[Azalin]

[Azalin]

Hi again,

I'm building a multi power air cylinder. Is it OK to use delrin (8mm thick) as separator?

[ianagos]

Hi again,

I'm building a multi power air cylinder. Is it OK to use delrin (8mm thick) as separator?

Depends on the size and force of the piston. I recommend you just use alluminum. Delerin is pretty soft and I believe it absorbs moisture as well.

[Azalin]

Thanks. I'd like ask about the sealing as well. Is it better using rubber o-ring or silicone o-ring?

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[mactec54]

Thanks. I'd like ask about the sealing as well. Is it better using rubber o-ring or silicone o-ring?

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Regular neoprene, is the norm for air cylinder orings, Viton would be the next choose

[ianagos]

Thanks. I'd like ask about the sealing as well. Is it better using rubber o-ring or silicone o-ring?

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Most of what I’ve seen is normal oring material. The guy above said Víton that sound right.

[RCaffin]

Neoprene would be fine. You only go to the more expensive Viton if you are looking at high temperatures. You are not.

Cheers
Roger

[Azalin]

Thank you all.

Another question is about how it should return. Spring return or the one like Tormach power drawbar cylinder.

I don't like the idea of spring return but want to ask your opinion. Which design do you prefer?

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[ianagos]

Thank you all.

Another question is about how it should return. Spring return or the one like Tormach power drawbar cylinder.

I don't like the idea of spring return but want to ask your opinion. Which design do you prefer?

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My fadal has a spring return for the actual piston. Obviously the drawbar is spring return due to the Belleville’s.

[mactec54]

Thank you all.

Another question is about how it should return. Spring return or the one like Tormach power drawbar cylinder.

I don't like the idea of spring return but want to ask your opinion. Which design do you prefer?

Sent from my MI 5s Plus using Tapatalk

You can use a spring, this is very common, if you only want a one way air control valve, it's just as simple to do it though with your air control valve, that will give you up / down control of your cylinder, if you have a multiple stage cylinder you only need the return to act on one stage of the cylinder

[RCaffin]

Spring return with a stack of Bellevilles is 'standard'. Trying to get a power return at 20,000 RPM requires significant engineering, for very little return.
Designing the Belleville stack does require a little text-book work, but there are plenty of tables for that.

Cheers
Roger

[RCaffin]

Spring return with a stack of Bellevilles is 'standard'. Trying to get a power return at 20,000 RPM requires significant engineering, for very little return.
Designing the Belleville stack does require a little text-book work, but there are plenty of tables for that.

Cheers
Roger

[Azalin]

Thanks.

I have a quick question. How tight should the Pistons be?

Say ID of the cylinder is 80mm and I will be using 4mm o-ring. With the o-ring installed the OD of the piston (I guess) will be 80.1mm. is that too much?

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[RCaffin]

It would be fine to have 0.1 mm clearance on the PISTON. What matters a bit more is the compression on the O-ring. It should be about 10% of the O-ring diameter. Note that this assumes both the bore and the groove are SMOOTH.
You can check this by looking up the Instructions and FAQs from the really good O-ring makers.

Cheers
Roger

[Bvbang]

I found some info. here:AS568B Standard O-Ring Groove Design | Seal & Design, Inc.

[mactec54]

Thanks.

I have a quick question. How tight should the Pistons be?

Say ID of the cylinder is 80mm and I will be using 4mm o-ring. With the o-ring installed the OD of the piston (I guess) will be 80.1mm. is that too much?

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For Oring compression you most likely need 3 x that number, your piston should be smaller than the Bore, and should never be able to touch the Bore, so your shaft Bushing needs to only have enough clearance so the rod slides freely

[Azalin]

Thanks.

Here are the parts so far.

The last pic is of the internal turning tool for the small o-rings. I installed a 4mm round insert.

[RCaffin]

Ah - I may have missed something here!
Are you trying to fit a piston of 80.1 mm OD into a bore of 80.0 mm? That really will NOT work! But you will find that out quickly.

The piston can be up to 0.2 mm SMALLER than the bore because it will be riding entirely on the O-ring. You do not want too much clearance though as that can lead to damage to the O-ring if it tries to extrude into the gap.

For a 4 mm O-ring the compression should be about 0.5 mm all around. Without that compression the O-ring will leak. Some silicone grease is advised.

I see you have made the groove round at the bottom. That is OK, but the groove should be maybe 5 (five) mm wide for a 4 mm O-ring, not a snug 4 mm. You MUST allow room for the O-ring to be squeezed.

Cheers
Roger

[handlewanker]

I have to wonder what prevents an O ring from rolling or twisting in the groove when under reciprocating forces......the good old fashioned leather cup in a bicycle pump never had that problem............tongue in cheek etc.
Ian.

[RCaffin]

The friction between the O-ring and the sidewall and bottom of the groove are greater than the friction between the O-ring and the bore.
And yes, greased leather washers worked quite well - over a limited range of sizes.

Cheers
Roger