Member postings for PatJ

I apply a thin skim coat of sheetrock wall patching compound to my 3D printed patterns, and then sand back down to the original surface.

This gets rid of the lines that you get with a 3D printer.

The Prusa produces a much better surface finish than the first 3D printer that I had.

I see people using bondo and wood putty for fillers, but the problem with those is that the are too hard, and so it becomes a chore to get then sanded down, and the pattern is often damaged during sanding since it is softer than these types of filler.

The wall patching compound is not very hard when it dries, and so sanding goes quickly.

The secret is to use a compound that sands very easily.  Don't use hard fillers.

I apply a coat of shellac once the pattern has been filled.

It seems like a tedious process, but with the wall patch compound, it does not take very long.

Below is an example of a frame for a small engine that I filled.

This example uses more filler than I normally use these days, but you get the idea.

This example is also painted, which I no longer do; I use shellac which dries very fast.

If I am making a one-off casting, the wall filler will be sufficiently strong to make a few molds.

If I want a more durable pattern, I use a double shrinkage factor in the 3D print, and then cast a permanent pattern in 356 aluminum.

One feature I like is to make the surfaces of a pattern slightly convex.  A 3D printed pattern with a flat side looks visually concave, and so making the surfaces slightly convex if possible seems to make a part more visually appealing, and not have such stark lines to it.

Edited By PatJ on 30/01/2021 04:42:22

I saw someone using Solidworks in about 2011, and marveled at the many useful features, such as the transparent views.

I said to my self "I have got to learn that".

It took me perhaps a year to conceptualize exactly what I was trying to do with 3D modeling, and a bit longer to learn how to use a 3D printer.

I gave up numerous times during that year learning period, and would yell at no one in particular "I WILL NEVER FIGURE OUT THIS &%&$%&^%^&&^ SOFTWARE !!!!!".

It was very frustrating to say the least.

2D CAD was so firmly engrained in my head, that I think people learning 3D from scratch without ever having done 2D perhaps could have an advantage.

These days, I try to leave a paper trail about everything I have learned about 3D modeling on various forums, so perhaps others can avoid some of the trials and tribulations that I suffered.

I do like 3D modeling.

I wish 3D printers were larger and more reliable.

Pattern making is an extra step on top of 3D modeling, and you have to add machining allowances, allow for shrinkage, parting lines, draft angle, fillets on everything. I toggle most of these features off when I create the 2D drawings from the 3D model.

When I started working in 1985, it was all manual drafting boards, and many slide rules were still used.

The computer we used was a mainframe running FORTAN, reading punch cards.

Things have changes a lot since 1985.

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Edited By PatJ on 29/01/2021 11:22:53

Edited By PatJ on 29/01/2021 11:24:04

I was able to convert a downloaded gear model from a supply house, with teeth at 45 degrees, to a Solidworks part file, and then add two of those into an assembly.

The teeth appear to mesh ok.

I used that same tooth form to create two new gears, with 30 and 60 degree twists, and those gears do not appear to mesh.

I will have to try and find the article that Rod mentioned above, and try to replicate his machining method in Solidworks.

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I have a Prusa MK3.

I have designed engines by making drawings manually on a drawing board, using AutoCad for 2D drawings, and 3D modeling using Solidworks.

I have made patterns by hand in wood and steel, and have made engine parts on the lathe and mill from bar stock. I have also made patterns on a 3D printer.

I have made castings and machined those.

The reason I use a 3D printer and Solidworks is that I can make the same patterns I would normally make by hand, but can make then more accurately and sometimes more quickly.

It is easier to get the srinkage factor uniform across a pattern if it is 3D printed.

So I recommend learning to do things by hand, but once you have that mastered, then using computers and 3D printers just speeds things up.

My dad was old school, and he would never consider using a computer for anything except a boat anchor.

I am required to use computers and software for work, so it is a natural thing for me to use them, and I am fluent in them outside of the hobby.

To each his own. Its whatever makes you happy.

I started using Solidworks in 2012, and not to many were using 3D at that time.

Many more of those same folks I notice now use 3D modeling, so it seems to be a trend.

I do like to be able to do things by hand, because there is a touch and feel aspect that you can't get with computers and software.

Using the CUT command in Solidworks is much like machining the real metal (virtual machining I call it), and it helps conceptualize how I will machine a part.

I also assemble the 3D components and run them virtually, to test for inteferences, etc.

If the model won't simulate in 3D, then it won't run in the real world either, so that is a helpful verification step before I start cutting metal.

I don't use a CNC, but I see a 3D printer as being very similar to a CNC.

I don't have plans to "go CNC", since I find a 3D printer much more useful for pattern making, especially with hollow items, where I can use a 3D printed pattern also as a core box.

I guess it really just boils down to time. I can start a 3D print, and let it run overnight, and in the morning (if all goes well) the pattern is sitting on the printer bed.

I can design with software faster than any other method I have available.

Use the tools you have available I guess.

Edit: On a side note:

I am having lifting issues with the Prusa bed.

Anyone have a solution for that.

I have not tried the purple stick glue yet, but need to try that.

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Edited By PatJ on 29/01/2021 10:28:17

Edited By PatJ on 29/01/2021 10:28:37

Edited By PatJ on 29/01/2021 10:30:46

For the full sized Frisco Standard engine, the distance from the centerline of the camshaft and the centerline of the crankshaft is 2.7625", and so that determines the gear sizes, which I assume forces the gears to be custom sized?

My initial approach I guess will be to pull in the profile from CAD files for a commercial helix gear, and then scale two of them to fit the centerline-to-centerline distance.

This may or may not fit a standard gear cutter size, but as I mentioned I would 3D print and cast my gears.

Alternatively, I could find a commercial gear size that was a close fit to the size of a scaled model, and adjust the model scale slightly so that a standard gear cutter size could be used.

I could end up with an odd model scale, but I have always used odd scales anyway, and don't feel the need to adhere to any particular scale. 

The only scale that is important to me is a scale that allows engine parts that are large enough for me to see and handle while machining.   I just can't see the small parts very well, even with reading glasses.

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Edited By PatJ on 28/01/2021 23:37:42

I think that issue is addressed at 9:36 in this video?

It seems like for the gears above, I could lay out the profile for the first one, rotate a cut to make the 3D model, and then take a section from an appropriately skewed plane to come up with the section for the other tooth form, and then rotate that.

This way, I know the gear profiles would mate correctly.

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Edited By PatJ on 28/01/2021 14:28:14

Thanks Rod.

It took me a while to figure out how to make decent gray iron castings, but I can do it consistently now, and am not having any defect or machinability problems.

The machinability is maintained by using a slight amount of ferrosilicon.

I am trying to obtain some additive(s) to make ductile iron, and if I can get that worked out, I will cast my own crankshafts too.

I have machined a lot of different metals, and I prefer gray iron to anyt other metal I have machined.

Gray iron makes an engine that machines well and wears well too.

I never really thought I could figure out how to do iron, but I finally did.

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Here are a few castings I made for fun last year in gray iron.

There is only a slight amount of sand remaining on the castings when they are pulled from the mold, and a light wipe with a paintbrush was all it took to completely clean off the sand.

The ceramic mold coat works wonders with surface finish, and basically eliminates virtually all sand adhesion to the casting.

The last two photos below show exactly how the castings came out of the mold.

They were not wirebrushed or buffed at all, just lightly wiped with a dry paintbrush (2nd to last photo before brushing off with the paintbrush, and the last photo after brushing with the paintbrush).

Ahhhhhhhhh................thanks very much Jason and Rod.

I knew that knowledge base was here.

So it seems there is a bit of magic to this gear arrangement, at least in my mind.

I can't quite wrap my head around the speed difference caused by a variation in the angles, but I will take your word for it.

My plan for fabricating these gears, which may or may not be viable, is as follows:

1. Draw a standard spur gear in 2D in CAD (or download a profile from a supply house.

2. Pull the profile into Solidworks, and extrude while rotating the necessary degrees.

3. 3D print the gears.

4. Make resin-bound molds around the gears.

5. Heat the 3D printed gears until soft, and carefully extract from the mold. The center of the 3D printed pattern can be mostly left open, such as with the gear on the right in the photo above.

6. Pour the mold (with gray iron), clean up a bit with a file, and then run in the gears with some fine lapping compound.

7. The shrinkage factor will have to be pretty close for the gears to work, but not exact.

8. I use a ceramic mold coat, and so the finish on my iron castings is almost perfectly smooth, and I don't have to wire brush the casting to clean off the sand.

9. The resin-bound sand make a very accurate casting, since unlike greensand, you do not rap the pattern in order to withdraw it from the sand.

I could also use a lost-PLA (or a similar filament that is designed to burn out cleanly), and use a ceramic slurry, although I do not have the slurry, and am not set up for that method at the moment.

I think the resin-bound sand method would work.

The slurry has a fixed shelf life, which is perhaps 1 year?, and so I don't really want to purchase that for just two gears.

The lost PLA method is extremely accurate though, assuming your shrinkage factor is correct.

The profile on the gear on the right above does not look the same as the one on the right though, so that may be a fly in the ointment.

I will ponder this further, but I greatly appreciate this information.

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Edited By PatJ on 28/01/2021 13:14:10

I am not finding any magic to helical gears.

Seems like it is just a spur gear design, and then twist it at whatever angle suits your needs, as long as the sum of the angles of the two gears equals 90 degrees.

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I need help with the helical gears for this engine.

As with all 4-stroke IC engines I am aware of, the camshaft turns at 1/2 the crankshaft speed.

I have verified with videos of running Frisco Standard engines that the vertical camshaft is indeed running at 1/2 of the crankshaft speed.

My problem is that the helical gears at the camshaft-crankshaft junction appear to be the same size, both in photos and on the patent drawings.

So my question is, how do I get a 2:1 gear ratio using cross helical gears that are the same size?

Obviously I am missing somthing.

My understanding of gears is not good, so that is hampering things.

If I increase the diameter of the camshaft gear to twice that of the crankshaft gear, then the camshaft gear does not fit the engine (it strikes one of the vertical supports).

I am stumped on this problem.

Is there an obvious solution that I am overlooking?

Anyone have any experience with side shaft helical gearing?

Thanks in advance.

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I do a lot of 3D modeling, where sometimes I only have a few photos of an engine available.

I insert the photos in Autocad as a raster image, and then scale them up to some known dimension, or if no known dimensions are available, assume a dimension on one of the major parts, and then keep everything proportional to that.

I built the green twin oscillator from 3 photos, and was shocked to later discover how close I came to the dimensions of the original engine.

Sometimes I draw a grid over a photo in CAD, and use that for proportion.

If I have a drawing of one piece of the engine, such as the cylinder head on the Frisco Standard, then I begin with those dimensions, and propagate outwards one part at a time, so that all the parts fit.

For fasteners, rods, etc., I generally round off the measured decimal number to something that matches a standard metal size, or a standard fastener size in case of a fastener.

I always use decimal when designing, but on drawings I use fraction and decimal notation, since people are use to using drill bits and metal sized like 1/4", 3/8", 7/16", etc.

Photos are often taken at an angle as opposed to being taken directly from the front or side, so I often start measuring at the center of the object in the photo, with the understanding that the lines get closer together for objects farther away, and get farther away as the object gets nearer.

It took me a few tries to master converting old drawings and photos to CAD drawings, but it can be done with practice, and it can be done accurately using only a few photos.

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Great information.

Thanks much.

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Thanks. Yes I would like some info on casting brass. It would be nice to be able to cast that material, but there are some tricks to use, and I don't know what those tricks are.

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Thanks, yes I will be making my own patterns.

In the past I have made many of my patterns by hand in either wood, or metal.

More recently, I have started to 3D print my patterns on a Prusa, and so that speeds up the process of pattern making, and adds accuracy too.

And another benefit of using 3D to make patterns is that they can be printed at any scale.

I prefer grand scale models, because my eyesight is failing, and larger parts are easier to see and machine for me.

I intend to cast this engine in iron at a 40% scale, which will produce a 12" flywheel.

But as I mentioned, with 3D patterns, any size engine could be built.

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Thanks, I appreciate the kind words.

I contemplated making iron castings for many years, but never considered it achievable in a hobby setting.

In 2012 I discovered that gray iron can be cast on a hobby level.

It took me a few years to perfect the method, but I now get consistent results in gray iron without hard spots, inclusions, or other defects.

Good information about how to cast gray iron is very difficult to find anywhere, especially how to do it with an oil burner. I could never find the coke that is required to run a cupola.

So I have tried to leave a paper trail about how to cast gray iron and get good results every time.

Gray iron makes for some really nice model engine parts, and I can control the quality of the castings and the patterns, so if they are not right, I have nobody but myself to blame.

I think I posted these photos previously.

I tried casting 356 aluminum, brass, boat shaft bronze, and gray iron to make steam engines.

The aluminum was ok if tempered to an approximate T6 level, but lacked much mass.

The brass and bronze generated a lot of zinc fumes, and I had to wear a powered respirator. The castings did not turn out well.

I finally tried casting gray iron, and after some experimentation, I got that figured out.

This was my first iron pour.

I had no idea what I was doing at the time, and safety was a bit lax with the laced shoes and such.

I have come a long way with safety and casting techniques since then.

Edited By PatJ on 11/01/2021 08:46:37

Edited By PatJ on 11/01/2021 08:47:03

Edited By PatJ on 11/01/2021 08:48:38

Edited By PatJ on 11/01/2021 08:49:48

Edited By PatJ on 11/01/2021 08:51:14

I have admired the old 4-stroke marine engines for a long time, and finally got a short break from work, so I am taking a few days off and trying to hash out a design for a 3 hp Frisco Standard at about 40% scale, which would give a 12" flywheel, and almost a 2" bore.

Lots of tricks and turns in this design, but i really like the side-shaft layout.

There is a twin kit available, but it is quite costly, and I really want a single, so I am making up my own 3D models and then 2D drawings, using photos of old Friscos.

So far so good with the design.

It seems to be coming together.

Edited By PatJ on 11/01/2021 08:38:55

Another great looking engine.

I need to go faster.

I am getting hopelessly behind.

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