DIY hot knife

I bought some plastic boards from New market last weekend. I say plastic board cause thats the only name the shop keeper could tell me. I think its a closed cell polyethylene board. I am probably wrong. but the properties are similar. Its hard, its relatively light but approximately 10 times heavier than Styrofoam and does not bend. It breaks before deforming.

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Plastic Board. Source: ABC Stationary New Market, Dhaka


They are pretty strong but i was able to make a clean cut with a Utility knife just as the shop keeper told me. But it takes a lot of patience and skill to make a clean cut and large shapes are just that difficult to pull off.

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Recommended cutting tools by shop keeper


As always the lazy mind has a tendency to look for easier ways. And I came across “heated knife” the tool used to cut this type of materials with ease. I tested the concept by heating some Utility Knife blades using fire and it worked.

Unfortunately i dont have a heated knife lying around. Googling around looking at how it works I thought it would be relatively easy to make one using a soldering iron.

I have this pretty “old” soldering iron with wooden handle and large tip. Since I have a spare i decided to make a knife out of it.

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Flattened Soldering Tip with some sanding to sharpen the edges.

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How thin it is from the side











The method I used is simple. I heated the soldering iron tip high and then hammered it to make a flat shaped head.

Once I was satisfied with the hammering a little sanding gave the edges some sharpness.

CAUTION: Using hot knife to cut plastic will release hazardous fumes. Try not to breath on them.

I tested the knife on a piece of board.

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Hand cut plastic board using home made hot knife


Although it wasnt like cutting butter. But it was definitely close to cutting vegetables :) . I managed to cut a square board with smooth edges in less than a minute. It takes a while to get the tip heated. And perhaps due to its extended surface it looses heat faster and needs a break after cutting a while.

The edges are relatively smooth as well. You can make the edges better by slicing off the extra melted drops of plastic with a knife.

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Rough margins but smooth ends.

I am pretty impressed by the results, I will surely use this new plastic board for my future prototypes. I cant wait for the weekend to get around. ;-) .


DIY Thermo Electric Air Cooler

I made this thermoelectric air cooler a while back, almost forgot about them. I was clearing out my smartphones memory and found some image. So decided to post the idea here.

Things you need:

1 peltier device (Thermo electric cooler) I got this from china courtesy of a friend Bijoy

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2 CPU AMD cooler (any square shaped model but both same size preferred) I am not sure what model I used I just went to elephant road and got the cheapest available. Costs 100tk each From Elephant road. I bought 3



Heat sink compound. Found elephant road as well not sure about price 10tk per pack i guess. Also you get some compound free wit the CPU heat sinks.

Voltage source. I am using CPU power supply Any old atx power supply will do.



Some thin wire to bind the coolers
Apply some heat sink compound to the peltier and place it on 1 of the heat sink.

Apply more compound and put the other cpu cooler on top.

Make sure both cooler has the same orientation. The aluminium fins must be horizontal to each other.

It should look something like this-

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hold the 2 coolers on place tight and attach them using a thin wire rounding through the heat sink fins. Or if you can find appropriate nuts and bolts use them.

wire join


Yellow marks show wire joining the 2 heat sinks.

Connect the 3 red wires together, do the same for the black.

Red is 5v, black is ground and yellow is signal for CPU cooler. In my model the signal was optional so I didnt use them.

since we are connecting 3 in parallel same voltage will be maintained in 3.

If you have a power supply connection pin thats a good thing. otherwise just add the power and the ground to a power cable manually.

Same way ground is black in most power supply cables. and red is 5v.

The cooler was working good. I can feel the cold side getting cool in less than a minute. The heat generated on the other side is very high on the other hand.

you can use this cooler in a lot of applications. I was planning to use an array of these things to make asealed box computer casing( air conditioned) no dust but cool.

The cold air coming out of the heat sink is pretty soothing . Feels like putting your hand before an AC at 26*

The peltier looses its efficacy if the hot side is too hot. So the heat sink on the hot side is more important. And use of larger heat sink will increase overall performance.

I have seen a video on youtube someone making a box out of Styrofoam (Shola) and place this on the wall to make a mini freezer.

Feel free to comment your ideas.




Hardware Shop BD

When you are a robotics / hobby project enthusiast like me the electronics are just 1 part of the problem. We still have a lot of trouble collecting all the hardware and body parts. Specially for someone lazy like me. I hate to roam around markets to find a specific item. And the situation just gets worse for hardware. For example specific bolts/gears/rails and other raw materials for crafting the robot chassis.

Site like techshop are doing a great service to students and robot DIYers but I still wish for a hardware and raw material shop completely web based and offering wide range of items with easy to find interface. At least a service to start Laser cutting / 3d printing on request would be a good start. Although a fresh company (makerlab) is offering to print your models in 3d recently but the price is still high I would love to try them if ever have the opportunity

Price (Standard PLA Filament Types) :
=> Superfine (0.1mm layer resolution) = BDT 30/- per gram
=> Fine (0.15mm layer resolution) = BDT 27.5/- per gram
=> Average (0.2mm layer resolution) = BDT 25/- per gram
=> Low (0.25mm layer resolution) = BDT 22.5/- per gram
=> Fast (0.3mm layer resolution) = BDT 20/- per gram

If someone can estimate a cost of total items printed of a Reprap that would be useful. I havent found one on the net. I would prefer RepRap morgan since it has fewer vitamins.


I found some plastic board made by partex on ABC stationary New Market. They look pretty easy to handle. I will post further in future about my progress with these boards once I start working on a prototype.


I found this piece of information on facebook.  I asked a question there and got reply- wanted to share in case fellow Bangladeshi hobbyits are interested.

Q: “Can anyone here help me out, I am trying to find the best source in Dhaka for robot chasis. Not ready made chasis kits. I want to make the chasis myself so I need supplier of Acrylic sheet and Laser CNC cutter services. Any idea where I should start looking?”

I also found a CNC service provider with home deliver here-

An initiative

Originally posted on rezwanislam's Blog:

I am thinking about taking this 3D printer movement to next level. I believe we may innovate and invent a lot more, when we can start building our own prototype at low cost.  But need some honest feedback(s). Here are my thought(s)/initiative(s),

1) I have already started printing out another set of printed parts for a reprap.

2) I will replicate those using metal die casting (Aluminium/brass).

3) I would like to provide kits to educational institutes only for material cost + labor only. I don’t want to gain any profit for this.

4) I would like to train key personnel at educational institutes on building and operating reprap.

PLEASE  broadcast this post to key personnel / educational institutes and feel free to leave comment with suggestion and contact info.

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The Human Factor


Computers don’t mind if I must make effort to communicate with them or if it is easy to communicate with them. They don’t care if I put the numbers of instruction byte sequences in a file and feed it to them to run, or if a very high level language generated the instructions. The computers don’t care. We humans care about the effort we pay. Often people, especially computer engineers, focus on the machines. They think, “By doing this, the machine will run faster. By doing this, the machine will run more effectively. By doing this, the machine will something something something.” They are focusing on machines. But in fact we need to focus on humans, on how humans care about doing programming or operating the application of the machines. We are the masters. They are the slaves. – Yukihiro Matsumoto