3d Printed Patterns or Wood?

Yes, see the attached pdf of original drawing. I do not have one showing draft, resize, etc. yet.

 

Drawing look good Andy, thanks. Did you develop the main round shapes (not the triangle gussets) as extruded sketches or a revolved surface? A revolved sketch might make some of the draft and machining tolerance modifications easier.

 

I used extruded shapes in Fusion. I don't think I know about the revolved surface.

 

It's an extrusion that is rotating around an axis. Here is one in Inventor, Fusion is similar (same parent company Autodesk).

 

I see, I also watched some Fusion videos. That would definately be a better way of drawing.
Thanks for showing me the trick!

 

What do you guys suggest as the best printer to get for this type and size of job?

 

A large format core xy machine that has a 12x12x12 working envelope would suit you very well. Grab some large nozzles.

I purchased something like this:

https://www.3dprintersbay.com/corexy-3d-printers/sapphire-pro

But then I have at least another 500 in upgrades.. 120v heated bed, encloser, full klipper software upgrade, new fancy hotend...list goes on. A few years back I had some success 3d printing and investment casting with suspenda slurry but getting the print to be watertight was a point of frustration for me.

 

Does anyone on here have experience with larger 3d printers? Something like a 20x20x20 working envelope?
It seems to me like I will probably want a big one while I am at it, but that does somewhat limit my options...

 

Good Evening, All,
As I am working at this project, there is one question that Google hasn't been able to satisfy yet.
How do you determine how much to resize your patterns? Do you simple add a certain fixed percentage to your drawing in Fusion 360 or does it vary based on the thickness of your part?
Best Regards,
Andy.

 

Try for find some online info for 'pattern shrink' as it relates to foundry metals and beware of 'outliers' proposing excessive values. For the aluminum I recycle (cast tooling plate) 1.5 to 2% seems good.

https://maritime.org/doc/foundry/index.php#pg25 is the US Navy's foundry manual's take on this

I would keep the CAD for the pattern 1:1 in Fusion and apply the shrink (positive scale of CAD data) when you slice to 3D print or at the CAM stage for CNC . component. If you need to make stuff by hand I would scale the original part into a new Fusion file and take dims off that.

 

Thanks so much for the link, @Tops. When you are scaling the pattern in Fusion or whatever you use, does it work to simply add a uniform percentage of scale to the whole pattern? How does that work with a circular diameter such as I have here and the I.D is larger than it should be? Will it just compress the sand and shrink to the proper I.D if I calculate shrinkage percentage correctly?

 

Andy, I forgot that you are working on a tail housing for a gearbox. You will probably have to do a combination of pattern shrink to get the overall size of un-machined blank where you want it and add material to critical surfaces to machine away for any faces, diameters, bores, etc. that are critical. I don't think it is going to be accurate enough to just apply pattern shrink and get the part to bolt up to something that has already been (most likely been) cast and machined with shafts and bearings and seals and gaskets and stuff.

I used to flame cut large steel blanks that needed to be machined. We did not have pattern shrink but we did have significant torch kerf cutting through 6" (150mm) of steel along with the overall straightness of the cut. All of the outside diameters were bigger and the inside diameters were smaller so the parts could be machined to be concentric to their finished bore and the outsides faced and sized to fit into the next assembly piece.
For us this was maybe 1/2" to 1" (12-25mm) over/under to yield good parts after machining.

Casting I would imagine this number to be less as the process should be more controlled and repeatable, but you may need advice from someone who does more machine work themselves (I do not) as to how much, hopefully it is more on the order of 1/8 to 1/4" (3-6mm) added to each critical surface (inside diameters becoming smaller, flat surfaces taller, etc).

 

Thanks @Tops. I appreciate your assistance. I realize how much to add for machining tolerances, but the shrinkage in the casting is what I was not sure about.

 

Shrink is going to depend on the metal you're casting the final part(s) in .
But as Top has noted in addition to the shrink you need to add machining allowance for areas that need to be machined. This allowance needs to factor in shrink, draft, and final tolerances. For some parts I've seen folks use as little as 1/8" or as much as 1/2" or more. It depends on the complexity of the mold/part and # of castings. for example if it's a 1 off you might go on the high end just to make sure you get it in 1 cast. If it's a run of 100 or 1000 you aim for the least possible per unit as chips add up (tooling, labor, machine time are expensive).
Good luck Andy!
Bruce