Akshay Harlalka
Curious Builder

July 26, 2020

This weekend, I was trying to learn how to do modal analysis in a new FEA software package. I wanted to gain more confidence with the use of this new FEA package. So, I decided to set up a simple cantilever beam problem in the FEA package and compared its first three modes to theoretical calculations and experiment as a sanity check.  It was a fun exercise.  

April 10, 2018

So, this week, as I was preparing to pack my bags for travelling to MIT, I used the snapfit buckle to secure the clothes in the bag. I began to think about snapfits more and wondered how the engineers ensure that snapfits would not fail due to fatigue during the expected service life of the bag. So, I decided to do a basic analysis and small test to check if my analytical model is correct. Following that, I decided to calculate the expected life of the snapfit.

July 11, 2020

Bearings are everywhere. This week while at the gym, I was using the seated leg curl machine. I noticed the bearings which were supporting the shaft of the machine and decided to be do my Seek and Geek report on that. I wanted to learn the process that engineers might have gone through to determine the size of the bearing.
Before one can select a bearing, it important to understand the loads that the bearing must support and the type of operating conditions it will be subjected to. For the seated leg curl machine, the criteria to determine the size of the bearing should be based on the static load conditions because the bearing of the seated leg curl machine is not rotating continuously nor is it subjected to high dynamic loads.

February 09, 2018

​​This week, I analysed a Vise Grip® which I found in the MIT Hobby Shop. This is a very powerful tool to clamp the parts on the worktable for various machining operations. This tool makes use of singularity to provide a huge clamping force on the workpiece. It can essentially be modelled as a four bar linkage as shown above. To clamp the part, a force is applied at point E, which causes the distance between the points A and C to increase. When AC = AB + BC, i.e. the links AB and BC become collinear, the mechanism locks and the part gets clamped on the work table. As it is generally very hard to restore the mechanism to its former orientation, a small link (numbered 2) is provided. This link presses against the bump on link AB to break the lock. For mounting the Vise Grip on the table, a slider (part numbered 3) is provided at the bottom which fits into the slot on the worktable. 

May 11, 2020

This week, while cutting wood at the hobby shop for my sketch model, I opened the lid of the table saw and discovered a belt drive power transmission system. I wonder why belt drives are so common on machine tools. Almost every machine has one be it the table saw, band saw or the drill press. The reason is that they allow huge power transmission at high speeds and at relatively low cost. So, this week I wanted dive into how belt drives are designed and what governing equations play a role in determining the thickness and width of the belt.

April 29, 2018

This week, I had ordered a helical spring from McMaster to make an anti-backlash nut assembly. I decided to predict the stiffness of this helical spring and check my calculations against the specifications listed on the McMaster website

May 06, 2018

This week, while machining the leadscrew on the lathe, I noticed that the deflection of the workpiece due to the cutting forces caused significant deviations in critical dimensions. Therefore, I used a test part and tried the predict the deviation from the true dimension value by using the first principles. The initial diameter of the rod was 12.72 mm. The target dimension was 10.9 mm. The workpiece stick-out was 80 mm. Based on this initial data, I used the cantilever beam formulas to come up with a prediction for dimensional accuracy.

April 06, 2018

The lever handle consists of many parts. But on the outside what we see is just the lever handle and the round part which is called the rosette. The rosette is fixed to the door and does not move with the handle.
What makes the lever handle come to its original position each time is torsion spring. We will be going into the details of the torsion spring further. A spindle (square shaft passes through the center and couples both the inside and outside lever handles. The spindle also passes through a cam driver which in turn is connected to a latch puller. When the handle is actuated, the latch also moves inside the housing of the door. 

March 16, 2018

This week, I decided to work through the process of selecting a lead screw for a lathe machine and checking if my calculations predict a reasonable and close enough estimate for the lead screw dimensions compared to the actual machine in the shop. To start, I checked the typical rated power of a motor in a lathe machine which was close to ¾ HP or 560 Watts. The lowest speed setting in the lathe was 100 rpm. Ideally, the lathe is operated at 75% of its rated power for max efficiency, which will correspond to 420 W of power roughly. However, we don’t want the lead screw to buckle at any condition, so we assume the lathe is operating at the peak load.
Estimating the maximum cutting

July 01, 2020

This week, I took apart the housing of my thermostat to see how the principle of elastic averaging works in real. The function of the snapfits was to provide an easy pathway for assembly and disassembly of the thermostat with respect to the wall mount. Snapfits are used extensively because they are easy to manufacture (injection molding) and predictable to design. Elastic averaging is everywhere in the world. Even the phone with which I took the picture of the thermostat had its back panel snapfit on the main assembly. And what strikes me the most is that the engineers relied on these humble snapfits to provide the phone with waterproof capability. The figure below shows the picture of the small snapfits injection molded onto the phone.

January 10, 2018

This week I took apart a hand cranked food processor and analysed the gear train design to understand what aspects would have been the most critical to its design. This food processor had two options for the user: high speed operation and a low speed operation. To provide the high speed operation, the food processor made use of a serial gear train. The sketch of the gear train is as shown below. I took apart the food processor and calculated the transmission ratio for high speed operation. To do this, I first determined the driving and the driven gears and the direction in which they were moving. Finally, I multiplied the gear ratios (driving to driven) to find the transmission ratio.