Router Lifts: the basics - Part 6
The TPI measures of how many turns of a screw exist in a linear inch. This is important to you because the more turns per inch the more you have to turn the adjustment knob (or crank) to adjust your router bit height. The higher the TPI, the more accurate the settings can be and the easier it is for you to lock in small adjustments. But there is a trade off. Higher TPI means you must make more cranks to travel a given distance. This comes into play when you move from one cut to another and need to make a large adjustment. For example, 16 TPI means it takes 16 cranks to raise the lift 1 inch. 32 TPI means it takes 32 cranks to raise the lift 1 inch. One way to work around this is with what is called Dual Adjustment capability, in which two separate threads are used: one for large movement up and down, another for fine adjustments.
Using a lift made easy .... choosing the right TPI for router table lifts can make a big difference.
Let's look at some real life examples. Let's ay that you use an 8 tpi screw. This is ideal for moving up and down quickly, so you might prefer this in a production type environment where speed is most important. An 8 TPI router lift makes quick adjustments up and down possible, but leaves some 'slack' in exactly how accurate you can get your router height. Compare this to say a 16 tpi screw which would allow precise adjustments but might take a long time to raise an inch or more. This better suited for the casual wood worker who cares less for speed, but still wants some good height resolution. For very precise application, we typically use a 32 TPI lift. These very accurate lifts almost always employ a dual-setting system to avoid the tediousness of cranking all day for larger adjustments!
Another important thing when adjusting your router bit height is knowing exactly where you are setting it. Toward this goal, most lifts have a system built in that shows bit height. This is an important feature to consider. Some manufactures like Jointech have high-tech digital readouts that actually display the true height of the bit above the router table rather then the lift's settings, while others take a more traditional approach such as with the easy and highly rated rotary scale on the lift in a Bench Dog router table.
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