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Best Product to Use for Fillets and Curves in a Simple Aluminum Pattern

carrdo

Well-Known Member
Hi All,

I am making a simple pattern in aluminum (to produce several non ferrous - silicone bronze castings). It has several curves where I need to form a root fillet or blending radii. What is the best product to use here and one which will stand up to repeated and rough handling in a foundry? Also, is there any product which will stand up to light final contour shaping using a HSS ball end mill?
 
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Not quite sure I follow, maybe a picture? Typically an external corner 'round-over or bullnose' is milled with a corner rounding profile cutter. An inside corner fillet like at the base of a pocket typically uses a ball ended end mill. Blending & smoothening is typically abrasive paper, rubberized abrasive wheels, Scotchbrite type pads.... those kinds of tools. But the aluminum is only as strong as the alloy itself in terms of rough handling. Nothing to do with the fillets, true for any of its surfaces.
 
OK here is my crude sketch of what I am trying to do. The pattern is a uniform x-section and will be 1-1/16" long, 3" wide at the base and 1-1/4" high.

Is this feasible or am I out to lunch? I want to keep it as simple as possible so that I don't need to use both sides of a matchplate.
 

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Is the end result to make a female mold roughly like the red outline? Maybe it will be cast using a softer durometer silicone or urethane & the underlying 'male' pattern is what represents the finished product when poured into this female mold?

- if so, the tiny amount of datum contact area (yellow) may not warrant aluminum. Its just a flat surface. But considering all the other surfaces are shapes with filler & probably shiny top coat, why bother? Make it out of MDF or similar low cost & easy to cut material. Also if this mold represents one half & there is another half, you would need some kind of alignment fixtures on the yellow surface.

- I've shown blue circles representing a better plan for the circular sections. If you make them the full diameter then you don't need a relatively thick layer of putty filler whatever you were envisioning peripherally around it. That would be much harder to control thickness/accuracy. Now maybe I'm missing design intent & that added thickness is textured or engraved or the section twists in an axis into the page. Then the circular sections are basically a glorified 'filler' support. Is that the case?

- maybe your original question, if we are talking hand work to make these fillets, that's probably easier done with simple templates to basically 'screed' filler material. Think of a piece of 1/16" aluminum with a rounded corner. That would be the 'tool' to make the shape using an appropriate filler. One edge of the tool contacts the circle, the other the flat datum. Or a circular template contacs both of you rround (blue) circles in the middle. Bondo comes to mind as a filler, but I'm not sure about your end design. It will involve handwork & multiple progression steps to get it right. Then top coat finishing to a state where the mold could be poured, release agent, all that good stuff. Smooth-On has a really good video series on YouTube, might be worth watching as it kind of looks like what you are trying to do.

1744397709596.png
 
Hi Peter,

Attached is the drawing of a very similar part. I just want to make a fully male 3 degree taper mold where the flat bottom surface is attached to one side of a matchplate and the male outline is pushed into the sand to create the female cavity into which the molten metal will be poured (forget the bottom legs). I don't want to get into making cores or anything like that. Just keep it simple. It may be a waste of material but I don't really care about that. As you can see in the print, there are end ribs which I would like to have cast in as well. I could go with wood in place of aluminum also.

I am not experienced in the ways of pattern making so my thinking always has been, keep it as simple as possible. 3-5 cast parts are all I will ever need so no commercial foundry will ever take on this piddly "nuisance" job.
 

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I get you now. If its only purpose in life is to hold the shape of sand & its not too long, why not 3DP it? The CAD work for that is trivial. A few of us on the forum could do that. Even if you paid to have it printed by outsourcing probably would be cheaper than materials & runaround time, but I'm not sure what you have on hand vs need to buy.

I mean wood + filler is a perfectly viable way to go too. Requires hand work, sanding, finishing, attention to dimensional detail etc. (but do-able).
 
I am making a simple pattern in aluminum (to produce several non ferrous - silicone bronze castings). It has several curves where I need to form a root fillet or blending radii. What is the best product to use here and one which will stand up to repeated and rough handling in a foundry? Also, is there any product which will stand up to light final contour shaping using a HSS ball end mill?

There's always JB Weld ... bonds well, machines easily, easily smoothed with a damp finger and quite durable.
 
I second the JB weld idea, except I use Oatey fixit stick in the plumbing section. At $10 for a big stick it works well. It’s. Putty you cut off what you need, knead it, and it sets faster than most of the JB weld stuff. Probably because it has a lot of BPA in it…it sets quick and sands/machines well.
_Fix it stick - Oatey

If it’s not a big fillet, I use Dynapatch pro, much softer though, but holds up ok on my patterns.
 
Very difficult to help with details without a side and top view or standard 3 view drawing.
I think I know what you want but…..

Personally for so few castings I would use solid hardwood like eastern maple but I have a full woodwork shop so it is pretty easy for me to do that. Most foundry patterns were made of wood back in the day.

So it depends on your skillset and what machines you have etc. I also like the idea of a 3d printed pattern. Easy to get the exact details you want with draft etc.

Just for your info the pattern is not pushed into the sand as that would be very difficult if not impossible. The pattern is attached to a larger plate and forms the bottom of a box then the sand is poured into the box and slowly tamped into place a layer at a time. Then the pattern is pulled out of the sand, this is the tricky part and why draft is needed. I am sure there are lots of videos on the process, sand mix etc.

Good luck,
Michael
 
Hi All,

Many thanks for all of your very helpful comments on this simple pattern making job. I really needed the education in this area and for all future projects will go the route you have suggested.

But, being as stubborn as ever, I decided to stick with the devil I know for the time being and produce a wooden pattern which I have already managed to partially construct as seen in the photos.

I know I am up to my old "doing it the hard way again" and you can have a good laugh if I fall flat on my face, which sometimes happens.

To fill in all of the details, I will start a new thread in the Your Active Projects section and will describe everything encountered on the journey including the good, the bad and the ugly and how it took 10 times longer than it should have.

So stay tuned.

PS: I know machine tools and cutter bits are not the best by far for wood turning but I managed.
 

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Looks good so far. I often cut small wood parts on my metal lathe and it works well.
Just the other day I needed to cut a plug to 1.388” and that is easy on a metal lathe but not so easy on a wood lathe.
Not sure if you have done this but I would have made a two piece rectangular block and then drilled or bored the two holes. Now you can just cut away to the shape you want for the top piece.
If the pattern is going to sit as it is now at the bottom of the mould then all sides need a slight taper to the top of the piece. Otherwise the mould will be damaged when you remove the pattern. Also all patterns I have seen have been finished, usually with paint.

Good luck,
Michael
 
Nearly anything soft enough to work after hardening will work. Likely even use silicone/ calking, glue, wood putty etc. smooth it with a finger. Make sure no overhangs, a little bit extra on the draft, can make it easier to remove pattern, a bit of tapping the pattern (rapping) will slightly loosen the pattern, making removal easier. Have a hole in the base of the pattern for a wood screw, to be put in to remove the pattern, a handle. Water/moisture proof it with paint, vanish, even spray on, it will be in the casting sand a short time. As has been posted above, mold the sand around the pattern, with the flat base of the pattern on the split of the cope and drag.
I wish I could do some casting, but not set up for it. Yet/maybe.??.
 
Lately I've 3D printed a lot of patterns and used Lepages wood filler along with shellac. It's water soluble so after you've smeared it on and let it dry you can use a wet finger to do much of the smoothing. When the shape is close and some sanding improves it I coat it with a layer of shellac. A bit of sanding again and the shiny parts show dips. Add more wood filler int the depressions. The shellac prevents the previous filler from dissolving from the water.

I have used bondo too. (Auto body filler) but for tiny complex fillets etc. it's overkill. Also the primer from Cdn. Tire is the thick filling kind. Not just for paint to stick. Fills up lots of imperfections.

Here's an example of 3D printed patterns.
RawPatterns.jpg

And then the ready to cast finished patterns.
PatternsReady.jpg
Project #42 to cast them. Real soon now.
 
Lately I've 3D printed a lot of patterns and used Lepages wood filler along with shellac. It's water soluble so after you've smeared it on and let it dry you can use a wet finger to do much of the smoothing. When the shape is close and some sanding improves it I coat it with a layer of shellac. A bit of sanding again and the shiny parts show dips. Add more wood filler int the depressions. The shellac prevents the previous filler from dissolving from the water.

I have used bondo too. (Auto body filler) but for tiny complex fillets etc. it's overkill. Also the primer from Cdn. Tire is the thick filling kind. Not just for paint to stick. Fills up lots of imperfections.

Here's an example of 3D printed patterns.
View attachment 63133

And then the ready to cast finished patterns.
View attachment 63132
Project #42 to cast them. Real soon now.

Great example John - as I'm reading the thread and all the process steps to make the cast I keep wanting to say 3d print it! I'm a noob at casting - why is the shellac and additional smoothing done? Just to improve the finish of the final casting? I think @kevin.decelles (or was it someone else?) was embedding his 3d parts right in the sand and melting/burning out the plastic with the pour. Kevin are you still doing that? Anyone else doing that? and people out there are printing sand with their specialized 3DP machines and casting right into that. An engine block I think.?
 
Great example John - as I'm reading the thread and all the process steps to make the cast I keep wanting to say 3d print it! I'm a noob at casting - why is the shellac and additional smoothing done? Just to improve the finish of the final casting? I think @kevin.decelles (or was it someone else?) was embedding his 3d parts right in the sand and melting/burning out the plastic with the pour. Kevin are you still doing that? Anyone else doing that? and people out there are printing sand with their specialized 3DP machines and casting right into that. An engine block I think.?
Hi John,
Some people are perfectly happy with ugly castings using the coarsest sand and poor fit of cope to drag with metal running out between that has to be trimmed. Rough woodwork finishing on the patterns too.

I like to be able to show a casting that has the machined parts machined and the non-machined parts as silky smooth as my rather coarse greensand can produce. The finer petrobond does an even better job of reflecting pattern texture be it rough wood working or 3D print lines.

Lost PLA (or Lost Wax) coats the single use pattern in a series of plaster type slurry and sand layers until it's thick enough to be put into a kiln and have the pattern melted out. Just pouring metal into the PLA results in gas pockets and left over carbonized plastic. The other advantage of lost wax/pla is that this outer shell is now almost red hot and when the metal is poured it doesn't shatter from the stress of temperature change.

And if you like 3D print lines in casting then it's a good way to go. As soon as you add filler/primer/paint you can't use it as lost PLA anymore. It's now a real pattern. And if the casting or machining doesn't work it's a quick job to cast another. With lost PLA and the shells the time to reach a casting is way way longer.

In both the attached photos the problem isn't so much the patterns as is my ability to cast but I'm not upset with the overall surface finish from either wood patterns for the lathe or the 3D printed pattern for the draw bar
 

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I have not done lost PLA, but I did do an experiment a few years ago with a rough and raw PLA print with ZERO prep, straight into the greensand as a pattern and was pleasantly surprised by the results. They're not "great", but they're honestly not as bad as I thought they would be. The sole purpose was to see how quick I could make a prototype from an idea to a solid part, and I was pretty happy with the results. I can't remember exactly, but I think it was around or under 4 hours. I did take some of those patterns and smooth and paint them later, but have yet to cast them again to see the difference. Project #42 must be contagious......have not done any real printing or casting in a couple years. My interests are cyclical.....

If I could get off my ass and stop watching the Masters I have a foam pattern ready to cut for my first try at lost foam. Couch gravity is pretty strong today.....
 
I have not done lost PLA, but I did do an experiment a few years ago with a rough and raw PLA print with ZERO prep, straight into the greensand as a pattern and was pleasantly surprised by the results. They're not "great", but they're honestly not as bad as I thought they would be. The sole purpose was to see how quick I could make a prototype from an idea to a solid part, and I was pretty happy with the results. I can't remember exactly, but I think it was around or under 4 hours. I did take some of those patterns and smooth and paint them later, but have yet to cast them again to see the difference. Project #42 must be contagious......have not done any real printing or casting in a couple years. My interests are cyclical.....

If I could get off my ass and stop watching the Masters I have a foam pattern ready to cut for my first try at lost foam. Couch gravity is pretty strong today.....
I weed whacked around most of the boulders today. When the whacker ran out of gas I went in for a coke. Arms and hands tingling. Only 8 more boulders to go and then the lawn.

At this point I'm not sure what I'll cast first if I ever get around to it...
 
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