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My 3D printed cross feed nut is here!

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Ststephen7

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#1
OK… here it is… my new cross feed nut arrived today! It looks an exact match for the original, other than the hole in the original is off center (as you can see in one of the pictures).

I told Dennis at FDM prints (FDMprints@gmail.com) that I had almost a half turn of backlash. I sent along the screw so he could make the nut fit as well as possible. The screw, of course, has the most wear in the center, so the new nut is pretty tight at the ends, and perfect in the middle of the screw. He also made a 3D printed change gear to replace a stripped formica/fiber gear.

2 things... I have no affiliation with Dennis or his company (I found him selling 3D printed gears on ebay). In my limited experience I feel he did a great job with both the gear and the nut; he is very easy to work with, very affordable, and relatively quick turnaround. And... He would not tell me what the gear or nut is made from, so... I cannot help you there.

My backlash is now less than 0.003… which I think is perfect.

Once I get some time under my belt perhaps I’ll attempt to make myself a new cross feed screw.

I'm planning to post this in several forums/categories, as I think a lot of people might be interested in hearing about a 3D printed cross feed nut. It that is not OK either delete them, or ask me to, and I will oblige.

Steve

IMG_3359.JPG
IMG_3355.JPG
 

rambin

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#2
I would think the plastic would wear jn very quickly and you'd be back to the backlash prblm in no time at all???
 

Ststephen7

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#3
Time will tell... It is certainly possible that this particular type of plastic... or perhaps any 3D printed plastic, is not a good, long lasting choice for this application. And... since I don't have another way get a replacement for the VERY worn one that came with the lathe, this 3D printed one is a great choice! At least for the moment. And at around $20 plus shipping even if it doesn't last that long I'm fine with getting another until I have the skills to make one for myself
 

Ststephen7

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#4
Time will tell... It is certainly possible that this particular type of plastic... or perhaps any 3D printed plastic, is not a good, long lasting choice for this application. And... since I don't have another way get a replacement for the VERY worn one that came with the lathe, this 3D printed one is a great choice! At least for the moment. And at around $20 plus shipping even if it doesn't last that long I'm fine with getting another until I have the skills to make one for myself
 

RJSakowski

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#5
One thing to consider in using plastic materials for load bearing surfaces is lost motion. Backlash is the amount of driver movement that is observed when direction is reversed before any driven movement occurs. Lost motion, on the other hand has to do with distortion due to flexing or of drive train in addition to backlash.

In the case of a lead screw nut, there will be some compression of the flanks of the threads in response to the applied cutting pressure. Depending upon the material used and the design of the nut, it may not be significant. A cutting test will tell. I check backlash by rotating the crank clockwise about a 1/4 turn and setting the dial to zero. I also set my DRO to zero (a dial indicator will work as well). I then continue rotating clockwise a few thousandths, then rotating counterclockwise until the DRO returns to zero and note the reading on the dial. This will be my backlash.

For lost motion, I do the same except lock the carriage to create a moderate drag. The difference will be the lost motion, which is the sum of the backlash and any flexing such as lead screw twist, compression of thrust washer(s), flexing of the lead screw nut, etc.

On my G0602 lathe, I measured .0036" of backlash and .0061" of total lost motion.
 

Ststephen7

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#6
Thank you for bringing this up! I had not considered this issue at all.

For me, at least for the moment, it's inconsequential. I had almost a half turn of backlash, and now I have about what you have. I would bet there is some lost motion, and with what I'm doing it is not noticeable.... yet.

I should (and might) measure backlash and lost motion with an indicator now... with only a couple of hours on the nut, and again every few weeks to see what happens.
 

RJSakowski

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#7
Thank you for bringing this up! I had not considered this issue at all.

For me, at least for the moment, it's inconsequential. I had almost a half turn of backlash, and now I have about what you have. I would bet there is some lost motion, and with what I'm doing it is not noticeable.... yet.

I should (and might) measure backlash and lost motion with an indicator now... with only a couple of hours on the nut, and again every few weeks to see what happens.
That would be useful information, along with the plastic used, for others that might be thinking of doing the same.
 

cjtoombs

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#8
I think it will probably be good for a while, depending on what it is made of. they have some pretty stout materials that can be 3D printed (carbon fiber filled nylon, for one). One thing you might think about doing before you find out if this one will last is to build a leadnut "shell". Make a bronze or steel leadnut that will clear the crossslide with a hole big enough to insert a printed threaded insert. That way, if the stem breaks off, or the bolthole strips out, you can just have the treaded part printed and epoxy it into the shell. The bolthole, in my opinion is probably the weakest part of the part. I just got a 3d printer for Valentines day and have been making stuff for the shop nonstop for the past couple of weeks (I got a late start on using it). I really enjoy the capabliity. I've been printing custom hangers and racks for shop organization. I've only printed PLA right now, but I want to step up to nylon and flexibles, but that will require mods to my printer. Good luck with the part.
 
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