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Projects ... A3 Journal Boxes, Bearings, and Columns   3/06/06, 3/12/06, 3/23/06

This page covers the machining of the Journal Boxes, Bearings and Columns ... Section 3.0 pages 12 through 18.
Another page will cover the rest of section 3.



The Journal Boxes (all 8 of them) are made from 360 Brass bar stock. I have been getting my stock from McMaster-Carr. I started out with a 5/8" square rod and cut each box to an approximate length of 7/8" using my HF band saw (and I thought 12L14 cut easy). Then placed each one in the four jaw chuck for facing and turning for final length of .8125" (13/16"). This sequence is fairly simple ... so I skipped the pictures.


Where does that bearing hole go?!


A deviation on finding the bearing hole: Kozo provides a method using a Center Test Indicator with a four jaw chuck. After thinking about that for a while (and asking Dan a few questions) I decided that using my mill/drill with a DRO could do the job with the same accuracy (or better). Plus once I found the center ... I could use the stationary jaw and a stop for the remaining 7. But it gets better, drilling and tapping the 32 holes can be done using the same idea. Find the location hole "A" in the x and y plane (using an electronic edge finder) then at the location for hole "A" zero the DRO ... the location for hole "B" is .3750" away in the x direction. Hold on ... I'm getting ahead of myself. Let's back up and show a few pictures of the bearing hole and groove operation then the hole sequence.



The picture on the right shows the boring operation on the last of the J-Boxes. The center drill and a 3/8" drill was used to get things started. The hole location was simply found by using a electronic edge finder in the x - y plane, move table to that point now zero them (although not shown, I did a use a stop in the x direction). Lock down the table and we are good to go! The hole diameter spec is very tight at .3940" to .3950", so we need a "go - no go" gauge (on the right). It has two diameters ... at the very end it's .3940" (the go), then the diameter changes to .3950" (no go). I lost a few J-Boxes because I wasn't careful enough in boring the bearing hole, the gage would "drop" in the hole .. diameter was about .397" plus in one case ... more scrapped parts!

In boring ... you (I, that is) need to take into account flex and any change in the diameter setting is actually doubled! Go slow and take measurements after each cutting!!
The groves milling was the easiest part ... just place them side by side in the middle of the vise, find y edge move over .0625" from the edge and start your cut ... move over a little more until the grove diameter is .3120" to .3130" (a little tight but manageable). Find your depth and your done! I actually didn't lose any J-Boxes for this or the 32 hole drilling operation!


The "W" on the side ... it is actually a "3". I numbered each one and labeled the cutting side (the red line on top). It makes things a lot easier and quicker to know what side I need to cut before cutting!

Drilling and tapping the 32 holes  (over 318 operations) ....

These three pictures shows the center drilling (left), drilling using #47drill (middle) and finally the tapping (right). Without using a drill fixture.
Finding the hole location was easy enough using the DRO, once found I simply placed the J-Box against the stop, clamped down the vise, moved the table to the location required ... zeroed and drilled. Removed center drill, used a #47 drill and carefully drilled to the required depth (.1875"). Can't go too deep otherwise a breakout could occur in the bearing hole. Finally replaced the drill bit (without moving the table) with a 3-48 starting tap. Without power slowly turned the tap about a 1/2 turn or so then back off a 1/4 turn. Once both holes were tapped, I would remove them and finish the tapping operation using a bottom tap (get a few more threads). As you can tell this sequence required many chuck operations. I was wondering if I could have center drilled all 8 J-Boxes (32 holes), then drilled all holes and finally tapped all holes. That certainly would have reduced the amount of chucking and un-chucking. I guess if I thought that I had very good repeatability in the setup I could ... on the other hand, it really wasn't that bad and I knew everything would be lined up exactly ... so I did it the hard way.


Now for the exterior milling ....
 
This required two fixtures to get the correct cutting angles on each side. The top left is for the short side and the top right picture is for the long side. I used material on hand, with the aid of a CAD program they were easy to make.




The final 8 Journal Boxes except maybe for finishing. A little 600 grit sand paper and rounding the edges might be in order .. however, if I paint why smooth them out ? Painting would prevent discoloration in the future, but the brass look would be gone. So later on another decision needs to be made ... paint or not.
Now the Bearings (update 3/12/06)
Those 8 very little (.392"x.270") Journal Bearing are made from 936 Phosphor Bronze, a premier bearing alloy that has low coefficient of friction and anti-seizing properties. This is exactly the material that is needed between the axles (Stainless 303) and journal box (360 Brass). Recall that the tender wheels are fixed to the axle using Loctite, the axle with the wheels are rotating on the Phosphor Bronze rather then Brass. These bearing have a 3 taper so that each wheel can tilt on it's axles independently from the other wheels. I ordered 13" x 1/2" round stock from McMaster Carr for $6.16 plus shipping. I thought 13 inches would be plenty. There is a lot of waste due chucking and parting off the bearing.
To start with I cut each bearing to a length of 3/4", this provided enough material to chuck and part. So the waste is about 1/2" each or about 4". But of course I must include a few that I will probably lose. In this case 5 were lost due to turning the diameter too small or not leaving a flat diameter length of .020" (not critical, but should have some flat top). It has a tight diameter between .392" and .393" which leaves about .002" to .003" room within the journal. My first 5 were rejected but I finally got the method down and the next 8 were acceptable. Good thing too as I was running out of material!
Drilling the axle hole was simple and straight forward as was reaming to .250", go slow and easy.


The above pictures shows the method of obtaining the 3° tapers. The same idea Kozo introduced for the tender wheels. i used the same fixture for the tender wheels, plus a taper and a negative taper. The red ink mark on the bearing is used to know when to stop and start the tapers. Using X10 loop and calipers I judge the width of the flat top. It should be 0.020", in most cases I was able to get between 0.015" and 0.025".

After trimming the right taper for proper width, parting the bearing was next. With my modification to the top slide and lots of lube it was easy. Again, I just went slow, feed evenly and
the job was done in no time.


Remember those rejected axles? Well here is perfect place to use one! After parting the bearing it needs to be re-chucked to get the final length of 0.270" and face the other tapered end. Kozo suggests using the reamer for alignment, I tried but was not happy with the marks that were left on the inside of the bearing.

So I switched to the axle ... worked much better for me.




So how did my bearing turn out?
Bearings
Measurement Specification High Low Spread Average
Outside Diameter 0.3920"-0.3930" 0.39325" 0.39225" 0.00100" 0.29270"
Length 0.270" 0.27260" 0.26665" 0.00595" 0.27190"

Very pleased with the work even with them a little on the high side of the spec, they will fit the journal boxes without any binding. And I can always take a little off if needed! The length has no real spec, as long as they are not protruding out from the Journal Box we should be okay.

   
So here is what they look like ... from raw stock to the finished part.

And here is what the Tender Wheels, Axles, Journal Boxes and Bearings look like ... nice.

Moving on to the Columns (3/23/06)
Kozo starts out with the fact that the thickness and clearance between the columns must be accurate. And how is that done? With an accurately made fixture , of course! Since we'll be silver soldering using the fixture made from 360 Brass this will  keep thermal expansion same for all the mating pieces.


To start with the columns are machine from 5/16" square stock. A recessed area is cut out leaving a small lip of about 0.011" that rides against the bolster (above left photo). To get this accurately I hung the brass outside the jaws then made a small cut to get a depth and width. Once obtained I cut the full length of the square rod. My Calipers did not do the job for me as I could not get repeated measurements so I switch to the micrometer ... now not a problem! The accurate part is the 0.311" to 0.312", since it is already 0.3125" (5/16" stock) no cutting is required. Once that is done reposition the bar to mill off the top area for a thickness of .250". One thing that did surprise me was that after milling the top, the bar was warped a small amount, different feeds and depths of cuts didn't help. Not a problem though, as it only about .010" over the 7" length so a small adjustment brought it back without a problem. Next I cut them in lengths of 1.3" then placed them in lathe using a 4 jaw chuck. Turned them down to exactly 1.250" ... all eight of them! We're getting good at this!


The top of the column came from a stripe of brass (1/16"' x 1/2") material so that I only had to mill the width to .312". Cut them to about 1" or more in length, stacked them and milled them down. Easy enough. The drilling for the screws and tapping for the column was next. The only issue was not being able to find 1-64 screws, looked everywhere but just couldn't find them in brass. They must be brass because they will be silver soldered into the columns and then filed flush with the top. Since they will be re-drilled for a 3-48 screw to attach the Ties and Arch bars, I switched to 1-72 that worked fine.
Here we can see how everything is put together ... the fixture that holds both columns together at a precise gap of 0.625"; the top that is fasten to the columns with 1-72 screws and the two screws holding our fixture. A small amount of silver solder is placed on the inside joint that holds the top and column together. Position the assembly so that gravity will pull the solder into the small gap (about .001" or so). This photo shows that the assembly is a little too hot, after a doing a few joints I was able to get the process down. See my review of the soldering torch that I used Silver Solder Torch.





My final results ... the top photo show a close-up of one of the columns. A lot of oxidation that comes off real easy. Notice there is too much solder on the right joint, after a few tries I was able to apply the correct amount to get a good joint. The top right photo show the column at various stages of assembly. And finally the finished product! Nice and bright! I will drill/tap the top and bottom later when I'm forming the Ties and Arch bars.

One word of caution ... remember the column dimension of 5/16" that did not require any machining? The stock is actually 0.3115" (mine was anyway) compared to the final dimension of 0.311 to 0.312" ... be careful as that only leaves 0.00025" on each side that can be removed. It is very easy to remove too much brass when cleaning and forming the edges. Mine was reduced to about 0.3105", however, looking ahead at the bolsters I don't think this will be a problem.




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