Z Axis trapezoidal nut is difficult to thread onto lead screw
 

Z Axis trapezoidal nut is difficult to thread onto lead screw  

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jay-1
(@jay-1)
Active Member

I am in the process of assembling my new i3 MK3S kit and am on the Z Axis stage.  One of the trapezoidal nuts threads easily on and off either of the lead screws.  However, the other nut is very difficult to threat on either lead screw.  It doesn't look like the threads are damaged and I can't see any bits of plastic in the way.  I would prefer not to wait for a replacement nut to ship.  Does anyone have any suggestions?  Is this an easy part to locate at the hardware store?  If so, what are the specifications?

Thanks, Jay

Posted : 19/06/2019 3:30 am
Tim
(@tim-m30)
Illustrious Member

Wait for the replacement.  A tight T-nut on a lead screw will cause problems. 

As far as I know, and I did a reasonable search a few months ago, the Delrin T-nut is unavailable unless someone is selling personal spares on eBay (and that pair was too expensive). I purchased a new set from Prusa.

 

It is always wise to get more than one opinion......
Posted : 19/06/2019 5:54 am
RHDreambox
(@rhdreambox)
Prominent Member

If you have got a defective component then you should contact Prusa chat so that they send you a new component completely free.
You should definitely not have to buy any new components for your new printer.

Bear MK3 with Bondtech extruder...
Posted : 19/06/2019 12:48 pm
jay-1
(@jay-1)
Active Member

I did contact Prusa chat, and the following is the response they sent when I described the problem exactly as above.

we get this quite often and we ran many more and more accurate quality tests in the last year only to find out that the production of these parts is nearly flawless all our accurate tests which we currently do for every single trapezoidal nut in the quality control, led us to believe that the only way of damaging these parts is during the assembly when sliding these parts on from top of the Z motors screw in fact the trapezoidal nuts are inserted on the threaded bar one by one manually and you would unscrew those smoothly before even start the insertion of the X axis on the Z axis we were clearly instructed and unfortunately this is not covered under warranty for Kits

I know I was careful removing the part, and while I recognize I could have caused the problem, I don't think I did.  If I did, then I would suggest that if it is so easy to do so and so many people report the issue, then that suggests to me a design flaw or a problem with the durability of the parts they are supplying.  Either way, this is not the kind of response I expected for the first interaction with their support.  Not a positive experience to get started with.

When I then shared my disappointment with that response, she proceeded to tell me again how it is my fault and I that I was warned several times how to handle it properly.

I decided not to argue with her and just asked where to get the part ordered, considering this one plastic part is rendering the entire machine useless now after waiting to receive it for so long.  She sent me a link to their online store that when I clicked on it, displayed an error stating I didn't have permission to view it and I can't locate anywhere in their online store to purchase it.

This should be a warning to anyone considering purchasing from them.

Posted : 19/06/2019 7:55 pm
jay-1
(@jay-1)
Active Member

Update, the shop website displayed the error because I wasn't logged on.  I incorrectly assumed that since I was logged on via the forum site, I would be logged in on the store site.  Seems to me that a more logical error message would have been "You need to logon to view this"

Also, I asked for the specifications for this nut and was told it was a Black trapezoidal nut Tr8x8 Trapezoidal Screw Nuts made of POM material.  There appears to be a seller on Amazon with a part matching that description.  I placed the order and will see if it works.

Posted : 19/06/2019 8:12 pm
jay-1
(@jay-1)
Active Member

I will say the Prusa support rep did offer to expedite the shipment of the replacement part.  It is unfortunate that the shipping cost is almost double the price of the part.

Posted : 19/06/2019 8:28 pm
Tim
(@tim-m30)
Illustrious Member

Most you see for sale have a flange diameter that is smaller than what Prusa sells.  You'll need to ream/cut the screw holes to make them fit. 

It is always wise to get more than one opinion......
Posted : 19/06/2019 8:34 pm
jerry.s3 liked
RHDreambox
(@rhdreambox)
Prominent Member

I am really surprised that Prusa did not take its responsibility and replaced the defective component.
I do not think that you have damaged the nut yourself because then there is a strong need for over-violence to deform it.
But I hope this does not ruin the joy of your new printer.

Bear MK3 with Bondtech extruder...
Posted : 20/06/2019 7:50 am
guy.k2
(@guy-k2)
Noble Member

When the new nuts arrive, do NOT bolt them onto the x-ends before spinning them onto the z-screws. Attempting to thread z-screws into already mounted T-nuts is just plain asking for damaged T-nuts. 

Instead, support you x-axis on a couple filament boxes. Put the (free) T nuts onto z-screws and spin them down to the x-ends. That lets you feel thread engagement and how freely they spin. Once they are spun down to the x-ends, bolt them in place. 

Posted : 20/06/2019 9:57 am
guy.k2
(@guy-k2)
Noble Member

The ones on Amazon have a screw hole spacing of 16 mm and diameter 22 mm.

Prusa bolt hole spacing is 19 mm. You definitely will need to modify the nuts. New bolt holes will be so close to outer diameter that the holes will not be fully enclosed, but more like slots. Here the outer dark circle is diameter of nuts on Amazon. You can see where the screw holes will end up.

This post was modified 1 year ago by guy.k2
Posted : 20/06/2019 10:22 am
jay-1
(@jay-1)
Active Member

Thanks for this information.  You are correct, the ones that arrived from Amazon are the wrong size.  I decided to order the one from Prusa and wait for it.

Posted : 21/06/2019 1:32 am
tbsailor260
(@tbsailor260)
New Member

I had the same issue.  I resolved it by gently heating the shaft (away from the motor) with a lighter. Then running the T-nut up and down past the heated area a few times by turning the motor shaft.  It softens the nut just enough and insures it conforms to the shaft correctly. Now they spin smoothly and easily.

Posted : 18/08/2019 7:21 pm
guy.k2
(@guy-k2)
Noble Member

Someone finally has the right size ones on Amazon. I received one set and the dimensions are correct. However, have not tried using them yet.

https://www.amazon.com/gp/product/B07SYX8P8F

Posted : 18/08/2019 7:26 pm
Tim
(@tim-m30)
Illustrious Member

Oil resistant! Woot!

It is always wise to get more than one opinion......
Posted : 18/08/2019 8:04 pm
guy.k2
(@guy-k2)
Noble Member

Test fitted one. Spins up and down Z-screw nice and smooth. Dimensionally I can't tell it from the Prusa ones.

Finally have a second source for spares on these. Prusa rations them two at a time.

Posted : 18/08/2019 8:54 pm
Tim liked
Tim
(@tim-m30)
Illustrious Member

Thanks Guy - I have my order in.  I'm hoping they really are not Delrin, but the POM material they hint at.  Delrin - at least the stock T-nuts - seem to not like Superlube (which I semi-accidentally applied to the lead screws while greasing things).  Mine are slowly dissolving and increasing Z play... lol.  I had a spare set from Prusa ... but now feel more comfortable if I mess them up again (as in not getting the lead screws clean enough this next rebuild).

This post was modified 1 year ago by Tim
It is always wise to get more than one opinion......
Posted : 19/08/2019 9:28 am
guy.k2
(@guy-k2)
Noble Member

I thought Delrin is a POM. 

I never put any grease on the lead screws, but I do have them coated with a molybdenum dry lube like I use on my Delrin airgun hammer components. Thus far seeing no issues. Just wanted more spares for eventual needs.

Posted : 19/08/2019 6:45 pm
scottsh
(@scottsh)
Active Member

I know it is too late for you, but I noticed that if I put the trap-nut back onto the screw it came off of, it fit a lot easily.  I had 1 that fit easily on both screws, but 1 that would only fit back onto the one it was on when shipped.

Posted : 19/08/2019 7:18 pm
stephen.h14
(@stephen-h14)
Estimable Member
Posted by: guy.k2

I thought Delrin is a POM. 

I never put any grease on the lead screws, but I do have them coated with a molybdenum dry lube like I use on my Delrin airgun hammer components. Thus far seeing no issues. Just wanted more spares for eventual needs.

I believe it is.

I use Sailkote on the Z screws. I hold a paper towel behind the screw to collect any overspray, you don't want to get that on anything else. Won't hurt the Delrin.

Posted : 19/08/2019 7:40 pm
Tim
(@tim-m30)
Illustrious Member

And, to my surprise as I looked more deeply at POM vs Delrin: my new POM T-Nuts will need the lead screws thoroughly degreased. lol.

Delrin, Acetal, and its many trade names is a material properly known as Polyoxymethylene or POM.

It is always wise to get more than one opinion......
Posted : 19/08/2019 8:08 pm
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