Re: RnC Sanhui165 broken wrist
Posted: Sun Nov 27, 2016 2:25 pm
Well, its been a while - sorry.
If you're just looking for a result you can stop reading and come back later - its not done yet.
If you're interested in what went on, I'll try to explain below.
Considering the ups( good grip) and downs( too large) of something like the shaft connector pictured in the last post I thought about something that may not be fully round but still allow gripping onto the rod ends with screws.
Looking for stuff that might already be available I thought about these units - intended to connect cables. They feature a round opening on both sides and one screw on each side for tightening the wires or in our case the rod ends. Here you can see single ones cut out of the plastic - the two I had were just slightly too small so I needed to get one meant for larger wires.
I also found the screws to be lacking in being both too nimble and too long - they're meant to lock wires down, not just lock onto a rod end almost filling the cylinder, so I ordered shorter ones - you can see one each of the original and replacement on the upper left connector. The new ones use an allen key, good to handle, there is also a tiny strip of sandpaper that I used. For reference, here is the glue used this time. On 1st attempt I used the strip of sandpaper on the two rod ends and surrounding area, then cleaned with Q-tips and Aceton.
Next I mixed the glue, put some on each rod end, then some into the cylinder, attached the cylinder onto one end, tighened the screw enough so be stable, inserted the other rod end and tighened both screws as much as I dared.
The I let it cure for about 36h or so.
I could move the hand up and down ok a few times afterwards, but it resisted movement sideways and after trying with a little more force the end at the arm came off.
Well, not good, but the considerable force it had taken let me to investigate the rotation mechanism a little closer.
Its always easier in hindsight, but I should have done that before I guess - I just didn't want to tamper with the bandages around the joint that the silicon sticks to very well.
Turns out apologies and corrections are in order - my only excuse is that I must have been deluded by all the posts about chinese improvements I read of late to actually think they would have done an elaborate ball joint.
This joint is a simple hinge - it will only do an up/down movement, so Samara's comment that the sideways movement is considered the main cause is spot-on, any such movement or an attempt to rotate the hand instead of the arm will result in damaging the fragile rod from this joint to the hand - however, going beyond about 60/75ish degrees up and down will as well.
Alright, knowing this now I made a second attempt, this time starting by using a power tool( Dremel) on the rod ends non-broken sides to try gaining a tiny bit more overlap for the sleeve, after that, same procedure as above.
Even being careful I did hit the outer silicon with the dremel slipping and gripping into silicon a few times - oh, well. Again, it held ok for some up and down movements, but I do want the hand to be somewhat useable again so before attempting to just glue the arm back together I wanted to make sure it would hold - well, it didn't - it just came off again on what was about a 60/75 degree downward move.
To sum it up:
Yes, a lot better than before ... but still not good enough.
So TheIQF++ will get his wish and I'll have to take this apart further still( he actually means well and really wishes me luck but is curious because he will face similar issues).
Stay tuned for further revelations, including Sanhuis way of threadlocking.
Kind regards.
If you're just looking for a result you can stop reading and come back later - its not done yet.
If you're interested in what went on, I'll try to explain below.
Considering the ups( good grip) and downs( too large) of something like the shaft connector pictured in the last post I thought about something that may not be fully round but still allow gripping onto the rod ends with screws.
Looking for stuff that might already be available I thought about these units - intended to connect cables. They feature a round opening on both sides and one screw on each side for tightening the wires or in our case the rod ends. Here you can see single ones cut out of the plastic - the two I had were just slightly too small so I needed to get one meant for larger wires.
I also found the screws to be lacking in being both too nimble and too long - they're meant to lock wires down, not just lock onto a rod end almost filling the cylinder, so I ordered shorter ones - you can see one each of the original and replacement on the upper left connector. The new ones use an allen key, good to handle, there is also a tiny strip of sandpaper that I used. For reference, here is the glue used this time. On 1st attempt I used the strip of sandpaper on the two rod ends and surrounding area, then cleaned with Q-tips and Aceton.
Next I mixed the glue, put some on each rod end, then some into the cylinder, attached the cylinder onto one end, tighened the screw enough so be stable, inserted the other rod end and tighened both screws as much as I dared.
The I let it cure for about 36h or so.
I could move the hand up and down ok a few times afterwards, but it resisted movement sideways and after trying with a little more force the end at the arm came off.
Well, not good, but the considerable force it had taken let me to investigate the rotation mechanism a little closer.
Its always easier in hindsight, but I should have done that before I guess - I just didn't want to tamper with the bandages around the joint that the silicon sticks to very well.
Turns out apologies and corrections are in order - my only excuse is that I must have been deluded by all the posts about chinese improvements I read of late to actually think they would have done an elaborate ball joint.
This joint is a simple hinge - it will only do an up/down movement, so Samara's comment that the sideways movement is considered the main cause is spot-on, any such movement or an attempt to rotate the hand instead of the arm will result in damaging the fragile rod from this joint to the hand - however, going beyond about 60/75ish degrees up and down will as well.
Alright, knowing this now I made a second attempt, this time starting by using a power tool( Dremel) on the rod ends non-broken sides to try gaining a tiny bit more overlap for the sleeve, after that, same procedure as above.
Even being careful I did hit the outer silicon with the dremel slipping and gripping into silicon a few times - oh, well. Again, it held ok for some up and down movements, but I do want the hand to be somewhat useable again so before attempting to just glue the arm back together I wanted to make sure it would hold - well, it didn't - it just came off again on what was about a 60/75 degree downward move.
To sum it up:
Yes, a lot better than before ... but still not good enough.
So TheIQF++ will get his wish and I'll have to take this apart further still( he actually means well and really wishes me luck but is curious because he will face similar issues).
Stay tuned for further revelations, including Sanhuis way of threadlocking.
Kind regards.