Piston Rings, Socket Head Cap Screws, Set Screws

[HughT]

During the development of my steam engine plans many questions arise and I hope you don't mind if I bundle a few questions here?

Question 1:
Piston Rings - many plans refer to 'off the shelf' components for piston rings, but I don't seem to be able to find any information on suppliers and more importantly 'standard sizes' that would be suitable for steam engines.

Question 2:
Socket Head Cap Screws - most of my plans feature these fastenings for the majority of fixings - under what circumstances would you use washers under the head of a socket head screw and what are the potential problems with fastening dissimilar materials?

Question 3:
Set Screws - when using set screws for fastening to shafts do you allow a small indentation in the shaft to facilitate the fixing or do you just tighten down onto the face?

I do apologize if the answers are rather obvious but I am keen to ensure that when my plans are complete that I account for all eventualities in the potential end build.

Regards
Hugh

 

[Philjoe5]

Hugh,

I'll throw out some answers to your questions but I have far less experience than many on the forum so keep that in mind.

Ques 1: I personally don't use piston rings BUT I run my engines on compressed air. Three or four oil grooves in the piston work fine and one of my early engines had over 100 hours on it with no signs of failure. That's with a bronze piston in 6061 aluminum cylinder block.

Ques 2: For strictly appearance sake I don't use washers under any of the cap screws that fasten stuff to the engine. I do use them to fasten the engine assembly to the base plate. Since they are underneath, they aren't visible.

Ques 3: If you put a small indentation in a shaft where the set screw hits it, you'll avoid making a burr on the shaft that can be troublesome during any disassembly. Sometimes I don't do this and I get a slight burr that has to be removed to avoid scratching a soft brass bushing.

Hope this is of some help,

Cheers,
Phil

 

[Bluechip]

Hi Hugh

(1) As you are UK based there is a maker of piston rings, they advertise in 'Stationary Engine Magazine'. I don't know of the sizes they do or prices/delivery times. I onlly know of the ad. Will get the info for you if reqd.

(2) During my working life I've very seldom seen washers under cap screw heads. Occasionally split shakeproof, cannot recall flat washers used. But maybe others have.

(3) Set screws (pointed) have a tendency to move if you use them to fix flywheels etc. to shafts. Use a cup point screw, as per this:

http://shop1.actinicexpress.co.uk/s...t&ActinicSID=4411fccc9d2114dfda868772ab36ed16

If you need to refine angular position they won't migrate back to the indent you first made. When satisfied, I would flat the shaft.

Dave

 

[mklotz]

Typical practice is to mill (or file) a small flat on the shaft where the setscrew will bear. When the setscrew is tightened it may raise a burr on the shaft. The flat ensures that such a burr won't interfere with later removal of whatever part is secured with the setscrew.

Like Phil, I think washers look tacky on a model engine. In most cases they aren't needed since the hole through which the bolt passes is accurately sized (clearance hole size) to the bolt. If in doubt, leave them out.

 

[Jasonb]

Hugh

1. For piston rings you have a couple of choices, either split cast iron or "O" rings, these tend to come in standard imperial graduations, take a look at Reeves for both, Stuarts for just CI. You can also use graphite yarn and PTFE.

https://vault1.secured-url.com/reeves2000/shop_subcategory.asp?cat_id=15

http://www.stuartmodels.com/accessories.cfm/mainaccess_type/14/the_type/Piston Rings up to 2 inches.

2. I don't use washers under bolt heads or cap screws but do use them under nuts. Bare in mind that if you are making a steam engine to look like an old cast iron one then cap screws would not have been used. If its just a barstock engine then it does not matter.

EDIT just been looking at the engines on your blog. I would say that cap screws will look totally wrong, these engines would have had studs for 90% of the fixings with flat washers and nuts. The nuts would also have been somewhat taller than the standard metric ones sold now and would only have been chamfered on the top, hence the need for washers under them to stop the hex corners damaging the surface. You can still get this type of nut from the likes of EKP

http://www.btinternet.com/~ekp.supplies/

3. A small flat or indent in the shaft is teh best way, as has been said if you tighten straight onto the shaft it makes a burr that will damage any bearing surface as you withdraw the shaft.

Jason

 

[HughT]

Thank you all for your very prompt and detailed responses.

The solutions for the piston rings and set screws are well described.

The Cap Screws! During my research of model steam engines I have come across a few examples of washers used under the head of the Cap Screw, whilst I am conscious that this would not be 'normal practice' I reasoned that this may be something to do with using dissimilar materials or the use of lock washers. However I generally agree that washers are not required and was curious about any exceptions that experts, like yourselves, may know about.

 

[HughT]

2. I don't use washers under bolt heads or cap screws but do use them under nuts. Bare in mind that if you are making a steam engine to look like an old cast iron one then cap screws would not have been used. If its just a barstock engine then it does not matter.

EDIT just been looking at the engines on your blog. I would say that cap screws will look totally wrong, these engines would have had studs for 90% of the fixings with flat washers and nuts. The nuts would also have been somewhat taller than the standard metric ones sold now and would only have been chamfered on the top, hence the need for washers under them to stop the hex corners damaging the surface. You can still get this type of nut from the likes of EKP

http://www.btinternet.com/~ekp.supplies/



Jason

Hi Jason,

Just noticed your edit.

Interesting point about the caps crews - okay if I am creating these drawings, which I hope to make available at later date, should I be targeting the 'authentic' finish in the design or the 'new look' with cap screws?

I should explain that the model drawings I am doing are based on currently available designs - I am essentially converting them to mm dimensions (although the drawings will be dual dimensioned) and hoping to try to standardise on components across the range. I am also incorporating 'operational studies' which explore the various aspects of motion and parameters of the mechanism linkages.

 

[Metal Butcher]

Hugh,

I'll throw out some answers to your questions but I have far less experience than many on the forum so keep that in mind.

Ques 1: I personally don't use piston rings BUT I run my engines on compressed air. Three or four oil grooves in the piston work fine and one of my early engines had over 100 hours on it with no signs of failure. That's with a bronze piston in 6061 aluminum cylinder block.

Ques 2: For strictly appearance sake I don't use washers under any of the cap screws that fasten stuff to the engine. I do use them to fasten the engine assembly to the base plate. Since they are underneath, they aren't visible.

Ques 3: If you put a small indentation in a shaft where the set screw hits it, you'll avoid making a burr on the shaft that can be troublesome during any disassembly. Sometimes I don't do this and I get a slight burr that has to be removed to avoid scratching a soft brass bushing.

Hope this is of some help,

Cheers,
Phil

I concur on #1 and #2

On # 3, I use a flat on the shaft at the mounting point of crank disc's and eccentrics that are not normally adjusted, or when called for in plans to assure proper timing. Others pieces that do not require precise locating such as collars. flywheels, ect I will use a brass pellet dropped in the tapped hole before installing the set screw, or a short brass rod if there is room.
Once a shaft is marred by a set screw removing the part becomes problematic.

MB

 

[tel]

Hi Jason,

Just noticed your edit.

Interesting point about the caps crews - okay if I am creating these drawings, which I hope to make available at later date, should I be targeting the 'authentic' finish in the design or the 'new look' with cap screws?

Most definitely lose the socket cap screws and go with studs and hex bolts. Not even modern engines make much use of socket cap screws. Why? 'cos the sockets clog up with crap.

Like your designs tho'.

 

[David Morrow]

I like the socket head cap screws and for a slightly more refined (imho) look in certain instances, I like button head cap screws. With a BHCS you shouldn't need a washer due to the wider head.

 

[Philjoe5]

MB,
Tha brass pellet/rod idea sounds great. Then, no worries about making the flat in a place where it's hard to adjust the timing.

Do you think it's workable on a 3-4 pound flywheel rotating at 400-500 rpm?

Cheers,
Phil

 

[mklotz]

Tha brass pellet/rod idea sounds great. Then, no worries about making the flat in a place where it's hard to adjust the timing.

Or...yet another reason to have a bag of bird shot in the shop. Get it from your local gun shop/reloader supply. Great stuff for making dead blow hammers as well.

 

[tel]

I like the socket head cap screws and for a slightly more refined (imho) look in certain instances, I like button head cap screws. With a BHCS you shouldn't need a washer due to the wider head.

I too, like socket cap screws, and use 'em when appropriate, but they look out of place on a period engine.

 

[Metal Butcher]

MB,
Tha brass pellet/rod idea sounds great. Then, no worries about making the flat in a place where it's hard to adjust the timing.

Do you think it's workable on a 3-4 pound flywheel rotating at 400-500 rpm?

Cheers,
Phil

On something that heavy I would be very leery. Most of my stuff has small 1-1/2" to 2-3/4" flywheels that are very light. My heaviest to date is a 2" brass with a little Swiss cheesing, that one is set screwed to a flat.

I'm really leery of set screw at an angle and have seen this on a few plans. ???

-MB

 

[Jasonb]

As Tel says it depends on the look of the engine, for a period style engine like the vertical twin you should have period fixings. If its a bar stock engine or a IC one then the cap screws would look more in place.

Not knocking any of the designs or builds on here but I much prefer a steam or hit & miss engine to look like old cast iron. For example I built a zero-six engine which looks like this but is mechanically the same as the original, just did not like the bar stock look.

Jason

 

[kuhncw]

Hello Jason,

You've built a very nice looking engine. Where did you get the flywheel castings and what diameter are the flywheels.

Regards,

Chuck

 

[Jasonb]

Hi Chuck

They are from Stuarts, the standard 7"x 3/4" ones that they use on several engines. I think you could get away with 6" ones maybe from the 1 1/2" Alchin traction engine. They were the only castings used all the rest was fabricated as you can see if you scroll back through the photos in that album.

http://www.stuartmodels.com/accessories.cfm/mainaccess_type/5/the_type/Flywheels

Jason

 

[kuhncw]

Thanks for the information Jason. Yes, I noticed the fabricated parts. Interesting to see all the parts laid out on the bench. Nice job.

Regards,

Chuck