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A post from 2018 lists this email for Bob: [email protected] There is also a user on this thread: 1/6 P&W R-985 Wasp Jr by Bob Roach / Vernal Engineering that has a set of drawings. If Bob has passed and the drawings are no longer commercially available, you might be able to get a copy...

My boring head has 3 gib screws. I have them adjusted relatively tight, and I use the center gib screw for locking. So I loosen the center gib screw, adjust the screw, and then tighten the center gib screw to lock it. Doesn't take much time, doesn't mess with the gib adjustment, and holds...

Here's a set at manually-machinable chessmen from Popular Science December 1968. Carl

That's a lucky 12 year old. Nice starter setup. Carl

I know a guy who has a company that makes custom babbit bearings. I don't know how much he charges or if they would work for your tractor. I can give you contact information if you'd like. Carl

I have no personal experience with their machines, but FoxAlien seems to have some good cnc capabilities at reasonable prices. Here is one of their more expensive systems: https://www.foxalien.com/collections/cnc-router/products/cnc-router-machine-vasto-with-20w-laser-bundle-kit It comes with...

Have you got a copy of this manual? https://manuals.harborfreight.com/manuals/44000-44999/44859.pdf

There are two different shrinkages discussed in this thread. Solidification shrinkage is the volume change on solidification. It leads to shrinkage porosity in the case metal. The purpose of risers is to make the last solidification happen in the riser so that the shrinkage porosity is in the...

You can also use nitric acid to remove taps from aluminum.

K2, do you have a reference for this data? I've never heard of a metal having compressive strength that is 20% of the tensile strength. Metals (especially ductile metals like copper) have nearly equal tensile and compressive strengths, in my experience. I'd like to learn more about thjis...

Actually, the 9/16 diameter hole probably doesn't have a 9/16 diameter (as measured with a true cylindrical go/no-go gage). So instead of putting a diameter, I usually just say to drill with 9/16 drill (or whichever size I prefer -- 9/16 is too small for a clearance hole on a 9/16 bolt). Carl

And if you don't specify the temperature, you don't have a prayer of having a 240" part to even within .010, let alone .0001. Carl

I had a student this year put a clearance hole for a 7/16 inch bolt at 0.40 inches. Oops! Carl

Another 2D Cad product that is free is QCAD. It's a German prouct Carl

Hardwood or micarta. Possibly corian.. Carl

I used FreeCAD for a while. It was good for solid modeling at the time, but the drawing modes were not powerful enough for my needs. I'm now using Onshape with a free license. Great 3D CAD and drawing module. Programmable feature creation. Free to use, with the caveat that your models are...

I haven't used DeskProto for a while, but when I did use it, it didn't work off the actual geometry, it worked off an STL file. STL files are made of triangular facets, so every curve you can make on the part is a series of short line segments. If DeskProto still works like it used to, it...

Many years ago I had a graduate student do this as a means of easy fixturing for rapid (minimal knowledge) CNC machining. We used DeskProto as well. We used plaster of paris, instead of epoxy, and it worked well for machining on aluminum or plastic. We didn't try it on steel. Carl

I agree with the worry about the structure, but the way I read his design, the box is not structural; it only holds up the lid. A heat sink bonded to a hole in the box with some kind of adhesive, or screwed in place and sealed with adhesive would seem to.meet the listed requirements. If you...

Here's a listing for a 10" x 12" aluminum heat sink. $109. Has a thermal resistance of 0.21C/W, which means that if it is mounted vertically into the side of your box, it can dissipate 60W with a 12 degree temperature rise using only natural (free) convection. Unfortunately, this doesn't work...