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Old 08-07-2010, 02:50 AM   #1
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Default exp. design for a dbl. acting mini. hydraulic cylinder

Hello everyone,

I have a few mechanical model projects I would, like to design and build,
using hydraulics, so this is going to be a experimental project in designing tooling and such, to be able to fabricate micro-miniature double acting hydraulic systems.

Building a single acting cylinder in hydraulics, is easy because there is no need to have a seal at the top of the cylinder, to contain the fluids, as long as the piston to cylinder fitting, is properly done with good compression, and very minute leakage, at the top.

But designing and building a double acting cylinder is more of a challenge, as I need to cap off both the bottom and top, of the cylinder for fluid pressure to push the piston in both directions.

I have decided I want to make a hydraulic system with a 3/8" dia. steel rod, with an internal bore dia. 1/4", so a piston with a dia. 0.249", and a length of 1/4" can be used and the piston rod to be made of 1/8" drill rod.

I looked at the idea of using my follower rest on my lathe, and makeing the piston and rod one piece, however I want the rod to be over 3", and to get a precise turning cut that way for that long of length could run into bending problems, somewhere if not some inconsistant rod diameter.

So I decide it would be best to use 1/8" precision rod, (drill rod) that ensures perfect dia. along the length of the rod. This means now I need to make the piston and rod 2 seperate pieces.
I thought about threading the piston and rod, than assembling together and then machining the piston down to final diameter. Or to press fit a aluminum piston, already to finished diameter, onto the rod.

I decided to go with the press fit method. This means to keep the 1/8" dia. rod from bending, I would need to fabricate a dedicated pressing jig, that I could utilize on my manual press.

I look at a project as being not only the finished work itself, but all the tooling and setups needed to be made in order to build and complete the project.
So building tooling is all part of building the final project itself.
-----------------------------------------------------------------------------------------------------

So here is a run down of what I have done so far, in fabricating a pressing jig:
Since this is a work in progress thread, I will give a lot of detail as possible.

The idea of this design is to press the 1/8" dia. 4" long rod onto a piston, 1/4" dia. x 1'4" long, for
a depth of 1/8".

This jig must support the rod along its entire length, as best as possible, so my design uses a solid rod, and a top plunger, spring loaded.



I start out by machining a 5/8"dia. rod to 4" overall length, measuring the length of the spring and its inner dia. shows I need to maching a stem on the end of this rod 5/16" in diameter, for a 1" length.



.





Now to support the 1/8" dia. drill rod its entire length I need to take my time and precisely drill the work piece with a thru hole of 1/8" dia., then finish it with a 0.126" reamer.

So I need to use my smallest 1/8" screwmachine size drill bit, followed by a 1/8" jobber size, finally following that with my 1/8" aircraft size bit.











Now I'll ream it with the 0.126" reamer as far as it can go.



Before I take the workpiece out of the chuick to turn it around to finish thru with the reamer from the other side, I need to drill and ream for a 0.249" hole 1/4" deep at the bottom of the workpiece.





Now I can turn the workpiece end for end to finish the reaming thru the workpiece.



Now here it is with the thru hole as precisely as possible drilled and reamed through, and the spring that will slide on top of it.







Now its time to make the top plunger, that will rest on the spring and glide over the base and have a stop after it traveles for 1/8". This plunger will be 2" in length.

Here is the plunger blank machined to final length of 2"



And the drawings for the dimensions.



this will be done in 3 phases.



The first will be a thru hole 1/8" dia.
after that I will drill a 19/64" hole 1-7/8" deep, followed by a 5/16" reamer.







phase 2, I need to drill a 1/2" dia. hole 1-5/8" deep.





Phase 3. now bore this hole to a final insde dia. of 5/8" - 0.626" by 1-5/8" deep to make a sliding fit with the 5/8" base previously made.



Now the parts before assembly



And the jig in it's final assembled stage.





Now a 36" drill rod 1/8" dia. is slid through this jig, to test the accuracy of the assembly.
it slides with no excessive play along the entire length of the drill rod, very presisely done, so this may work in supporting the rod from bending during a press operatiopn.



The way this should work would be, the machined piston will be loaded at the bottom of this jig, then a 1/8" dia. drill rod machined to exact length, will be loaded at the top of the jig, the top of the rod should be just about flush with the top of the plunger cap, that is resting on the spring, now placing the jig under my small manual press, I should be able to press the rod into the piston, for an depth of 1/8" before the plunger hits its stop thereby keeping consistancy with every pressed rod. The spring does nothing more than keeps the cap plunger around 1/8" floating above the base stop. Thereby preventing any bending to occur imediately at the top of the rod where it will be pressed against.

This completes the first part of this project,

----------------------------------------------------------------------------------------------------------

Now time to build a miniature cylinder:

I will use a 3/8" dia. steel rod for the cylinder.
In order to get an accurate inner bore 1/4" dia. it needs to be a thru hole drilled and reamed,
than to cap off both ends with appropriate fittings, I need to drill and tap for 5/16-24 threads on each end for a depth of 1/4"











---------------------------------------------------------------------------------------------------------------------

That's all for now, next the piston rod:




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Old 08-07-2010, 03:57 AM   #2
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Default Re: exp. design for a dbl. acting mini. hydraulic cylinder

very interested!


something I am also interested in making



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Old 08-07-2010, 07:59 AM   #3
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Default Re: exp. design for a dbl. acting mini. hydraulic cylinder




Very nice work.

Just a thought, unless you really want to use a press fit, why not use permanent
locktite? I've not used it yet myself but John Bogstandard and others more knowledgeable than I have used it say its great.

Anyway I thought I'd throw that out for what ever it's worth.

Keep up the good work.

I'll be following along.

Ron
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Old 08-07-2010, 10:09 AM   #4
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Default Re: exp. design for a dbl. acting mini. hydraulic cylinder

Hi Hobby, why not ''freeze fit'' the piston shaft to rhe piston...make the hole for piston shaft a couple thou under, gently heat piston, spray end of shaft with liquid nitrogen, fit shaft into hole and it wont be moving from there any time soon.
All the best for now,
John.

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Old 08-07-2010, 06:37 PM   #5
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Default Re: exp. design for a dbl. acting mini. hydraulic cylinder

Michael, Ron and John,

They are all great suggestions, you guys gave me, thankyou,
I definately will keep them all in mind, if my jig doesn't work properly.


Today I started working on the hose bibs, for the cylinder, the tubing I have available is 1/8" inner dia. so I made the bibs, from 1/4" alu. rod, and formed a spigot to put a 10-32 thread at one end.
then drilled a 5/64" thru hole for the fluid inlets.












Then I began working on the top end cap, the cylinder is threaded at the top and bottom with a 5/16-24 tap. So I measured the tap I used and got around 0.320" for the outside dia. then the spigot on the cap is turned to that dia. for around 1/4" length, later it will be reduced to around 3/16".














Next I will work on the bottom end cap, then drill and tap for the 2 hose bibs,
I looking at 2 options, for the tube connectors (hose bibs),
I have aprox. 1/16" thickness on the cyl. walls to tap into, that's plenty in steel.

The first option is to tap for the tube con. straight into the cylinder, or to tap at an angle
by tapping at an angle into the cylinder facing away from the end caps, would direct the pressure onto the piston.
By placing the conn. 90 deg. would direct pressure and fluids more towards the end caps.

So this is something I will be thinking about. As I proceed with this build.



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Old 08-07-2010, 11:54 PM   #6
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Default Re: exp. design for a dbl. acting mini. hydraulic cylinder

The idea of tapping into the thin cylinder wall at an angle did not work, there are heavy leaks as well as too much tube connector inside the cylinder that could interfere with the piston rod, on the top of the cylinder.



I need to redo the cylinder, connectors and end caps over again, and this time, make the end caps to be able to acomodate the tube connectors, I think I will be able to get a good seal doing it that way because I can make the connectors as large as needed without interfering with the piston rod, by using larger dia. endcaps, to accomodate the connectors.

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Old 08-10-2010, 01:29 AM   #7
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Default Re: exp. design for a dbl. acting mini. hydraulic cylinder

Hello,

In order to eliminate any fluid leakages involved in making seperate cylinder and tube connectors to thread into it, I decided it would be best to make the cylinder and connectors as one piece.

I want at least 3/16" tube connector to stand above the cylinder side, so I opted, to usiing a 5/8" dia. aluminum round bar, that would be offset 1/8" offcenter, and then turned down to 3/8" outside dia, leaving 2 places on both ends for the entire diameter of the rod to be machined later on, for the tube connectors.

To machine the cylinder in this fashion, requires a homemade split collet to be able to hold a 5/8" round bar offcenter by 1/8", and have it be used in a 3 jaw, self centering chuck, on the lathe.











The 5/8" dia. cylinder stock, I'm scribing a centerline, for locating in the collet.





Now I am beginning the process of drilling and reaming the inner bore to 0.249".





No that the cylinder bore is done, I need to loosing the collet and slide the work piece out so it can be machined, this is why the centerline was scribed earlier, so as to have a locating reference for the collet.



The finished workpiece, after the eccentric turning in the lathe.



Now I clamped the workpiece to a V block, and drilled 1/4" deep hole for a 5/15-24 tap, on both ends on my drill press.



And then put it in my micromill-drill to line up and tapped the hole 5/16-24 both ends,
these threads will be needed to be able to put endcaps on both ends, of the cylinder.



And the final work piece (cylinder) before the machining of the tube connectors.



Next I will fabricate a fixture for holding the cylinder blank, either in my lathe or on my rotary table, so I can machine the tube connectors onto the cylinder, where the eccentrics are seen at, in the above photo.










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Old 08-10-2010, 08:21 AM   #8
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Default Re: exp. design for a dbl. acting mini. hydraulic cylinder

Hi Hobby, I'm very new to machining. That's an interesting way to make an eccentric part, I'm enjoying your thread and soaking up your ideas.

Thanks

Nick

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Old 08-10-2010, 08:27 PM   #9
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Default Re: exp. design for a dbl. acting mini. hydraulic cylinder

Hi, this is very interesting, how will you power the hydraulic cylinder will you make a pump? Also what will you use it for out of interest

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Old 08-11-2010, 03:00 AM   #10
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Default Re: exp. design for a dbl. acting mini. hydraulic cylinder

Nick,
I'm glad your enjoying this thread, as you can see from this, jigs and fixtures are a big part of any build, but that's what make s this hobby so fun and challenging, is figuring ways to machine parts, that from the outset look simple to make, but the preparation for making that part can be longer than making the part itself, I just finished making another fixture for holding the workpiece iin my lathe for machining the tube conectors, but when I went to try it out, it didn't work properly, and I know why, and what I need to do to make this fixture work, you soon discover that machining parts is a lot of trial and error, but through that, is how you learn better ways of approaching the same task.

I went through about a dozen designs and prototype builds for my lathe tapering jig, every fail;ure brought temporary discouragement, but then I would learn from that failure and kept at it until I got what I think is the perfect design (for me) for that bguild, had no problems with it's performance whatsoever, but it took a lot of redoing over and over again.

So this thread may be like that, I may go so far and hit a snag, and have to use a whole new approach, but once I get this working properly, I will then get it down to a science, and post step by step procedure to get the same results everytime.


Speedhound,
The actuation will be with another piston cylinder arrangement, i will have 2 one each to push the piston, in each direction.

If I get it working properly, I will display this one as a mechanical model, with some extra fancy stuff with it working some sort of linkage or something.

If it works excellently, and I have the procedures down to a science, in buildiong these, then I was thinking of designing and building a miniature mechanical type flight simulator, where the airplane would move different directions via the pistons pushing and pulling it, with the mechincs modeled a little like the full size versions you see on TV, and the innernet, for training pilots.

But that is just way on the back burner for now, right now it is just a challenging project in itself to build one cylinder arrangement that works satisfactorily.

Thanks guys for your replies.

Have a great day...



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