Thursday, March 16, 2017

NEW TO THE BLOG THIS MONTH

This month with snow and cold allowed me to spend some more quality time with my computer. A few topics that have been sitting in my Work in Process pile for a long time came to the fore. The first is my Belt Grinder Motor Guide. It's an effort to answer some of the many questions that arise when makers start down the "I am going to build me a belt grinder" path. Motors are complex, yet with some basic knowledge you can make a decision on the suitability of a motor before you buy.

Another page that's come through the pipe is Part 5 of the VFD series called VFDs: Part 5 - Remote Control. This segment is all about speed control and remote start/stop for your VFD. The tutorial is mostly generic, with a focus on the popular TECO Westinghouse L510 VFD.


Hope to be back in the shop soon as warmer weather comes our way. I've got a belt release lever coming for the BG-272 and a variable speed grinder wheel turning machine that uses a DC treadmill motor. Lots of exciting stuff.

As always, if you have a question or want to fire a comment off, your input is always appreciated!

Dan

Wednesday, January 18, 2017

Belt Speed Calculator

I get asked a lot about what speed a motor with a drive wheel and a ratio of pulley 1 and pulley 2. It's a lot of stuff to figure out especially if you factor in a VFD driving the whole lot.

Being shut out of the shop for another cold week where the temperatures were dipping to the -30°C (-22°F) mark. I put on my programming hat on and made a simple to use online belt speed calculator which covers a whole bunch of scenarios.




Hopefully you will find this useful if you are designing a belt grinder or working with different ratios to get belt speed to match the material that you are grinding or polishing. You will find some recommended belt speeds for different materials as well as some other useful information from Klingspor in their technical document.

Stay warm and happy grinding!

Sunday, December 18, 2016

The Dreaded Bevel Angle Calculation

Online Knife Bevel Angle Calculator

http://dcknives.com/public/grind_angle.php

It's been super cold the past two weeks and I haven't had a lot of quality time in the sub-zero garage working on knives. I have to keep busy, and warm, so I've been working inside on a tool that lets us set the bevel angle on a blade by the grind height and thickness.

To work this out we need to look at the thickness of the steel and the height of the grind and make a simple right triangle.











Here our steel is laying on the flat. Imagine we want bevels that look like 'A'.

Adding a horizontal center line will divide the steel in half.

Adding a vertical line at the grind stop will allow us to extract a right triangle. Voila! High School was finally useful!

 


In order to get from a right triangle to real world grinding angle, we need to assign the Adjacent (A) and opposite (O) values.


 



There is a mnemonic used to remember which trigonometric function to use when we need to find some missing part of a right triangle. This mnemonic is SOH CAH TOA. Okay... what the?

SOH CAH TOA helps us remember to use the Sine function when we know the Opposite and Hypotenuse, we use the Cosine when we know the Adjacent and the Hypotenuse and we use the Tangent when we know the Opposite and Adjacent values.

In our example for blade grinding we us TOA or Tangent for Opposite divide by Adjacent.

Let's put some real numbers in. Say our knife is going to be a hefty 0.25" thick. We take 1/2 of that to make the right triangle, so O is 0.125".  We'd like a grind height of 3/4" or 0.75".

Using the ATAN function on our calculator we can determine the angle in radians. But, radians is not degrees. We need to multiply radians by 180/pi to get the degrees.

Here's the link  for Imperial and this link is for the Metric Grind Angle Calculator.

I promise no more math for the rest of the year.

Merry Christmas,

Dan

Thursday, November 10, 2016

2x72 Grinder Wheel Set

2x72 Grinder Wheel Set

I am building another low-cost 2x72" grinder and I am super fortunate to have made a friend at Oregon Blade Maker.


Marinus at Oregon Blade Maker is offering some high performance, yet light-weight and durable grinder wheels for a low cost 2x72" DIY build.

These wheels are computer engineered, glass-filled nylon (durable composite plastic) with 1616RS bearings.

The wheels in this set are two 2-1/4" wide x 2" and one larger diameter crowned 2-1/4" wide x 3" which is designed to assist in belt tracking.

The wheels will mount with any 1/2" bolt. Plan for three 1/2" NC x 3" to 3-1/2" grade 8 bolts and suitable nylon lock nuts and washers.


These are low drag and spin freely.

Of course, the OBM glass-filled nylon wheels are not going to take over the aluminium premier wheel's top spot in roller Olympics, but these OBM nylon wheels offer value that cannot be denied.



Dan

November 10, 2016.