Pressing concerns

After my slight misadventure with the cam, it became clear to me that there comes a time in everyone's life (ok, maybe not everyone), when it is time to build a press. Today's post is about turning this into that.

The "this" in this case are mostly parts that I took out of my mill when I was converting it to CNC.

The two key ingredients here are the thrust bearing (for transferring axial load)...

...and the trapezoidal thread lead screw. I'm also going to reuse the giant bushing (with the blue paint on it). The bearing and the bushing were used to move the head of the mill (which weighs about 250lbs) up and down the column, so they are hefty enough for the job I want them for.

The bearing used to sit inside the bushing at the top of the mill column with the weight of the head (and the 1HP motor) hanging on it, so the first job is to flip the bushing around so that it can be used to push instead of pull. 

There are a pair of perpendicular tapered dowel pins holding the steel bearing seat to the end of the lead screw, one of which I am reusing to hold a new brass nut (I also cut off part of the end of the lead screw journal to provide space for the nut).

The plastic spacer sits at the bottom of the hole in the bushing and draws the bearing seat and the bearing tight to the back.

The business end!

Now we make a series of holes in a piece of 1" steel pipe (which is painted and looks suspiciously like it may have come from a pipe clamp, which is odd because I don't have any pipe clamps, so sorry to whoever it was that lent it to me, you can't have it back now)...

...and weld on a couple of threaded end caps.

Now it is time for the base, which is a square piece of 5/16" mild steel plate.

The crossbar is made from some super-duper 2" stainless square tubing...

... which is drilled to receive the outside diameter of the tubing at the extremities and the lead screw in the middle. 

Then I flip the tube and cross-drill for the 1/2" pins that will hold the crossbar.

The lead nut that used to attached the head of the mill to the screw is an exceedingly rough iron casting. My disgust with the quality was such that I didn't take photos of the "before", before I cleaned it up to fit inside the crossbar.

Now it fits nicely inside the square tubing.

The finished frame.

Then I cut the screw in half because it is way too long as is. Definitely no going back now.

Add a new journal to the cut end...

...cut a flat...

...and put one of the old manual control wheels from the mill table on the end. 

I made a quick adapter for the cam bracket and (messy work space aside)...

...we have achieved 100% compression.

Piston assembly part 6 - wobble wobble!

Happy New Year!

Tons of progress over the last few weeks. I have lots to report, but the first post of 2018 is the last part of the piston build which I started before the holiday.

Unlike the other parts of the piston assembly, the head is a wetted surface and consequently needs to be made from a lead-free material. I bought some 2" diameter C69000 quite a long time ago for this purpose, but it has taken a while to get to it. Partly, this is because this stuff is expensive (even for brass). I also have to get it from the states, which is a huge added expense and hassle. SO: no mistakes! 

The rough diameter is pretty close to the diameter of the piston so I have to chuck the stock carefully to avoid excessive run-out. Unfortunately, it is too large for the internal bore of my trusty 6-jaw so I have to use the 4-jaw annoyance.

Remove a little material to get close to the desired piston diameter (close in this case is within 0.001"). Then the last thousandth is removed with a sanding block and a succession of grits (from 400 all the way to 2000). This puts the P in precision as far as my shop is concerned. 

Then we add the seal and relief grooves.

Once the grooves are finished, the internal bores at the top end are added.

And, after chamfering all the sharp edges, the piston head can be cut off from the stock.

The lathe work done, the part is put on the mill to drill the mounting holes on the top side. The copper foil is to prevent the steel chuck jaws from marring the hard-won surface finish of the flanges.

... and the pressure vents on the bottom. Having said NO mistakes, I then made one here. If you look carefully, you can see a seventh centre-drill mark where I drew an extra point for construction in the CAM file and forgot to erase it. Fortunately, this is just cosmetic as it doesn't pass through the flange.

A better shot of the vents.

Here is the collection of the parts for the assembly: the piston rod plus floating head, the piston head, three stainless machine screws and washers and an 8mm dowel pin (more on this last part another day). The little red arrow shows the relief groove that the washers will fit into to keep the head in place.

A close up of the connection detail with the washer in place.

And, the free-to-wiggle result!

Piston assembly part 5 - aluminum beds

Part two of this holiday build is the piston rod arm. Thanks to this part I now have a new favorite material: Aluminum 7075 - this stuff is awesome! Extensively used in aviation, it has similar mechanical properties to steel but obviously doesn't rust. It is easy to machine and the chips are non-magnetic (so they don't stick to the rare-earth magnets I use for holding chip shields etc in place). I just love this stuff. I think I'm gonna build my next house out of it - walls, floors, beds ... everything!

The blank is cut on the cold saw - the band saw takes too long with this stuff. 

Then it is turned down to the right diameter.

Then I turn down a stub to the major diameter of M10 (i.e. 10mm - got to love the metric thread system!) and add a thread relief groove at the shoulder.

Thread the stub with an M10x1.5mm die.

Cross-drill the other end of the arm for the the 8mm pin...

... and test the fit.

The finished piston arm assembly.

Piston assembly part 4 - aspirational wobble

Holiday special post!

After spending quite a while thinking about how and whether to re-engineer the piston I finally decided to duplicate an older Aurora assembly shown to me by Dr. Pootoogoo, famed baristorian. This design allows the piston head to "float" and self-align to the cylinder bore and compensating for any machining error (the so-called axial alignment problem that I identified with the first prototype of the group body casting a number of months ago). Although it obviously slightly more complicated than a fixed piston (extra parts and assembly) it will resolve any alignment errors that may be present in the first run of production castings. Additionally, swapping to the fixed piston design will be easy as the piston head itself will be machined from the same rough casting or stock.

Starting from a piece of 2" C360 brass:

Then I add a couple of angled cuts to the tip to approximate a radius - this is quicker to setup than cutting an actual arc and makes no difference to functionality.

Then, using a cut-off/grooving tool I add an undercut below what will be the flange.

Another groove is cut above the flange to create the boss that will align the spring.

Then the part is cut-off from the stock...

... and flipped around to be drilled...

... and tapped with an M10 thread.

After that I move the part to the mill and centre it with a probe.

Three clearing holes are drilled in the flange and boss.

To be continued!