New Tube Bender Design Input

Alright guys as you know I bend seat hoops and stuff.
I use a JD2 Model 3 bender that I just converted to hydraulic with an air over hydraulic ram.
I hate it.
It has to be stopped, disconnected and the ram pushed back in 3 or 4 times for each 180 degree hoop.
Manually this was no big deal but with the ram it makes each hoop take forever, the opposite of why I "upgraded" the stupid thing.

SO with this in mind I have been designing a new bender based on the JD2 M3 die set.
This is what I have come up with and I would like you guys input here on any glaring flaws you see in the design

Basically the through bar through the bender and die now is connected at the bottom to a sprocket, the sprocket is engaged in a chain that is connected to the ram. When the ram is actuated the sprocket turns, turning the die and bending as a result.
There's a spring attached to the other end of the chain so that when you release the hydraulic pressure it will spring back to neutral position on its own.

This effectively makes the bender capable of doing 180 degrees in one shot.





The bottom section with the chain would be enclosed with some sort of chain guard to prevent injury if the chain were to snap, keep your fingers out, etc.


What are your thoughts here?

Looking at it now, its obvious that the cylinder needs to be mounted further forward, so that the spring can return it to neutral.

I think the chain will fail first use.

Somebody has some plans for building a mandrel tube bender. Look around for that. Maybe I saw it on eBay.

AlphaDogChoppers said:

I think the chain will fail first use.

Somebody has some plans for building a mandrel tube bender. Look around for that. Maybe I saw it on eBay.

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+1
(note this is my opinion)
Personally I would do something along these line. It is a interesting idea. But the chain is going to be a huge stress point and likely to fail.

Instead of a chain, i would look into using a steel arm welded to the sprindle that would give you the proper stroke length. That way there is less likely hood of breakage.

That's exactly what I have if you read the first post
It blows.

A good 530 chain has a tensile strength of over 11,000 lbs, what makes you think it would fail so easily?

Here's an interesting simple design. Probably won't work to do 180 in one shot.

If you look at the photo Bucky posted you can see the issue.
That ram is almost at full extension and the tube is not even at a 60 degree bend, so to get 180 degrees you have to stop, turn the pressure off, pull the pin, manually push the ram back in, put the pin back in, reapply pressure, rinse and repeat

Check this home build bender out: http://www.pirate4x4.com/forum/shop-tools/376183-homebuilt-tubing-bender.html

Bucky685 said:

Check this home build bender out: http://www.pirate4x4.com/forum/shop-tools/376183-homebuilt-tubing-bender.html

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Exact same issue.
Good for 60 degrees or less without reset

SONIC. said:

That's exactly what I have if you read the first post
It blows.

A good 530 chain has a tensile strength of over 11,000 lbs, what makes you think it would fail so easily?

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I realized that after I typed that. Oops.

I don't nesscary think it wold fail first go, but it is a weak point in your design, that would eventually fail and there would be allot of built up tension that could hurt someone. I tend to over design things. I think the same thing could be accomplished with steel instead of a chain.

What about something like this:

I think you would have a more linear relationship from the ram to the sprocket if the ram were parallel with the spring mount line, wrapping the chain 180 around the sprocket.

Bucky685 said:

I realized that after I typed that. Oops.

I don't nesscary think it wold fail first go, but it is a weak point in your design, that would eventually fail and there would be allot of built up tension that could hurt someone. I tend to over design things. I think the same thing could be accomplished with steel instead of a chain.

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That's why I posted to get Input
I also looked at a design similar to the linkage on a backhoe or excavator bucket but the chain is much easier and cleaner and I mean hell it could be a huge heavy chain it makes no difference.

I'm more interested in why you think it would fail and what the factors are that would cause it to fail.
"I think it will fail" doesn't work haha I want to know why so I can prevent it.

gordner said:

I think you would have a more linear relationship from the ram to the sprocket if the ram were parallel with the spring mount line, wrapping the chain 180 around the sprocket.

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agreed.
That was what I was trying to say in my second post.

funny people are certain the chain will break when we do not know the chain gauge or the gauge of any of the steel you are using....the highest stress point would be the pivot pin I would think, the chain is in tension, it would probably quite easily stop the ram extending at full pressure before it would break.

It also just occurred to me that if I extend the sprocket rod and put a race with a bushing below the sprocket it would alleviate a huge amount of lateral stress on the rod itself as the ram moves.

gordner said:

funny people are certain the chain will break when we do not know the chain gauge or the gauge of any of the steel you are using....the highest stress point would be the pivot pin I would think, the chain is in tension, it would probably quite easily stop the ram extending at full pressure before it would break.

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Thanks, see my reply above, we came to the same conclusion there.
As for the chain, a 530 has 11000 lbs of tensile strength, the ram is 8 ton so 16000 lbs. so I'd need to go up a size in the chain but that's still relatively small and manageable

SONIC. said:

A good 530 chain has a tensile strength of over 11,000 lbs, what makes you think it would fail so easily?

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That's only 5 1/2 tons. I think you are going to need more than that.

If you did something like that, you would want to put the mount point of the cylinder on a pivot, maybe.

Bucky685 said:

+1
(note this is my opinion)
Personally I would do something along these line. It is a interesting idea. But the chain is going to be a huge stress point and likely to fail.

Click to expand...

We have this bender if there are any pics or measurements I can take that would help.