Slot Mortiser Z Axis - 10 or 16 Threads Per Inch Better?

[Bill Webster]

I am designing a horizontal slot mortiser, which will actually be a router attachment for my clamping beam (H-beam). Would it be better to have 10 or 16 threads per inch on the threaded rod used for the vertical router adjustment? In either case, there would be an appropriate calibrated dial on the threaded rod. I can see how 16 tpi might be nice, since most router bits diameters are in 1/16ths. But using a digital caliper or dial indicator is a huge plus and that would would work out better with 10 tpi.

H Beam.jpgbeam.jpg

[Mike Cutler]

16 tpi. It's pretty easy to count crank turns and be very close.
16 will also probably have less hysteresis than 10, unless you have matching guide blocks.

[John TenEyck]

I use a 16 tpi rod on mine. Either would work with a calibrated wheel, but as you said, most router bits we use in the US are some fraction of the inch scale so 16 tpi seems like the easier approach.

John

[Bill Dufour]

16tpi will require about 50% more turns to move a given amount. How often and how far it moves depends on your use. If you move it a lot the extra turns will get tiresome. OTOH 16tpi reduces force needed to move and the maximum force that can be achieved for the same input torque.
Bill D

[David Micalizzi]

I would go with 16tpi and set it up so it can be rough adjusted with a cordless drill for the times you find yourself having to crank it back and forth.