Stuart Twin Victoria from scratch

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Crank at 180 degree will not selfstart when the steam engine has double acting cylinders. Better set crank at 90 degree to selfstart. :)
Uh Oh. Got a major problem. In upsizing for shrinkage of the metal, I must have gotten too much. Stuff isn't fitting according to it's plan size. I will upload photos later to show some of the issues, but this is going to cause a lot of "modifications" to many parts. In particular, the bases are too long and too wide. Everything is off by a small amount, but one thing leads to the next thing and so on. In particular the bellcrank mount for the steam chest/eccentric isn't wide enough if made by the plans. By slotting it works, but need to sleep on this one for a bit. Not pleased, but I guess the challenge is to make it work out. Make it look like it is right, only a true expert would know, they would have had to build one to notice the issues. Kind of upset at this point, don't like effing up. Don't handle failure well, so got to make it work out. At this point, self starting is a minor issue.

But, this is the hobby, and my lack of experience. Learning has been done on this one, that is for sure. Got to looking at my costs for materials so far and we are beyond the price for a kit, heck just in bronze I have $300 invested. Here's to hoping shiney and fancy looking distracts from the errs.
Well lets try to put this in perspective. The rails for the cross slides are too short by about 3/8 of inch. Those all had to be remade and remounted in the rear only (toward flywheel). Along with this, the cross slide rails are way too far apart even if mounted too much toward the center, which looks odd. At this point just a pair of teflon spacers that just so happened to be the right thickness (1/8) for now, can make some bushes later. Specific issues with the red pentagons(?).

Then the mounts for the cylinders, the brackets, will fit, but not sure exactly how to place yet, as the con rod needs lengthened I think, but not assembled enough to tell for sure. Need to get the top and bottoms on the cylinders as two holes on each end fit those brackets, so they need to be on the correct plane.




Wow, thanks for posting step by step, and thanks for being upfront about failures/mistakes, its really helpful.
My ego taking a huge hit on this one. I will finish it. The goal now is just to see if it will work, much less the appearance issues due to open threaded holes.

Working on it today, the connecting rod needed 3/4 extra length to get the full stroke. So involved with figuring, testing, trying, redoing, haven't taken a singe update photo.

I should move this to boo boos and blunders. LOL. :fan:

Thank the Lord I didn't go blindly drilling holes according to the plans, I would really be :wall::hDe: ans saying vast numbers of unprintable words. Here I really thought I was planning correctly by increasing the 5% in the PLA side of things. Possibly 1% would have been fine. These parts are so small the shrinkage is negligible, but add 5% and you got a mess.

I am frustrated, but enjoying the challenge now of trying to make it look as good as possible and work properly. If the lengths and throws are correct in the end, it should work, and work just fine. I mean, a cylinder is a cylinder and turning things turn, so long as nothing is out of time or hits, should work. Let us all learn.
I will be darned if it didn't run right out of the chute on air....Just one side. Was so concerned, just blasted thru all of what was necessary. Will document for you folks as I do the other half. There were so many little issues. One, not related to my casting was the valve slide tho made to specs did not fit correctly and had to modify that, but as you can see, it does run.

It actually runs pretty slow too, this was the immediate startup as you get a few seconds before the compressor comes on, but I got it down to where the valve was just cracked a smidge and the air compressor was able to keep ahead of it at that speed. Timing was just eyeballed for first shot. Heck even the set screws aren't tightened down and locktited yet.

What a relief.

Well after all that excitement yesterday, we shall pick up where things went to :fan:.

We were somewhere around, you got to have the cranks 90 degrees off to be a self starter. Well, making that hole go all the way thru without screwing up the threads in the crank was the challenge. Therefore, only enough of the shaft was drilled enough to act as a detent, the end of the bolt was made pointed and as it mounted it slid

Moving on to the crossslide rails. This was the first part that needed to be modified due to the sizing issue. Initially they were too short and the crossslide itself would hit the stanchions. These were lengthened by about 3/8 inch and mounted further rearward than plans show, but with the 0.983 throw of the con rod it was perplexing. Of course at this point, the piston rod itself was too short, so nothing seemed correct.

The plastic bushes were removed from the first side and bushes were made for both out of 3/8 brass. These lathed up quickly. The rails were then set in place and checked for both BDC and TDC alignment. Just one hole was drilled and threaded at a time to maintain the alignment, using a transfer punch.

And, that is as far as I got yesterday. But running it was the highlight, and still makes me smile thinking on it.




Today's update will be short as about 10 photos are somewhere between phone and my email. But I did get these of the setup that transfers the Eccentric to the steam chest. This part isn't long enough and I don't want to cast another chunk of bronze to remake them. Because of the design, the shaft can be moved toward the eccentric and still have bearing surface and align with the steam chest.

The balance of the day was working on the studs for the cylinder and mounting stuff to that, once I get the photos will update.

Interestingly I learned a new trick, you can use a broken tap to make a bottoming tap by just grinding flat carefully.



Ah the rest of the photos showed up. As mentioned earlier the piston rod needed to be lengthened. Along with that, at the cross slide end, it was threaded a bit more and a lock nut put on as in messing with the other it was determined that the piston could rotate itself and thusly the shaft would turn. But this first photo shows the added length, the added threading, the locknut, the piston itself, and the O-Ring. Follow that with the piston and shaft installed and again a view of the completed eccentric bellcrank setup.



That step was followed with just a basic put the cylinder on and get the basic idea where BDC and TDC were best located. Since the mount holes have been upsized to 3 mm those were the first pair drilled and tapped. To get them square to the steam chest, two parallels were used, one flush against the valve face, and the other of the proper thickness to align the already drilled holes from the cylinder head. Marked with a transfer punch and first one drilled and tapped, then the other. This allowed the head to be held firmly in place to mark the rest of the holes. Of note, the the piston was in place for the initial marking and drilling to help center in the bore more accurately. The same was done with the gland packing, along with the O-Ring for the rod, drilled and tapped 2 mm as well as the exhaust port after making the gasket. Finally the rear mount is attached and trial fit. The drilling process will be duplicated on the head/top part.




Locating the mounts to the base and aligning and checking for proper height. Seems all 4 of these mounts are wrong, looks like they will need to be remade so they look proper, they are off to one side on both. But for now, I want to just get it all going and then refit what is necessary. Not even drilling the base holes for head end on this second cylinder for now, no motion during movement so should be okay for testing purposes.20180510_104247.jpg

Moving on to the steam chest now, and this is one place a modification was made to the plans as casting in the bump for the end of the shaft sucked. So, a bushing was made to fit that end of the steam chest. First the 1/8 hole, then 1/4 for the gland. Drill and tap the opposite side for the end and of course the gland fastening. Not hard to do, just time consuming and needs to be accurate.




Wasn't sure if the cranks should be 180 apart or the same. Photos I have seen have them most of the time haphazardly, so the idea of balance seemed appropriate in this case so 180 it is. Then assembled all that on the crankshaft, lined things up and lightly tightened them down so as to not score the crankshaft too badly at this point. Not sure if I can upload video here or need to upload somewhere else and link it so will do a different post for that. But, with all the weight and piston rods and eccentrics dragging it still turns smoothly without a lot of effort, and it isn't lubed yet.

Nope, 180 is "wrong".

When you have them at 180, both cylinders will be on "dead center" at the same time. in that case, the engine can't always self-start.

You want them set at 90 degrees to each other. That way one is at mid-stroke when the other is at dead center. Applying steam/air and the engine will start running without needed the flywheel to be pushed over by hand.

There's nothing to say you *CAN'T* have it at 180, if that's what you want aesthetically, but they really should be at 90.
Nope, 180 is "wrong".

When you have them at 180, both cylinders will be on "dead center" at the same time. in that case, the engine can't always self-start.

You want them set at 90 degrees to each other. That way one is at mid-stroke when the other is at dead center. Applying steam/air and the engine will start running without needed the flywheel to be pushed over by hand.

There's nothing to say you *CAN'T* have it at 180, if that's what you want aesthetically, but they really should be at 90.
That has been modified and shown in one of the more recent posts.
Well this is the ending. The steam chest was drilled for the mount studs to the cylinder using the top plate to mark and drill slightly oversized holes thru the entire chest. Then as an assembly transfer punched into one spot on the cylinder, that drilled and tapped (2.5 mm). Tightened that down so the rest of the holes could be located with the transfer punch. Balance of holes drilled and threaded. Assembly left open to set the timing.

But, the device that creates/holds the bellcrank was so far off I had to make a completely new one. (I will be re-making another for the other side as well for appearances). Timing was set, the top put on and the fitting for the intake installed with gasket. Swapped the air attachment from the cylinder we have seen work and tried out the other side, which probably is better than the first side, it seemed to be able to run slower.

I don't have a boiler big enough to run this even for 1 minute after seeing how much air it needs to run. Wouldn't mind hearing from others the size of theirs, currently I have a PMR #2.

At this point I call my project a successful task. It is intended to remake the cylinder mounts, slightly differently so they look more appropriate. Of course some piping, oiler and so on but those are something every steam engine should have.