Kozo A3 in 1.5" scale - new project
Moderator: Harold_V
Re: Kozo A3 in 1.5" scale - new project
So a month ago I took the loco to the club for the annual hydro (its second). Fail! Cylinders full of water and no pressure. Pulled the steam dome cover and the throttle valve was closed, so I had to assume that the valve's mounting plate had gotten loose. Sure enough, two of the 4 screws that hold it to the boiler were loose, as if the threads were stripped. Took the loco back home where it's sat for a while. I couldn't think of a better or easier way to mount the valve, so today was time to fix it.
Originally I'd tapped the 4 mounting holes 8-32, mainly because that was the only size of SS screws I had. I figured that the steam pressure would press the mount down anyway. Here's the view inside the dome:
The large hole is the pipe to the clyinders, and the two rear holes are open to the boiler. The mounting plate sits on the bottom in this orientation, held by 4 screws. The large hole is where the globe valve screws in.
The underside of the plate has a channel connecting the valve to the steam pipe.
Looking at the gasket reveals the problem.
To make the plate more secure, I decided to drill out the tapped holes and re-tap to 10-32. Problem is that the dome is 3" deep, and my drills and taps are less than that. Checked out McMaster for a 6" #21 drill bit and 10-32 tap:
To ensure drilling and tapping straight, I used some scrap aluminum bar with two tight fitting holes for the drill and tap. Marked the drill with some tape to get the holes 3/4" deep.
Off to the hardware store to find some SS screws then a new gasket, and we'll see if it will pass.
Originally I'd tapped the 4 mounting holes 8-32, mainly because that was the only size of SS screws I had. I figured that the steam pressure would press the mount down anyway. Here's the view inside the dome:
The large hole is the pipe to the clyinders, and the two rear holes are open to the boiler. The mounting plate sits on the bottom in this orientation, held by 4 screws. The large hole is where the globe valve screws in.
The underside of the plate has a channel connecting the valve to the steam pipe.
Looking at the gasket reveals the problem.
To make the plate more secure, I decided to drill out the tapped holes and re-tap to 10-32. Problem is that the dome is 3" deep, and my drills and taps are less than that. Checked out McMaster for a 6" #21 drill bit and 10-32 tap:
To ensure drilling and tapping straight, I used some scrap aluminum bar with two tight fitting holes for the drill and tap. Marked the drill with some tape to get the holes 3/4" deep.
Off to the hardware store to find some SS screws then a new gasket, and we'll see if it will pass.
Re: Kozo A3 in 1.5" scale - new project
Be sure to put some anti-seize compound on the ss screw threads.
Dan Watson
Chattanooga, TN
Chattanooga, TN
Re: Kozo A3 in 1.5" scale - new project
I'm assuming you're working in cast iron. Coarse threads are generally a better choice. I most likely would have chosen a 10-24 in lieu of the 10-32.
Harold
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Re: Kozo A3 in 1.5" scale - new project
It's all steel, but I thought about that after I'd already finished.
Re: Kozo A3 in 1.5" scale - new project
Most likely a non-issue in steel. Cast iron has little tensile strength.
Well done!
Harold
Well done!
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Re: Kozo A3 in 1.5" scale - new project
All buttoned up and ready for retest on Wednesday, weather permitting.
Re: Kozo A3 in 1.5" scale - new project
The redo in May failed.
After the last post in May I took a break from the A3. But now that it's cooler and steaming is more comfortable, I decided to try to fix the throttle leakage. The plan is to cover the channel in the bottom of the throttle baseplate so that there is more "meat" in the paper gasket.
The cover is a plate made from some 304 SS sheet that I machined down to .065" thickness, Drilled the mounting holes on the Bridgeport and then the profile on the CNC mill. To keep the throttle rod at the same height I took .06" off of the bottom of the throttle.
I then fastened the cover and baseplate together with red high temp RTV (good to 600F). Then made a new paper gasket and reinstalled everything in the steam dome,
Hope to retry the hydro test on Wednesday; if I succeed may fire it up too.
After the last post in May I took a break from the A3. But now that it's cooler and steaming is more comfortable, I decided to try to fix the throttle leakage. The plan is to cover the channel in the bottom of the throttle baseplate so that there is more "meat" in the paper gasket.
The cover is a plate made from some 304 SS sheet that I machined down to .065" thickness, Drilled the mounting holes on the Bridgeport and then the profile on the CNC mill. To keep the throttle rod at the same height I took .06" off of the bottom of the throttle.
I then fastened the cover and baseplate together with red high temp RTV (good to 600F). Then made a new paper gasket and reinstalled everything in the steam dome,
Hope to retry the hydro test on Wednesday; if I succeed may fire it up too.
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Re: Kozo A3 in 1.5" scale - new project
Please be sure to let us know in what manner it failed. As my Dad used to say " I curse the innate ornerynous of inantimate objects!" Thanks!
Re: Kozo A3 in 1.5" scale - new project
Just came across this build. With myself considering "simple" engines as a possible beginner project, this looks pretty good. I see you take it to CSPPRY too, I was up there last week helping Bill cut/paint some wood for the new train shed.
Re: Kozo A3 in 1.5" scale - new project
After many attempts to seal the throttle plate with various types of gasketing, I've decided to cut off the steam dome. A plate with a channel between the dry pipe and the valve mount will be remade and welded to the top of the boiler, and a removeable steam dome will be fabricated.
I removed the boiler from the chassis yesterday in preparation, as well as all the piping. A friend tells me his plasma cutter can sever the dome (wall thickness .6"), and then i'll mill the remaining stub flat to the top plate.
I modeled the new dome in SW (dimensions still to be finalized):
I removed the boiler from the chassis yesterday in preparation, as well as all the piping. A friend tells me his plasma cutter can sever the dome (wall thickness .6"), and then i'll mill the remaining stub flat to the top plate.
I modeled the new dome in SW (dimensions still to be finalized):
Re: Kozo A3 in 1.5" scale - new project
First stage of rebuild is to get rid of the old dome, which is welded to the boiler. Buddy with plasma torch made quick work:
Got it home and applied face mill to clean up the cut.
The dry pipe is threaded 1/4 NPT, so I tried this setup. I think it should work.
John from the club has some steel pipe that's 3.5" OD and 3/8" wall. I redid the SW model to use a flange inside the dome for attaching to the boiler, and it appears everything will fit:
Bottom disc is welded to the boiler plate and then drilled and tapped. An almost identical piece is welded to the bottom of the main pipe, and drilled clearance to match. The flange for the throttle pipe is welded to the main pile, and then the holes are drilled. The lid is drilled for clearance holes to match the tapped holes in the upper edge of the dome, and the lid has NPT tapped holes for the safeties and for filling the boiler.
The new dome will be slightly taller than the old, as well as wider (old OD was 3.25"). With the old mounting plate not covering the top plate of the boiler I plan to drill an extra steam supply hole as the two small existing holes will be somewhat blocked by the flange.
The throttle tube and turret will rest slightly higher than before, meaning a good opportunity to redo most of the piping. Given that the Superscalte Economy injectors are lifting, it makes sense to place them in the cab where the drain pipe is visible.
Got it home and applied face mill to clean up the cut.
The dry pipe is threaded 1/4 NPT, so I tried this setup. I think it should work.
John from the club has some steel pipe that's 3.5" OD and 3/8" wall. I redid the SW model to use a flange inside the dome for attaching to the boiler, and it appears everything will fit:
Bottom disc is welded to the boiler plate and then drilled and tapped. An almost identical piece is welded to the bottom of the main pipe, and drilled clearance to match. The flange for the throttle pipe is welded to the main pile, and then the holes are drilled. The lid is drilled for clearance holes to match the tapped holes in the upper edge of the dome, and the lid has NPT tapped holes for the safeties and for filling the boiler.
The new dome will be slightly taller than the old, as well as wider (old OD was 3.25"). With the old mounting plate not covering the top plate of the boiler I plan to drill an extra steam supply hole as the two small existing holes will be somewhat blocked by the flange.
The throttle tube and turret will rest slightly higher than before, meaning a good opportunity to redo most of the piping. Given that the Superscalte Economy injectors are lifting, it makes sense to place them in the cab where the drain pipe is visible.
Re: Kozo A3 in 1.5" scale - new project
Glad to see you on this again Kirk....
Ken-
Ken-