Cheap Acme Threads for Cheap X-Y Table

[matthewsx]

Hi,

I'm trying to improve a Chinese X-Y table and was looking for a way to reduce backlash. Just wondering if anyone has done something like this guy does in his video? If so, what kind of plastic would you use, I have a suitable piece of delrin that might work if the properties are right.

Thanks,

John

 

[RJSakowski]

Delrin would be the plastic of choice. Fairly good lubricity and mechanical properties. I have done similar things with Delrin. I made a .009" hole in a 2" long piece of Delrin by pulling a hot wire through like a cheese slicer.It gave our head machinist fits trying to figure out how I managed to drill that long a hole of that diameter. Delrin handles melting fairly well. I woulde avoid using a torch though. You will get some oxidation of the Delrin. A hot air gun would be slower but less chnce of burnng. The fumes that arise from heating the Delrin are highly irritating to the eyes and nasal pssages so do it in a well ventilated area.

 

[matthewsx]

Delrin would be the plastic of choice. Fairly good lubricity and mechanical properties. I have done similar things with Delrin. I made a .009" hole in a 2" long piece of Delrin by pulling a hot wire through like a cheese slicer.It gave our head machinist fits trying to figure out how I managed to drill that long a hole of that diameter. Delrin handles melting fairly well. I woulde avoid using a torch though. You will get some oxidation of the Delrin. A hot air gun would be slower but less chnce of burnng. The fumes that arise from heating the Delrin are highly irritating to the eyes and nasal pssages so do it in a well ventilated area.

Thanks, I'll give it a try with the heat gun....

John

 

[BenW]

Epoxy?
You can use a thin film of oil or grease to prevent it from sticking too bad to the leadscrew. If you drill the current nuts out and cast the epoxy in place, alignment should be good, and you don't need to figure out how to mount it. It might be a good idea to buy a new piece of acme rod and replace the current leadscrew, so you have an extra piece known to be the same diameter.
I don't have any personal experience with this, you may need to lap the nut to get it to move freely, or use a piece of screw with cut grooves like he did in the video.
I believe there is epoxy ment for sliding surfaces like this, maybe with metal particles in it, but it probably costs a fortune.

Sent from my LYA-L29 using Tapatalk

 

[matthewsx]

Epoxy?
You can use a thin film of oil or grease to prevent it from sticking too bad to the leadscrew. If you drill the current nuts out and cast the epoxy in place, alignment should be good, and you don't need to figure out how to mount it. It might be a good idea to buy a new piece of acme rod and replace the current leadscrew, so you have an extra piece known to be the same diameter.
I don't have any personal experience with this, you may need to lap the nut to get it to move freely, or use a piece of screw with cut grooves like he did in the video.
I believe there is epoxy ment for sliding surfaces like this, maybe with metal particles in it, but it probably costs a fortune.

Sent from my LYA-L29 using Tapatalk

I had thought of using epoxy and I'm sure someone at West System can steer me in the right direction. Unfortunately the cost of metric lead screw here exceeds what I can get cheap ballscrew kits for on ebay so I will first try making replacement nuts from the delrin I already have.

Cheers,

John

 

[Bi11Hudson]

This may or may not help; a lot depends on how much room is available. I have made zero backlash followers that used two acme nuts separated by a compression spring under pressure. The nuts were of brass and I did have an acme tap the right size. They were 5/8-8 LH. They did the job well, but the application wasn't looking for that low backlash, there may have been a few thou.

Plastics are wonderful, but the application was on a ceramics machine and I didn't think delrin would hold up that well to the grit involved. The brass I used was actually a grade of "bushing bronze", salvage of course.

I do have acme taps, SAE thread, down to 1/4" or so from the aircraft industry, also salvaged . But never bothered to make smaller ones for my machine fittings. I just learned to accomodate the backlash into my cuts and lived with it. Maybe this can make the mind wander a little and solve your problem.

Bill Hudson​

 

[matthewsx]

Well, delrin isn't going to melt enough with my heat gun (yes it's a good one).

I'm going to explore the composites angle a little since I have some west system and can probably get graphite pretty cheap.

John

 

[bill stupak]

Do a search for "Evan-nut" . Its an easy way to make delrin lead screw nuts. I've made about a dozen of them myself, for my lathe and mini mill. Stu

 

[matthewsx]

Do a search for "Evan-nut" . Its an easy way to make delrin lead screw nuts. I've made about a dozen of them myself, for my lathe and mini mill. Stu

That’s almost exactly what I tried. Will give it another go with a bigger vise this time.

Thanks,

John

 

[matthewsx]

Well, I was able to get some threads done but didn't like the first try results.

On the second try I think I have it, Y axis nut complete.

Offset hole drilled and reamed in round stock.


Cut off one side for the flat that bolts to the underside of the X carriage.


I didn't get pictures but I cut the other 3 sides, drilled and tapped mounting holes and slotted the bottom to get the screw in.
Then I used my heat gun to get it good and warm and used a 6" milling vise to clamp down. I also added additional delrin into the slit to bond the nut back together.

The result.


And bolted into place.


I did a test fit with the screw and it's nice and tight, I think this will be a substantial improvement to this cheap table. Now to do the one for the X axis and build the stepper mounts.

John