X2 Electric-*Hydraulic* drawbar

[SScnc]

Pete, Hope you get feeling better soon, I know how rough that stuff can be.

Since I already knew that the electric actuator could compress 10 Bellevilles directly, I made the cylinders the same bore, so if the main piston moves .100" the mill head piston will move the same .100". That is "if" the hose isn't expanding, which of course it is. So the main piston is traveling a bit more right now.

The Tormach engineer was very clever with his design, I was very impressed when I saw that video of it. On an X2 I don't see a real need for that detail, at least not on mine. I seldom ever switch from the 3/4" collet for the TTS's and since I converted the spindle bearings to tapered rollers I'm not concerned with putting too much pressure on the bearings. Maybe you'll be able to get back to having fun soon !

2_many_hobbies, the O rings were just some I happened to have that came from Ace Hardware months ago. And since you asked, here are some pics and dimensions of the cylinders...

[Nateg281]

Originally Posted by SScnc Let me know if anyone has *any* ideas on improving this hydraulic setup.........

Steve,

I posted just yesterday an idea I had about using a low profile hydraulic cylinder with .25 inches of travel like this one available from harbor freight.

http://www.harborfreight.com/cpi/cta...emnumber=95978

It's VERY small and would mount perfectly above the head of an X2. It is a 5 ton cylinder, but I didn't think that would matter much if you were sure of the amount of travel you needed and adjusted the mount to fit. I have no experience with hydraulics or access to a lathe to make the parts I would need to get it up and running. I would love to hear your thoughts on this and whether or not you think it's practical.

I was hoping to find parts off the shelf to make an electrical linear actuator driven hydraulic pump to move the hydraulic fluid. From the best of my calculations you would only need to move about .25 cubic inches making the time to release your drawbar VERY short in theory.......just my .02

[SScnc]

I see no reason why that won't work, I'm no hydraulics person myself, I just understand how they work and used to have a Cat D3 dozer and had to repair and replace hydraulic parts and cylinders on it from time to time and so I learned allot back then.

You say "pump" and I assume you mean a similar setup as mine so you'll need 2 cylinders of course. I would think that a pair of inexpensive pneumatic cylinders would work fine too. I have a pressure gauge the goes to 5000 psi but have not checked what pressure this setup maxes out at, someone like Ray probably knows how to calculate it and this would be good to know before using pneumatic cylinders.

Also, keep in mind that depending on what power actuator and number of Bellevilles you use you may need to use a smaller diameter "master" cylinder as the pump to gain more force at the drawbar cylinder. The travel will be longer at the pump and therefor the cycle time. Just some things to keep in mind.

I have been making allot parts with my mill and the power drawbar has made running the mill so simple, quick and more enjoyable so I highly recommend going to the trouble of doing some sort of power drawbar setup.

Please post pics and info if you do this, I'm very interested to see what you and others come up with. Please ask if you have any other questions and I'll help if I can.

Steve

[Nateg281]

I just went back and looked at that cylinder from Harbor Freight and saw that the working pressure is over 9000 PSI. Not sure how hard that would be to generate with a second cylinder somewhere....

Again, I don't know much about hydraulics, but I'm assuming if you used less than 9000 PSI that you would have less than 5 tons of force? Maybe if PSI is directly proportional to force than 4500 PSI would get you 2.5 tons and so on and so forth or do I have that wrong? I'm just wondering if one of us figured out how to run it at a lower pressure if the hydraulic cylinder would still work like it should.....

[HimyKabibble]

Originally Posted by SScnc I see no reason why that won't work, I'm no hydraulics person myself, I just understand how they work and used to have a Cat D3 dozer and had to repair and replace hydraulic parts and cylinders on it from time to time and so I learned allot back then. You say "pump" and I assume you mean a similar setup as mine so you'll need 2 cylinders of course. I would think that a pair of inexpensive pneumatic cylinders would work fine too. I have a pressure gauge the goes to 5000 psi but have not checked what pressure this setup maxes out at, someone like Ray probably knows how to calculate it and this would be good to know before using pneumatic cylinders. Also, keep in mind that depending on what power actuator and number of Bellevilles you use you may need to use a smaller diameter "master" cylinder as the pump to gain more force at the drawbar cylinder. The travel will be longer at the pump and therefor the cycle time. Just some things to keep in mind. I have been making allot parts with my mill and the power drawbar has made running the mill so simple, quick and more enjoyable so I highly recommend going to the trouble of doing some sort of power drawbar setup. Please post pics and info if you do this, I'm very interested to see what you and others come up with. Please ask if you have any other questions and I'll help if I can. Steve

The force, in pounds, generated by a hydraulic, or pneumatic, cylinder is equal to the pressure, in PSI, times the piston area, in sq. in.:

Force = Pressure x Area

or,

Pressure = Force / Area

So, a 1" diameter cylinder has an area of:

Area = Pi * (Area ^ 2) / 4 = 3.14 * (1 * 1) / 4 = 0.79 sq. in.

At 1000 PSI, that cylinder will exert a force of:

Force = 1000 * 0.79 = 790 pounds

If using two cylinders, you need to master cylinder to be a relatively small diameter, to keep the force requirement reasonable. You *can* generate very high pressures with very little input force, using a very small cylinder. But, the displacement of that cylinder will also be small. This means the larger slave cylinder will move an even smaller distance. So, the smaller the master cylinder, the longer its stroke needs to be, to achieve a given displacement.

Suppose you have a 1/4" master cylinder, and a 1" slave cylinder, and you need the slave cylinder to move 0.1" and exert a force of 1000 pounds.

Slave Area = Pi * (1 ^ 2) / 4 = 0.79 sq. in.

Slave Pressure = 1000 / 0.79 = 1265 PSI

Slave Displacement = 0.79 * 0.1 = 0.079 cu. in.

Master Area = Pi * (0.25 ^ 2) / 4 = 0.049 sq. in.

Master Pressure = Slave Pressure = 1265 PSI

Master Force = 1265 * 0.049 = 62 Pounds

Master Stroke = 0.079 / 0.049 = 1.6 in.

This is how commercial power drawbars on large machines work - A long-stroke air cylinder, at perhaps 150-175 PSI, drives a long-stroke small diameter hydraulic cylinder, with the hydraulic pressure moving a short-stroke large diameter cylinder (typically 3-5" diameter) doing the actual work. It's called a pneumatic/hydraulic force multiplier.

Keep in mind, generating, and containing, 1000+ PSI is non-trivial. When you get up into several thousand PSI, it becomes downright dangerous. The flow from a pinhole leak in a hose can cut right through skin.

Regards,
Ray L.

[SScnc]

Excellent write up Ray. Until your previous post about the large commercial mills I thought they were pneumatic only. My father was a civil engineer and he used to write out things almost exactly the same as you have here. I remember asking him about a 20 ton hydraulic jack we were using one time when I was a kid and he explained it similar and I just stared at him and he and I started laughing then he explained about a small cylinder able to move a small amount of fluid to a larger surface and so on.

Since I didn't know what the psi was going to be, that's another reason why I made my cylinder walls so thick. As for high psi fluid being dangerous, I know that for a fact. A friend of mine had a Bobcat loader and he was doing something with the hydraulic lines on the front of it while it was running and the hose burst a small hole in it and it blew right through the palm of his hand and and out the the other side. He still suffers from that. Not to mention it was scalding hot fluid too.

Thanks for the write up,

Steve

[philbur]

Stroke length is really only an intermediate issue. To stroke your drawbar you need to do a certain amount of work in a give time. This equates to power.

work = force times the distance moved by the force
Power = work done divided by the time it takes to do the work.

These two equations, plus losses due to friction etc tells you the size of the motor, solenoid or comressor required. Once you have this it's relatively easy to calculate piston sizes, lever arms lengths or the cam profiles to achieve the desired effect. If you under spec the power source you will have to increase the stroke time.

Work (ft-lbs) = max compressed Force/2 (lbs) x drawbar stroke (ft)

Power at the drawbar (hp) = Work /stroke time (minutes)/550

multiply by 0.746 if you want kW.

A good starting point would be to assume at least 50% loses due to friction etc. If you want to be more accurate it is possible to estimate the losses.

Phil

Originally Posted by Nateg281 Steve, I posted just yesterday an idea I had about using a low profile hydraulic cylinder with .25 inches of travel like this one available from harbor freight. http://www.harborfreight.com/cpi/cta...emnumber=95978 It's VERY small and would mount perfectly above the head of an X2. It is a 5 ton cylinder, but I didn't think that would matter much if you were sure of the amount of travel you needed and adjusted the mount to fit. I have no experience with hydraulics or access to a lathe to make the parts I would need to get it up and running. I would love to hear your thoughts on this and whether or not you think it's practical. I was hoping to find parts off the shelf to make an electrical linear actuator driven hydraulic pump to move the hydraulic fluid. From the best of my calculations you would only need to move about .25 cubic inches making the time to release your drawbar VERY short in theory.......just my .02

[Art Pentz]

Hi All;

Check out:

http://www.vektek.com/pdfs/Catalog/e...erSupplies.pdf

I use an air/hydraulic booster to get 3000 PSI for my drawbar from 100 PSI shop air.

Best regards;

Art Pentz

[Nateg281]

Originally Posted by philbur Stroke length is really only an intermediate issue. To stroke your drawbar you need to do a certain amount of work in a give time. This equates to power. work = force times the distance moved by the force Power = work done divided by the time it takes to do the work. These two equations, plus losses due to friction etc tells you the size of the motor, solenoid or comressor required. Once you have this it's relatively easy to calculate piston sizes, lever arms lengths or the cam profiles to achieve the desired effect. If you under spec the power source you will have to increase the stroke time. Work (ft-lbs) = max compressed Force/2 (lbs) x drawbar stroke (ft) Power at the drawbar (hp) = Work /stroke time (minutes)/550 multiply by 0.746 if you want kW. A good starting point would be to assume at least 50% loses due to friction etc. If you want to be more accurate it is possible to estimate the losses. Phil

Thanks for the info Phil. I appreciate all the support from the forum. I've almost decided to go with an air powered drawbar, but still like the idea of a hydraulic setup and might work on that as a back burner project once my CNC X2 build is finished....

[HimyKabibble]

Originally Posted by Art Pentz Hi All; Check out: http://www.vektek.com/pdfs/Catalog/e...erSupplies.pdf I use an air/hydraulic booster to get 3000 PSI for my drawbar from 100 PSI shop air. Best regards; Art Pentz

Those are nice, but what do they cost?

Regards,
Ray L.

[Art Pentz]

Hi Ray,

Pricing is on the web page - Vektek stuff is expensive, but very high quality w/ great support.

Art Pentz

[HimyKabibble]

Originally Posted by Art Pentz Hi Ray, Pricing is on the web page - Vektek stuff is expensive, but very high quality w/ great support. Art Pentz

Like I thought: $568 for the cheapest one.

Of course, the 7" air cylinder by itself will generate almost 4000# force at 100 PSI. Unless you specifically need to "remote" the actuator, the hydraulics are not necessary to do a drawbar. A 7" air cylinder could be home-built pretty inexpensively - probably under $30 in materials.

Regards,
Ray L.