[RCaffin]

is the force doubled when I use two pistons?
Yes.

Cheers
Roger

[G59]

is the force doubled when I use two pistons?

Like RCaffin said.
If the total surface area of one piston is 50 cm3, then having 2 pistons of the same size would double the total surface area (to 100 cm3)which would then translates to more power.
But, pay attention to how it's done.

[berberkenan]

Surface finish of the bore is probably the most critical issue in a pneumatic cylinder. Internal surface of an aluminium pipe might not cut it... You might want to look at buying section of internally honed pipe from a hydraulic/pneumatic store.

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[G59]

DIY honing. 600 grit sandpaper 'wet', held by hand while the cylinder is slowly turning in the lathe, using an In and Out motion will suffice. You don't need a perfect crosshatch pattern on the cylinder walls for a low pressure air cylinder.
The micro grooves left in the bore from sanding will suffice in retaining a thin film of oil that will completely seal the cylinder wall to piston ring .
It doesn't have to be perfect, especially since he will most likely be using teflon seals instead of cast iron rings, unless he decides to make those too, in which case honing will be a must.
.

[handlewanker]

Hi, I'd have to admit.....the design posted by G59 is quite crafty.........but also quite complicated to make to ensure the integrity of the multiple cylinder and piston alignment......that adds up to lots of turning and milling.

The only reason you'd go to a multi compounded piston type design is if you were stuck for space around a single cylinder diam.....otherwise the axiom of KISS is a must be for pure simplicity and ease of manufacture.

The force exerted is a product of the piston's surface area, so 1-1/2 times the piston area calculated will ensure that the drawbar does get pushed down.......nothing worse than doing the calculations and having a device that doesn't quite make it to the finish line.......it might be a bit of overkill in that case, but you only want to make it once.

The drawbar only needs to move approx. 5mm + some clesrance to release the tool, so the cylinder for a singe push job can be machined in one piece with the top end cap as the bore will be big in diam but not long.

That means the body could be made from an aluminium billet, one piece with the top end closed and have the top end with long through bolts......they go through to a steel base mounting plate that is spigoted and bored for the cylinder and piston rod guide.....no seal required at the bottom end, just a longish guide bush......retraction is by draw bar return and a light spring to keep it clear of the end.

The force against the top end will have the same tonnage on it as applied to the drawbar, so adequate thickness and bolting is needed......perhaps a ring of 8 smaller through bolts around the top of the cylinder periphery and into the steel bottom mounting base would be better than 4 of the same.
Ian..

[RCaffin]

the design posted by G59 is quite crafty.........but also quite complicated to make to ensure the integrity of the multiple cylinder and piston alignment......that adds up to lots of turning and milling.
They probably make them with a CNC ...


Cheers
Roger

[G59]

They probably make them with a CNC ...

Now the real question is hand coded or CAM???

[RCaffin]

Chuckle.

[handlewanker]

Hi......I 'm quite sure Azalin would love to spend a few hours drawing up a complicated device in CAD and then proving a CAM program and editing it ...... that can be knocked up with a manual lathe/mill in half the time.....provided it was KISS and not something out of this World as a one off.
Ian.

[Tkamsker]

It depends on how good his toolchain is but Keen vistors here have Seen he draws in CAD and still does all Manual but Great work anyway


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[G59]

.I 'm quite sure Azalin would love to spend a few hours drawing up a complicated device in CAD and then proving a CAM program and editing it

It's far from being a complicated device. Actually its no more complicated than a single piston air cylinder except, times 4. Drilled threaded rod and four disks, one cylinder, a few nuts and bolts, top and bottom plate, seals and voila, instant multi power cylinder. Truely trivial.

As for CAD, todays CAD is so user friendly the user barely has to think anymore.
So why be so negative???
If he has the space then make it a single piston.

[handlewanker]

Hi.....My opinion was that to KISS, the less moving parts the better not only for the making but assembly, alignment and subsequent maintenance too.

Anyone can design something that is complicated, but as the saying goes, "if all things be equal, then the simplest is the BEST".....in all cases.

I decline to argue on that point as it's the main axiom that all successful engineering practice is based on......a point of view is just a suggestion for the masses to evaluate to their desire and ability.

In reality, IF... Azalin does not have CNC capability, then it's going to be a manual solution to a simple problem, in which case the simpler the better......he might want to send it out for a commercial manufacture, but with that exercise he might just as well buy one ready made off the shelf and get it today instead of weeks of blood sweat and tears....metaphorically speaking.

BTW, the multi piston design does have lots of merit and I'm filing it away for future consideration when all the design work has been done, so no need to re-invent the wheel.......I have an oscillating steam engine design that could benefit from this principle.
Ian.

[Azalin]

Hi,

I'll design the cylinder when I have the time, hopefully soon.

I have a design in my mind and it is something like:
- 3 pistons
- The tubes will be 80mm ID and about 6mm wall thickness. Material is 6061 or 7075 aluminum.
- The caps will be made of aluminum too. I'll cut them wiith my CNC.

Not very detailed yet but the design time will clear up all the question marks.

By the way I just have received the grease.

[assink]

You can use a honing device on the inner wall of your tube.
They arent expensive, at least here.. About 20 euro's.
Something like this:
http://g04.a.alicdn.com/kf/HTB1vasuK...ont-b-Hone.jpg

[Azalin]

Yes, I have a hone but it is for small engines. I'm using it to hone my heli engines.

[Azalin]

I just checked my hone if it has the ability to expand 80mm but no luck. It is usable at 19mm-63mm range. I'll but a bigger hone.

[Azalin]

Hi,

Long time, no progress because I'm upgrading my lathe with a variable speed DC motor. It's more powerfull and faster but I don't need speed. My main need is lower RPM for threading.

I'll build the cylinder when the upgrade is done.

[andypugh]

The floating setup was introduced as a solution to high speed spindles using relatively small bearings, that wouldn't be able to take anywhere near the 1500 lbs being applied, during the tool release

My drawbar uses a pinching action (because I read that you could damage the bearings). I achieved this with a custom-made air cylinder.
http://www.cnczone.com/forums/vertic...09301-cnc.html
But the image links are broken now that Picasa is dead. This is the sectional view: https://goo.gl/photos/QfhQMHeJG75fUi257

Later I considered the static axial rating of the taper-rollers on my spindle and realised that this was a _completely_ pointless precaution in my case.

Also, there is no way that the actuation of an air cylinder can be considered a hammer blow, the piston will move to take up the gap the moment that the pressure is enough ti overcome the seal friction.

[G59]

Exactly, especially if you add an air restrictor in the input of the cylinder.
But all that is behind us now as he has already made and decided to follow the general consensus of the enlightened in this forum.
I tried but hey,what do I know plus, how long can you hold your breath till you realize....it doesn't matter. He had it in his mind to do it that way and that's what he did. Good enough for me.

[Maglin]

Excellent work. I've wanted to build a BT30 ATC spindle for my mill for a while. I have a BP 2J2 head that is QC30 and a lot of BT30 tooling. Reading this whole post has got me wanting to tackle this again.

I learned how to use CATIA for CAD/CAM and these hobbiest CAD solutions are alien to me. IE not so easy to use but definitely easier to learn than CATIA. Anyways excellent work. If you are ok sharing I would love to just duplicate your spindle as it appears near exactly what I was thinking of making. And I learned long ago the simple makes repairs down the road a lot easier.


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