Dumpster CNC Acme Nuts Tons of Backlash Help?

[Cartierusm]

I got my machine together with Mcmaster Carr Precision Acme Lead Screws and Dumpster CNC antibacklash nuts but I'm getting .01" backlash. That's a ton! I emailed him today and should recieve a response by tomorrow, I hope, but was wondering if this is normal. I tried his nuts, no pun intended, a few years ago and had the same problem but thought I'd give it another try as I couldn't afford ballscrews this time. With the nut mounted and everthing I can take the gantry and move it and see the nut shift. I wonder if I could use a heavier spring to push the part that grips the screws. Any help would be appreciated.

[CarveOne]

Originally Posted by Cartierusm I got my machine together with Mcmaster Carr Precision Acme Lead Screws and Dumpster CNC antibacklash nuts but I'm getting .01" backlash. That's a ton! I emailed him today and should recieve a response by tomorrow, I hope, but was wondering if this is normal. I tried his nuts, no pun intended, a few years ago and had the same problem but thought I'd give it another try as I couldn't afford ballscrews this time. With the nut mounted and everthing I can take the gantry and move it and see the nut shift. I wonder if I could use a heavier spring to push the part that grips the screws. Any help would be appreciated.

I don't see anything like this on my two machines that use DumpsterCNC nuts. The DumpsterCNC ABNs are spring loaded to keep the nut snug on the lead screw threads when reversing travel direction. Mine are already pretty snug on the 1/2" ACME rods with the included springs. Any tighter and they will probably just wear faster. The nut should not shift relative to the lead screw.

If the whole lead screw moves lengthwise then there is free play or flexing in the lead screw mounting system. Do you have the lead screw mounted so that it cannot shift but can easily rotate? Shaft collars and thrust bearings will be better than just letting the lead screws float inside the bearings.

Do not depend on the stepper motor alone to hold it steady. This will work on small machines with light cutting forces but will not work well on heavy gantries or higher cutting forces.

CarveOne

[Northboy]

I just installed dumpster 1/2 10 2 start in my project and I am getting less than .001 backlash in mine. I concur that your movement if it really is .01 is not in the nuts.

Northboy

[Cartierusm]

Thanks for trying but when I wiggle the carriage by hand you can see very clearly the nut shifting on the screw and the screw is not moving, and I'm not forcing it the carriage is very light maybe 5-10 pounds and it's fully supported. Trust me it's very obvious. Dumpseter emailed me back and said it could be the lead screw being slightly undersized.

[vlmarshall]

I've nearly finished a 25x25 gantry router using Dumpster 1/2-10 single start nuts, and they're quite snug, with no noticable backlash, but I haven't put an indicator on them yet.

[Cartierusm]

I think the problem is the acme screw from Mcmaster. The nuts fit so it's some sort of acme screw but not exact for some reason. Maybe they sent me the wrong thing. I went over to a shop that makes acme nuts and brought the screw and their nuts didn't fit at all, they start to go on but after 3/8" of an inch they tighten up considerable. Screw it, no pun intended, I'm going for Roton ballscrews with which I'm very familiar, $140 for both axis 5/8" and 4 ball nuts to create anti backlash that's adjustable. I'll sell my Dumpster ABN as they're new and the problem is with the screw.

[Kent23]

I am also having backlash problems with Acme screws fom McMaster and Dumpster nuts. Is there a way to measure the ACME screws to see if they meet spec? What are other good sources of lead screws that are reasonably priced.

[amplexus]

A ballscrew would be a better plan but you can try a pair of nuts with a spring between them that should fix a lot of your problems.
Amplexus

[Cartierusm]

Kent, I'm not sure who's fault it is but something isn't matching up. But for the price Roton.com ballscrews are pretty cheap and beefier. Yes you'll need 2 ballnuts per axis but each ball nut for 5/8" is only $23. So for 4' of ballscrews and 4 ballnuts INCLUDING shipping I paid $150 and they shipped the day after I ordered them. I've used roton ballscrews before and I love them for the price.

[CarveOne]

Originally Posted by Cartierusm I think the problem is the acme screw from Mcmaster. The nuts fit so it's some sort of acme screw but not exact for some reason. Maybe they sent me the wrong thing. I went over to a shop that makes acme nuts and brought the screw and their nuts didn't fit at all, they start to go on but after 3/8" of an inch they tighten up considerable. Screw it, no pun intended, I'm going for Roton ballscrews with which I'm very familiar, $140 for both axis 5/8" and 4 ball nuts to create anti backlash that's adjustable. I'll sell my Dumpster ABN as they're new and the problem is with the screw.

I have the low cost 1/2-10 1 start ACME rods from ENCO and DumpsterCNC nuts on my Solsylva 25x37 machine. The rod measures 0.495" diameter with my digital caliper and when I set the caliper to 1.000" and place it on the rod lengthwise I get exactly 10 threads between the jaws of the caliper. This machine does not have any visible free play when pushing in the gantry.

I have new McMaster-Carr 1/2-10 5 start ACME rods for my second machine that is under construction. The one rod I measured is 0.508" diameter and there are exactly 10 threads between the caliper jaws as measured above. This machine is not assembled to the point of having the anti-backlash nuts installed yet, so I can't check for free play yet.

If you check your McMaster-Carr rods you should have something similar. If you don't, there is the possibility that you received a metric rod part number by mistake. I would think that the DumpsterCNC nuts would not start on a metric rod at all, but being soft Delrin, it can be possibly started part way. A steel nut would not go on at all.

CarveOne

[SatanKlawz]

Just curious because I was thinking of ordering acme rod from mcmaster..... Did you order the standard acme rod or did you get the precision rod from them?

[revwarguy]

I have new McMaster-Carr 1/2-10 5 start ACME precision rods and the Dumpster leadnuts, and they seem quite solid. They initially fit quite tight, I could start them but couldn't get them all the way on by hand. Running a file edge lengthwise over a cutoff piece of the rod to use as a simple tap, along with some teflon spray lube, did the trick.