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Acidicheartburn
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Any engineers or repairmen here? Need help

Thu Feb 07, 2019 9:41 pm

The tilt brake on my office chair broke and now it freely leans forward or backward making it unusable (sitting in it normally makes you lean forwards and nearly slide out). I've taken it apart and found the culprit to be this flanged pin which has sheared in half which I'm not entirely sure the name of.

Here's the pin: https://www.dropbox.com/s/hg7kvkkwm1j5z ... 9.jpg?dl=0

Here's how it was being used: https://www.dropbox.com/s/5vvqfo2p7qjug ... 1.jpg?dl=0

It was going through those metal blades just like the other pin that's intact in the image, and when I pulled on a two-position lever it would apply pressure on the broken pin and a third long partially threaded shaft somehow which would lock the seat of the chair in place.

I need to find a replacement pin that's strong enough. I've measured the broken pin using my calipers and have found it's 5/16th inches in diameter and about 2+5/16 inches in length. The length doesn't have to be too terribly precise because I can cut it down if I need to. The thickness of the flange on the head is about 1/32 of an inch (here's a pic: https://www.dropbox.com/s/bdfyzjpo2a8xm ... 1.jpg?dl=0). The head can't be too thick or it won't fit underneath part of the chair mechanism. The head diameter is nearly 7/16 of an inch.

Anyone know what this pin is, and how can I find an appropriate replacement pin that will be at least as strong? What kind of steel should I look for?
 
anotherengineer
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Re: Any engineers or repairmen here? Need help

Thu Feb 07, 2019 10:55 pm

Go to the hardware store and buy a 5/16" grade 5 bolt and cut to length if you have to. Cut off the head, if its long enough it shouldn't fall out even without a head, could always glue it in place.
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SecretSquirrel
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Re: Any engineers or repairmen here? Need help

Fri Feb 08, 2019 12:00 am

A 5/16" clevis pin is probably the closest "off the shelf" part you will find. If you look at the broken pin, on the left, you can see where the end has been expanded like a rivet. The cotter pin would provide the same function when passed through the clevis pin.

https://www.grainger.com/product/ITW-BE ... -Pin-2MUZ1
Another example with more detailed dimensions: https://www.pivotpins.com/products/bb-c ... holes/1224

The above is going to be a bit softer than grade 5 steel. The are effectively grade 2, low carbon steel. You can easily find them in stainless steel as well, which will likely be a big stronger, but Grainer didn't carry tempered carbon steel clevis pins and a quick google search says they will be much harder to find.

--SS
 
Acidicheartburn
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Re: Any engineers or repairmen here? Need help

Fri Feb 08, 2019 1:36 am

anotherengineer wrote:
Go to the hardware store and buy a 5/16" grade 5 bolt and cut to length if you have to. Cut off the head, if its long enough it shouldn't fall out even without a head, could always glue it in place.

I don't think a bolt will work because the threading will interfere with the function of those metal blades.
 
Acidicheartburn
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Re: Any engineers or repairmen here? Need help

Fri Feb 08, 2019 1:39 am

SecretSquirrel wrote:
A 5/16" clevis pin is probably the closest "off the shelf" part you will find. If you look at the broken pin, on the left, you can see where the end has been expanded like a rivet. The cotter pin would provide the same function when passed through the clevis pin.

https://www.grainger.com/product/ITW-BE ... -Pin-2MUZ1
Another example with more detailed dimensions: https://www.pivotpins.com/products/bb-c ... holes/1224

The above is going to be a bit softer than grade 5 steel. The are effectively grade 2, low carbon steel. You can easily find them in stainless steel as well, which will likely be a big stronger, but Grainer didn't carry tempered carbon steel clevis pins and a quick google search says they will be much harder to find.

--SS

This may work, but I might need one a bit longer since the cotter pin would take up a bit of the usable length. I figured going stainless steel would make for a stronger pin.
 
One Sick Puppy
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Re: Any engineers or repairmen here? Need help

Fri Feb 08, 2019 2:06 am

Clevis pin might work. I don't know why you'd bother with a Grade 5 bolt unless stronger bolts are not available anywhere - the price difference should be negligeable considering you only need one. Grade 8 minimum, I'd say. Most specially fastener stores or automotive supply stores should have much stronger bolts in a variety of sizes. All you need is one long, high grade bolt that has the correct span of unthreaded shank - most common bolts have only a fixed span of thread, regardless of their length. Then get someone with an angle grinder to cut it for you so you can make it fit and use the nut to keep it in place.
 
Acidicheartburn
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Re: Any engineers or repairmen here? Need help

Fri Feb 08, 2019 2:14 am

One Sick Puppy wrote:
Clevis pin might work. I don't know why you'd bother with a Grade 5 bolt unless stronger bolts are not available anywhere - the price difference should be negligeable considering you only need one. Grade 8 minimum, I'd say. Most specially fastener stores or automotive supply stores should have much stronger bolts in a variety of sizes. All you need is one long, high grade bolt that has the correct span of unthreaded shank. Then get someone with an angle grinder to cut it for you so you can make it fit and use the nut to keep it in place.

I don't believe a bolt will work because the head of the bolt will be too thick. It has to be thin enough to leave clearance for another part of the seat mechanism to slide over it. I don't think even a pin that uses a cotter pin to lock will work either, though I'm pretty sure I can leave the cotter pin out. I may be able to cut both ends off of a bolt and hope it doesn't fall out on it's own but I can't be sure that will work. It would be tough to glue as well given how there has to be clearance for part of the chair mechanism to move. Plus, if I glued it (what glue would I even use?) it would make it pretty much impossible to fix if it breaks again.
 
One Sick Puppy
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Re: Any engineers or repairmen here? Need help

Fri Feb 08, 2019 2:27 am

I missed that photo. Yes, you're right. But nothing an angle grinder can't fix. I've ground down bolt heads plenty of times. You probably don't have access to a lathe, but a cheapy angle grinder would cost you about $20-30 if you HAD to buy one. If you have a drill press you can even use it as a lathe and round off the head with a file or angle grinder and make it fancy. Another option is to cut the bolt head off with a hack saw (higher grade bolts might not cut so easy with a hack saw, tho), then whack the end with a hammer a couple times to flare out the end just enough to prevent the bolt from slipping entirely thru the hole. I'll make you one if you like. Shipping from up here in Canada would probably be about $20, tho. One or two bucks for the bolt.

https://www.princessauto.com/en/detail/ ... -p8056042e
 
Acidicheartburn
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Re: Any engineers or repairmen here? Need help

Fri Feb 08, 2019 3:33 am

One Sick Puppy wrote:
I missed that photo. Yes, you're right. But nothing an angle grinder can't fix. I've ground down bolt heads plenty of times. You probably don't have access to a lathe, but a cheapy angle grinder would cost you about $20-30 if you HAD to buy one. If you have a drill press you can even use it as a lathe and round off the head with a file or angle grinder and make it fancy. Another option is to cut the bolt head off with a hack saw (higher grade bolts might not cut so easy with a hack saw, tho), then whack the end with a hammer a couple times to flare out the end just enough to prevent the bolt from slipping entirely thru the hole. I'll make you one if you like. Shipping from up here in Canada would probably be about $20, tho. One or two bucks for the bolt.

https://www.princessauto.com/en/detail/ ... -p8056042e

I do have a drill press, and I get I can get through the bolt head with my dremel, though it may take a while. This may be the solution. I'll head to the hardware store tomorrow (today) and see if I can find a grade 8 bolt in my size. If I really can flare out the cut end then it should work. The sucky part will be doing this in the garage when it's going to be a high of 9 F (-13 C) while wearing gloves and goggles that are going to fog up.
 
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Re: Any engineers or repairmen here? Need help

Fri Feb 08, 2019 9:07 am

IME, the harder the steel the easier the dremel cut-off wheel will cut it.
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roncat
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Re: Any engineers or repairmen here? Need help

Fri Feb 08, 2019 11:35 am

You need this...
https://www.boltdepot.com/Product-Detai ... duct=19786
but the clevis pin will work, also.
 
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Re: Any engineers or repairmen here? Need help

Fri Feb 08, 2019 12:35 pm

Yeah, I'd just go to a hardware store and get a 6-ish-inch bolt (long enough to have enough unthreaded length to use as your pin) and just cut/grind off the parts you don't need. If it's a soft bolt, you can peen the end with a hammer to 'mushroom' the opposing end, if you need it to stay in place. Personally, I'd just either drill a hole in the bolt, or use the dremel to cut a groove and use that to hold a hitch clip pin.
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Acidicheartburn
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Re: Any engineers or repairmen here? Need help

Fri Feb 08, 2019 6:16 pm

Bolt solution worked. I know a guy who let me borrow his angle grinder, so I bought a bolt and ground the head down so it was thin enough to fit, then used my dremel to cut it to length. My drill press made getting an even grind and cut a piece of cake. Ace hardware had the grade 8 bolt I needed. I'm stoked because I've been using an awful old kitchen table chair for 2 years now. Finally I have something a little better for the cost of 3 bucks. Good thing I didn't throw out this chair when I had a dumpster this summer.
 
DPete27
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Re: Any engineers or repairmen here? Need help

Mon Feb 11, 2019 6:29 pm

Kinda looks like a rivet nut. Can you confirm if there's two pieces that thread together?
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Acidicheartburn
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Re: Any engineers or repairmen here? Need help

Tue Feb 12, 2019 4:24 am

DPete27 wrote:
Kinda looks like a rivet nut. Can you confirm if there's two pieces that thread together?

I figured out it's basically a clevis pin without the hole for a cotter pin. See my previous post for a solution.

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