Joining small al-u-minium parts

RatLabGuy

RatLabGuy

You look like a monkey and smell like one too
Joined
May 18, 2005
Location
Churchville, MD
One of our robotics teams has designed a 3-jaw grabber thing kind of like a ratching oil filter wrench. Sun gear in the middle rotates 3 planetaries that have fingers on them.
Parts will be aluminum. I will have a need to attach a flat bar of sorts to the top of a small gear (probbaly 3/4" diameter). Not a ton of surface area.
Don't have clearance for bolts, so some type of fusion is necessary.
Debating between JB weld or brazing. JBW is easy and would allow for getting adhesion under/between the surfaces. Brazing is presumably stronger but there's only a little bit of corner/edge for adherance. But a cooler (well hotter) experience to students.

The force would be in sheer between the surfaces. We're not talking about a lot of pressure, the driving servo only has a few lbs, but there is a risk of the fingers getting whacked during a competition, but even then its probably like several 10s to a hundred PSI (previously this was all 3d printed and a finger got broken off at an imoportune time).

Any particular thoughts?
(Ideally we'll 3d CNC the parts but the budget doesn't allow it... maybe next year....)

EDIT - if it matters I have 10x more confidence in my JB Weld slathering skills than my brazing skillzzzz
 
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Braze, I hate JB weld
 
JB Weld, bound to be better quality than your aluminum brazing. :flipoff2:
 
Any reason you're using aluminium vs steel? Pre-Made gear set? I wouldn't think weight was an issue in these competitions.

What is the size and oreintation of the flat bar on the gear? If there is enough space for good mechanical contact, there should be enough space for a number of very small countersunk socket head screws...
 
Tell them to buy a laser welder, I welded some thin aluminum on one at my last job
 
zuke said:
Any reason you're using aluminium vs steel? Pre-Made gear set? I wouldn't think weight was an issue in these competitions.
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Weight. For reference the whole robot starts off the comp fitting in an 18" cube. It expands after that. But this is on the end of a pivoting arm that extends up to 4' away from from the base. We're only allowed to use a specific type of small DC motor so you have to be careful about speed/torque tradeoff etc. Typical whole weight is like 30 lbs.
FYI this is for FIRST Tech Challenge. The really big robots are in FIRST Robotics Competition (but that is capped at 125 lbs too)

What is the size and oreintation of the flat bar on the gear? If there is enough space for good mechanical contact, there should be enough space for a number of very small countersunk socket head screws...
Click to expand...
They haven't finished designing it yet :D but it's likely a bar thats like 6-8mm wide and 2.5mm tall, with a mounting length of like 13mm along the flat base.

I guess an M3 or maybe M4 countersunk screw is a possibility, we'd have to tap the gear to match bc there isn't room on the bottom for a nut.
 
trevoringle said:
Tell them to buy a laser welder, I welded some thin aluminum on one at my last job
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Interesting to note for the future, but aside from the cost, thats a lot to take on in less than a week ;-)
 
jeepinmatt said:
JB Weld, bound to be better quality than your aluminum brazing. :flipoff2:
Click to expand...
braxton357 said:
He not wrong. Maybe not jb weld but there are a lot of excellent aluminum bonding epoxies out there now, it's how a lot of late model vehicles are held together.
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Oh he's absolutely right. There's a difference between what should be done and what could be done properly by some teenagers led by my dumb ass. Really more of a question of which has a wider margin for installer error.
You have a particular AL epoxy in mind?
 
I have very little experience to add - well actually I have exactly 1 use case of experience.

A small manufacture we rep for (not our primary one I talk about here at times) needed to add a long aluminum lip to an aluminum box due to a design flaw found in the field.

They shipped us the aluminum lip and some stuff called infinity bond 190. It was a standard 2 part epoxy but had a more permanent applicator. The tubes loaded into the applicator like a double barrel caulk gun. It took a while to begin to set up, in fact too long ideally for our application - Maybe 20 minutes., but once it cured none have failed in the past year and a half.

That is all I have to offer.
 
Don't limit yourself with an M3. You can go smaller than that, though you may not have taps and drills for it. You can get a 1mm and 2mm if you needed the smaller size.
 
RatLabGuy said:
Interesting to note for the future, but aside from the cost, thats a lot to take on in less than a week ;-)
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It’s crazy how much you start using one once you have the option though, I miss that thing haha.
 
RatLabGuy said:
Oh he's absolutely right. There's a difference between what should be done and what could be done properly by some teenagers led by my dumb ass. Really more of a question of which has a wider margin for installer error.
You have a particular AL epoxy in mind?
Click to expand...

I've used something from sika and a 3m product both need a special mixing gun and are expensive.
Something like this ought to be plenty strong enough for your application though
Hy-Poxy H-455 Alumfast 6.5 oz Rapid Cure Aluminum Putty Repair Kit https://a.co/d/bxuc0Lx
 
RatLabGuy said:
Weight. For reference the whole robot starts off the comp fitting in an 18" cube. It expands after that. But this is on the end of a pivoting arm that extends up to 4' away from from the base. We're only allowed to use a specific type of small DC motor so you have to be careful about speed/torque tradeoff etc. Typical whole weight is like 30 lbs.
FYI this is for FIRST Tech Challenge. The really big robots are in FIRST Robotics Competition (but that is capped at 125 lbs too)


They haven't finished designing it yet :D but it's likely a bar thats like 6-8mm wide and 2.5mm tall, with a mounting length of like 13mm along the flat base.

I guess an M3 or maybe M4 countersunk screw is a possibility, we'd have to tap the gear to match bc there isn't room on the bottom for a nut.
Click to expand...

Yeah, if it's got to be in the air 4' away from the base of the robot, Weight is a huge factor to keep it from falling over!

justjeepin86 said:
Don't limit yourself with an M3. You can go smaller than that, though you may not have taps and drills for it. You can get a 1mm and 2mm if you needed the smaller size.
Click to expand...

^^^^^ This! If you can get 4 counter sunk 1MMs through the bar and into the gear, that'll will actually be much stronger than 2 m3s.

braxton357 said:
Hy-Poxy H-455 Alumfast 6.5 oz Rapid Cure Aluminum Putty Repair Kit https://a.co/d/bxuc0Lx
Click to expand...

^^^^^ And finally this,

If you use an epoxy, along with the 1mm screws; Drill the holes all the way through the gear, and so the screws are tight but go in, then fill the hole with epoxy, and put everything together before it dries, finally after it dries, grind/file/sand the back side of the gear smooth. That should give you a pretty strong mechanical bond with stuff you can pickup quickly, and not have to obtain any crazy tooling (taps) or fancy adhesives.

Does the competition allow for repairs between rounds? You could have a couple gear sets ready using different assembly strategies in case one doesn't work so well :)
 
justjeepin86 said:
Don't limit yourself with an M3. You can go smaller than that, though you may not have taps and drills for it. You can get a 1mm and 2mm if you needed the smaller size.
Click to expand...
zuke said:
^^^^^ This! If you can get 4 counter sunk 1MMs through the bar and into the gear, that'll will actually be much stronger than 2 m3s.
Click to expand...
You guys have way too much faith in 16 year olds and their ability to (1) drill a 1mm hole and (2) tap it without snapping the tap.
zuke said:
^^^^^ And finally this,

If you use an epoxy, along with the 1mm screws; Drill the holes all the way through the gear, and so the screws are tight but go in, then fill the hole with epoxy, and put everything together before it dries, finally after it dries, grind/file/sand the back side of the gear smooth. That should give you a pretty strong mechanical bond with stuff you can pickup quickly, and not have to obtain any crazy tooling (taps) or fancy adhesives.
Click to expand...
Its looking most likely to be epoxy. They changed the design today and now the part for the protruding finger covers most of the gear, sort of form-fitting, w/o a lot of side area fro brazing (sorry @WARRIORWELDING ). We'll first 3d print a version and esnure how we like it, then the final may be CNCed sicne it will be a 2d part. M3 Bolt/epoxy combo may happen if its thick enough for countersinking.
zuke said:
Does the competition allow for repairs between rounds? You could have a couple gear sets ready using different assembly strategies in case one doesn't work so well :)
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Absolutely. You have a pit area to do whatever you want, the biggest issue is time. The first comp in Dec they broke one of the fingers clean off and replaced it bc they had spares. Thats what seperates the vet from rookie teams... how ready they are fix stuff. Actually by the end of the comp their grabber included one of my hair ties b/c they realized it would help hold the target object in.

What I will probably do is have them epoxy some pars together held in a vice and then having them apply weights to it to show the strength. Then beat w/ a hammer etc.
 
RatLabGuy said:
You guys have way too much faith in 16 year olds and their ability to (1) drill a 1mm hole and (2) tap it without snapping the tap.
Click to expand...

I think you don't have enough faith in them! Sure... I can't drill a 1mm hole with a hand drill without snapping the bit... But with a drill press? I'm sure even a 16 year old with severe ADHD could do it... Now if you were going to try and tap it, I wouldn't think most adults couldn't even do that :)
 
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