Go Back OFN Forums > Shop and Tool Talk > Benders and Bending

Benders and Bending Which bender is best? How do you use a bender? How do you calculate bends? Everything Bender related...


Benders and Bending Which bender is best? How do you use a bender? How do you calculate bends? Everything Bender related...

Reply
 
Thread Tools
  #81  
Old 12-09-2014, 02:10 PM
TheBandit's Avatar
TheBandit TheBandit is offline
Instagram @chevyhotrodder
 
Join Date: Jan 2006
Location: Ventura County CA
Posts: 4,268
I found a reference stating type II pumps put out 3.5gpm. If that rate is at 1,200psi, the power is around 2.5hp. Not really sure what the efficiencies of the motor and pump are, but you are pretty well in the ballpark of working just fine, especially since you will likely operate at around half the pressure if my calculations are right.
__________________
Clint

Last edited by TheBandit; 12-09-2014 at 02:36 PM.
Reply With Quote
  #82  
Old 12-09-2014, 03:36 PM
bullnerd's Avatar
bullnerd bullnerd is offline
Master Fabricator
 
Join Date: Apr 2008
Location: Jersey
Posts: 705
Nice job bandit!

Is there a way to test the flow rate of a pump, within the reach of a DIY-er?
Reply With Quote
  #83  
Old 12-09-2014, 04:21 PM
TheBandit's Avatar
TheBandit TheBandit is offline
Instagram @chevyhotrodder
 
Join Date: Jan 2006
Location: Ventura County CA
Posts: 4,268
Yeah. You could have it pump from one bucket into another and time how long it takes to fill a particular volume (for example 1 gal or 5 gal). Divide volume by time and you have flow rate. Another option is to allow it to run for a full minute and measure what you collect. That volume is the rate per minute. Assuming it's a positive displacement pump, doing this without a backpressure should be fine. Centrifugal pumps have a pump curve where flow rate depends on pressure, so it's a bit more complicated.
__________________
Clint
Reply With Quote
  #84  
Old 12-09-2014, 04:35 PM
TheBandit's Avatar
TheBandit TheBandit is offline
Instagram @chevyhotrodder
 
Join Date: Jan 2006
Location: Ventura County CA
Posts: 4,268
This is a decent primer on hydraulics as a reference: http://www.pirate4x4.com/tech/billav...ng/index1.html
I'm definitely no expert; just doing some back-of-the-envelope calculations.
__________________
Clint
Reply With Quote
  #85  
Old 12-09-2014, 04:41 PM
Fattcat69's Avatar
Fattcat69 Fattcat69 is offline
Fabricator
 
Join Date: Nov 2014
Location: Washington state
Posts: 54
You Rock Bandit!

Thanks for that info! It has been Documented!! I will do a flow test on it. iI may as well test it and compare it to a couple of the other pumps i am hordingw At this time i dont plan on doing anything larger diameter that 2" but who knows down the road..

Now if i where to go to a 2:1 ratio would be around 1612 rpm... Would this increased flow allow for more psi? Not that i would need to im just curious...

My jeep has 40 inch tires and i know dry steering it i bump the rpms up to 2000 and it steers much easier.

I have also heard of people shimming the pressure spring.... to increase the psi??
also alot of the offroad peeps will dill the pressure side hole out a little bit to increase flow rate i assume..

Sounds like i shouldnt need to do any of this.. I like your calculations Bandit and thanks for taking the time to do that!!
Reply With Quote
  #86  
Old 12-09-2014, 05:00 PM
TheBandit's Avatar
TheBandit TheBandit is offline
Instagram @chevyhotrodder
 
Join Date: Jan 2006
Location: Ventura County CA
Posts: 4,268
Just remember I am just an armchair engineer type and I've made more than my fair share of mistakes talking outside of my expertise. Take what I say with a grain of salt!

Your motor has a maximum power output above which it lets out smoke. When you change the drive ratio between the motor and the pump, the maximum power available remains the same. So speeding up the pump will actually reduce the pressure your motor is capable of producing. Said another way it will put more load on the motor for the same pressure. This is just like gears on a bicycle or a car; when you change to a lower gear ratio, it is easy to pedal (you put our more torque) but you can't go as fast. In this case, it's easier to produce pressure, but at a lower flow rate.

I can't really explain why it is the power steering is easier when you increase RPMs - it may have something to do with internal bypassing within the pump, cavitation, insufficient flow, or other factors. I know the phenomenon you are referring to though.

As far as running at 2:1 instead of 4:1, you could try it but I think you are already going to be moving plenty fast with this setup and you'll probably just end up throttling the control valve so you can go slow enough to hit your target bend angle.
__________________
Clint

Last edited by TheBandit; 12-09-2014 at 05:02 PM.
Reply With Quote
  #87  
Old 12-09-2014, 05:13 PM
Fattcat69's Avatar
Fattcat69 Fattcat69 is offline
Fabricator
 
Join Date: Nov 2014
Location: Washington state
Posts: 54
Sounds like it should be good to go. Im going to leave it and see what happens. I still need to find a pulley for the motor as it has the smooth wide 4 groove pulley from when it was an aircompressor.. I basically took my kids go cart motor that they quit using and turned the compressor into a gas setup and i found a pulley for the gas motor on ebay for 10$

Thanks for the info and yes a grain of salt is noted. I plan on doing some 1.75 roll cages and some light duty gates for my moms ranch when i get my pipe die set. So nothing insane this year lol

Well now im excited again and the honey do list is long!! so time to get busy!! you guys Rock! have a kick ass day!!
Reply With Quote
  #88  
Old 12-09-2014, 06:41 PM
bullnerd's Avatar
bullnerd bullnerd is offline
Master Fabricator
 
Join Date: Apr 2008
Location: Jersey
Posts: 705
Hmmm..so a variable RPM motor and a CVT style drive we can find the exact pulley ratio and motor RPM to get the perfect flow/pressure we need?

Ive heard of the pressure spring trick also.

Good luck Fattcat, keep us up to date. Looking forward to you figuring this all out for the rest of us once and for all!
Reply With Quote
  #89  
Old 12-10-2014, 10:05 AM
Fattcat69's Avatar
Fattcat69 Fattcat69 is offline
Fabricator
 
Join Date: Nov 2014
Location: Washington state
Posts: 54
Heck yes!

Well Bullnerd im going to document everything i can on this. I know there are people out there that have done it with positive results. I watched a Tube Vid with a guy that used a PS setup to move a Hydraulic motor and a ram. No pressures or flow info though.. If this works decent for the bender i would like to find the correct cylinder and also set one up on my press. I think it would make Dimple die work a lot quicker. Which is something i have not ever done yet but will be soon.

Bandit i have a good understanding i believe of axle ratio, I couldnt stop thinking about how u explained the pump in relation to a bikes torque, or ring and pinion ratio.. Mabie im overthinking this which is totally normal.. well to some i guess... So using the fluid being pushed by a vane setup as a ring gear as to not increase flow will bring a higher psi? like peddling a bike faster in that easy gear and not going anywhere? So by changing the ratio to a larger or higher number say 4.56 to 5.13 adding torque, will this bump my psi up? I imagine the pump engineers found max flow and set the ratio as it is for the size passages the pump has.

Im just curious because looking at the info on the web i see people shooting numbers all over the board, from 6gpm to 8gpm lol psi from 600 to 1800.. so in wondering if these pumps GM had different internals.. I have 5 pumps here all gm from different year rigs and the pulleys are all the same...
Reply With Quote
  #90  
Old 12-10-2014, 01:05 PM
TheBandit's Avatar
TheBandit TheBandit is offline
Instagram @chevyhotrodder
 
Join Date: Jan 2006
Location: Ventura County CA
Posts: 4,268
Here is another cool thread for reference:
http://www.offroadfabnet.com/forums/...ad.php?t=10217

And some benders done or in progress to inspire you:

My little twin cylinder 1hp pile: http://www.offroadfabnet.com/forums/...read.php?t=218

mymechanics mandrel bender: http://www.offroadfabnet.com/forums/...ead.php?t=1661

jaysinspaceman rotary draw electric chain driven bender: http://www.offroadfabnet.com/forums/...ead.php?t=5851

zag chani drive 3hp: http://www.pirate4x4.com/forum/shop-...en-bender.html
__________________
Clint
Reply With Quote
  #91  
Old 12-10-2014, 01:18 PM
CarterKraft's Avatar
CarterKraft CarterKraft is offline
Master Fabricator
 
Join Date: Oct 2009
Location: DFW
Posts: 845
Quote:
Originally Posted by TheBandit View Post

I can't really explain why it is the power steering is easier when you increase RPMs - it may have something to do with internal bypassing within the pump, cavitation, insufficient flow, or other factors. I know the phenomenon you are referring to though.
I feel like this is due to the inefficiencies of a gear pump at low RPM. In a gear pump there is flow loss through the pump, around the lobes of the gears between the case and gear tip. At low RPM the pump can't not overcome this so the pressure loss is high enough to not be able to build the pressure (force) to swiftly moved the tires. Obviously the flow is lower so tires move slower as well.
If you could use a piston pump, very low loss compared to a gear pump then you would notice full system pressure is available at any RPM.

I know this is obvious for hydraulics just thought I might try to add something.

I am looking forward to seeing this completed though. I enjoy a re-purposing of items especially when they are cheap and readily available.
Reply With Quote
  #92  
Old 12-10-2014, 01:32 PM
TheBandit's Avatar
TheBandit TheBandit is offline
Instagram @chevyhotrodder
 
Join Date: Jan 2006
Location: Ventura County CA
Posts: 4,268
First let me say these are all ballpark calculations because as you pointed out we really don't have a solid understanding of the pump performance.

What you are putting together is a system. Each element in the system has a transfer function, meaning it converts something to something else in a predictable way. For example, the motor converts current and voltage into rotation and torque. The pump converts rotation and torque to pressure and flow. The cylinder converts pressure and flow to linear force and speed. The mechanics of the bender and cylinder arrangement convert linear force and speed to rotary torque and speed. Eventually that energy is absorbed by the deformation of the tubing. Energy is also lost along the way because each component has <100% efficiency.

I think about systems in this way partially because I've been trained to do so and also because I find the system-based approach gives me the clearest picture of power in -> power out.

As a designer of a system with many possible variants, you have about a million places you could start and lots of things to iterate on, constraints to establish, and components to select. I'll start this out kinda how I started my bender project by considering power and output torque.

Knowing the maximum tube size you intend to bend and knowing the power rating of your motor, the fastest bending speed is already determined. Let's assume you're designing for 5,000ft-lb of torque and you have a 3hp motor. Knowing torque and power, we can calculate maximum possible speed:
3hp x 550 ft-lb/sec-hp / 5,000ft-lb = 0.33radian/sec = 19deg/sec.
So if you had a full 3hp of output and you optimized the mechanics of the system, you could theoretically bend 90 degrees in just 3.5seconds - plenty, if not stupid- fast for a hobby bender that has no CNC control (see videos of Zag's bender for an example; he also used a 3hp motor).

Now let's work our way back from the tube to the motor and try to fill in some gaps. If the cylinder is mounted to the bender at 45* 18" from the center pivot (IMPORTANT ASSUMPTION) and angle changes are small, to rotate at 19deg/second, the speed the cylinder has to travel can be calculated as follows:
19deg/sec x 18in x pi/180deg x cos(45) = 4.2in/sec
Since you’ve selected a 3” cylinder, the flow rate required to move at this speed can be calculated based on the swept volume of the piston as follows:
4.2in/sec x pi x 3in^2 / 4 = 29.8cuin/sec
Converted to gallons per minute:
(29.8 cuin/sec) x (60sec/min) x (1gal/231cuin) = 7.7 gpm
So, based on the above calculations, you should set your pulley ratio for a flow no more than ~7gpm if you want to respect the 3hp limit of your motor. Once you get your motor and pump connected, you can measure the flow rate as I described before and find out where you are at and whether or not you can use a different pulley ratio to speed things up.

We also need to consider the operating pressure of the system for the above conditions. We have many options for calculation this, but I am going to do it using the power delivered by the cylinder. We know the power is approximately 3hp and the cylinder speed is 4.2in/sec. Let’s calculate force:
3hp x (550ft-lb/sec-hp) x (12in/ft) x (sec/4.2in) = 4,714lb
We could also have made the same calculation using geometry and output torque as follows:
(5,000ft-lb x 12in/ft x 1/cos45) / 18in = 4,714lb
Okay so now we know the force on the cylinder, let’s calculate the pressure based on the size of the piston 3”:
4714lb / (pi x 3in^2 / 4) = 667psi.
Whatdya know – very little pressure is required. This of course assumes a nice frictionless lessless system where the cylinder maintains no more than 45 degrees from perpendicular to the bender arms, so you should definitely err to the side of conservative when choosing your pulley ratio / flow rate.

FYI I reposted this after making some important corrections to my calculations and I give no guarantee of accuracy or correctness. Be sure to check it over. You really should get the dimensions of your bender to refine the calculations above.

So in conclusion – hook the damn thing up and see what it does!
__________________
Clint

Last edited by TheBandit; 12-10-2014 at 02:21 PM.
Reply With Quote
  #93  
Old 12-10-2014, 02:04 PM
Adam Gardiner's Avatar
Adam Gardiner Adam Gardiner is offline
Master Fabricator
 
Join Date: Feb 2014
Location: United Kingdom
Posts: 133
Wow that's very complicated I've been trying to follow this post as I'm interested in making a hydraulic upgrade when I get a JD2 model 32. Now I'm lost with all the figures. I have a 3.8cc group 2 pump and motor rated at 55 bar (i think this is low as motor is 220v 1kw) sat waiting for my conversion which I think may be to fast for my needs so may down size the pump to be able to up pressure without overloading the motor.
Excellent thread looking forward to seeing the finished project
Adam
Reply With Quote
  #94  
Old 12-10-2014, 03:10 PM
TheBandit's Avatar
TheBandit TheBandit is offline
Instagram @chevyhotrodder
 
Join Date: Jan 2006
Location: Ventura County CA
Posts: 4,268
Adam - What is the motor speed? 3.8cc is probably the pump displacement per revolution. 55bar is about 800psi and 1kw is about 1.3hp for the metric challenged like myself.
__________________
Clint
Reply With Quote
  #95  
Old 12-10-2014, 03:54 PM
Adam Gardiner's Avatar
Adam Gardiner Adam Gardiner is offline
Master Fabricator
 
Join Date: Feb 2014
Location: United Kingdom
Posts: 133
I'm not sure to be fair but was looking at the pumps in a catalogue and found that a smaller pump could produce 200 bar from a 1kw motor of the displacement was small enough I think about 1.5cc from memory. Will check hydraulic catalogue tomorrow. I'm not concerned with speed if it takes 30s or 90s to make an bend.
Reply With Quote
  #96  
Old 12-10-2014, 04:13 PM
bullnerd's Avatar
bullnerd bullnerd is offline
Master Fabricator
 
Join Date: Apr 2008
Location: Jersey
Posts: 705
I just found two really sweet quotes!....

" I give no guarantee of accuracy or correctness. "

"So in conclusion – hook the damn thing up and see what it does! "
Reply With Quote
  #97  
Old 12-12-2014, 02:29 PM
Fattcat69's Avatar
Fattcat69 Fattcat69 is offline
Fabricator
 
Join Date: Nov 2014
Location: Washington state
Posts: 54
Sir Bandit!! Thank you Very much !

Wow Bandit Thanks man! Wicked calculations!! Very good stuff to know!! As far as bender dimensions would you like the distance from the ram to the arms, Arm length and center of the bender? angle of the ram as well? let me know and ill go get it all!! Whatever i can get to complete the calculations you have im game!!

Heck yes Adam id like to see your setup as well! post pics and build info man, We can feed off each others ideas and have the best of both worlds! If this doesnt work ill be looking for something similar to what you have...

Bullnerd!! i like Bandits Quotes as well!! very true The Conclusion Rocks!!

Hook the damn thing up and see what it does lol

Well i ordered a motor pulley that may kill the ratio.. we will see. Its the smallest one i could find on ebay for 5/8 keyed shaft... Also ordered a set of 3/4" weld in bungs for the tank, so in waiting i hooked up a power switch and some paneling as well.. ill try and make the pics work here....
Reply With Quote
  #98  
Old 12-12-2014, 02:37 PM
Fattcat69's Avatar
Fattcat69 Fattcat69 is offline
Fabricator
 
Join Date: Nov 2014
Location: Washington state
Posts: 54






I think my phone is dirty!! foggy pics... Finished the wiring for the motor and some panels last night.. I think im gonna mount the Tank vertical... leaves me a little more room in the lower level of the stand.. Im going to try and build a lower section to mount the valve to so that just the handle sticks thru the top of the stand... we will see..
Attached Thumbnails
Click image for larger version

Name:	IMG_20141211_232813_656.jpg
Views:	236
Size:	33.1 KB
ID:	8087   Click image for larger version

Name:	IMG_20141211_232745_451.jpg
Views:	229
Size:	34.3 KB
ID:	8088   Click image for larger version

Name:	IMG_20141211_232757_314.jpg
Views:	233
Size:	40.8 KB
ID:	8089  

Reply With Quote
  #99  
Old 12-12-2014, 02:50 PM
Fattcat69's Avatar
Fattcat69 Fattcat69 is offline
Fabricator
 
Join Date: Nov 2014
Location: Washington state
Posts: 54
Also Bandit those bender links are wicked!! Your bender is amazing as well!! Very nice job man WOW! I couldnt build my own bender yet.... When i am competent though i would like to design one similar to the mandrel style! Very cool setup
Reply With Quote
  #100  
Old 12-12-2014, 04:22 PM
bullnerd's Avatar
bullnerd bullnerd is offline
Master Fabricator
 
Join Date: Apr 2008
Location: Jersey
Posts: 705
My neighbor's version doesn't have an external tank, just the power steering reservoir on the pump. But, I'm not sure what diameter the ram is, it looks thin and long. The hossfeld geometry may be different than the new style benders? Requiring less power?
Reply With Quote
Reply

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 09:36 PM.

Powered by vBulletin® Version 3.8.0
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Template-Modifications by TMS
Copyright ©2012, Offroad Fabrication Network