Machine Design Question (School Related)

[Tazzer]

I am taking this machine design class currently and I ran into a little scuffle with my teacher. We (group project) are designing a horizontal boring machine. The problem that I am have is that my teacher wants us to use a hydraulic cylinder to feed the part into the boring head. The Part is attatched using a v-block bridge that is attatched to a dovetail table that the hydraulic cylinder connects too.

I asked my teacher for a reason on why we are using the hydraulic cylinder and he said because that is what I (he) wants. I have no problem on drawing the cylinder up and attaching it to the machine, I would just like to know why! For one I do not know much about fluid powers (hydraulics) but is there a benifit on using the hydraulic cylinder. Because I would think it would be better to use a stepper motor and ball screws to move the table as for what I have seen here on some of the cnc machines I have seen here. Plus would you get a real smooth feedrate using a hydraulic cylinder as you would with a stepper motor.

Any light that someone could shed would be great because I just want to know the reason behind his thinking.

Thanks
Chris

[Al_The_Man]

You can achieve a smooth feedrate with the proper hydraulic flow controls etc, the problem is, is if you have to alter the feedrate you would have to do that manually unless you went with a hydraulic servo valve and feedback scale or encoder,This works exactly like a servo motor and ball screw etc. but now you are really getting up there cost wise. Perhaps he is worried about the use of a stepper stalling & losing steps under high load.
Al

[DareBee]

I believe it all comes down to cost. The stepper system can easily be double the cost of the hydraulic.
The stepper system is more versatile, controllable and accurate but if the machine is to do exactly the same thing for the next million parts, you set the hydraulics once and watch it make parts.
It's always about money, The least expensive way of getting the job done wins.

[ESjaavik]

Originally Posted by Tazzer For one I do not know much about fluid powers (hydraulics)

Maybe that's why he want you to use it?
Thinking it's easier for you to seek the necessary knowledge when having a practical problem to apply it to. Beside that, hydraulics can be the preferred choice of motion control if you already have the power pack. It is very tolerant to most kinds of dirt. The sensitive parts are contained almost perfectly shielded from the environment. High power electric systems are very expensive in explosive areas (EX-zone) like many sites in the oil industry. It is very compact (power per cubic whatever) Call your local rep for a hydraulic motion control company, and I suppose you will get many more arguments.