[ngr1]

Hello, I am building an air cylinder and planning to use drill rod for the ram shaft. I will need to thread both ends so I would like to know which type of drill rod is most easily machined?

Are there alternate materials I should consider?

Thanks… Norman

[Mcgyver]

Drill rod is just tool steel, meaning it has enough carbon content that it can be hardened via heat treating. While there are lots of kinds of tool steel, typically drill rod is going to either water or oil hardening, usually oil hardening. The difference is in the speed of the quench. Neither , as far as I know are any easier to machine than the other. When you buy drill rod it is annealed and can be machined however is less machineable (sp?) than free cutting steel, maybe by 50%. To make threading easier, undercut or use a larger tap drill.

I would consider something other than drill rod. Soft precision shafting is a good choice. It will be rounder and to better tolerances than the drill rod with a better surface finish – all important characteristics of a cylinder. The advantage of drill is that it can be hardened, but you are not planning on doing that, correct?

[ngr1]

Thanks Mcgyver!

No, I do not need for it to be hardened but it does need to resist rust due to the mositure introduced by the air pressure.

I am currently using stainless steel tubing and inserting (half way) long set screws to each end of the tube to provide the threads I need.

How expensive and accessible is soft precision shafting in comparison to drill rod? How about using solid stainless steel rods?

Norman

[ViperTX]

I am guessing that this is just the ram and won't have any o-rings riding on it's surface?

12L14, very easy to machine
Any cold rolled steel rod (1018, etc.) is the cheapest.
Stainless steel rod...more expensive and harder to machine.

[ngr1]

Yes ViperTX, the rod will pass through an o-ring.

The cold rolled steel will rust, right?

Norman

[ngr1]

Online Metals (http://www.onlinemetals.com/app_groups.cfm?step=2&id=2) states the following materials can be used for "free-machining".

CARBON ROUND ROD 12L14
STAINLESS STEEL HEX ROD T-303
STAINLESS STEEL ROUND BAR T-303

Will a regular die work on the T-303? Will 12L14 resist rust?

Thanks... Norman

[ViperTX]

Any steel will require some plating except for the stainless. Looks like that stainless is anealed...so, you should be able to thread it / machine it.

[One of Many]

Online Metals (http://www.onlinemetals.com/app_groups.cfm?step=2&id=2) states the following materials can be used for "free-machining".

CARBON ROUND ROD 12L14
STAINLESS STEEL HEX ROD T-303
STAINLESS STEEL ROUND BAR T-303

Will a regular die work on the T-303? Will 12L14 resist rust?

Thanks... Norman

Norman,

The 12L14 might be free machining, but it is one of the softest steels out there and it will rust quickly. It would not be advisable to attempt running a threading die on anything over 1/4" rod and even that is questionable for thread alignment or anything that connects to it.

Hex rod is great for non-rotating shaft, but very hard to get a seal on. I don't think many cylinders that use hex shaft even offer a seal beyond a brass bushing. Drill rod has little more to offer and heat treating it will surely take the staight out of it.

There is rod made for hydraulic cylinder shafting/yoke that I think is stressproof 1144 and it comes pre-chrome plated. It will require machining to fit the application as would most any material. The chromed shaft won't rust, but exposed portions of the steel will.

I would look around for a used hydraulic cylinder of the size you really need. No reason it cannot be run on air. If anything else, get one extra long, it will already be threaded on the end and all that might be requires would be for you to fit the shaft to your purpose on the other ends piston connection.

You do not mention the size of rod or how much pressure will be applied. Why would it need be custom made when there are lots of cheap cylinders out there. Some may already have the stainless shaft too!

Just trying to save you some time and frustration....


DC

[ngr1]

Thanks for the advice DC.

I would like to find the right material and process to machine what I need in case I need to produce larger quantities.

The cylinder will be a miniature one by industrial standards and will be used for a model airplane with 100lbs of air pressure. 1” stroke with a 2” cylinder.

My tolerances are not exacting and I have a die holder for my tailstock which works very well.

I have ordered some Stainless Round 303 Annealed from Online Metals so I can give it a try.

Thanks Everyone!

[One of Many]

Hello Norman,

Do you mean 2" bore? If so, at 100psi that will produce 314 pounds of push force and a bit less with pull force due to the rod. With 3.14 sq inches and a 1" stroke it will consume roughly 6 cu inches of air for each full cycle, based on zero leakage. A bit more calculations could be required to see where your tank would fall below a useful PSI. If this is for landing gear, I wouldn't think it to be a problem. That just sounds like a lot of force for landing gear.

I'd sure like to hear more about the plane and your application. Sounds like a neat project.

DC

[nicksam]

At Metals supplies Generally in 3.000 to 3.200 Metre lengths although in certain sizes longer lengths are available. Commonly in Grades T/303, T/304, T/316, T/321, T/410, T/420 & Grade T/431. Visit: Stainless Steel | Stainless Steel Round Bar