Intro: Cheap Professional Carrousel Pipette Stand
If you work in a laboratory doing chemical analysis or biological research you will usually have to work with micro-pipettes which are special kinds of syringes that allow you to dispense precisely quantified amounts of liquids in the milliliter to micro-liter range by mounting disposable plastic tips on the pipette and dialing the volume to dispense on the knob located on the pipette handle.
Sooner or later you will also encounter tasks where you have to use different pipettes in sequence and you will have noticed that laying unused pipettes on your bench is not a good idea, especially if you have little space. Indeed by doing so you risk 1) to contaminate the bench, 2) contaminate the disposable pipette tips, 3) residual liquid - eventually present in the plastic tips - may run into the pipette piston shaft and contaminate or corrode it, 4) your workspace becomes chaotic.
This is where you need a pipette stand to hold several pipettes vertical and well organized in a reduced space on your bench. To my surprise I found that such stands are rather expensive ranging from 50 to 100 euros from the simplest rack type to the smarter carrousel type.
I wanted a carrousel pipette stand for our lab but because of a critical financial situation we could not afford one at the moment and so I decided to make one by myself by using common items that I partly had at home and others that I could buy at the supermarket and local hardware shop.
Build time is about 2 day and cost around 15-20 euros depending if you want to color or not your pipette clamps with several colors.
How does it perform ? Look at the video to get an idea and consider the following "goodies" if you want to build one yourself:
- since I build the stand with elastic clamps it can easily hold many different sized/shaped pipettes from different manufacturers - which is not common for all commercial stands.
- it is ergonomic, pipettes are easily inserted and removed without using much force and can be mounted in different positions and orientations
- a carrousel stand is quite "smart" . You rotate the carrousel to bring only the pipette you need in place to be grasped.
- it is robust and pipettes are reliably clamped even if you move the stand around
- the stand will not tip over and it is easily transported thanks to its handle.
- you can add other clamps later if you need more of them, coloring and shaping them as you like.
- it is relatively easy to dismantle and reassemble for washing it.
One improvement that probably can be made is to make it slightly less "bulky" by using a bottle with a smaller waist and eventually finding a different and/or cheaper way to stabilize the base of the stand using a different type of weight. Also the handle could be made smaller.
Step 1: Collect Components and Tools
The stand is basically build from a plastic bottle and plastic dish and a rotor supporting rubber pipette clamps made of "oogoo" rubber (see also mikey77's instructable for preparing oogoo using silicone caulk and cornstarch).
The bottom half of the bottle is filled with heavy objects such as gravel or better metal parts. I used screws. Everything is securely clamped together by a rod and metal clips made from paperclips and washers. Finally a very useful oogoo rubber handle can be added but is not absolutely needed.
The components and materials you need are the following:
- a round plastic bottle with a big screw cap.
The bottle must be high enough for your pipette. I found a suitable disinfectant bottle ("Amuchina").
cost about 1 euro
- a metal rod at least 10 cm longer than the height of the bottle. You can get one at no cost.
Just rip it from a broken scanner or printer
- borrow or buy a micro-pipette.
It is just used as a "sample" to size the stand correctly and as a "mold" to shape your pipette clamps.
- a rigid plastic dish (baby dish, not a "floppy" party dish).
It will be used as the base of the stand. If you're lucky you can find one for
- a fair amount (1 kg) of screws or other small metal parts
they will serve as weights to fill the bottom of the bottle
< 6 euros
- a wooden board or other board sized to fit inside the cavity of the plastic dish. It's actually even better if you find a plastic or metal board but I took a wooden board because it is easier to find and cheaper than plastic or metal boards. Look for scrap boards in your house. It just serves the purpose of reinforcing the plastic dish.
- 4 big washers (outer diameter >=3 cm) , 2 small paper-clips , 1 larger paper clip
cost: Few cents
- a plastic bowl and dish-washing soap
You have them in your kitchen !
We will make the clamps to hold pipettes using "Oogoo" rubber (invented and presented by mikey77 on instructables). To make Oogoo you can first look at mikey77's instructable but then I recommend you to follow my instructions here to prepare it since you need to do it slightly differently for the present purpose . In any case what you need to prepare the amount of Oogoo rubber needed for the present pipette stand are:
- silicone caulk the acetic type that smells like vinegar, (should be transparent 100% silicone).
- cornstarch (500 g)
- plastic cups and spoons and a rod to mix it. I suggest using a metal rod or another strong rod, since you will need to apply some force to mix Oogoo after adding lot's of cornstarch.
- a supply of nitrile gloves (some tens of pairs).
- If you want to color the pipette clamps you need oil paint pigment paste ( 5 euro)
In addition you need some common tools some of which you likely already have in your home:
- a drill and a drill bit (3 or 4 mm)
- a metal saw
- files: a small one ( few mm shaft diameter) and a bigger one.
- a hot-glue gun and glue sticks
- a sharp knife
- strong adhesive tape (for instance "american tape" or "gorilla tape")
Step 2: Make Oogoo Rubber Clamps
Let's "get our hands dirty" now !
We will start making our stand by hand-molding "Oogoo" silicone rubber clamps for our sample micro-pipette.
No ! Don't do it with bare hands !
I did it and after hand-molding lots of oogoo silicone caulk my skin got very dry and started to peel off. Fortunately peeling stopped the third day.
So absolutely wear gloves whenever you work with "Oogoo" !
First we need to prepare a suitable oogoo mixture for hand-molding our rubber clamps.
According to mikey77's instructable you mix about 1 part silicone caulk and 1 part cornstarch. We also will start this way. I suggest you to first pour the silicone into the plastic cup before adding the cornstarch. In this way mixing the two is easier. Oogoo prepared in this way is a sticky cream and sticks to everything, to the walls of the cup and to gloves and can hardly be hand-molded and would result in clamps that are too elastic.
We need to add more cornstarch into the cup and continue mixing until at some point, after enough cornstarch has been added, the mixture stops sticking to the walls of the cup.
Now pour the mixture onto a table. Also pour cornstarch onto the table and onto your nitrile gloves. This "high cornstarch oogoo" doesn't stick much to your gloves or the table and is a kind of dough and you work it the same way you knead dough for cake or pizza. So you knead it until you get a smooth, homogenous dough. You have about 10-15 minutes working time before its starts to loose its plasticity. So keep your micro-pipette ready and mold the "oogoo dough" around the handle of the pipette and shape it to your taste, making two "fingers" that will hold the pipette handle but leave an open space between the "fingers" so that you will be able to remove the pipette sideways. After having molded the clamp and waited for about 30 min you can remove the rubber clamp safely from the pipette.
To make other clamps I suggest you to add some oil-paint pigment during the mixing process to get different colors for the different clamps. If you use oil paint pigment paste like I did then a 5 mm long segment of pigment paste will be enough to color a single clamp.
Step 3: Coat the Rubber Clamps With a Silicone Glazing
At this point I suggest you to test the oogoo rubber clamps you just made by inserting repeatedly the pipette to look for any problems. For instance if you left a too small space between the clamp "fingers" it will be hard to insert the pipette. In this case you can cut away excess oogoo rubber with a sharp knife until you are satisfied. The pipette should insert easily, yet stay clamped well. Also make sure the pipette will not be able to slip out from the clamp if by chance it should slide downwards when kept vertical. If needed you can make some corrections adding more oogoo in critical points since fresh oogoo will stick to already solidified oogoo.
One problem that you will recognize immediately is that oogoo rubber will abrade / wear each time you insert or remove the pipette from the clamp. This is because of the high cornstarch content of our "oogoo dough". We need to do something about it since otherwise our pipette stand will be a source of rubber/cornstarch dust contamination which is unacceptable.
Fortunately there is a way to solve this problem by coating the clamps with pure silicone caulk.
This can be done by following the "world's easiest silicone mold" instructable of audreyobscura:
- prepare a plastic bowl filled with water and plenty of dish-washing soap and pour a string of silicone caulk into the soap-water. The soap-bath serves both as a catalyzing agent to provide a source of water for the silicone to solidify later and to prevent silicone sticking to your hands.
- Keeping your hands submerged in the soap bath, gently clump the string of silicone together and slowly massage it. Fold it, stretch it out, and work it very much like one would knead dough. While you can do this process with bare hands with little risk for your health (the soap covering your hands will prevent silicone from sticking to your hands and reduces absorption of eventually present harmful components of silicone such as antibacterial agents) you better do it with gloves. While audreyobscura did it with bare hands - which gives you greater sensibility - I found it works also with gloves (I used nitrile gloves).
- Then take the silicone clump out form the water and pour some dish-washing soap onto your gloves and start molding and smearing the silicone caulk around your previously made "oogoo clamp" , covering it fully. You want to get a transparent/translucent silicone "glaze" coating your clamp, thus protecting it from wear/abrasion. Cover especially the clamp fingers with sufficient caulk since here the abrasion is most critical.
Step 4: Make the Carrousel
Lets' now make the carrousel which supports all the pipette clamps and rotates around the bottle axis. We can use the screw cap of the bottle as a rotor.
- First we polish away with a file the screw on the bottle cap so that it can rotate freely instead of screwing on the bottle.
- Once done with this we prepare new "oogoo-dough" as already described and hand-mold it around the plastic cap giving us a "oogoo-cap".
- we then make a "oogoo-dough socket" for each of the clamps as follows: we prepare "oogoo-dough" and hand-mold it between the clamp and the "oogoo-cap" to shape a connection socket. Once satisfied with the shape of the socket we gently remove the clamp, thus leaving only the "oogoo-socket" attached to the "oogoo-cap". The reason why I remove the clamp at this stage is that "oogoo-dough" is not very sticky and doesn't stick very well to the glazed clamp while it sticks sufficiently well to the "oogoo-dough" cap.
- Once the socket is solidly attached to the oogoo cap (just wait about 10-15 min) we need to "glue" the clamp to the socket.
We do this by using as a "glue" the standard 1:1 silicone : cornstarch oogoo mix ("sticky-cream" type). This standard oogoo will stick well to both "oogoo-dough" and silicone glazed clamps. Do this for all clamps that you had prepared to finish the carrousel.
Step 5: Make the Stand
To make the stand we start preparing the metal rod that will hold all parts of the stand together.
- Normally steel rods ripped from scanners or printers have grooves at their ends for fixing them with clips. If yours hasn't such a grooves you can make them with a saw. We want to insert a big paperclip into these grooves, so if you saw the groove by yourself make sure the paperclip fits inside the groove.
- bend the ends of the paperclip with the pliers so that there are no sharp ends pointing to the outside. Then insert the clip into the groove and press on it eventually deforming it so that it will sit in the grooves.
- To secure the clip in thsi position we wrap strong adhesive tape (for instance "american tape" or "gorilla-tape") around the end of the rod and around it.
- Then slip a washer onto the rod. If it does not fit increase the size of its hole with a file.
The next step is to prepare the plastic dish.
- first glue the wooden board to the cavity of the dish using hot-melt glue
- then with a drill - using a 3 or 4mm drill-bit (not larger) - carefully drill a small hole into the dish and wood, preferably drilling from the wooden side. Keep the dish well fixed somehow while drilling. preferably press it against another wooden board. Note that the plastic dish can crack when drilling if you use a too big drill-bit and by chance the dish "jumps" when the drill-bit passes through. Note that having glued the wooden board to the dish reinforces it and drilling from the wooden side reduces chance of cracking. I recognized this only after having it done wrong.
- now with files enlarge the hole until the metal rod fits in.
Now prepare the bottle:
- drill a small hole into the bottom of the bottle and enlarge it with the files until the rod passes through.
- enlarge the hole in the bottle neck with the files so that the bottle can be inserted onto rod.
- now fill the bottle with about 1 kg of heavy metal parts. I used screws since they are easy to find/buy. You may use also other
heavy stuff that will not "flow" out from the bottom hole of the bottle.
Finally we assemble the stand:
- insert the rod with the washer into the hole in the reinforced plastic dish
- then slip the rod through the half-filled bottle and insert the rod
- we now glue the bottom of the plastic bottle to the plastic dish using hot-melt glue. First apply hot-melt glue to the bottom of the bottle or the top of the dish and then slide the bottle along the rod, pressing it strongly against the dish. Then apply glue around the bottle rim.
- we then fix the rod on the wooden board by once more applying hot-melt glue covering the clip ad washer.
- finally we drill a small hole in the plastic cap of the bottle and enlarge it once more with the file so that we can insert it on top of the bottle with the rod passing through the cap.
The stand is now ready to mount the rubber carrousel.
Step 6: Clamp All Parts of the Stand Securely Together
We now mount the rubber carrousel and clamp all parts securely together as follows:
- we insert the oogoo rubber carrousel on top of the plastic cap
- we insert a washer onto the rod.
- we saw two slots into the rod to fix a paperclip. We saw the slots just above the washer.
- we insert a paperclip into the slots and bend it so that it stays in place. Bend it so that no sharp ends stick out.
- finally we fix the paperclip in place with hot-melt glue.
The washer+paperclip are necessary since the weight of the stand is considerable (1 kg) and hot-melt glue alone is not enough to keep the bottle glued firmly enough to the plastic dish. By adding the washer+paperclip we strengthen the strand considerably
and it won't break apart now.
In principle our carrousel pipette-stand is now ready. However to transport it and use it more comfortably we will add a handle at the end of the rod.
Step 7: Add a Handle to Your Stand
Adding a handle to the stand is not necessary but turns out to be very useful for more ergonomic use of the stand and of course to more easily move it around on the bench or in the lab. Commercial carrousel stands usually have some kind of handle.
To easily make a handle that is both secure (will not slip off from the rod) and easy to make we use again oogoo. To make the handle we need quite a lot of oogoo and it is worth to consider recycling oogoo scraps that you might have accumulated. Indeed you will have noticed that lots of rubber scraps remain on your cups, spoons, mixing stick, gloves and table when you prepare oogoo. You can recycle all this material collecting and grinding it and use the resulting "powder" to make recycled oogoo by adding just a little bit of pure silicone caulk and cornstarch. For a detailed description on how to recycle oogoo see my "recycle oogoo" instructable. If you don't mind using lots of silicone caulk ignore what I said above and just go on making as much fresh oogoo as you will need for making the handle. However notice in the following photos that I used "recycled oogoo", which has a grainy texture instead of the usual homogenous texture of normal oogoo. Only for the final coating of the handle I used blue colored fresh oogoo.
- To start making the handle you need to saw slots onto the end of the rod if they are not there already.
- insert a washer onto the rod.
- insert paperclip into the slots and bend it so that it stays in the slots. Secure it with strong adhesive tape.
- move the washer up to just below the paper-clip's position.
- prepare "oogoo-dough" as previously described or use "recycled oogoo" and mold it around the rod end to shape the handle. I made it using "recycled oogoo" to make the core of the handle and then coated it with fresh blue "oogoo-dough".
Once the handle is solidified it is in principle ready but has the disadvantage that it can't be disassembled. If you want a handle that can be disassembled - which is useful if some component of your stand needs exchange - follow the simple steps below.
- cut out a circular disk on top of the handle, following a circular path with a diameter smaller by about 5-8 mm than the diameter of the washer. This is very important ! Don't cut it too large. A small enough disk cut-out will allow the washer to remain clamped inside the handle.
- to disassemble the hand you now just push it downwards. The washer will slip out through the hole you cut on top of the handle.
- insert a second washer above the paper-clip and push up the handle and push the washer into the handle until they are clamped inside the handle.
- finally close the hole by filling it with hot-melt glue.
Our stand is now finally ready ! Hard work but worth it , at least for me.
happy pipetting !