Round Tubing Construction

[Orion.DeYoe]

I'm interested in some of the robot designs that revolve around bent round tubing. Primarily 1024's usage of this unique build style. I have several questions (if someone from 1024 could address these it would be great):

1) What is the tubing? I assume it is 1 in OD x .065 wall aluminum or similar.
2) What do you use to form it? Is it a rolling machine of some sort? Or just a simple conduit bender?
3) What are the fittings you use to join the tubing and where do you get them? They aren't very recognizable from pictures. Are they clamp on, press fit, etc.?
4) What kind of tolerances are you able to hold on bend angles and such? I can see getting OAL and bend offsets right being very difficult.
5) Would you recommend this build style to other teams? What advantages do you see it having over more traditional methods (sheet metal, extrusion, box tubing, etc.)?
6) Are there any CAD models available that I can mess around with for more details?

If someone who has experience with this build style can shed some light on this it would be greatly appreciated.

[Allison]

Thanks for the interest in our design style.

1. We use 1" O.D. .065 wall 6061-T6 aluminum with a 3" radius for all of our bent tube. We have tried to bend .035 wall tube but it kinks.

2. All of our bending is done with a manual draw bender.

3. We uses a couple different types of fastening methods. Tube connector nuts pressed into the end of the tube is our main method, they can be purchased from McMaster 94290A550. We also use u bolts, rivets, through bolt, and custom FDM parts.

4. Typically we measure our bends with a printed 1:1 layout of the design and match it. We normally cut the tubes after they are bent as to not worry about OAL. If a tube as multiple bends we do one bend then measure for the next location. Tube is very forgiving if you over bend or under bend you can usually adjust the tube slightly by pushing or pulling on in. If hole locations are critical they are drilled after bending.

5. Round tube works very well for 1024 but it is not for everyone. The main advantage is strength to weight ratio. For us structures are easier to make out bent tube because we can typically make them simpler and with fewer parts compared to square which requires mechanically fastened joints or welding.

6. I will look and see what I can find.

1024 is open to answering any additional questions you may have. I will keep an eye on this thread.

Allison

[lynca]

This is a great post ! Thanks for sharing your details. We might attempt to build something this Fall to test our our pipe fabrication process. I have a few questions.

Originally Posted by Allison

1. We use 1" O.D. .065 wall 6061-T6 aluminum with a 3" radius for all of our bent tube. We have tried to bend .035 wall tube but it kinks.

Do you have experience using thicker wall than 0.065 " ?

Where do you usually get this material and how much does it cost ?
McMaster doesn't have the size that you mentioned.
http://www.mcmaster.com/#aluminum-pipe/=t5e992

Originally Posted by Allison

2. All of our bending is done with a manual draw bender.

My mileage has varied with these types of tools ?
What do you recommend ?
http://www.amazon.com/Manual-Hand-Al.../dp/B001Z0U5HM

Originally Posted by Allison

3. We uses a couple different types of fastening methods. Tube connector nuts pressed into the end of the tube is our main method, they can be purchased from McMaster 94290A550. We also use u bolts, rivets, through bolt, and custom FDM parts.

Those tube connector nuts are awesome ! http://www.mcmaster.com/#94290a550/=t5ebwx
I'm interested to see how you did some of the other fastners, pictures or CAD of your robot up-close would really help if they are available !

Thanks !

[MetalJacket]

Originally Posted by lynca

Where do you usually get this material and how much does it cost ?

I can't speak for where 1024 sources their tubing but my team buys most of our rectangular tubing from onlinemetals.com, and they also have round tubing
EDIT: This link has the size they mentioned using

[Allison]

We have experience bending up to 1/8" wall tube and also bending steel tube for non FRC projects. 1/8" wall steel tube usually takes two student to pull the die around. We have not found a need for thicker tubing in our designs. We have only had a few failures all of which have occurred where holes where drilled in bends.

We source our materials locally from AED Motorsport which saves us on shipping since we have mentors that work close by. Our cost last season was 3.30/ft which is cheaper than McMaster and Online metals.

We have a Hossfeld Bender which we bought used.

http://www.hossfeldbender.com/bender...-tube-pipe.php


I won't be in our shop till next week but I will follow up with pictures as soon as I can after that.


Allison

[Orion.DeYoe]

Originally Posted by lynca

Where do you usually get this material and how much does it cost ?
McMaster doesn't have the size that you mentioned.
http://www.mcmaster.com/#aluminum-pipe/=t5e992

The part number is 9056K75.
You should look under "tubes for fabrication". What you're looking at is typically referred to as "pipe" (there actually is a difference between "pipe" and "tube").
McMaster is a horrible place to get raw material from though. It's ridiculously expensive.

[msimon785]

I do a lot of work with tube bending at the company I work for.
For bending aimed towards FRC there are a few benders I can recommend, sourced from JD^2 and ProTools.

Within JD^2's catalog, their Model 3 manual bender (their bestselling product) is decently effective and is a machine I have worked extensively with on precision bends. It does have some shortcomings. One of the caveats of tube bending is that to achieve a certain bend angle it's necessary to overbend by a precise amount to accommodate for spring back - this will vary based on alloy and profile dimensions for the tube you're bending. Additionally, in manual draw benders, there is a small element of friction which can skew what is interpreted as the final bend angle post-springback. This requires a little finesse and testing to massage out of your bends.

An excellent way to calculate and deal with springback and overall design for tube bending is using Bend-Tech software. I've only used Bend-Tech's EZ3D package which is limited, but the advantage of Bend-Tech is that it provides an unfolded model with LRA (Length/Rotation/Angle) data. Upgrading to Bend-Tech Pro allows for assembly design and notch calculation. Essentially it will provide you with specific instructions for the operator in order to produce the desired part. You design to CLR (Center Line Radius), but it does give flexibility as to designing to the apex (projected intersection) of the bends or bend tangents.

As to precision with this class of benders, I can comfortably say you should be able to achieve, with the raw bend, within +/- 1.5 degrees of the desired angle. From that point, it's trivia to manipulate the already-bent part into the desired precise angle. Distances between bends, assuming marks are clean and a precise point on the bender is used as reference, can be close to perfect. Eliminating cutoff takes some prototyping time, but Bend-Tech does feature a machine calibration feature that theoretically will calculate your bend offset automatically (though in my experience, it's far better to add 0.5" cutoff and create a clean cut post-bend).

[Allison]

Here are some close up of different ways of connecting tube


This picture shows taking a round tube and inserting it into a square tube with a slight press fit. A star nut secures the tube.


This picture shows both a bolt through connection and also attaching IGUS bearing blocks for a pivot point.


This picture show both rivet connected sheet metal but also a tube being used as a linear slide.


This picture shows tubes being connected together using a tube connecting nut (we call them star nuts).


This picture shows a custom FDM bracket used to connect tubes together.




I hope the pictures help let me know if there is anything else you would like to see or know.

Allison