a chop saw (though careful hack-sawing would easily work), some bits of scrap metal for holding the tiny bits, and a belt sander (optional).

Whether this works as a heater or not, time will tell.

Wednesday, June 16, 2010

Parts ordered, keeping busy.

I finally dropped the hammer on my RS Components order this AM.
The damage will be almost 700 euros. Of course with RS Components, I have minimum orders on quit a few things, so take a hundred euros off the cost of actual repstrap content. I feel that I'll be getting a very flexible and adaptable bot for this price though, so hopefully no buyer's remorse. I expected that I'd be printing for under a thousand euros, and with what I've already bought, and the few little things I'll have yet to buy, I'll be getting up there...

While waiting for the bits to arrive, I decided to build my end-stops, and more Pololu boards. Then I just had to plug it all into my Mega and have a play.

I'm quite happy with my breadboard setup. I have all motors turning together with a bit of code I bashed up...

Closeup of "the jungle"...

I'm thinking that if a Pololu shield doesn't come available within the timeframe, I may just go with this and mill myself my own board.. that would be cool. Not sure how much current these bread-boards will take though.. if I go Parallel on the motors, and turn up the current.. could be some burning plastic in my future... (even before I make an extruder).

Last night I decided that I'd start with the Hydra-MMM firmware/control software. Played a bit with it today, and didn't get anything moving... I suspect I need to get more sensors hooked up (I didn't have my optos in yet). It compiles fine and talks to the host, but when I try to send commands, or feed it a g-code file, it just hangs. I'll fake up a thermistor tomorrow and see what happens.

Saturday, June 12, 2010


Something I had trouble getting to grips with, was how small all the electronics are.

Even though the webspace is full of pictures similar to the one below, it's hard to realise just how small things are until you have it in your hand.

As you can see, I decided to go with the (as yet experimental) Arduino Mega, with Pololu stepper drivers. Some RepRap info on this setup can be found here and here.

I ordered the Arduinos and stepper motors from reprapsource in two batches.. both orders came without delay or hassle.

I put one of my Nema 23 motors in the picture for comparison. I honestly didn't realise that the Mega would be this small either... In fact I ordered an Arduino Nano (pictured below), so that I would have a small Arduino micro around for play and a special need... Had I realised just how small everything is, I'd not have bothered...

One of the things about the Pololu boards, is apparently they run hot.. I decided that I would make some heatsinks, as my steppers are rated for 1.5A. I am still at a loss as to how you can design a 5mm chip die that will do 2A.

Pictured below is my heatsink design. I simply sliced a strip of copper, and bent it over a 3mm thick bit of scrap metal. Pinched the sides with some ViceGrips, and tapped a flat on the bottom with a hammer. It looks big on the Arduino, but positively giant on the Pololu.

Not realizing that I could get the Pololu driver boards here in Europe (though I notice no one seems to be in stock), I ordered them directly from Pololu in The States. It took 13 days for the order to get to my door in The Netherlands, and I got dinged an extra 37 euros in customs/handling fees. (The order had other stuff in it, totaling $137 US.)

I also bought a Mega Shield from reprapsource to mount everything on as per johnnyr, but will buy a custom designed one if it becomes available before I'm ready to start mounting everything.

Thursday, June 10, 2010

A start

After a month and a half of reading, thinking, reading and designing, I'm ready to start on this journey.

It occured to me one day, that a lot of my 'play' in electronics, and mechanical things were working me towards some sort of robot. I have been designing and building things for years, and after a long break, was thinking of starting something biggish.

I stumbled across an engadget post about RepRap one day, which made me aware that rapid prototyped parts are not just for gently handling and looking at, but can be quite structural as well... (the RepRap's key feature is that much of the structural components are printed on other RepRaps) I looked at my pile of stuff, and decided, "I can do that"... So I started to read....

I decided I wanted to design my own cartesian bot, based on things I've read, rather than try to follow someone elses 'recipe'.

A month later and using all sorts of ideas from all sorts of people (if it looks like something you did, and posted about, I likely got my ideas from it), I came up with this initial design:

The bearing design was presented to me one day by Gilles on the RepRap IRC channel, and I really liked it... it was a pivotal moment for me as it caused the design, which was constantly changing around in my head to suddenly 'gell'...

I have, and like to use, a tig welder to make things out of aluminum, so I altered things to make use of it, and save some space.

T-SLOT Strap

In the end, I didn't like the idea of using MDF to build my machine out of. I expect to move this printer between my upstairs electronics room and my outside shop. The thought of lugging a big MDF box up and down my steep Netherlands stairs didn't appeal.. I have a decent metal working shop, with a chop-saw for cutting aluminum, belt sander, the welder, and various fabrication tools, unfortunately not including a milling machine, or lathe.

I liked the idea of using t-slot beams. They keep things looking clean, give me adjustability for lining things up as I assemble, and can be used for something else later if I want.

I came up with this:

It is based on FlexLink t-slot from RS Components, the XC size (44mm square)... It is a bit beefy, but I figure I may be wanting to push a palm router with this, and want it as stiff as possible. Plus I like the idea of using a double-wide vertical beam for fore/aft stiffness, and the smaller size wasn't available from RS in the double width. I also may decide to make it all larger if I get more space. By starting heavy, I will be able to keep all my connection hardware and just change some extrusion (and the drive system)...

More details:

I decided to use the FlexLink linear bearing for my Z-axis...

Bearings are mostly as per Gilles design...

I'm using 12mm bearing bar, and over constraining the bearings for added stiffness.. I think I'll be able to keep my tolerances close enough by drilling all the holes for the mounts in a stack.... We'll see in a couple weeks... =)

As you can see, it follows quite closely to the Mendel layout, but doesn't use RP parts.

I feel that I can scale it up to a larger size if needed at a very reasonable cost in time and money.

I also gave thought to replacing the belts (which are full 10mm thick and not cut down as per Mendel) with leadscrew drive for milling. I would have gone directly with leadscrews right away, but it seems that no one is doing a great job of printing with them at this point, and the added speed of belts seemed prudent. With the t-slot I can change things around relatively easily to suit.

I'm using Nema 23 motors for strength, Pololu 1/16 stepper drivers for added precision, Arduino Mega mother board. It all seems a lot heavier duty than a Mendel, but hopefully it will give me the added strength to do 'beefier' things with it.

I have the motors and electronics already, 350 euros worth of t-slot hardware and 2 to 3 hundred more in other bits are sitting on my RS account ready to be ordered in a couple days...

I'll report back on how things go.