Mike's P.M. Research No. 6 Steam Engine

[macardoso]

I'm working on the Cylinder now which I bored the 1.5" hole to 1.5005" (exactly what I was shooting for) and the fit to the piston is beautiful. I'm struggling with the Valve cylinder (machined into the same piece parallel to the main cylinder). It is .6250" and 3.4" long. At 7:1 extension ratio (1/2" bar) it is too long to bore so I settled on using a reamer. I've done some test pieces in 1018 mild steel and have gotten holes with cruddy surface finishes and diameters between .6255 and .6258 which is too loose and sloppy for the .6235" valve. With lots of oil it is moderately air tight but with a normal amount of oil for running it is leaky.

I've had hit and miss results with reaming and it is possibly due to the quality of the reamer. The two I have tried are some I inherited. Good name brands and moderately sharp.

I'm wondering if I will just have better luck with machining the casting? Maybe a new reamer? Maybe an undersize reamer (.6240")? Would love any tips for getting this right. I checked my tailstock a month or two ago and found it to be well centered (within .0003") and true to the spindle (within .0004" over 4" ).

My goal is a nice air tight sliding fit (maybe .0005"-.0010" clearance?)

EDIT: Worst case I can make a new valve to fit the finished bore, but the surface finish is really bad too, so at a minimum I need to improve that.

 

[bakrch]

1018 is incredibly difficult to get a finish on. Can't say I remember reaming this material (my guess is that engineers know to avoid this in the design phase), but turning/boring usually requires a bazillion RPM's and cermet tooling to get a passable finish. Are you able to test in a different material? I can probably send something to you, but I surely do not have cast iron. F22, F91, 416, 316, 17-4 PH, 440C are all available for me to send.

Personally, I would ream undersize and hone it to finish if possible. It is impossible to know how that reamer is going to cut in your particular setup unless you have a spare pc to work with to cut under the same conditions.

edit: on second thought, boring it with a solid carbide 1/2" bar may chatter a little bit, but honing that away would produce a straighter hole.

 

[ErichKeane]

FYI, I love this thread! It has encouraged me to get my own PM Research kit! I ordered the No 3 Steam Engine last night!

Assuming I can get it finished, my idea is to see if I can attach it to a tea-light powered steam boiler

 

[macardoso]

1018 is incredibly difficult to get a finish on. Can't say I remember reaming this material (my guess is that engineers know to avoid this in the design phase), but turning/boring usually requires a bazillion RPM's and cermet tooling to get a passable finish. Are you able to test in a different material? I can probably send something to you, but I surely do not have cast iron. F22, F91, 416, 316, 17-4 PH, 440C are all available for me to send.

Personally, I would ream undersize and hone it to finish if possible. It is impossible to know how that reamer is going to cut in your particular setup unless you have a spare pc to work with to cut under the same conditions.

edit: on second thought, boring it with a solid carbide 1/2" bar may chatter a little bit, but honing that away would produce a straighter hole.

OK well that makes me feel a lot better. I got really frustrated trying to get this right last night. Here are some pictures from my test part. Photographing surface finishes is hard but maybe these will help show my difficulty. It looks like a bad boring job rather than precision reaming.





Another difficulty is getting a 3% pre-ream drill for .625". I don't have anything close to a .608" drill so I was boring it (with a TON of chatter) to around there and then reaming. My closest drill is 9/16" (.563").

I'd definitely be game to try another material as a test piece. I don't know what the closest thing to cast iron would be. I'd be happy to pay for a small cut of whatever you think is good. (Let's skip the stainless, I hate stainless )

Found a new .6240" reamer on ebay for $28. I'd have to reduce the shank, but I think that would work for me. A carbide boring bar is an option, but I just don't see being able to get a great finish. How would you hone the bore? Ball Hone? Link Here

FYI, I love this thread! It has encouraged me to get my own PM Research kit! I ordered the No 3 Steam Engine last night!

Assuming I can get it finished, my idea is to see if I can attach it to a tea-light powered steam boiler

Congrats!

I'm having an absolute blast with this. Be warned, they are a lot of work. I've been counting my hours and I'm looking at around 50 hours setup and machining so far and I don't know if I'm halfway yet. That doesn't count cleaning the workshop, researching, or recording my progress here.

I'm also a bit of a perfectionist, so if I get a dimension out of tolerance and I have replacement material (so everything but the castings) I will start over. Probably not necessary to get a working engine but I want it to be perfect for my buddy.

 

[ErichKeane]

3/4" Cast Iron is about $1/inch on speedy metals: https://www.speedymetals.com/pc-4274-8388-34-rd-gray-cast-iron-class-40.aspx

I'm assuming on the size However, for about $20 shipped, you could get a dozen tries

 

[Lo-Fi]

Meehanite is lovely to work with, mess aside. No hard spots or inclusions and great machinability. I've made a load of bearing journals, gears and suchlike out of it.

 

[bakrch]

OK well that makes me feel a lot better. I got really frustrated trying to get this right last night. Here are some pictures from my test part. Photographing surface finishes is hard but maybe these will help show my difficulty. It looks like a bad boring job rather than precision reaming.

View attachment 317416

View attachment 317417

Another difficulty is getting a 3% pre-ream drill for .625". I don't have anything close to a .608" drill so I was boring it (with a TON of chatter) to around there and then reaming. My closest drill is 9/16" (.563").

I'd definitely be game to try another material as a test piece. I don't know what the closest thing to cast iron would be. I'd be happy to pay for a small cut of whatever you think is good. (Let's skip the stainless, I hate stainless )

Found a new .6240" reamer on ebay for $28. I'd have to reduce the shank, but I think that would work for me. A carbide boring bar is an option, but I just don't see being able to get a great finish. How would you hone the bore? Ball Hone? Link Here

I will look for some 416. Sure it's stainless, but it machines very easy believe it or not. It finishes pretty dull, but doesn't tear like 1018 would. The above cast iron solution is also a pretty good idea. Up to you, the offer still stands. (no charge for this, these are in the scrap bin anyway)

Yes, a drill hone is what I was thinking ... assuming you can deal with the bottom of the bore, like maybe putting a lead on the part that slides in to account for the unreachable areas (if it even matters).

 

[macardoso]

I will look for some 416. Sure it's stainless, but it machines very easy believe it or not. It finishes pretty dull, but doesn't tear like 1018 would. The above cast iron solution is also a pretty good idea. Up to you, the offer still stands. (no charge for this, these are in the scrap bin anyway)

Yes, a drill hone is what I was thinking ... assuming you can deal with the bottom of the bore, like maybe putting a lead on the part that slides in to account for the unreachable areas (if it even matters).

I'd really appreciate that if you wouldn't mind. Might also look into the Cast Iron.

This is actually a through bore. There are valve heads on each side, so the machining is surprisingly easy given what it is.

 

[bakrch]

I'd really appreciate that if you wouldn't mind. Might also look into the Cast Iron.

This is actually a through bore. There are valve heads on each side, so the machining is surprisingly easy given what it is.

Okay, no luck with 416 but I did snag a pc of 440C (1.5" dia @ close to 4" length). Still not going to be too bad to machine it.

 

[macardoso]

Okay, no luck with 416 but I did snag a pc of 440C (1.5" dia @ close to 4" length). Still not going to be too bad to machine it.

You are awesome, thanks.