Pullies and lead screw

https://youtube.com/shorts/6r-MS5sE5aU

I've replaced another 3d printer pulley with a cast one, and also added the apron for the cross slide. The cross slide moves about 0.2 mm for each rotation of the lathe l.

The 3d pullies were starting to fail where the bolt was placed to tighten them on to the spindles.

Shaking out, still no biscuit

 So I added the riser, and the shrinkage is sorted, but I have a small hole in the casting, where the metal didn't flow.

hotter pour next time, I time from when the last piece melts.

I also checked to see if the pattern is wrong. It turns out that this section should be thicker, 3/16, not 1/16. Doh.

At least the riser seems to have sorted the shrinkage.

Close, but no biscuit

The two halves of the pattern are held together by pins, if the pin is too tight, then the pattern won't separate when you split the mold, so you can get breakage around the edges. If the pins are too loose the pattern can slide to one side and things won't line up...

I think that I can clean this up well enough with a file, as it's for a slow speed pulley....

 

Shrinkage

I forgot to add a riser, whatever cools last tends to shrink, particularly if it's thick.

Next times I'll add a big riser.

The riser has to cool after the part so that it can keep feeding in liquid metal as the part cools and shrinks.

A boring jig

Once you have a hole, you set the depth of cut by eye, then measure the diameter.

Then you can use this jig, with a set of feeler gauges to expand the hole by a set amount. Touch the floating bolt off the blade, back it off till you can fit the feeler gauge with a hint of friction, loosen the cutter, and move it forward to the bolt, tighten up and off you go.

Pretty rough and ready, but with practice you can get a hole bored to within 0.1mm, or about 4/1000" of an inch.

A little less breakout on the mold

 That came out pretty well, especially compared to the previous result below..

There was a lot of breakage at the edges here. That was from before I made up the template to hold the sand in place as I pulled out the pattern.

The template helps support the sand, and I've gotten better at rapping the pattern. If you don't rap enough, sand sticks to the mold and tears away as you pull out the pattern, if you rap too much, you break off parts of the mold. It's very much a trial and error thing that you learn by feel.

Drag, cope and hat

 Ok, it's not called hat by anyone else, apparently it's called an upset. I don't have a proper molding bench, so as the cope fills up, sand spills everywhere, add an extra frame, and I can fill the cope and ram it down with a lot less mess.

You can see the over-centre latches that hold the cope and drag together, a lot easier than trying to balance weights on the sand to stop the hydrostatic pressure lifting the cope.