Lathe Gear Cover

As part of the lathe restoration project I started here...

http://forums.thehomefoundry.org/index.php?threads/dro-mount-for-lathe-restoration.1397/

I converted it from a bench top to a cabinet model with countershaft under the lathe. There’s a lot of family history with the lathe. 60+ years ago, my Grandfather installed aftermarket quick change gear box instead of opting for the OE QCGB so the OE change gear cover/guards for cabinet models no longer completely covered the opening……..



……… so I decided to cast one to suit. Design-on-the-fly, a cardboard template translated to a couple pin router jigs.



……and after a visit to my pin router three pieces popped out.



Glued them up and let them set up overnight



……and then some rough sanding and detailing




Then removed what didn’t need to be there similar to the original.



….Test fit, looks good. It uses the same hinges as the OE guard.



Sprued. Thin walled parts can be a bit of a challenge so I ran large runners to the perimeter.



Coated. The other challenge with larger thin walled lost foam parts is they’re fragile and since I dip coat, the parts are quite buoyant and it can be hard to submerge them without breaking them, so submerge what I can and use a cup and ladle on the coating…..but you still have to be able to handle it wet, when it is a lot heavier.



It's ready for metal. -More (hopefully success!) to come.

Best,
Kelly

 

Hmmm, this one should be fun...

 

I use a fine point sharpie permanent marker because it's what I have in my bench drawer. The solvent attacks the foam so is marks easily, but a ball point probably works just as well.

Andy, it's mostly casting weight and experience that guides me because in lost foam, it's the evaporation rate of the foam that paces runner and gate metal velocity, not runner or gate area and head pressure.

Now, I do occasionally visit the naturally pressurized sizing guidance for open cavity casting, but in my experience, thin walled lost foam castings always have long pour/fill times compared to similar parts in conventional open mold casting so they tend to fill independent of the size of the feed system. I've timed my pours on identical parts in my videos with radically different feed systems and really no difference in fill time, just time to evaporate pattern total per pound of the pour.

When you get to more massive foam patterns (higher volume/surface area ratio), that can change because the foam can evaporate in a hurry and the feed/gate system velocities can approach those in open cavity systems.

This is also why top feeding tends to work so well in lost foam because doing so in open cavity molds just allows the metal to turbulently tumble into the mold, whereas doing so in lost foam just lets the metal front sit on top of the gas/liquid interface with the foam pattern as it tranquilly consumes the foam pattern.

So, it's a windy way of saying lost foam is less/insensitive to feed system geometry. In fact, this is even evident in industry because there is no consensus on gating and feed system design and things like sprue tree and feed system are designed for strength for coating and pattern stability versus feed system geometry..........but I still strive to minimize the amount of foam in the feed system because it consumes energy from the melt.

Best,
Kelly

 

Good weather for casting today so I got at it. Happy dance.

Here it is in the flask….



As Cast....



Degated and cleaned up.



The entire morning’s bounty.



Best,
Kelly

 

Thanks ESC, good to hear from you and hope you had a good holiday.

I hear ya on variable speed. I already have a 1/2hp 3 phase motor so I bought a VFD. I bought a digital tach for $10. Any reason you prefer DC to VFD AC?

Best,
Kelly

 

Thanks Mark. I'm having some fun.

I drilled and tapped a couple of holes and hung it on the lathe.



Best,
Kelly

 

You have a sharp eye OIF. No through defects just two small fold flaws as shown below.



If I was going to have a flaw they're right where I'd expect them to be.......where all the converging metal fronts meet and probably the first part of the melt to leave the cup. They are off center away from the half round feature which drew more metal from the feed system. Sometimes, on can put a bob on the bottom of the casting and try to attract that first instance of melt which often has oxides that create folds.

Like above, I think the flaws are folds that result from the very initial part of the metal that reacts with the foam in open air in the cup. If you have a good idea of how the metal will travel, put a bob on the bottom of the part to train that initial melt into the bob......but that often takes some imagination. As far as runner size, I can feed a 10lb part that is 1/4" wall with some thicker sections, with a 1 inch diameter sprue (so~3/4 in2 compared to your 1 in2) I use 1.25" square sprue for up to 20lb pour.....these are 1/4" wall high surface area/volume parts. How you divide that into the runners can vary depending upon the part. Ideally, I try to feed the part so the molten metal doesn't have to travel more than 6-8" from a hot runner and this is usually 1450-1475F pour temp. If it gets to 12" or more, fails become more common if you don't up the pour temp or add vacuum assist. 1/2 ATM of vacuum will usually get you to 12" back at <1475F.......it's a lot of seat of the pants but it's been working for me.

I don't put a center mark in the pattern. In fact, on these pulleys, I have a 1/2" hole from the pin jig and I fill that hole with a foam plug so it is solid....if I don't they tend to wreak havoc with flaws. I'll grip a circular casting on the OD and then bore the shaft. I plan on doing that with these step pulleys, then press fit an arbor, chuck on the arbor and machine the grooves and faces. I need to put a dial on the casting to see how flat they are. I may have to push them around a little to get them flat enough to turn because <.060" material rich sounds like a lot but if you have a little run out on a 9" diameter part.....plus not flat.....not so much. The concentricity of round features produced by the pin jig are usually pretty good.........but not good enough to not require machining for most of my purposes.

What it really takes to make working machinery is often underappreciated......

Best,
Kelly

 

If this was a structural or sealing part they'd probably spell trouble and need to be tigged. I suppose they could be filled with plastic, but I'll probably just leave them. Take a look at the swiss cheese on the iron headstock casting at the top left of the pulley speed chart........apparently I was just making the part period correct.....LMAO!

Best,
Kelly

 

Came out really well.