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Laboratory Pipette

by lewisite, published

Laboratory Pipette by lewisite Oct 1, 2013

Thing Info

13038Views 2003Downloads Found in Hand Tools
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Summary

Modification and redesign of existing pipettes on Thingiverse to allow dispensing using commercial 200ul pipette tips. I have yet to calibrate it and measure its accuracy, but this will come down to the setting and fit of the lower gear. My dispensations of liquids have been very consistent so far.

The idea was to move from getting suction from a balloon membrane to instead using a plunger and a tube as I had difficulties with retaining the siphon pressure.

The things you need to get it to work besides the prints are the following:

3 o-rings (3 x 7 mm) in EPDM, Nitrile or other suitable material
PEZ dispenser spring or similar
Lubricant
Commercial tips, such as from Eppendorf

To print, use the highest possible setting for the plunger, gears and the pipette tube. I used 100% infill with 2 shells. Use 15% infill for the main body.

Prior to assembly, I suggest you have sand paper ready and try to assemble the plunger with o-rings and pass them through the pipette tube to make sure you have a good fit. Have some water handy and test its fit and suction like you would with a syringe. I suggest you lubricate the o-rings to make this work better. When you are happy with the fit and function, with as little friction as possible while retaining the siphon effect, disassemble and go on for the final assembly.

To assemble, put the pipette tube into the main body and push it in all the way so it protrudes slightly at the top opening. On the plunger, thread the spring. Now the more tricky part. Insert the gears into the top cavity and thread the tip of the plunger into the top opening and through the centre of the gears. With the tip of the plunger protruding through the lower gear, use your fingers or tweezers to slide over the three o-rings. Lubricate them in advance as well as the opening of the tube as this may facilitate the process. The tip of the plunger has two recesses. The o-rings should be fitted so that the middle ring is locked in place by a top and bottom o-ring in their recesses. When in place, insert the tip of the plunger into the pipette tube and start rotating the gears so that the plunger is inserted further into the pipette and until the top gear can no longer be turned. Test the spring function and the siphon effect and calibrate as needed.

I have further modified mine to use a stronger spring as the PEZ one was a bit weak and I will likely redesign the plunger to accomodate a round spring soon, unless anyone beats me to it!

I hope this is useful to any DIY biologist or molecular gastronomist out there =)

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Hi Lewisite,
I bought some 3x7mm orings from theoringstore.com and - they clearly won't fit.
Can you tell me what i should have ordered? or where you get your o-rings?

Has anyone done a calibration curve using one of these pipettes? Just wondering what is the accuracy, compared to the balloon diaphragm types that are out there on the thingiverse

just to clarify - these orings have a 3 mm thickness, and a 7 mm outer diameter?

Hi, did you ever figure this out? I am printing one and don't want to order the wrong size o-rings. Thanks!

Nope. I didn't figure it out.

Awesome work lewisite. I used 100 infill, 1 shell, 0.1mm layer height for the pipette tip and plunger but somehow couldn't print. The tip holder is too big for the actual body and the plunger didn't print properly on the grooves. Would appreciate your help.

Hi

Try printing with two shells and sandpaper the pipette tip to a very smooth
surface with 600 grit paper. You will need some tinkering with the settings as
we all use different machines and do post-processing with tools. Did you print
using only rafts or supports? I only use rafts.

awesome stuff. What resolution did you print this at? This is because I am having difficulty balancing the tightness of o-ring. Too tight they can hardly move in the tube. Too lose the air will be leaking. I used olive oil for lubrication. So far I managed to print all remaining parts and get them to work, but I am having trouble with air leaking from the tube. Do you have any advice for that? Thanks!

Hello Kai

I don't know if you got me e-mail reply or not, but I thought I would reply
here as well.

I did a lot of different tests and designs before I got it to work. The
walls must be 100% solid for the siphon and the PLA printouts have difficulties
with this in many prints. Here is what I did:

The pipette tip and plunger must be set at the highest resolution possible:
100% infill, 1 shell and 0.1mm layer height.

When printed, take very fine sandpaper and roll it so it fits inside the centre
of the tip and work the inside walls so that they become very smooth. Also,
this will help the plunger fit nicely with the o-rings, and then use any
"food grade" grease as lubricant for the o-rings and work until they
glide into the tip tube.

Let me know how it works out!

.

I...I'm speechless. This is fantastic!

You've just made a cheaper, more available pipette than anywhere else I've ever seen (Next lowest is $25/per, and this probably doesn't even crack $5), and I can't emphasize enough how important this would be for areas where work requires precision tools like this but budgetary concerns prevent them from being purchased.

Do you know if it's possible to scale this to make 1uL, 10uL and 1mL pipette tips work as well?

Thank you again for making this, and if it's at all possible to get this into the "Featured" section, I will push to get this included!

Thank darkPrince010 for those very kind words. Coming from the medical sciences, I very much appreciate the value of this tool in any research setting, and I hope this can contribute to the accessability of such tools to those lacking resources.

The plunger tube has sufficient volume to accomodate 10uL to 1mL I am sure, or with very slight modification of the pipette tube. The only shange needed is wi make the tip of the tube wider (for 1mL) and narrower (for <200uL). I'll try to get a range of tips and experiment if possible and I welcome anyone to assist me with this as I am currently not i a research setting.

Well, my 3D printer (A Makibox...) should finally be arriving here in a month or so, so I can always tote a pippette along to work and see how well it calibrates.

That would be great, and good luck with the Makerbot. My Replicator 2 has needed a lot of tinkering but works prety much flawlessly now.

I have an idea for more precise control of the volume in the pipette with grades for exact measure, and for a multipette and a dispencer. I just need to find the time =)

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