LeadScrew Nut Question

[Michael Simpson Virgina]

I am in the process of designing and building a verfy heavy duty cnc machine. I am a bit concerned about some of the lead screw nuts available.

I have been using the 5 start nuts from CNCRouterParts and while they work very well they tend to wear and eventualy devleop slop (Backlash).

I also have a couple of the Dumpster CNC 5Start nuts and could also work them into the design.

Another thought I had was to use double Nuts on both of the X-Axis rails. This would not only reduce wear but also allow me to adjust out the slop if needed.

Any thoughts?

FYI for now I am locked into 5 start ACME leadscrews as they present a resonable cost for the build and I have several 6foot screws on hand.

[John McClanahan]

Are the threads of the screws smooth? It sounds like the screws have a rough finish thats wearing out the nuts. I had an acme screw that was had a rough finish down in the threads. I wrapped rather coarse steel wool around it and squeezed it with my hand while wearing a leather glove. I then turned the screw and screwed the steel wool up and down on the screw, knocking out little burrs and smoothing machining scratches. I then stepped down to medium, then fine steel wool. When finished, the nut turned smoother with less resistance.

John

[Scott Shepherd]

All acme thread screws and nuts have backlash. If they didn't, they wouldn't go together or come apart. Ball screws are better at not having it (and much more expensive).

[Rob Wright]

Michael,

I agree that finishing the leadscrew is important to help longevity of the AB-nuts. There were a few burs on mince, and I felt that the machine ran far better after I "polished" them with steel wool as mentioned above. There are a few members on Joe's CNC that use double nuts from dumpster on the lead screw version of the machine. It seems to work just fine for them. The second AB nut's bracket is slotted to allow adjusting the distance between the 2 nuts. It is doable - I've seen it!

[Michael Simpson Virgina]

I have 4 lead screws. They are the coated ones from McMAster and are very smooth. I will look at this a little closer though. I have not yet used the Dumpster CNC nuts yet so dont know how well they work. Just looking for some input from some one who has.

All my last machines used the nut from CNCRouterParts. I like this one because of its design it is very easy to mount in various configurations. In my last build I got quite abit of slop. Personaly I think its the little rubber retainer they use its not as powerfull as a spring and does not seem to provide good tension on the threads over time.

This build is a lot larger than my last and since the dual X rails are steel and the gantry is aluminum and steel there is much more wieght and therfore more load I am worried about how the various nuts will hold up over time.

@Rob
Double screws makes sence to me. Its kind of like having an adjustable antibacklash nut. As an upgrade I think I will look at double leadscrews. It would be easy to add them later.

[Gene Crain]

Take a look at the Techno website, techo-isel punto com high quality screws, also pcblinearlinear punto com has some interesting pre assembled linear slides up to 96" length with custom widths.

[Rob Wright]

A pic of a double nut on a member of Joe's CNC. The left nut is adjustable. the nut on the right is fixed in the white HDPE piece on the inside of the carriage. These are dumpster nuts on McMaster 5 start lead screw (2tpi)


dble ab nut.JPG

[Greg Holt]

I am in the process of designing and building a verfy heavy duty cnc machine.

I know this is not what you want to hear but..........

"Very Heavy Duty CNC" and acme screws with acetal nuts do not really go together IMO.

Reasonable quality ballscrews can be had on ebay for not a lot of money.

Personally, I could not go past rack and pinion.

Greg

[Mike Heidrick]

Maybe the point was heavy duty as much as can be done while still utalizing the investments already made (in lead screws in this case).

[Michael Simpson Virgina]

I need at least 65" screw. Wont find one that long on ebay. I looked. For now its going to be a lead screw. Once built and working and a take down my last cnc I will build a R&P version. Allthough I would be interested in how those hold up.

[Mike Heidrick]

Interested in how R&P holds up? You doing nema 23 or 34? The cncrouterparts R&P kits are pretty beefy overall but I have heard the 34 design is quite a bit more substantial. The nema23 set I have has a small thin belt and faily puny stepper belt cog (not sure tthe correct name of it- piece tham ounts to the stepper). It seems to work awesome and has since May. The pinion gear works well with Moore Gear's rack.

[Gene Crain]

I need at least 65" screw. Wont find one that long on ebay. I looked. For now its going to be a lead screw. Once built and working and a take down my last cnc I will build a R&P version. Allthough I would be interested in how those hold up.

http://cgi.ebay.com/NSK-AMADA-BALL-S...item1e5fc1a08a

[Michael Simpson Virgina]

@Gene
Well $450 is pretty steep and 23 shipping Im not willing to spend almost $1500 on just the screws. I think for that kind of money I can go with a very high end RP system for the X and Y. Also looks like they only have one available.

[Gene Crain]

@Gene
Well $450 is pretty steep and 23 shipping Im not willing to spend almost $1500 on just the screws. I think for that kind of money I can go with a very high end RP system for the X and Y. Also looks like they only have one available.

only wanted to show that there is what anyone wants on the net...just gotta go an do the right ip address or something like that !