Thursday, January 23, 2014

Controlling a chamber heater

My lab is in the basement and it is pretty chilly there, usually about 18C. I have trouble with prints warping, even with PLA. A few weeks ago I borrowed my wife's small space heater and put it in the chamber with the printer, raising the temp to about 40C.  This seems to help the prints a lot by both slightly preheating the incoming filament and also reducing the shrinkage of the plastic during the print.

I gave her back her heater and she got me my own, a 1200 watt ceramic heater for $15 from a local store. The problem is that it had no thermostatic control as hers did, so even on low, it got so hot that it melted some of the parts on my printer (70C - my parts are mostly PLA). I thought about getting another heater with a control, but I decided that if this was going to run unattended, I didn't want to trust the cheap mechanical control that's likely to be on those things.

I had a 25 amp AC solid state relay sitting around and I decided to try using the printer to control the heater. I cracked it open and determined the best place to hook up. You really only want to switch the heat on and off, not the fan, because if you turn the heat and the fan off at once, you're likely to eventually damage the heating element.

I then hooked up a battery to the relay to just hold it on, switched to the highest heat range and watched it run for 30 minutes as a worst case test.  I don't expect to run it on high but I didn't want to put something together that might melt or catch fire if left unattended.

The result was that the relay got a little too hot for my liking, creeping up over 110C and still going (though slowly).  So I opted to put a small heat sink on it.  Since the relay reached 110C with no heat sink at all (the back panel was up against an insulator) I figured a couple of aluminum fins would work nicely.  I cut a bit of aluminum, bent some tabs up and stuck it to the back of the relay with some heat sink compound.

After assembling with the heat sink, a subsequent test only reached 76C which is within my comfort zone.

I then put a thermistor in open air in the chamber and hooked the relay up to the bed control - I don't currently have a heated bed so that's the easiest way to deal with it for now.  Eventually I'll recompile the firmware to control chamber temp on the 3rd MOSFET channel.  If I ever want to mount dual extruders again, I will probably just toss a separate Arduino on it to control it as a standalone.

It still needs some insulation on it because the bottom terminals are live 120v mains, but it works very well in testing.

Sunday, January 12, 2014

Basic maintenace: Chain cleaning

Keeping your bicycle chain clean can really increase the lifespan of your drivetrain, not to mention making it quieter and more pleasant to ride.

If you have a bicycle with a rear derailleur, the easiest and best way to clean the chain is with an on-bike chain cleaner. For me this gets chains cleaner than the method I describe below (removing the chain and washing it) because the chain cleaners have brushes that get between links, and honestly I'm just not willing to go to that much effort manually.  FWIW I find the Finish Line chain cleaner ($20 on Amazon) to be good and durable.  I just use warm water with a small squeeze of Dawn dishwashing soap in it, then dry and lube.

If you have a single speed or internally geared hub bike, you'll need to remove the chain from the bike to clean it properly.  Before you do this, make sure you have a master link to put the chain back on again.  If your chain doesn't have one, you'll have to get one.  There are at least two different sizes of master link, but for single speed the 7/8 speed links are pretty much universal.  Don't get 9/10 speed master links

Step one, remove the rear wheel, using whatever method is normal for your bike.

Step two, if you have a master link already, find it, separate it and remove the chain from the bike.  If you don't, then use a chain tool to remove a pin.  Also remove the adjacent pin on the half link with the outer plates, so that the chain's two ends are the half links with the narrower, inner plates, which will be compatible with your master link later.

If your chain is quite dirty, as was mine when I cleaned it in January after a few hundred miles of winter snow/salt/slush riding, it'll look like this:

I really do not advocate letting a chain get that bad, but in the winter time, when it's well below freezing, I just can't bring myself to work on the bike much, and besides, a clean chain will look like that after 2 days of riding, so it's hard to get up much ambition for the job.  Still, it should be done at least occasionally.  In the summer, I would never let a chain get to this point.

Get a plastic jar that can easily fit the chain inside.  I use a peanut butter jar.  You probably want to use plastic, not glass.  Put the chain in there and we will begin a series of washes.  Generally I do one in hot water to start with, just to bust loose the random salt and mud.  Then I follow up with at least 3 or 4 washes with hot water and Dawn dishwashing liquid.  Finally I'll use hot water and a tablespoon or so of Simple Green.

For each wash, swirl the chain around, then let it sit for 10 minutes or so, then swirl again vigorously for 2 minutes or so.  Drain, rinse, and go to the next step.  After the last step, do one more with just hot water again.  Take the chain out and let it dry.

Lubricate each link with your choice of fluid.  Apply the lubricant to the edge of the chain, drawing it across both sets of plates and the roller. If it's cold out, let the chain sit for half an hour or so inside to let the lube get inside the rollers.  I'm currently using Chain-L, which is extremely thick, like honey, and stays on the chain really well.  But others have their own preference, so whatever you like.  Finally, put the chain back on the bike.

New printer: JGAurora A3

This week I decided I'd had it with all the other printers in my stable.  The CTC is stable and decent but it just bugs me (can't st...