Team Build 8

[Path]

Chris,

If I may ... would give me the dimensions of the Piston and what O-ring are you using... maybe a 012?


Thanks

Pat H

 

[dreeves]

Question to mods can the name of this thread be changed to team build 8 without deleting the info in it?

Dave

Name changed -- Gail in NM

 

[chrispare]

Path the piston is .490 on the outer edges and
I believe I went to .435 on the oring grove ( I will have to double chech when I get home)
I'll check on the oring but I am pretty sure it is a #11 the 12 would be too big on the outer diameter I think anyway.
I will get a rough measurement on the oring when installed for you too.

 

[Path]

Thanks ... also the grove dimension for the O-ring (drawing has it as .067") which is too small for this O-ring.

Thanks,

Pat H

 

[dalem9]

That will be fine . I will bore as close to .500 as I can . The name change is a good Idea . If it can be done , Thanks Dale

 

[chrispare]

Ok the ring grove is .420 the piston is .490 and.070wide
With the ring installed it is about .530 when it makes contact. The ring is a #011
Finished piston will still be the same .187 so as to not have to worry about any Interference issues.

Chris

 

[chucketn]

I'm working on cutting material today.Can I use stainless for the connecting rod keeper plate? I havs quite a bit in 1/16 stock. At least I'm guessing it's stainless. It's not aluminum but it's also non magnetic.

Chuck

 

[Path]

Chuck,

Yes, SS would be great.


Pat H.

 

[Path]

Ok the ring grove is .420 the piston is .490 and.070wide
With the ring installed it is about .530 when it makes contact. The ring is a #011
Finished piston will still be the same .187 so as to not have to worry about any Interference issues.

Chris

Thanks for the measurements.

After reviewing the data I suggest that a design change is in order for the piston. Not a big change.

The sizing for the piston was based on a Cast Iron Ring or Delrin or Teflon.
Since we are using an O-ring (a good choice) the gland area needs to be changed so that O-ring will provide a good seal but not too tight.

Since the cylinder has a bore of .500" the correct O-ring size is the 012. It is designed for that bore, the .011 is for a 7/16" bore. If the 011 is used with the diameter .420" (inside diameter for the .011 is .301") it will be stretched over 25%. The manufactured suggested stretch is 0-5% with typical at 1-2%, the excessive stretch can overstress the material.
The next issue is the squeeze. For reciprocating applications 10-20% is generally acceptable. The squeeze using the current the piston / O-ring is over 43% ...very tight and unnecessary. Aiming for 15% would allow some variation the Bore and gland diameter.

Finally the gland width , typically in this application 15% is usually the norm. Due to the squeeze, heat expansion etc the O-ring will need that extra room.

So in summary:
Use a AS568-012 O-ring.
Inside groove diameter should be .375-.380" .
Grove width should be .081 to .085

The cylinder should be as close as possible to .500 and smooth (a little honing may be needed). All corner and holes should have a smooth radius to prevent damaged during insertion and using.

The Piston Rod Gland (item #23) and Valve Gland (item #21) needs to be reviewed to insure that it will not be too tight.

Pat H.

 

[chucketn]

I'm working on cutting material today.Can I use stainless for the connecting rod keeper plate? I havs quite a bit in 1/16 stock. At least I'm guessing it's stainless. It's not aluminum but it's also non magnetic.

Chuck

I found some more of this material (inhereted from my Dad, over 10 years ago) and found markings indicating it was 304 SS. Woohoo! It machines nice! Dad was a maintenance electrician in a factory that made electrical contacts for aircraft and military applications. That same factory produced the magnitos used on the Spirit of St. Lewis. He used to bring home all kinds of scrap and cutoffs from work. My brother works there today and I get brass bar ends from him.

 

[chrispare]

Pat, those changes will not be any problemm at at all

how are the resr of you doing? any progress?

Chris

 

[ninefinger]

I just picked up some material to get started on my parts, I'll be starting with the lathe made bits first (eccentric) as I'm tweaking my mill at the moment to get a bit more accuracy and reliability out of it...these are small parts and I have too much backlash at the moment for really small cutters....

Dave,

If no one has claimed the last "B" color base I'll request it.

Hopefully some progress this weekend.

Mike

 

[dreeves]

There is a problem with the Color B. I was moving it to cut it and it fell and broke. I got 1 good peice form it. I got a darker color to replace it with. I have 2 of the darker color. I cut the rest from the E color. Im Sorry to the guys that picked B i was so pissed at myself.

I cant open the spreadsheet on my laptop so to who ever is cutting the side plates are you drilling the mounting holes to print so I can finish the bases.

Dave

 

[maverick]

No worries Dave, I've been there myself. A dark color will contrast well with
the aluminum side plates, anything you find will be fine.
Chuck, that material sounds fine for the keeper. If it machines well, so much
the better. 304 is not noted for ease of machining. It's great you have a
source for bar ends and such, very handy.

Regards,
Maverick

 

[Path]

There is a problem with the Color B. I was moving it to cut it and it fell and broke. I got 1 good peice form it. I got a darker color to replace it with. I have 2 of the darker color. I cut the rest from the E color. Im Sorry to the guys that picked B i was so pissed at myself.

I cant open the spreadsheet on my laptop so to who ever is cutting the side plates are you drilling the mounting holes to print so I can finish the bases.

Dave

Dave,
I will be machining the side plates to the drawing.
Not a problem, the darker the better.

ninefinger,
I'm missing the width dimension for the top of Side Plate where the Beam Pivot Bearing Base (#38 page 19) is mounted. I scaled it up from the drawing then contacted don-tucker ... the width should be .890".

Thanks,

Pat H.

 

[ninefinger]

Pat,

I drew it up in CAD and came up with .875" - I guessed it would be some fraction like 7/8" - but I can change to 0.890" - I bought 1" wide brass to work with.

Dave,

No worries, whatever you supply will be fine. Thanks,

Mike

 

[Path]

Mike,

Thanks .... that's very interesting. How did you get the .875" using CAD?

I scaled the pdf up to 170% to get the overall width (6.25") on paper then measured the top. Of course there is a of lot room for error but I came with .887". Emailed don-tucker suggesting that it might be .875". He came back with .890".

Another important measurement that is missing .. the step that has the two mounting holes (.375" above the bottom on left) for the Bottom Cylinder Head (#12). I came up with .500". What do you have for that?

All the other dimensions that are not on the drawing ... I did the same scaling up since none of them are really critical.

Pat H.

 

[ninefinger]

Pat,

Sorry can't help with the cylinder head mounting - I only drew up the parts I'm making (so I could generate G-code for the mill). If you want I can try and have a look later.

I made an assumption to get 0.875" - which could be wrong! For example the center to hole center distance is 0.343", the edge to hole center is 0.094", so I assumed an even amount of material on the missing dimension to match the width. 2 x (0.343 + 0.094) = 0.874" and rounding for lost precision gets 0.875"

Likewise I have assumed the raised portion on the base matches the cap.

Mike

 

[dalem9]

Dave Any color base will be fine with me . Have all the cly ruff cut .Hope to get more work done sunday. Thanks Dale

 

[Path]

Mike,

Thanks for the info ... I thought that the CAD drawing provided measurements that drove the width to .875", but actually we both made a guess at it. I'm going to use the .890" as it will provide a little overhang and Don actually made the engine.
The step height for the cap is also okay as .500" since when I assembled the parts it came together okay.

Pat H.