My next project is to convert my mini lathe to CNC. After reading posts here, and looking at pictures in the photo section of converted lathes, i see that helical beam couplings are a popular choice. But compared to lovejoy type couplings, these are expensive. I used lovejoy type couplings on my mill, and it seems to work well. Is there anything that sets helical beam couplings apart from lovejoy to justify spending the extra money?

'Lovejoy type' is a bit vague as they make several types of couplings, I prefer the Uniflex type, they have zero backlash, high load capability and will tolerate a high degree of mis-alignment. The Sflex type have a much higher inertia and also have a degree of backlash.
Helical are fine for encoder coupling, if you use this type for motor/load coupling, you should use Stainless not aluminum. They are fairly expensive in stainless.
Al.

Your right, it is vague.
By this I am reffering to ones I used on my mill, or the type sold at Enco
McMaster Carr is where i got them
THey are the Iron ones with a Buna -N plastic spider. I hope this clears stuff up a bit. thanks for a reply

The lovejoy couplers your refering to have backlash in them, they are decent and will work just fine depending on what your aiming for. The helical beam couplers dont have backlash in them, but as Al said they are better suited for hooking up encoders, although I can disagree, for smaller applications like mini mills, mini lathes etc it shouldnt be a problem to hook them to a motor and screw.

Jon

If you want to select a helical type, see the heli-cal site www.heli-cal.com some of theirs go up to 1800lb/in. I don't know how they compare with price with the Lovejoy UniFlex, but if you ever need a high torque type, take a look at the Uniflex type.
Al.