Category Archives: heated lid

The heated lid

Hi rock stars,

Many thanks to the thoughtful, smart suggestions in Name that component!, from Kyle, David, AdamT, Kyle@otyp, and Ben. All together, we worked through the panini/linkage idea, browsed camera shops to find ball joints, and really set out to get the best design that’s easy to build. That said, it can be impossible to find off the shelf parts to bring a new design to reality. More specifically, I’ll say that my current source for searching (McMasterCarr) has lots of really *big* things, lots of door hinges or refrigerator hinges, but not so much in the *small* side of things. Is there a good source for electronics-sized components that you like? Digikey and Mouser stick to electronics components, what I’m wondering about is a digikey+mcmaster love child. Of course, this will be helped in the near future with the rise of 3D printing and Makerbots, where small batches of custom parts start to make sense. Maybe a Makerbot is in my future.

The best design turned out to be the most simple one, suggested by AdamT — 4 springs pushing down the aluminum plate, the whole assembly floats on 4 bolts. The lid gets locked down into a low position, and the springs/hinge float around as needed. I prototyped it up, showed Josh, and we like it. We’re going to be mounting a heater and really testing it out over the next few weeks.

2 opportunities for improvement are:

  • how to lock the lid in the “down” position (magnets would be great, a bolt with a thumb screw is more realistic).
  • Secondly, the nuts/bolts in the picture are metal and heat up a lot. I’m planning onfinding nylon screws (M3), though their operating temperature is 85C (the lid is heated at 100C to 110C, the melting point of nylon is over double that). Suggestions welcome :)

(Skinny shoulder screws/binding barrels would be nice so that the plate can slide easily up and down except I need 2 nuts on each bolt, one nut to hold the bolt in place at its base, the other nut to keep the aluminum plate/spring on. A bolt with threads at the beginning and end but not the middle would be good.)

Thank you to everyone!

Tito

Bottom view of the heated lid. 4 nuts show where the springs are

Took off the front side of the heated lid so you can see the assembly inside. Springs and bolts hold the aluminum plate in place

Re: Treat your machine/pcb/acrylic/laser shop professionally

Update: 9/25/2010 to http://openpcr.org/2010/07/treat-your-machine-shop-professionally/

Good comment from mo – spread the love around. I want to point out that the relationship with your machine/PCB/acrylic/wood shop can be challenging! It’s important but not necessarily easy!

If you can’t meet in person it’s tougher to build repertoire over email or telephone, no matter how charismatic you are. And though I’m usually close to my email, people in shops are on tools and machines most of the time. A phone call is a lot quicker and more personal, but conversations on the phone often lead to miscommunications and frustration. What’s worked for me is talking on the phone, and then summarizing in a follow-up email immediately afterwards. Other points of friction I’ve found are in file formats (I was in Bangalore, India, bouncing between coffee shops and I just couldn’t get the right program in order) and computer use  (for instance a shop that insists on printed 2D drawings of a nice 3D CAD file you struggled to put together…), and one guy that always returned calls around a week later.

Experience says: lavishly praise shops you come across when everything goes smoothly.

Right now: I’m working with a shop called OharaRP (out of Dayton, Ohio) on a PCB board and they kick ass!

Tito

Name that component!

Welcome to an exciting round of “name that component”. Here’s your host, Tito!

Hi everybody,

We are working to design our heated lid so that it can adjust to small differences in the size or height of tubes. In PCR, we’re cycling the temperature of a small aluminum block between 50C and 100C. We place a plastic tube in each well of the aluminum block, which contains a liquid DNA sample. Now, if we simply have this setup, we will heat our samples to 100C and they will evaporate and condense in the lid of the tube. This is a problem, which is commonly solved by something called a “heated lid”. The 100 C lid needs to make contact with the caps of the PCR tubes, to prevent condensation of the sample. At this point, we have a flat aluminum plate with a heater mounted to it, and are able to reach 100 C. The issue is having the plate make flat contact with all 16 (4 x 4) tubes in the OpenPCR. I’m looking for some sort of a ball joint that we can mount the plate to so that it will rotate every so slightly (10 degrees would be enough).

Now, I know I’ve seen a part like this in existence, but we have little idea where to find it or what is it called?

I would describe it simple as 2 flat plates with a ball joint in between. The size of the plates should be smaller than 1.5″ square, with a few holes in each plate for mounting. I’ve drawn up a crude illustration to attempt at describing this, and have searched mcmastercarr (“ball socket”) got me the closest, but no cigar.

Here’s some “similar” products to what I have in mind…but looking in the <$10 price range and much smaller: http://www.thorlabs.com/thorProduct.cfm?partNumber=SL20
(car gps mount) http://www.cabelas.com/p-0012344012724a.shtml
http://www.newport.com/RN-Series-Ball-and-Socket-Stages/144558/1033/catalog.aspx

Hope you have ideas in mind!

Tito

Thermal pads

Just received the 2 test thermal pads in the mail from Digikey.

BER165-ND is 3 mm thick and pliable. It runs about about $3.50 per OpenPCR (28 parts fit in a $94 sheet). 3M9601-ND is 2.5 mm thick and very soft, and about $1.20 per OpenPCR (25 parts fit on a $30 sheet)

We’ll want to test these out with our current heated lid to see that they work great and make it easy to maintain the temperature of samples. Once we receive the first set of aluminum and a new wooden case from Ponoko, we’ll be able to test these out even better.