Another 1.5" A3

[kvom]

I have made a start on the frame, which has 5 main pieces:  2 side rails, a front bumper, a rear footplate, and a crossmember.  I didn't take any pics milling the side rails from 1/2x2.5" CRS, so here are a few more recent progress shots.

The left side rail needs a 1.125" hole for the blowdown valve.  My largest drill is 15/16, so I bored it out:



Next, fabricated the rear footplate from 1.5" square CRS milled down to 1.25x1.25.



I used the footplate holes as a drilling template on the side rails:



The frames are too big for my little tapping stand, so I used the mill spindle to start the 10-32 tap straight.



Here are the side rails, foot plate, and crossmember in "position".  I'm waiting to get fasteners from Enco.  The crossmember needs to be remade due to "operator error".  



Next is the front bumper, made from 1.5x1.5x13.375 CRS.  After milling and drilling the mounting slots, I used the CNC mill to round the ends:





The front bumper will get a lot more threaded holes, but I'll hold off until I make the parts to mount there.

The engine has a few hundred parts to make, but these are the largest sizewise.  The side rails are 3' long, and are the largest pieces I have ever machined.  Though the Bridgeport table is 9x42, the spindle X travel is abou 24" max, so I needed to move the rails sideways a couple of times to mill and drill all the features.  For alignment, I use a pair of ground rods that fit in the table slots.  The pieces are pressed against these rods before clamping.  I used parallels under the rails to clear the table.

I have ordered the driver castings from Friend's Models, and will start on those when they arrive.

I have a pretty good supply source for free CRS/12L14 steel cutoff pieces in various random sizes, so I will likely try to make parts in random order as I find drops that seem to fit them. I also ordered some SS bars from Enco that will be used to make the fire grate, so that's a likely nearterm job too.

No lack of things to do.

[kvom]

Managed a bit more progress by milling the opening for the tee in the side rails. First CNC op was a pocket using a .5" roughing endmill leaving .025" clearance:



Then a finish profile cut with a .25" carbide endmill:



After deburring the edges:

[kvom]

Only shop progress today was remaking the crossmember, which was a success this time.

I weighed the 5 members of the frame on a bathroom scale and got a total of 35 lbs.

[kvom]

A main difference in the 1.5 scale vs. 3/4 scale versions is the need for brakes on both the engine and tender. Today I made the first of many parts comprising the braking system. The spring stirrups straddle the side frames, rest on the axle boxes, and connect to a leaf spring assemble above.

Starting with a length of 1x1" CRS, I successively milled the slide profile for the four stirrups:



After cutting off at the bandsaw, the rest of the milling was manual:

[esteam]

Wow! what a fast start. Looks great as usual Kirk. I have just started from tender truck. I am still machining the arch bars. So I have too much work to do

Best Regards my friend.

Erdem

[kvom]

Dec 5, 2010 14:22:35 GMT -5 esteam said:

Wow! what a fast start. Looks great as usual Kirk. I have just started from tender truck. I am still machining the arch bars. So I have too much work to do

Best Regards my friend.

Erdem

Looking for pics Erdem! ;D

The 1/2" stainless 304L rod arrived from Enco, so I decided to make the 22 spacers for the fire grate. Drill 1/4", then part off .21" doughnuts.



A fellow in my club said that when he made a new grate, he used SS nuts as spacers! No machining needed.

Since I had to order 6' of the rod, I also made the two brake beams from the same material:



I still need e-clip grooves on one and fit the ends to bushings on the other.

[phutcheson]

kvom,

This is going to be fun watching!!


Keeper coming ....

Pat H.

[kvom]

The stainless bar stock showed up, so I decided to continue building the fire grate. The stuff from Enco is 304, not 304L and is pretty hard to work. I started sawing off 7.5" sections, and by the 5th piece my band saw blade was shot. In reality cutting with a roughing endmill would have been better. I had to go to school anyway and was able to cut off the remaining 5 pieces plus an extra while there.

Back home I used a 1/4" carbide endmill to cut to length. Here's my setup on the Bridgeport:



Afterwards:



It seemed to cut best with a fairly fast feed; my DRO showed me turning the y-axis at 10ipm. I then set up a stop on the fixed jaw to drill the 1/4" holes. Again, both the center drill and drill seemed to like a like of steady, heavy pressure. For the 1/4" drill I needed to peck twice to clear the swarf, and avoid chips welding to the drill; I used lots of cutting oil too. Afterwards I used a 60-degree countersink to chamfer all the holes.

After turning two pieces of 1/4" SS rod to length and center drilling, all the parts are ready for assembly:





The total width is .04" short of plan. I don't think that's significant, but I will wait until I've made the support rails and checked fit before staking the assembly.

[kvom]

Most of today's shop time was spent working on the grate supports. All the machining is manual on the Bridgeport as I was also researching a suspicious noise on the CNC mill. In any case, I will finish the front end profiles and the latch pockets via CNC later on.

Here's today's output:



And a trial install on the frame with the grate:



UPS showed up this afternoon with my order of bearing bronze and a 7/8" reamer, so I can start working on the axle boxes and drivers next.

[kvom]

I spent the best part of the past two afternoons working on the axle boxes. These are to be made from phosphor bronze. Since this material is mostly available in round rod, I calculated that the end dimensions of each half of a box could be fabricated from 1.25" rod, although ~50% ends up as swarf. Being conservative of the material, I parted off 8 sections 1.91" long (.10" over), then faced both ends of each piece. Before going into mass production, I did the first piece solo to check on the machining qualities of the material, which was new to me.



As each of these pieces represents about $7.50 material cost, I proceeded slowly, measuring frequently, to arrive at 8 nearly identical blocks:



Four of these represent the bottom halves, and need 4 through clearance holes for 8-32 screws. A small piece of aluminun underneath spared the parallels. The holes were then counterbored.





The four tops were drilled 3/8" deep and tapped 8-32. I started the first couple of threads in each hole using a tapping stand, then finished to depth with a normal tap wrench.





I left it for the day with the two halves fastened together with screws. The next operation will be to mill side slots to fit individually to the pockets in the frame.



Before quitting for the day, I took the first step and turned the treads on the driver castings. Measuring with the DRO on the lathe, the treads have a diameter of 6.63", which leaves a lot of extra material assuming a final tread diameter of 6.375.

[kvom]

I had a short shop day, so not as much progress as I'd hoped. The first order of business was to mount the 3-jaw chuck with the soft top jaws, and to turn a pocket that matches the 6.63" tread diameter that I'd turned previously on the driver castings. As long as I don;t remove the chuck, I should be able to take the casting on and off the lathe without losing accuracy.



I then faced each of the drivers' inner sides, turning at 300rpm and .001"/revolution. Quite a slow process with lots of messy black powder coming off.



The final op of the day was to center drill.



I had borrowed a 27/32 drill from school intending to drill the axle hole prior to reaming it, but realized that it was a 4MT rather than 3MT. Since I have a brand new, US made 13/16 drill bit with a 3/4" shank, I plan to use it and then bore the hole 1/32 larger before reaming 7/8. Before I do that to the first of the $80 castings, I'll check it out on some aluminum to make sure I don't overbore the hole.

I also realized I should have faced the outer side the same time I turned the tread. It's not a big problem as I can do it with the soft jaws as well; just extra work. Once I'm finished with the soft jaw setup, the rest of the machining will be done on a mandrel to cut the tread/flange profile.

[kvom]

Today's afternoon effort was more work on the drivers. After first taking a skim cut from the outside face, I proceeded to drill/bore/ream the axle hole from the inside face. I tried it on a piece of Al first to make sure that the hole after boring was still smaller than the reamer.

Drilled with a 13/16 drill; 500 rpm:



Next, bore to .843:



Finally ream to .875 at 200 rpm:



Buying the .875 reamer is likely a good "investment" as I still need reamed holes in the axle boxes and axle eccentrics.

I was trying to determine how thick the drivers should be, as this would determine the length of the axles. After doing some figurings based on the distance of the cylinder center bore from the frame and the thicknesses of the rods, it seems that the IBLS minimum of .750" is what I'll need, as that leaves a clearance between the inside face of the drivers and the axle boxes of 1/16". Given that, the axle length is 8.62 in order to fit the 7.5" gauge track. At their current state, the drivers are ~.88" thick; I plan to take the remaining .12" off the outside face to avoid reducing the cross section of the spokes any further. One the drivers are at proper thickness, the rest of the machining will be done on a mandrel, to be constructed.

I am considering the best way to form the .094 radius fillet between the tread and the flange. I think I probably need to grind a HSS blank to get the proper form, or else purchase a rouund carbide insert and holder. Alternatively, I may just wait to turn the flange and tread profile on the CNC lathe at school

[kvom]

After spending the morning with my truck leaking fuel all over the driveway and street (hopefully just frozen o-rings in the fuel bowl), I did some more work on the axle boxes. The goal is to mill slots along the sides that fit the pockets milled into the frame.

Although the frame mic out at .515, the slots cut with a .500 endmill fit very well. So my guess is that there is at least that much runout on the mill spindle or the collet. In any case, I "whittled" the first one down until I had a very tight fit, and then added .006 as per the tolerances Kozo implies in the book. This allows a little front to back flex on the axles.



I then made a start on milling stock to size for the retaining bars that attach to the frame under the axle boxes.

[kvom]

Today's work started with finishing the axle box retaining bars and fitting them to the frames. Here's my setup for spotting the mounting holes:



Next, I wanted to mill the two slots on the top sides of the axle boxes where the spring stirrups ride. As there are 8 slots, and I would be using two endmills (1/4, 1/8), I just developed a simple CNC program to mill them repetitively:

[kvom]

Today's work was to finish the bores in the axle boxes. I decided to use a CNC technique I hadn't tried yet, which is milling a hole rather than drilling it. The method is to have the endmill make circles around the center while steadily lowering the Z-axis. For me the advantage was being able to mill a 27/32" hole while not having a drill that size. Additionally the hole is rounder and straighter in theory than a drilled hole.

I first center-drilled each box, and then a .5" hole to allow the milling swarf to fall through rather than accumulating in the hole as it deepens:



The program used a 2-flute 7/16" endmill at 3000rpm and 20 ipm. Each 360-degree turn around was .010" deeper.

Next I used the .875 reamer on each bore. This reamer is over 7" long with a 3/4" shank, so not suitable for a mini-mill. It's not really necessary to ream the bore, but since I used the reamer on the drivers the diameters ought to match closely.