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3d printed steps

B

Bowmann94

New Member
Joined
Feb 12, 2020
Messages
28
Well I drew up a step design and am going to print and test it. I’m planning on using a cinch strap for testing, and a crane scale and forklift then pull till I see stress signs. based on material strength stated by the filament I’d expect it to be pretty strong. I should have printed it laying on its side that would have made it stronger but I didn’t think about that till 23 hours in lol. ill print the next one that way. What are normal steps/ sticks rated for weight wise? If I say 300 lbs is the working load, a bit of a stretch considering I weigh 175 with all my gear on, would 900lbs or higher be ok as a breaking strength for safety factor? I’m using PETG as my filament with a 5” long 2” thick step with a 1 inch gusset holding them together it’s a bit bulky but not bad compared to a stick. 2807BBED-8688-4B0B-8025-1001AE0DB427.jpeg
 
To be rated to 300 lbs, a tree stand platform must hold 900 lbs and the seat must hold 450 lbs (per TMA, according to Dan Infalt of the hunting beast). I'm guessing sticks and steps are similar.
 
Pulling on it with a crane until you see signs of failure will be closer to your ultimate. Without FEA or some kind of stress analysis it will be hard for you to tell at what weight you’re getting yielding. I’d also have to guess that the mechanical properties I.e. tensile and yield strengths are very low for this. You won’t be able to see micro strains you create, so next time you use it in a tree it might be too late when you expand the fracturing. Do be careful.
 
Thanks @raisins thats perfect so yeah 3 to 1 safety ratio is tree stand standard. Perfect now I have a base line.
@gcr0003 yeah I know I’m currently looking for the breaking strength the idea being to use that to get a safety factor based on that. Although I understand that one could get fatigue failure if the yield strength was lower then the working weight. I modeled it in fusion 360 and wanted to do a stress analysis using the model, problem being it doesn’t represent a 3d print well. Even though the filament makers page says yield strength is 4000psi I have a hard time believing that the layers melt that well together.
However I am surprised at the strength achieved in small scale pints.09F9F664-1220-4D7A-9793-42698A9D7C96.jpeg A hook like this in PETG broke at 88# if I remember his video right.
 
Bowmann94 said:
Thanks @raisins thats perfect so yeah 3 to 1 safety ratio is tree stand standard. Perfect now I have a base line.
@gcr0003 yeah I know I’m currently looking for the breaking strength the idea being to use that to get a safety factor based on that. Although I understand that one could get fatigue failure if the yield strength was lower then the working weight. I modeled it in fusion 360 and wanted to do a stress analysis using the model, problem being it doesn’t represent a 3d print well. Even though the filament makers page says yield strength is 4000psi I have a hard time believing that the layers melt that well together.
However I am surprised at the strength achieved in small scale pints.View attachment 25541 A hook like this in PETG broke at 88# if I remember his video right.
Click to expand...

I spoke with the guy that makes Silent Approach steps, and he discussed strength testing at low temperatures also.

Something to keep in mind.
 
@raisins yeah I thought about that to I’ll have to throw them outside for awhile next time it’s -20 and see what they break at.
 
Well I thought I had a good test setup but I guess not. I I’ve broken/cut 2 straps but the part seems unchanged. I made it to 300lbs befor the strap got cut on the beam. Anyone got any suggestions for a better test rig? F0BFCE96-9EEC-4E3C-B137-DD02FFEBFF0B.jpeg3C1D20B3-023A-4A65-A34D-CFA12496B241.jpeg
 
What size load cell is that? What’s your error?
 
It’s not a true load cell it’s a crane scale with an error of 5lbs according to its spec sheet. Mainly doing this for my own curiosity, and piece of mind. I’ve stepped on it at ground level seems rock solid and so far holding 300 before the strap got cut is a good start. There’s no way I’d let anyone but me use these and obviously would use them with a harness.
I wish I had access to proper test equipment. If anyone has proper equipment and would be willing to test it for me I’ll ship it to them otherwise I’ll keep up with my redneck way. Lol
 
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