Bushed

I have been continuing sporadic work on the beam engine with today being a relatively quick wee part: a bushing to hold the crank shaft onto the crank. Given that this part was about 1/”8 in diameter and 5/16″ long, it is one of the smallest things I have attempted.

My ML7 lathe was supplied with an excellent ER25 collet set that mounts directly on the lathe spindle. I thought it would be useful but I am still growing in appreciation of just how much. Holding onto the 1/4″ round brass bar I started with was no problem but niether was holding the finished 9/64″ barrel so I could turn off the remains of parting off. And, as is the special property of collets, it did so concentrically as far as I can tell. Which is just as well since I needed to finish reaming out the center hole from that side.

I find this especially exciting since this is getting into the range where I could turn bushing, bearings and the like for 1/4″ scale railroad models if I need to.

Beam Engine Crankshaft

Having finished the crank, the obvious next step is the crankshaft. This will link the flywheel to one end of the beam and introduce the first interesting motion to the project. It is also the start of the wee small bits, at least according to my experience. Learning experiences were anticipated.

First I tackled the end that goes on a pin sticking out of the crank. I again used the method of milling the piece out of a larger bit of stock with the extra used to hold on to. In a flash of enlightenment, I realized I could up the game a bit by using my small toolmaker’s vise to hold the stock. I could then rotate the part 90 degrees without unclamping the stock.

The major work was done with the vise clamped to the rotary table. The fun bit was getting the appropriate spot centered on the table. I did this by center punching the spot, deploying my fancy new coaxial indicator which came with a tip for just such a purpose and gently tapping the vise around until it was centered. I then clamped it down and rechecked to make sure I didn’t shift it. Surprisingly, I also managed to get the thing square in the x-y plane to within 30 arc minutes. (I needed to know where to start and stop the rotation of the table to be planar with the straight sides of the piece.)

After I got the main body of the piece shaped and drilled, I needed to drill a hole in the flat end for the shaft. This was easily done by clamping the vise on its side in the mill vise. I found the edges by using a drill blank because there wasn’t room to get my center finder in there next to the vise jaws. I know that things are at right angles because the toolmakers vise has precision ground sides for just this sort of thing. I may have committed a sin by clamping on the jaws of the vise, though.

The last operation was just reclamping the piece wide side up and skimming off the back side. This was easy in this case because there are two parallel sides unlike the crank.

Next, I made up the crank shaft itself which was a simple matter of threading one end of a 3/32″ brass rod and cutting it to length. For the exercise, I used the lathe to square and shorted to final length the cut end. Here is the piece to date. I still need to do the other end which has a fork to go around the beam. I added my machinist scale to the photo for a size comparison.

Fits and Starts

I have managed to get crank attached to the crankshaft. A simple operation of you do it correctly or, in my case, not so much.

The drawings call for a press fit. This is where the shaft is about .001″ larger than the hole. You usually obtain it by using an “under” reamer, in this case a .124″ reamer to go with a .125″ shaft (O-1 drill rod). I had no such reamer and my choices were order a complete over/under set which seemed expensive or buy a single reamer for double the per/unit price of the set and a trip across town. So, of course, I opted for the third choice, use the nearest drill I had.

That turned out to be a #31 drill at .120″. Surely 5 thousandths is close enough for me to press a shaft in. Technically, I proved this to be true. Now if you specify that the shaft in question should not acquire a bend in it during the process then, no, I did not. It would not line up the holes in the flywheel bearing which is kind of the point.

I knocked the erstwhile shaft out with a punch and hammer and ordered the o/u reamer set like I should have done. I lucked out in that I did not have to remake the crank so I figured I should quit while I was ahead.

Here is the properly press fitted crankshaft in place.

Next I need to drill and tap for a set screw on the flywheel hub and then I think I will do the bits to connect the crank to the beam so I can see some bits moving together.

Cranking It Up

I may be getting the hang of this milling thing. Today I got most of the way through making the crank for the beam engine. This was two setups and more tool changes than it probably should have been but I am pleased with the result. I just need to mill off the back of the part to separate it from the block of stock I used as a handle.

It looks like it should even if it may not exactly match the drawings. I realized that the only things that really matter are that the two holes are parallel, the correct size and the correct distance apart. Everything else is mostly shaping things to resemble the cast part a full size engine would have. As long at things are symmetrical, nobody will notice if the end radii are a bit too large or small.

I also improved my finding of the center of the rotary table by using a new gadget, a coaxial centering dial indicator. This device gets chucked in the mill spindle and you center on the hole while the mill is spinning (at low RPM). This is actually fun as opposed to the usual dial indicator spinning holder that makes you keep having to move around to see the readings.

The other improvement which is much less photogenic was the acquisition of some drill blanks. I used a 3/32″ dill blank chucked in the mill to center up the part on the table center for the second setup so I could round the small end. I previously just used a reversed drill bit and I don’t think it produced as accurate results. The drill blank is both more rigid and has not flutes to mess with the alignment.

Cylinder Head

I finished up the cylinder head this afternoon. I had long abandoned my plan to drill the remaining holes on the cylinder since they are all varieties of clearance anyway. Instead, I used a 1/16″ drill blank to center the piston rod hole previous drilling on the lathe under the mill spindle and worked from there. As long as I got the relative placement of the holes correct, all would be well. Or almost, anyway.

I used my milling pallet in the vise and clamped the head face down on a small square of hardboard. The hardboard is flat enough and allowed me to drill through holes without messing up the shiny surface of the pallet.

I had a bit of a bad moment when I went to test fit the head on the cylinder block and the screws would not fit in the alleged clearance holes. Only then did I remember that I needed bigger holes for the M2.5 screws I was using. Back under the mill and a bit of hole size increasing and it was done. Here is the head fastened to the top of the cylinder block.

Since I had some more time and had a head of steam up (hah), I took care of a couple of small tasks I had been putting off. I shortened the machine screw that holds the flywheel bearing to the main body so it no longer projects into the flywheel’s running space. I also cut and cleaned up a suitable length of 1/16″ drill rod for a shaft for the beam. After a bit of assembly, here is the current state of the engine. Flywheel shaft is still pending so the flywheel is just propped in place.

It Has Been Remade

While waiting for paint to dry, I got started on a second instance of the beam engine cylinder only this time with less broken taps embedded. I consider this a triumph of will over fear of failure. I also suspect that the diligent work on the lathe drawer project concealed a bit of anxiety about the second attempt. With the drawers done, my anxiety was left place to hide so off I went before some other project arose!

This time around, I exercised extra care about the depth of the M2.5 blind holes in the cylinder end. I purchased a set of M2.5 taps (taper, plug and bottoming) and used the two extremes to get my thread depth without any optimism about hole depth. All was completed without incident although I think I could use a somewhat smaller tap wrench for this work. The one I have will hold the tap but I fear its weight threatens a break all by itself. I will have to do some research.

I resorted to marking the required depth on the taps with a marker. This seemed simpler than counting revolutions of the tap. 🙂

The cylinder is complete with the exception of plugging the two small holes in the side of the cylinder. These were the result of drilling through the valve into the cylinder bore. Those internal holes are wanted, the outside ones are not.

Next up is drilling the matching holes in the cylinder cover.

Miscellaneous Update #2: Project Pileup

I have three projects in motion at the moment where motion is defined as taking up a work surface.

  1. Beam Engine: the chemical removal of the broken tap experiment is a bust. I will have to make a new cylinder. New tap just acquired so I can proceed.
  2. RS-3 Proto:48 conversion: all over the workbench but I think I can make it work
  3. Lathe Drawers: because that wasn’t enough balls in the air I am taking advantage of the nice weather to turn a sheet of plywood into some drawers for my lathe stand so I can clear up the shelf pile of lathe stuff and stack of assorted cases under the lathe.

I should have the shelves knocked out this weekend if only because assembly takes up most of the good floor space in the shop.

It Had to Happen Eventually

I was tapping the second of the two holes for the screws that hold the beam engine’s cylinder head onto the cylinder and carefully feeling for the bottom of the hole and…

That shiny silver bit in the bottom left small hole is what’s left of my M2.5 tap. It had to happen on the last thing, of course. I was turning the tap wrench with just two fingers on the barrel and apparently I can’t tell when it hits the bottom.

As a personal triumph of character development, I uttered only a single profanity, cleaned things up and went off to see what my options were. Unfortunately, tap extractors exist but not for taps this small. I had no luck sticking some straight pins down the flutes and twisting with pliers as an impromptu extractor. I do have some nicely spiral pins now, though. Further research brought me to the chemical approach. I am now attempting to corrode out the tap with an alum(potassium aluminum phosphate) saturated solution. And taking a day off to look at other projects/pieces of the beam engine.

Offset Turning

As discussed in the last post, I need the beam engine cylinder head partially complete as part of my plan for drilling the various matching holes in the cylinder. This is a fairly straightforward turning of a 1/4″ projection on one end of a 5/8″ round bar. The fun part is that the projection is offset from the center of the bar by 3/32″. I thought it would be fun to show how I get the part set up in the lathe to achieve that.

Firstly, I blue and mark up the end of the length of 3/4″ brass bar. (It was actually .748″) Knowing the diameter of the bar, I measure the height of the bar sitting in a vee block on the surface plate. Subtracting half the diameter from that gives me the height of center.

I use the scriber on the end of the height gauge probe to scratch a line on the bar. I then rotate the bar and scratch a line twice more. If I haven’t messed up anything, all three lines should cross in the same place and that is the bar center. I then scratch a line 3/32 below center as perpendicular to one of the center lines as I can manage and center punch that point.

Now comes the magic part. I put the bar in the four jaw chuck and I set up my wiggler in the tail stock with the point in the center punched mark. I then adjust the chuck jaws until the pointer stops moving when I manually rotate the chuck. (Some people can just put an indicator on the bar and move the bar via chuck adjustment. I one try at that was an unqualified failure. This method works for me.)

Lastly, I set a dial indicator against the pointer and and refine things until it shows no movement.

Visually, success is demonstrated when I power up the lathe. The center mark should not be moving even as the actual bar gallops around. This is the ML7 going flat out at about 1100 RPM. It really is in focus! 🙂

Lastly, here is the finished product. Brass is like aluminum in that is comes out nice and shiny and looks really good.

I just need to drill the appropriate hole through the projection, and then I can re-chuck the bar in the 3-jaw chuck, turn it down to 5/8″ and part it off.