Anti-backlash screw

Hi everyone. I just purchased the 48x30 LongMill and I am put the machine together. There is a gentleman on youtube name Garrett Fromme who does many tips and tricks for the LongMill cnc machine. He mentions that when installing all the backlash blocks to make sure to replace the anti backlash screw with the set screw this way you get the exrta distance of travel before hitting the sensors. The set screw did not come with my 48 x 30. Did anyone get these set screws with your LongMill. Let me know please

1 Like

I have the MK1, and got the regular screws. I went down to the hardware store and bought set screws to replace the stock ones.

thanks for the reply.


I have original MK1 and received both screws and set screws. They must have stopped doing that in later versions.

1 Like

Heyward43 you may be right. I have the last revision before the LM2 came out. But the mm screws at the hardware store were cheap.

1 Like

Not needed for the MK2. There’s no interference at all.


@VinceC I have a older MK1, mine didn’t come with the set screws either, I just cut off a little on the Y’s allen screws so the head is behind the gantry’s, all the others don’t effect movement.

I have the MK2 30x30 and no issue with clearance on the M5x16 screws in the anti-backlash nuts but after a couple hours of use the screws for the X and Z axis vibrated loose and fell out. Was just milling basswood with a 1/8 end mill at the recommended speeds. Anyone else see this? Should we be putting thread lock on the screw?

Hello @wilf_yyz and welcome to the forum! I have found the people here to be kind and helpful. I hope you do too.

As to your question about thread lock remember that you have to adjust the screws as the anti-backlash block wears so I would not use anything that is too hard to get undone. Personally I don’t use anything and have never had them fall out but I check for play in the system on a regular basis and adjust them as needed. Maybe a drop of glue on the outside were the screw meets the block would work without being too permanent.

Anyway congratulation on your MK2, I’m a bit jealous as an owner of one of the last MK1’s. My MK1 has served me well so far and I hope the MK2 does the same for you.

Thanks Michael. I decided to give the two M5-16 screws a little wrap of teflon tape which is very thin and soft to stiffen the thread fit in the anti-backlash block. Easily removable if needed.
This is my first CNC machine. I have lots of experience using larger routers for dovetailing and in various jigs but this is the first time I have let something other than my hands control the thing. Fascinating to watch.

Good call with the teflon tape! That should stop the movement and still be easy to adjust. Like I said mine have never fallen out but that doesn’t mean they haven’t vibrated out a little. Maybe I’ll put some tape on mine and see if I don’t have to adjust as often.

I find it fascinating to watch as well. My first machine was a 3D printer and the accuracy of the movements blew me away. I also like the sounds that the stepper motors make especially when doing curves. You can really hear them with a printer, no router to drown it out.

1 Like

Watching a CNC router is like watching a campfire, relaxing.

1 Like

@wilf_yyz , i guess don’t quite understand the issue, if the screws are tight enough to provide the proper resistance they shoudld not be falling out. Make sure they are tightened to the proper tension.

Hi Bill. It was my understanding that when the mill is first built and the delrin blocks are new there would not be any slop in the fit with the drive screw and no backlash. If this is the case then there should not be any tension on the M5 required. I have only had my MK2 for a couple weeks now and I have tested for backlash with a dial indicator and it is very good in all axis. My opinion is that the M5 tap in the delrin block should be done with an undersized tap which provides resistance to screw rotation.
I am very pleased with the accuracy of the mill though. I took a piece of hard maple and milled a 3" diameter pocket with a 1/4" end mill and in the other part of the board I milled out a 3" tenon using the same bit. When I cut the board and put the tenon in the pocket it was a perfect press fit.


@wilf_yyz i don’t believe it is a a thread resistance issue, but when looking at the anti backlash blocks the resistance/tension is created when the screw pushes against the opposing (other side of the gap) that creates the tension.

1 Like