How Do I ?

[speedre9]

Been wanting to build a ultra small drill press since forever. The only thing I don't know about is how to estimate how much return spring force to put into it. I plan on using a sewing machine motor to drive it
and just a simple slider to lift the head and chuck. Anybody know about springs?

 

[JimDawson]

I normally head to the hardware store, spring department. And just play with the springs until I find the one that feels right, sometimes I buy a few and try them out. Use the one that works and put the rest in the spring box on the shelf so you have some for the next project.

 

[Tony Wells]

A counterweight might be easier to adjust to exactly where you want the return force to be. Plus it would be linear.

 

[RandyM]

Also, there really is no way to recommend a spring without seeing your design.

 

[CluelessNewB]

Google "Hooke's Law" (an approximation for "ideal" springs)

Or skip the math and look at the springs on McMaster-Carr which should get you in the ball park if you know about how much weight you need to overcome.

http://www.mcmaster.com/#springs/=13waaj2

 

[Wreck™Wreck]

Weigh the parts that need to be moved then buy a constant force spring with a force higher then the combined weight if the components including some extra for friction.

As seen here http://www.mcmaster.com/#constant-force-springs/=13wafnc

 

[T Bredehoft]

Two old drill presses I'm using in the Propeller Shop came with a number of rubber bands replacing the (as sold) springs. It's surprising how good they are, and if/when one breaks, maybe you need to replace it, maybe not. They will pull the drill out of the work, but won't slam the spindle at the up-stop.

 

[RJSakowski]

Lee Springs is the last word in springs. It was my go-to when I was doing spring design. They have the largest range of springs that I have run across. There is enough information in their specifications to thoroughly characterize any of their springs. Back when I was doing design, I had set up a spreadsheet to give me the force at any given displacement for their springs.
They have a fairly steep price/volume curve but with the information given, you can find a substitute or wind your own springs. They also have great CAD models.
http://www.leespring.com/