Mechanics – Torsion theory help!?
Determine the diameter of a solid steel shaft which can trasmit 45kW at 400rev/min if the maximum shear stress is not to exceed 45MN/m^2.
If the wright of this shaft is reduced by 50% by drilling and axial hole through the centre, what will be the maximum stress is the power and speed remain unchanged?
I won’t work it out for you, but I’ll explain what you need to do. You are given the power (45 kW) and the shaft speed (400 rpm), so you can calculate the torque applied to the shaft. Shear stress in the shaft is given by
tau = Torque * r / J
where tau is the shear stress, r is the radius to the location where you want to calculate the stress (in your case the outer radius of the shaft), and J is the polar moment of inertia. So, you know tau & torque and can reduce the remainder of the equation to be in terms of shaft radius.
Next, weight of the shaft will be a function of radius squared so just calculate what the inner diameter would have to be for a 50% weight reduction. Then, recalculate the shear stress.
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Different Types of Drill Press and Safety Tips Using the Drill Press
There are lots of drill press machines available in the market. There are tips you need to consider when using this machine in order to ensure safety at all times.
A drill press is a permanent style of drill that can be bolted onto the floor or mounted on a stand or workbench. It helps drill holes in wood, metal and a variety of other materials. The drill press produces accurate holes. Repetitive holes can be drilled in the same spot and at the same depth accurately and quickly.
Speed can be adjusted via changing pulleys and belts. Drilling big holes usually requires a slower speed.
A floor-standing drill press is more powerful and can be used with many kinds of materials. Bench-top drill press is a lot more compact. These two types of drill presses are the best for lighter and easier jobs.
Besides drilling holes, there are also different types of bits and attachments you may get to add versatility to the machine. This includes mortise bits, planer heads and standing drums.
Listed below are some types of drill press
- Floor Model Drill Press – This drill press is the most loved type of drill that can be found in professional wood shops. It is equipped with longer columns and higher power motors. The column length of this floor drill presses are commonly 66” to 72” high. The advantage of this type of press is it allows you to handle larger work pieces because the table can actually run the full length of the column. The average price of this drill press ranges from 400 to 1,000 US dollars.
- Ryobi DP121l Drill Press – This is a type of 12-in bench top with multi-features. It has a dual laser type of guide, a 500-3000 RPM capability, a L.E.D work light, and speed readout. Speed can be changed just by moving a lever from the left housing, or adjusting the pulleys and belts. Average price 120 US dollars.
- 5 Speed Bench Drill Press – This is easy to use and can drill faster. The 5 spindle speed of this drill press is for drilling steel, wood, plastic or aluminum. It has a fully adjustable table with an angle indicator. The average amount of this drill press is 130 US dollars.
- Radial Drill Press – This drill press has an adjustable movable spindle. It is ideal on heavy work, where many holes are drilled.
Safety tips when using drill press
- Always be alert or aware where you are putting your fingers to avoid accidents.
- Do not use bits that are bent, damaged or dull.
- Ensure the bit is centered in the chuck and tightened before operating the drill.
- Use a clamp when drilling metal to avoid the material spinning to your hand or body.
- Never turn on the drill press before clearing the table.
- Never use drill bits that have a screw tip.
- Do not turn on the drill press with the Drill Bit is in contact with your work piece.
- Avoid awkward hand positions.
- Avoid drilling materials that do not have a flat surface.
- Avoid wearing neckties or gloves when operating the drill press.
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High speed structural steel drilling system by Voortman
