I got the nut block with the 8mm lead screw a while back. The lead screw diameter is really 7.76mm. Are there any recommended ball bearings and the couplers that can be used with these? Are there any adapters that can be used to bump the diameter up to 8, 9, or 10mm maybe?
Well, I made some adapters for my lead-screws a few years ago but for a different reason. See the attached pic. You would need a lathe or access to one to make 'em though.
Thanks for the reply. I unfortunately don't have access to a lathe. . Nice work by the way. After quite a bit of digging I found a stainless steel tube with an OD of 3/8 and the wall thickness of 0.035". That makes its ID 0.305" which is 7.747mm. I guess a ring cut from such tube should be just right as an adapter for a 3/8 ball bearing.
The real question is what is the concern here. The lead screws were sized down about seven years ago because the true 8mm screws were too difficult to get into the 8mm bearings. Are you using the screw in a true radially loaded condition? In an axially loaded system like most use them it is rarely a problem. Some have noted a slight clicking sound but most have had no issue. If it is an issue, filling the grooves with JB Weld or other filler and sanding down to 8mm will solve the problem. (Of course you'll need to have the nut on the screw prior to that.). Another option if you are using this in an axially loaded condition simply using thrust bearings. These tend to hold the screw centered without the clicking, just be sure and put the smaller diameter washer on the side toward the lead screw nut.
As I wrote in my original post, the diameter of the lead screw (measured with calipers) is 7.76mm. I can't file it down to 8mm. Filling the gap with JB Weld does not sound like a good idea either.
Hmm, when I use 8mm ID bearing like everyone else the lead screw wobbles a little (actually a little more than a little ). The bearing does not spin and the screw simply slips inside of it. Is the ID on the 8mm thrust bearings 7.76mm by any chance? I can't find the a drawing with the measurements here. If not I will have the same problem no matter what kind of bearings I use. I love the nut block that came with it since it would work just perfect for my project but at this point it'd be easier to buy an 8mm lead screw that's 8mm with some lame brass nut on it and be done with it. Thanks everyone for the help.
But now I'm thinking that maybe I don't really need to use bearings on both ends of the lead screw at all? Two slider blocks will keep the spindle motor in place anyway while the lead screw will just sit tight in the nut block while still attached to the motor coupler on the other end. I still don't have a 7.76mm OD coupler but if I use the 8mm clamping coupler (not the set screw coupler) it may actually be close enough to the center anyway.
Perfect, as designed. Its purposely undersized for many reasons, ease of assembly primarily. Its NOT an issue, the leadscrews are constrained Axially (radially DOES NOT matter) You do. Otherwise you transfer axial loads to motor bearings (a No No) The system has been proven over many years and thousands of implementations. Don't overthink it
