Power drawbar project (TTS system)

[doctor demo]

He meant to attach the second cylinder to the first one's rod, I think. That , while a bit impractical, would add the strokes.

If you put both pistons on one rod, you can get more force, but the stroke is limited to that of one piston, the shorter stroke one.

Way back in post#15 and 16 it is explained as to the op's intentions of how this will work,and a link to a commercial cylinder like the one he built.

Steve

[J Tiers]

I think you are wrong. The stroke of the piston doesn't change because you have another piston pushing on the piston rod. LOL. The stroke of the piston regardless of how many there are is limited by the length of its cylinder.

He meant to attach the second cylinder to the first one's rod, I think. That , while a bit impractical, would add the strokes.

If you put both pistons on one rod, you can get more force, but the stroke is limited to that of one piston, the shorter stroke one.

[Bob La Londe]

I think you are wrong. If you have 2 cylinders each capable of generating 20 tons of force and you connect them in series, you will wind up with
an assembly that can generate 20 tons of force with a longer stroke. If you want the forces to be additive, the cylinders should be in parallel and
the load evenly distributed between them.

I think you are wrong. The stroke of the piston doesn't change because you have another piston pushing on the piston rod. LOL. The stroke of the piston regardless of how many there are is limited by the length of its cylinder.

[DEVILHUNTER]

Here is the post about the automatic tool changer:

http://bbs.homeshopmachinist.net/threads/74956-Automatic-tool-changer-for-my-mill

Yeah I know about the shorter collet for the TTS system. In fact I went a bit further with the collet so I can actually use flat tools, without the recess.

[doctor demo]

I think you are wrong. If you have 2 cylinders each capable of generating 20 tons of force and you connect them in series, you will wind up with
an assembly that can generate 20 tons of force with a longer stroke. If you want the forces to be additive, the cylinders should be in parallel and
the load evenly distributed between them.

I agree with what you are saying,but as I understand what the op as meaning is a stack of pistons on one common rod with separate chambers.
I think under those conditions it effectively puts the cylinders in parallel.

Steve

[RichR]

Those of us who have pushed a car might rebel at the concept. If two guys push a car it moves. If one guy pushes a guy pushing the car then the guy in the middle collapses. However in the case of the pneumatic cylinder the piston rod can't collapse. The force is added just like stacking weights on a scale.

I think you are wrong. If you have 2 cylinders each capable of generating 20 tons of force and you connect them in series, you will wind up with
an assembly that can generate 20 tons of force with a longer stroke. If you want the forces to be additive, the cylinders should be in parallel and
the load evenly distributed between them.

[Black Forest]

Wouldn't some kind of failure come into the picture? If you have two 20ton cylinders connected in series, I don't think you would want to try to use them to generate 40t of force...

It would depend on the structural integrity of the materials used to build the cylinders. If the cylinder rods would only stand the 20 tons then yes you would be right. But if the cylinder walls and rod will handle 40 tons then it is no problem. Essentially what he is doing is increasing the piston area therefor increasing the amount of force that can be applied.

[Mcgyver]

great stuff - keep them coming

[dave_r]

I am sure its already been explained, but think of it like stacking weights.

Basically its 4 pneumatic cylinders. Each one is pushing on all the other ones. Each pneumatic cylinder is capable of so much force. Since they are contained in a fixed (immovable object) that force can only go in one direction. Pressing into the back of the next one.

Those of us who have pushed a car might rebel at the concept. If two guys push a car it moves. If one guy pushes a guy pushing the car then the guy in the middle collapses. However in the case of the pneumatic cylinder the piston rod can't collapse. The force is added just like stacking weights on a scale.

Wouldn't some kind of failure come into the picture? If you have two 20ton cylinders connected in series, I don't think you would want to try to use them to generate 40t of force...

[Bob La Londe]

One thing, and you probably already know this if you have researched TTS, is that the collet for TTS is machined flat so the ring on the tool holder consistently engages the nose of the spindle and does not hit the front of the collet. That way when a tool is added to the tool table on your machine its the same every time it loads.

[Sparky_NY]

Look forward to you doing a thread on your toolchanger. It looks great!

[Bob La Londe]

I still don't understand how they can get more pressure unless they are in parallel. It seems like if they are end to end type of arrangement they would all max out the same as if there was only one cylinder.

Anybody have an explanation of how they work? I looked at the fabco site and didn't see it explained.

Brian

I'd appreciate an explanation also. With some sort of a sketch to show how the multicylinders add.
..lew...

I am sure its already been explained, but think of it like stacking weights.

Basically its 4 pneumatic cylinders. Each one is pushing on all the other ones. Each pneumatic cylinder is capable of so much force. Since they are contained in a fixed (immovable object) that force can only go in one direction. Pressing into the back of the next one.

Those of us who have pushed a car might rebel at the concept. If two guys push a car it moves. If one guy pushes a guy pushing the car then the guy in the middle collapses. However in the case of the pneumatic cylinder the piston rod can't collapse. The force is added just like stacking weights on a scale.

[DEVILHUNTER]

But this new motor have a big problem, my power drawbar does not fit anymore! So now I have to go with an air over hydraulic system. Made a couple of pistons and cylinders, 30mm in diameter so the pressure will be around 300 BAR. This way I will connect the cylinder in the headstock with the cylinder in the air piston with a braided hose. It's very important that the hose is as rigid as possible radially. If the hose expands too much, won't be enogh oin to push the drawbar all the travel. Since the hydraulic system is closed, I have to ve very aware of any air trapped and oil leak.







And this is almost all right now. The braided hose should arrive soon, plus I still have to buy a new compressor. Now I'm thinking on through spindle coolant, but I will have to change the hydraulic piston on the spindle to get the coolant/air into the drawbar.

On parallel I have been developing my automatic tool changer, but I think it deserves it's own post!

[DEVILHUNTER]

I installed this motor in order to make the adapter for the new motor while waiting for the VFD, but turned out to be too low torque to mill even MDF. The motor I had and wanted to use was a 1.7KW AC servo motor, with the same size of the original motor. I bought VFD that was, in theory, capable of driving this motor, but I couln't get it working, so I finally bought a second hand 1.5-1.8KW 3 phase induction motor. Installed it with MDF and made all the final parts in aluminium. I actually messed up the pulley, made the bore 25mm while the motor shaft is 24.... I will have to make a new one in the future.







In the last picture, you can see the encoder disk I made from aluminium sheet stock. I probably won't use it, I will install an absolute magnetic encoder on the motor.

[DEVILHUNTER]

Well, It's been a while since last updated this topic, and a lot of things have happened. First of all I want to comment that I started having a lot of pullout problems and chatter, no matter how hard I screw the drawbar. I even got some of the safts a bit damaged. At first I though it was the quality of the toolholders, but finally I discovered that the problem came from the collet. It was only gripping on the top of the saft. Changed the collet for another one and no problem since then.

After finishing all the plates and bars that hold the power drawbar to my mill, It all fitted pretty well:



Unfortunatelly, soon after that my original DC motor got burnt. I was already expecting that, so I had been making a timming belt conversion, but couldn't finish it before it happened. To finish the HTD 5M spindle pulley and the 30x30mm bars that will support the new motor I had to use and old cordless drill that I had to connect to a power supply since it's battery was dead:



Using a router at the side of the headstock, made the plastic pulley and MDF adapters to an old washing machine motor: