Kerk Motion Leadscrew Possible Problem

[ThomasAlva]

I bought the HobbyCNC plans for building your own machine, and it tells you to buy the leadscrews from Kerk Motion Products. That's what I did and I recieved the 3 leadscrews at my doorstep just a few days ago.

Here's the problem:

Drawing number 14 in Dave Rigotti's book shows that a short section of one end of the leadscrew is completely rounded to accept a coupling. I just looked at the leadscrews they sent me and there is no rounding down at the end. Am I missing something? Or did Kerk Motion screw up? It just doesn't seem right to attach a coupling set screw and have it dig down into some acme threads.

Any help would be appreciated.

[HobbyCNC]

Originally Posted by ThomasAlva I bought the HobbyCNC plans for building your own machine, and it tells you to buy the leadscrews from Kerk Motion Products. That's what I did and I recieved the 3 leadscrews at my doorstep just a few days ago. Here's the problem: Drawing number 14 in Dave Rigotti's book shows that a short section of one end of the leadscrew is completely rounded to accept a coupling. I just looked at the leadscrews they sent me and there is no rounding down at the end. Am I missing something? Or did Kerk Motion screw up? It just doesn't seem right to attach a coupling set screw and have it dig down into some acme threads. Any help would be appreciated.

You got exactly what you ordered. This is why the plans show turning down the ends to fit 1/4" couplers. Of course, you can always use couplers that have 2 different sized holes in them.

Dave Rigotti

[ThomasAlva]

Oh, I don't have a lathe, and I'd just hate to put this precision part to a pedestal grinder and eye-ball it to 1/4 inch. Even if I use a coupling that has two different inner bore diameters, I'll still end up having a set screw dig down into some Acme threads!

Isn't that sacreligious to hand grind precision Acme threads? The nice machinists at Kerk Motion probably spent a lot of time to make these precision threads all shiny and purdy.

Wouldn't someone skilled in the art of building CNC machines question my judgement if I did that? Maybe Kerk motion would take them back and turn that one small end down to an unthreaded 1/4" OD.

One way or another, I'm going to get the steppers coupled to the lead screws.

I love your plans by the way. I hope to have the whole thing done before the Southgate, Michigan North American Model Engineering show in April.