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Marks Holt 75

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dnalot

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Sorry guys but this is my last post for the year.

Took the time to fix my rotary table. Almost no backlash, what a difference that makes. The small gearbox is mostly just a repeat of the big one. Also made the five bearings for the camshaft and three bearings for the small gear box. And a roughed out blank for the camshaft. The photo of the camshaft shows it being marked for the layout. for cutting I kept most of the shaft in the collet to start with and would work near the chuck. As I completed a section I would expose anther inch or so until all the detail was cut.

Time to make some gears now. It has been a while sense I cut any gears. This time I have the hardware to make it easier. I have an indexer with a stepper motor and a controller.

See https://www.homemodelenginemachinist.com/threads/arduino-rotary-table-for-dummies.26744/page-18#post-331050

I made my setup near the beginning of this thread. You can see my setup at post 53. I have used it a lot and it works very well. Well except for gears that is. The limiting factor is that the number of teeth must divide into 360 with no more than 2 decimal places. If there are more than two there will be an error that will accumulate. I needed a 32 tooth gear and that was no problem the indexer worked great. But I Also needed a 64 tooth gear. 360 divided by 64 gives you 5.625 degrees per tooth. The indexer would round that to 5.63, and that will leave you with a very skinny 64th tooth. To get around this I first made 32 cuts. next I would setup for 64 cuts but only made one cut before resetting for 32 cuts. That gives a serviceable gear with every other tooth being a little fat and the others a bit skinny.

Everything fit together nicely and turns smoothly.

Mark T

small gearbox.jpg


small gearbox Frn.jpg


small gearbox rear.jpg
 

dnalot

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Another part completed. This time its the camshaft. The Adrino controlled indexer made quick work of cutting the cam lobes. To form the apex of the lobes I made a custom cutter. Filing and polishing took about as much time as the machining.

Next I think will be the cylinders. The plan calls for aluminum jackets but I plan on using steel to allow for some fabrication of the part.

Mark T

Camshaft Cutter.jpg


Camshaft.jpg
 

michelko

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Hi, very nice work.
Waht material did you use? I think the cams and the followers will be unhardened?

Regards Michael
 

kuhncw

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Mark,

Thanks for a very well written and illustrated build thread.

Very nice work.

Regards,

Chuck
 

Robert Ritchie

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Another part completed. This time its the camshaft. The Adrino controlled indexer made quick work of cutting the cam lobes. To form the apex of the lobes I made a custom cutter. Filing and polishing took about as much time as the machining.

Next I think will be the cylinders. The plan calls for aluminum jackets but I plan on using steel to allow for some fabrication of the part.

Mark T

View attachment 113275

View attachment 113276
Fantastic nice work enjoyed your detailed descriptions, keep up the fine work
 

gbritnell

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Hi Mark,
The cam looks great. I have always made my cams and lifters as you said, drill rod cam (unhardened) and drill rod lifters (hardened and polished) and have never had any problems. You said that you were going to make your cylinder jackets from steel for some fabrication. If you could explain?
gbritnell
 

dnalot

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You said that you were going to make your cylinder jackets from steel for some fabrication. If you could explain?
Hi George

It looks to me that using steel would allow me to silver solder the square flange to the jacket and soft solder the ports for the cooling water. It just seems like an easier way to do it. And I want to get away from the aluminum look. I like a variety of color and texture in my models. Using D.O.M. steel leaves very little machining of the barrel. And the steel will look nice with a "Plum Brown gun finish" don't you think.

Mark T
 

gbritnell

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I do agree it will give it more of an authentic look. Th original castings were iron with iron sleeves. Bluing or anodizing would really set them off.
gbritnell
 

G54AUST

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G'day Mark (et al).

I too have purchased Georges' brilliant drawing with a view to constructing this engine and shall be watching this thread with keen interest.

I too have purchased "Hollow Bar" to make the cylinder jackets. Plan is to rough turn the OD and pilot bore the jackets, silver solder the square base and the water in/out ports, stress relieve and finish turn the ID and ends. Liners to be made out of grade 3D cast iron. All sealed with O rings. Unfortunately, blueing or black oxiding won't cover the silver solder so shall coat with epoxy paint.

Am currently redrawing this engine in metric but shall be constructing it 25 % larger. All dimensions multiplied by 31.75 (25.4 by 1.25) to get to 125%. ie. bore is 1" by 31.75 = 31.75 bore; rounded up to 32. 32 by 40 shall give me approx. 128cc capacity. Oversized water pump and water pipes for additional cooling. Radiator, probably a computer radiator with brass outer cover.

Manual CNC here as well. Gathering info and bits & pieces for CNC retrofit on my Mill. HM52/G0757.

Enjoying your "MO". (Modus Operandi)


Kind Regards,

Trevor,
Melbourne, AU.
 

Lukas Pils

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Hi

@ Trevor just a quick tip regarding imperial to metric conversions. If you multiply by 32 you get a slightly larger part but all dimensions have max. one decimal place ==> makes the drawing and machining easier.

Kind regards,
Lukas
 

dnalot

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G54AUST, looking forward to following your build. If your gathering materials you must be about to get started.

Mark T
 

G54AUST

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G'day Guys.

@ Lukas Pils. Fully understand what you mean Lukas, and I do tend to round off as much as possible. Mainly for stock sizing etc. Having said that, I am constantly working in plus/minus dimensions anyway.

@ dnalot. Mark, I'm rapidly approaching retirement so I'm amassing projects to keep the dark grey matter churning. My Wednesday TTR job (transition to retirement) is maintaining three steam locos on a private 7 1/4" gauge railway close to home. I intend to use the Holt 75 (plus 25%) in another project there.

You stated that this wasn't going to be a "step by step" build, but members following this thread may just be hanging on to every post you make. Many lurkers will be watching with keen interest but won't chime in. Please keep up you detailed posts …..


Kind Regards,

Trevor,
Melbourne, AU
 

mirek111

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Very nice and demanding work.
 

dnalot

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So here are the cylinder jackets made from steel. I started with cutting the flanges as a group. And then cut the barrels from D.O.M. Steel. Very little material had to be removed so they were quickly turned to size. Now some steel cuts very nice, this steel is not one of those. Never found a way to cut it with a smooth surface so I had to sand it.


Jacket.jpg


Jacket flange.jpg
 

dnalot

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I cut a slight shoulder in the skirt to hold the flange in the correct place for soldering. I cut the shoulder to fit the flange snugly to prevent distortion from the heat and then filed a bit of a taper to to it to allow the solder to wick in. And to prevent the solder form getting on the wrong surfaces I used some wite out.


Jacket flange Whiteout.jpg
 

dnalot

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Using a Lazy Susan I rotated the part to heat it evenly. I love to silver solder. It is easy once you get the hang of it. Everyone knows you need to have clean surfaces, but most people forget to clean the oxide off the solder with some steel wool. Makes a big difference in getting it to start to flow. And most people use way to much flux.


Jacket flange soldered.jpg
 

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