Constructing the Josslin Hudson

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Carrdo
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Re: Constructing the Josslin Hudson Part 54 (Update)

Post by Carrdo » Sun Jan 16, 2011 4:11 pm

Here are some photos of the stress relieving operation on the extra 9D axlebox castings. They have been soaking for about 2 hours now as I write this. Then the furnace will be turned off and the castings will allowed to cool down slowly for the next 24 hours before they are taken out of the furnace.
Attachments
66 At Stress Relieving Temperature.jpg
65 Axlebox Castings in Furnace for Stress Relieving.jpg
64 Richard's Electric Heating Furnace.jpg

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Carrdo
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Re: Constructing the Josslin Hudson Part 54 (Update)

Post by Carrdo » Sun Jan 23, 2011 6:33 pm

Oh well. The great experiment has started.

After a week of dithering, I finally decided to stress relieve the nearly finished machined axleboxes as well. If things go off the rails, so to speak at this point, I will be faced with making a new set of axleboxes. But Richard doesn't think so.

I just decided to do the one which has the least metal left on it (to machine off) so if this one is OK, the rest will go into the furnace. It is cooking away now.

The photo is of the remaining raw castings after days of cooling. You can see the result of the heat treating by the colour in the ends of the saddle arms.

I just don't want any more outward spreading of the saddle arms as they will only be 1/16" finished thickness on their ends.
Attachments
67 Stress Relieved Castings After Days of Cooling.jpg

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Carrdo
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Re: Constructing the Josslin Hudson Part 54 (Update)

Post by Carrdo » Thu Jul 28, 2011 3:19 pm

After a long period of working on other things, I finally got back to try and finish the axleboxes. It is now over a year since I first started working on them and at the time gave myself 2 weeks to complete the job.

Anyway, to continue the story, in the end all of the machined axleboxes and the extra axlebox castings were triple stress relieved. At the outset, I found an obscure reference on the net to stress relieve 9D at 500 degrees F for 1 hour per inch thickness. Richard thought that we could go higher with the temperature but I was afraid of what might happen to the long thin saddle arms. To counteract any spreading tendency, I inserted the long spring saddle base bolts and with them tightened the ends of the saddle arms to the exact distance of the saddle piece which was 1/2" (- 0.005") or 0.495".

The first run was made at 500 degrees F. The furnace was turned off and left to cool naturally for the next 24 hours. All the castings looked good and nothing had moved so everything was put back and heated up to 650 degrees F and then cooled down again. Everything still looked good so a third run was made at 800 degrees F.

At this point we figured there would be insignificant residual stress remaining so to leave well enough alone.

The operations to bring all of the previously paired (and now stress relieved) axleboxes to their finished external lengths, widths and thickness' were then completed.

This time, I got a little smarter and employed a C2 carbide tool bit to do all of the roughing cuts before finish grinding (see photos). There was no further spreading of the axlebox saddle arms. However, I did go gently on the depth of cut when machining the ends of the saddle arms. The last thing I wanted, at this point, was to have an arm crack or snap off.
Attachments
342 Flycutting a Stress Relieved Axlebox Using a C2 Carbide Toolbit.jpg
343 Grinding a Stress  Relieved Axlebox to Final Thickness Without Glueing.jpg
344 Paired Axlebox Assemblies as of July 2011.jpg

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Carrdo
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Re: Constructing the Josslin Hudson Part 54 (Update)

Post by Carrdo » Fri Jul 29, 2011 10:42 pm

Continuing with the final boring of the axle openings.

The axles on the Hudson are a nominal 3/4". I final bored the axlebox axle openings to 0.749" or thereabouts and then used a 3/4" hand reamer to act as a scraper with both axleboxes set up in the frame. My reasoning for this is if there has been any slight machining errors which have crept in unnoticed, the reamer will end up scraping the two opposite axleboxes dead in line with each other. However, this will only be true for the orientation each axlebox has when the reamer is put through. As a result, all of the axleboxes have to be marked to maintain their original orientation if ever the axleboxes are removed and reinstalled.

An 0.001" allowance for final scraping is not much so I have a lot of confidence that my axleboxes are truly matched and were machined square in every direction.

The first operation is to pick up the central bore of a matched pair of axleboxes from a close fitting plug. I only have one indicator I trust for this level of accuracy. See the first photo. Of course the mill itself and milling vise have to be indicated square as well.

The final boring was done with a C2 carbide boring bar as shown in the second photo.

Then a hand reamer (which was turned by hand) was employed to scrape out the last "thou." with the axleboxes in place as seen in the last photo.
Attachments
346 Picking Up Axle Bore.jpg
347 Final Boring the First Matched Pair of Axleboxes.jpg
348 Final Scraping with a Three Quarters Inch Reamer.jpg

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Carrdo
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Re: Constructing the Josslin Hudson Part 54 (Update)

Post by Carrdo » Fri Jul 29, 2011 10:58 pm

It all comes down to this.

Will a 3/4" diameter straight and on size bar now slide through both axlebox bores without binding or slop and will the dummy axle/axleboxes assemblies still slide up and down freely in the main frames and rock and roll as well with the spring base blocks and springs installed on the axlebox arms with everything tightened up?

Yes, they will but I found them on the tight side so they will have to be run in.
Attachments
349 A Dummy Axle Installed.jpg

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Re: Constructing the Josslin Hudson Part 54 (Update)

Post by Carrdo » Sun Aug 14, 2011 1:35 pm

The first fitting of the main driver assemblies.

No, I did not work all night to produce them. I got them about 2 years ago from Bill Shields who had an extra set and offered them here on Chaski.

To summarize, they are Hoffman Hudson Boxpok main drivers.They are both quartered and keyed. The back to back dimension on the main driver rim is IBLS (i.e. 3 - 9/32") whereas the Josslin drawings show 3-1/4". It all depends upon whether your drivers are machined totally flat back or not and whether they have an axle center hub on the backside of the driver and how thick you can make the hub. This depends upon how much extra metal there is on the driver casting in the first place and whether a sufficient machining allowance has been allowed to do this. On many castings, one finds one can't due to insufficient metal being there.

Bill, thank you once again for saving me so much time and effort in not having to machine them.

After reaming the first set of axleboxs in place in the frames, I didn't do that on the remaining ones. They were just fine bored in matched pairs without the plug. I first made certain the axlebox frame slots were exactly at the same height (checking with a vernier height gauge) when sitting on a precision flat surface and then aligned the axleboxes in the vise with their bottom surfaces set against the heavy square spacer block shown in the previous photos. As I hadn't changed the mill or vise positioning, what was bored on the first pair also was repeated on the second and third pairs.

In the past, I have used a fixture developed by Don Young on his Marie Estelle which was used to align the axlebox frame slots when the axleboxes were final bored in matched pairs on the lathe faceplate.

I do admit to using a little lapping compound to help with the final fitting. My axleboxes will now all drop down in the frame openings under their own weight (with the frame keepers installed) with absolutely no shake front to back. Also, curving the axlebox flanges allows the entire driver assembly to still rock and roll without any side movement of the axleboxs.

The above is very time consuming. It all depends upon how much effort and care one wants to go to. I always fit everything on the tight side initially, on the theory that it is easier to remove metal than to put it back on again but that's me.

In the fitting it became apparent that with my method one has to carefully and correctly mark everything including each axlebox cellar piece and spring base block. If anything is reversed or mismatched, the assembly will not go together properly with the exact fit involved. To do this, I used a Sharpie pen when machining as Jack Bodenmann recommends but for the final fitting everything will be etched. I said etched not stamped as with fine machined pieces in bronze such as the axleboxes are, stamping can distort the part/fit if one is not ultra careful. Ask me how I know. An etching pen is something I don't have so another tool to buy. Stamping heavy steel parts such as the main frames is fine.

Even at this stage, the clearance between parts is very limited. The only way the spring base block bolts can now be installed or removed is through one of the larger tapered openings in the Boxpok wheel. See the second photo. The third photo shows what little room there now is between the frame filling pieces,the axlebox spring arms and the main drivers. The axles have to have a bit of lateral float (.020"-1/32") so I am wondering how it will all function.

If this locomotive had all of the bells and whistles added, I don't think it would ever move!

One final curve the 9D aluminum bronze will throw at you is the axles should be glass hard if you want this running fit to last for centuries. As I am not going to heat (to case harden) a finished axle assembly, alternatively, one can polish and then commercially flash hard chrome (0.0005" total thickness) the axlebox bearing area of the axle. Its only money...

Anyway, back to the final fitting...
Attachments
350 First fitting of Drivers.jpg
351 Closeup of How the Spring Base Block Bolts Can Now Only be Installed.jpg
353 Very Limited Space Here.jpg
Last edited by Carrdo on Sun Aug 14, 2011 3:04 pm, edited 1 time in total.

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Carrdo
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Re: Constructing the Josslin Hudson Part 54 (Update)

Post by Carrdo » Sun Aug 14, 2011 2:21 pm

Just to show you what "tight" is:

An underside shot of a 3/4" scale Hoffman Hudson with all the bells and whistles on it and the backhead of the same locomotive.

The builder said never again.

It did move but I never saw it under steam although it was steamed and did run at the Richmond Hill Live Steamers a few times.
Attachments
Untitled-1.jpg
Untitled-2.jpg

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Carrdo
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Re: Constructing the Josslin Hudson Part 54 (Update)

Post by Carrdo » Thu Sep 08, 2011 10:22 pm

These axleboxes just won't give up but this time it was my doing.

For whatever reasons (the center axleboxes/drivers take the piston thrusts directly and the twisting force is greater due to the main rods being further out on the center driver crankpins), I decided to leave the center driver axleboxes 0.050" thicker than the first and third coupled drivers (0.675" vs 0.625" as shown on the Josslin prints).

This meant the clearance between the spring base block bolt heads and the back of the main drivers which was small before now vanished. So the bolts had to be recessed into the now slightly thicker axlebox saddle arms. To do this, with the minimum amount of metal removed, necessitated using a 9/64" dia. carbide stub end mill and plug gauge to first pick up the bolt hole locations.

Nothing special here, just additional careful work to ensure everything was square, centered and concentric. The thickness of the bolt heads themselves was also made as thin as possible (.065"). Still, there is not much clearance as the third photo shows. The axles still need to be able to move laterally in the range 0.010" - 1/32" for this scale and wheelbase so additional measures may be required. I do not want to recess the back faces of the drivers to provide additional clearance if at all avoidable.

Next is to permanently mark all of the pieces. I actually needed a full page of notes to have everything recorded correctly!
Attachments
354 Recessing the Main Middle Driver Axlebox Saddle Arms.jpg
355 Recessed Spring Base Block Bolts.jpg
356 The Limited Clearance even with Recessed Bolt Heads.jpg

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Bill Shields
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Re: Constructing the Josslin Hudson Part 54 (Update)

Post by Bill Shields » Fri Sep 09, 2011 6:15 am

I am with the builder of the other Hudson, as in 'never again'.

the underside of mine looks very similar (just as jamb packed) - 90% of which is useless brake linkage.

Yes, it looks cool, but there are 100's pieces of 'stuff' that is only good for sliding the drivers.

My Hudson runs quite well and has a LOT of hours under steam.

You are most welcome regarding the drivers. I am glad you are putting them to good use.

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Re: Constructing the Josslin Hudson Part 54 (Update)

Post by LVRR2095 » Fri Sep 09, 2011 6:28 am

Bill Shields wrote:I am with the builder of the other Hudson, as in 'never again'.

the underside of mine looks very similar (just as jamb packed) - 90% of which is useless brake linkage.

Yes, it looks cool, but there are 100's pieces of 'stuff' that is only good for sliding the drivers.

.
I am with Bill 100% on the brakes on a 3/4" scale locomotive. They may look good (assuming you turn the engine upside down...not recommended during a run) but they won't stop the train. You want the brakes where the weight is, which in my case is wherever I'm sitting.

Keith

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Carrdo
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Constructing the Josslin Hudson Part 57

Post by Carrdo » Tue Sep 13, 2011 10:05 pm

Just a peek at what comes next.
Attachments
357 Side Rod Fixture.jpg

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Re: Constructing the Josslin Hudson Part 57

Post by Carrdo » Tue Sep 20, 2011 9:47 pm

The first job I wanted to do was to determine the side rod crank pin spacing using the fixture as I was curious to find out how uniform and close (or not) was the spacing to the print dimensions.

This goes right the way back to the layout and machining of the main frame axlebox openings, the machining of the axleboxes themselves, how central the axle opening is in the axleboxes and how accurate and uniform are the crankpins and crankpin throws on the main drivers.

All of the above factor into where the crankpin openings in the side rods will come out. Also, any of the above must be constructed to a tolerance which may be random, additive or cancelling.

Remember, I use nothing digital, the axlebox openings in the main frames were laid out using a good graduated scale, eye loupe and scriber.

The side rod fixture merits some discussion first on how it is used.

The socket head cap screws are first loosened and the length of the fixture is adjusted until the fixture slips over the two driver crank pins without shake or binding. The correct press fit on the hardened drill bushings allow this to be done very easily if the crank pins themselves are machined dead on size. Now tighten the cap screws. Now check that both drivers will rotate 360 degrees without binding with the fixture in place.

99% of the time, on the first go round, the two drivers will bind usually at or near the front and back dead centers. Where binding is first encountered carefully loosen two of the cap screws at one end of the fixture (without touching anything else) and then carefully re tighten them without physically altering the length of the fixture. Now you will be able to rotate the coupled wheels just a bit more before the drive wheels again bind. Now, just repeat the process again carefully until the coupled drivers are just able to be rotated past their dead center(s). You have now found the sweet spot which is where the two coupled crank pins are exactly aligned radially. Carefully, fully tighten all cap screws and check to see that the wheels will rotate freely 360 degrees. If the fixture now binds in other locations, the crank pin throws are out.

Correctly made, the fixture is very sensitive in this regard and it will always show if your crank pin throws are out.

Some things to note.

Depending upon the length and configuration of the crank pins on any particular locomotive, different lengths and thickness of the spacer piece (or none at all) will be needed to have the fixture fully seat on the two crank pins. In the photo, one spacer piece is shown sitting on one of the wooden blocks while a thicker one (the dark metal) is on the fixture itself.

The slot length(s) in the various pieces need to be made so that the fixing cap screws are always free of the ends of a slot as a fixing screw restrained at the end of a slot behaves just like a drive wheel bind. Also, no part of the fixture should touch a crank pin when the wheels are rotated. Obvious, but easily overlooked.

As shown in the photo, when I measured over the pins (with the vernier caliper shown in the photo) inserted in the drill bushings, I got a vernier reading of 5.749". The Josslin print shows a distance of 5-5/16" centerline to centerline distance between the crankpin openings on the rear side rods. The two openings are 1/2" and 3/8" finish bushed.

You be the judge. I guess (any of) the errors made were in this case cancelling. Beginners luck?
Attachments
358 Determining Side Rod Crankpin Spacing.jpg

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