How important is ratcheting system for tube bender (rotary draw)

[OscarInline]

Hello. I Started working on a DIY project making a rotary draw tube bender needed for my upcoming projects. This is my first experience with bending tubes, so wanted to consult about a couple of questions.

Right now working on a 100mm radius die to bend 40mm outer diameter 2mm wall thickness tube. Bends needed to be made will not exceed 90degrees, so I'm making a 100degree die (to be able to over bend a little to take springback in consideration)

So my main question is how do you think in this case could I attach a simple lever straight to the die to make these bends (space a round the bender in garage would allow me to use at least a meter long lever arm) or the force needed to bend this kind of tube would be way too much to force these bends and I would definitely need to make this bender with this kind of ratcheting and pin reseting lever arm like most of these rotary draw benders are made.

Would save a lot of time and drilling holes in thick plate to make the lever arm simply attached to the die.

Any input will be greatly appreciated. Thank You.

 

[gaz1]

theres homemade versions of this

 

[Agroshield]

The ratchet gives you a great mechanical advantage. It is going to be impractical to achieve the same mechanical advantage with a simple lever. If a 90 degree pull on a ratcheted handle gives 9 degrees movement of the die, that is a 10:1 advantage. A simple handle would thus have to be ten times longer to achieve the same force.

 

[addjunkie]

Is suggest your 100 mm CLR is a bit small for 40mm tube. I used to bend a fair bit of 11/4” 10 gauge tube at 41/2 inch CLR and even with decent formers there would be a little bit of distortion on the tube shape.

Heres another suggestion if your making the bender.

 

[Agroshield]

There are plans for a ratchet bender here:

chopperbuildershandbook.com

check out our Tube Bender plans, we are the only place on the web that gives you free downloads for a pipe bender. Donations accepted and appreciated!

chopperbuildershandbook.com

If you download CBTB-1-1 and 4-1 you can see enough dimensions to do a calculation. The control handle on 4-1 is roughly 40mm from its fulcrum. If you make the overall length of the handle 1m, that is a mechanical advantage of 1000/40 or about 25.

You would need a >25m square garage to sweep an unassisted handle in a 90 degree arc and obtain the same mechanical advantage. I suspect there could be some significant flex and a certain weight and storage disadvantage in such an handle.

 

[Erie Fred]

You would need a much longer handle as sated above a few times ^^^^.....and a way to fasten the bender down to the floor.
Ratchet keeps most of the force integral to the frame, minus your handle inputs. (which are much less with the ratchet)

 

[OscarInline]

Huge thank You all for great input.
Decided to make changes so CLR of bends will be around 18mm.
And will make the bender with the plans @Agroshield provided. Just hope my on the cheaper side drill press will survive this project.
How do you think would it be possible to tweak the design and make the ratcheting arm with straight cut triangular teeth instead of the rounded ones (attached picture)? Would again save a lot of drill work, but I'm worried it would be maybe possible for the push bar to slide out when pressing and and the overall amount of teeth would be less, so more power input needed on each push
Other option I was kind of considering maybe to use those long ram jacks that are used in engine hoists instead of ratcheting arm. the downside to that though would be that I would need to use the manual pumping one, because air powered 8T versions seem to require about 120psi to work optimally, and thats about the max limit for my air compressor ( probably would struggle to compress quick enough).
Thank You again for helping!

 

[Erie Fred]

Huge thank You all for great input.
Decided to make changes so CLR of bends will be around 18mm.
And will make the bender with the plans @Agroshield provided. Just hope my on the cheaper side drill press will survive this project.
How do you think would it be possible to tweak the design and make the ratcheting arm with straight cut triangular teeth instead of the rounded ones (attached picture)? Would again save a lot of drill work, but I'm worried it would be maybe possible for the push bar to slide out when pressing and and the overall amount of teeth would be less, so more power input needed on each push
Other option I was kind of considering maybe to use those long ram jacks that are used in engine hoists instead of ratcheting arm. the downside to that though would be that I would need to use the manual pumping one, because air powered 8T versions seem to require about 120psi to work optimally, and thats about the max limit for my air compressor ( probably would struggle to compress quick enough).
Thank You again for helping!

View attachment 481124

I would suggest you make a .dxf file of the proper teeth and send it to a vendor for plasma cutting.

Straight line, long jack, you need to make a layout to see what it really going on. (hint: your not going to like what you see)

I helped on one of these, and I ended up with the linkage that looks like a excavator bucket curl
circuit.

 

[Agroshield]

Would save a lot of time and drilling holes in thick plate to make the lever arm simply attached to the die.

I do not think the issue you identify is so hard to overcome that any of the options you state above will be less work or provide a better finished product.

The ratchet arm is 1/2" (13mm) plate. That is not thick plate by any stretch. The holes are 7/8" (22mm) and those particular ones do not need to be super accurate, so a holesaw would be acceptable.

The number of notches in the arm correlates with the overall bend angle achievable on the device (giving it maximum versatility). If you do not ever need a bend anywhere close to 180 degrees, fewer notches will suffice.

You could also make a cardboard or plywood mock up of the ratchet arm and try it with the notches further apart (e.g. two notches in the space where the original has three). That will also result in fewer holes to drill, but you need the mock up (or good CAD skills) to assess the implications of doing so.

You could bend 40mm plastic pipe warmed with a hair dryer using the plywood arm and that will tell you if the concept will work or not.

Even if you make a dog's breakfast of the first ratchet arm you make out of any material, let alone metal, it is the only piece you will need to re-make. If you make a 'shortie' version and then in the future decide you need a 150 degree bend on something, again, you only have to make a longer version of that part.

What is in the plans is a proven design, known to work on a wide range of tubes over a wide range of angles. It is not something where you will be arrrested if you depart more than 1mm from its dimensions because you only need a limited subset of its capabilities.

 

[addjunkie]

Get it cut from a dx file, will save you hours of messing around. The file I posted uses a bottle jack, and the same dies as the pro tools bender. Takes up less floor space too.

 

[OscarInline]

Thanks, that is what I will do - locate a place that does plasma cutting.

But, also wanted to hear your opinions about the type of bender that user @addjunkie posted plans of. Actually the more I look at it, the more I like it. Also seems easier to build. Are there any major drawbacks to this kind of design compared to rotary draw bender style, that I don't know of?

 

[addjunkie]

Thanks, that is what I will do - locate a place that does plasma cutting.

But, also wanted to hear your opinions about the type of bender that user @addjunkie posted plans of. Actually the more I look at it, the more I like it. Also seems easier to build. Are there any major drawbacks to this kind of design compared to rotary draw bender style, that I don't know of?

View attachment 481128

Dies are you biggest hurdle….are you making or buying?

 

[OscarInline]

Dies are you biggest hurdle….are you making or buying?

Trying to make my own. Using a pre-bent tubing sliced in half length wise. Reinforced with with 10mm plate in the middle of bend an 10mm plate on each side, all welded together. YouTube videos seem promising using this technique, but still bit worried cause most of them show bending pretty small OD tubing or pipe.

 

[addjunkie]

Ive made a few dies in the past. But for a push through bender. Your 2mm wall will deform easily.

I machined a disc the correct radius, and cut it in half, then a larger diameter disc cut-in half, for the side supports. The two middle half's we chamfered before being cut. These were then welded together and dressed smooth. Then the cut discs were welded on. Rough but worked though the wall was thicker.

Aother idea for you.

Another I made

 

[OscarInline]

Ive made a few dies in the past. But for a push through bender. Your 2mm wall will deform easily.

I machined a disc the correct radius, and cut it in half, then a larger diameter disc cut-in half, for the side supports. The two middle half's we chamfered before being cut. These were then welded together and dressed smooth. Then the cut discs were welded on. Rough but worked though the wall was thicker.

Aother idea for you.

Another I made
View attachment 481140

That was my second idea how to make the die. What technique did you use to smoothen the groove, after fitting and welding all the plates together? I reckon it was a lot of free hand angle grinder work right? I guess it would be somewhat easier if the die would be full 360degree piece and it were possible to turn it even in a quick put together drill "lathe" while grinding it smooth at the same time. But how did you manage to get it uniform and smooth it being a 180degree piece?

 

[addjunkie]

That was my second idea how to make the die. What technique did you use to smoothen the groove, after fitting and welding all the plates together? I reckon it was a lot of free hand angle grinder work right? I guess it would be somewhat easier if the die would be full 360degree piece and it were possible to turn it even in a quick put together drill "lathe" while grinding it smooth at the same time. But how did you manage to get it uniform and smooth it being a 180degree piece?

The Ali one was turned with a form tool. The steel one was welded with Tig, so not much cleaning up required, a die grinder and 5 minutes effort.