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HD-BT0222] M3x50 for back of extruder stripping out back plate?
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Description

I've had a couple extruders that the M3x50 is not catching the threads in the back plate of the extruder. Swapping out the toolhead will work. We've also tried swapping the Interface board cover in case there was a thick or warped one, @MikeR tried re-tapping the threads, but these things did nothing. He also took some quick measurements and did not see anything out of the ordinary. So I'm wondering if this could be either a supplier mistake with the threads or just the fact that the screw has such little to grab onto, that maybe a longer screw would be a better fix? This problem is causing to slow things down a bit on the line.

Event Timeline

paulette created this task.Jun 6 2019, 1:48 PM
paulette created this object with visibility "LulzBot Hardware Products (Project)".
MikeR assigned this task to west.Jun 6 2019, 2:52 PM
tutley added a comment.Jun 6 2019, 3:06 PM

sounds like the hole was drilled off center?
@MikeR can you check one of these problem plates against the drawing?

MikeR added a comment.Jun 7 2019, 7:51 AM

I will look into it.

MikeR added a comment.Jun 7 2019, 11:11 AM

So from looking at a problem plate. the hole locations for the screw and for the tool head alignment feature look to be in the correct locations. And From looking at a plate that does mount vs the one that doesn't, nothing looks to be any different. @tutley any other ideas for me to check?

logan added a comment.Jun 7 2019, 11:17 AM

I think a look at the size of the holes/threads on some of these is worth a look. I also noticed what looks like a slight chamfer on that hole. If the chamfer is made large at that spot it could reduce the number of threads available to grab as well.

This fastener hole is utilized to mount the tool head to the test stand, it is also possible that this could be causing damage to the threads if not done properly. Checking that these aren't being over-torqued during that process would be a good idea as well.

MikeR added a comment.Jun 7 2019, 12:00 PM

According to the drawing, the hole diameter is 3mm with a .75mm +/-. This means the hole could be anywhere from 2.25mm to 3.75mm and would technically be in spec. After measuring the hole diameter of a back plate that does mount which was ~2.5mm and one that did not mount which was ~2.85mm. I think its possible if the hole is too big, the screw we use will not be long enough to grab the usable threads. I feel we could use a slightly longer screw to prevent this from being a problem. We currently use a M3x50, if we moved to a M3x55 i feel this could resolve the problem.

logan added a comment.Jun 7 2019, 12:04 PM

The ideal drill size for an M3x0.5 thread is 2.5mm. I think we would be in better shape specifying a 2.5mm diameter hole with a 0.25mm tolerance. This would allow the holes to be drilled from 2.25 to 2.75 prior to being tapped.

oliver added a subscriber: oliver.Jun 7 2019, 12:05 PM

@MikeR @tutley
Rather than looking at the machined part, could this be a tolerance issue involving one of the printed parts not lining up where it should be?

logan added a comment.EditedJun 7 2019, 12:06 PM

I don't think alignment was the complaint, the complaint was not grabbing any threads in that hole.

MikeR added a comment.Jun 7 2019, 12:07 PM

@oliver using the same printed part, one plate will mount and the other will not. I am not certain it is a printed part issue.

@MikeR where are you seeing that its a 3mm hole with +/- .75mm?
Im seeing that the hole is called out as M3x0.5mm thread

tutley added a comment.Jun 7 2019, 1:02 PM

I just spoke with @MikeR over here at Rockies, and he showed me the problematic part.
In this particular instance, the threads have been stripped out on the side that the screw engages, so the part is damaged beyond usability.
He was going to countersink the locating holes a bit more to see if that would help, but i dont think that will make any difference.
There are just no threads left to engage.
We discussed switching to a longer screw, however the m3x50mm is the longest screw offered in the blue dyed option.

Counter sinking the holes larger did not help with this issue. If we could move to stainless steel screws we would be able to get a longer screw that would engage with the threads more so if the first few threads are stipped we will still be able to screw the back plate onto the carriage. @eBeardslee what are your thoughts on this? I believe we went with blue screws for a marketing/tech support purpose.

MikeR added a subscriber: TyTh.Jun 7 2019, 1:25 PM
oliver added a comment.Jun 7 2019, 1:39 PM

@TyTh Tagging tech support in on this as well. Are the screws helpful to trouble shooting for tech support at all?

DaniAO changed the visibility from "LulzBot Hardware Products (Project)" to "Public (No Login Required)".Jun 7 2019, 2:25 PM
DaniAO changed the edit policy from "All Users" to "LulzBot Hardware Products (Project)".

So far they have not been used for troubleshooting, so I would say no

@eBeardslee please put your feedback asap so we can keep moving with the proposed change or start looking for a new one.

MikeR triaged this task as High priority.Jun 10 2019, 10:21 AM
DaniAO added a subscriber: karrad.Jun 10 2019, 10:24 AM

@karrad your feedback is requested as well!

I feel function is more important than the blue screw, has RnD been able to verify this is the issue?

@karrad I had spoken with @tutley on Friday and we both determined a longer screw would be better.

Seeing as this is the only screw on the back of the tool head I think it's fine to switch the screw color.

Would it be only the screw in the back or would it be all blue screws on this tool head?

i think that if we switch the rear screw to stainless we should switch the top blue screws to stainless as well. This would keep all toolhead removal screws the same color

@eBeardslee if you agree with @tutley on changing all the screws.. we will get this moving in a change order.

Thanks!

Greggb added a subscriber: Greggb.Jun 11 2019, 8:23 AM

I have no preference on the type or color of screws. Function over form is fine here.

@Greggb has final sign off since this is a cosmetic change

MikeR added a comment.Jun 11 2019, 8:50 AM

Ok then if we are all good, @DaniAO lets get a ECO going for this.

@MikeR or @EricNugent can one of you get the change order in?

Thanks!

@DaniAO I will get one started.

MikeR claimed this task.Jun 13 2019, 12:39 PM
MikeR closed this task as Resolved.Jun 25 2019, 11:41 AM

Since there is currently a change order in place for this issue, I will close this ticket down.