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Messages - Harold Downey

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121
Work and Events / Re: Sheepscot Turntable - Official Work Thread
« on: January 18, 2016, 10:47:48 AM »
I don't see the turning poles either.  The socket on the near end would be just out of the photo. You can see the track lock mechanism on this end -- a bar that is flipped back in the unlocked position in the photo.

122
Work and Events / Re: Sheepscot Turntable - Official Work Thread
« on: January 17, 2016, 10:03:29 PM »
And if you look closely, you can also make out the lantern hooks on each end - near side on the near end and far side on the far end.

123
Work and Events / Re: Sheepscot Turntable - Official Work Thread
« on: January 16, 2016, 11:50:09 AM »
The turning pole is clearly visible on the Albion turntable  -- see the last picture on the previous page.  The view here is not the side with the pole.  Both images seem to be the same time period, since both show the scabbed on piece of wood to stabilize the tall queen posts.

Harold

124
Work and Events / Re: Sheepscot Turntable - Official Work Thread
« on: January 10, 2016, 11:32:35 AM »
Here is a snapshot of the end of the turntable, showing both the turning pole and lantern bracket.  The turning pole socket will be forged from black iron pipe.

Harold

125
Work and Events / Re: Sheepscot Turntable - Official Work Thread
« on: January 09, 2016, 11:08:16 AM »
No problem, Gordon.

I am happy to discuss any aspect of the turntable.

Here's another couple of fun facts about the turntable:  On each end there is a lantern bracket, about 3 feet from the end, to hang a lantern for night operations.    There is also an angled socket on one side at each end to hold a turning pole. 

The turning poles must either have gotten lost, or the force to turn the table got too high, because some historical photos show workers down in the pit pushing on the side of the bridge to turn it.

Harold

126
Work and Events / Re: Sheepscot Turntable - Official Work Thread
« on: January 08, 2016, 10:59:20 PM »
I didn't really consider making the queen post angles different.  As you mentioned, the goal was to replicate the Wiscasset turntable, using the Portland Co. drawing as a reference.  Since I found no real design/stress issues with making both posts the same angle, I saw no reason to consider anything else.     

Not being a bridge design expert, I can't really comment on one design vs. another. 

Overall, this turntable bridge is a very robust structure.  The stresses in all the main elements are very low.  The primary limiting factor was deflection, which was governed by the longitudinal beams.  The truss elements function to keep the loads on the perimeter rail and wheels near zero once the locomotive is centered.  In fact if you look at some of the historical photos, there is only a partial perimeter rail. 

Finally, the bridge would still function without the truss, but it would be harder to turn.

For the stress analysis, I used the biggest WW&F locomotive as the design load --the 26 ton #6. 

It was quite fun to look at the historical photos and analyze the changes from the Portland Co. drawing.  Folks have noticed the tie rod between the queen posts so far.  There are quite a few other differences, some of them subtle.  Our turntable will be very much like the historical photos. 

127
Work and Events / Re: Sheepscot Turntable - Official Work Thread
« on: January 08, 2016, 05:49:04 PM »
Well, as a matter of fact, I do know.   The queen post angle if set at the optimal angle for the outer truss rods would have a resultant force that is directly in line with the queen post --pure compression.  Unfortunately the optimal angle for the inner truss rods is different, since the inner rod is at a steeper angle down to its anchor.  Thus one has to compromise; the best angle for the taller queen post is not the same as that for the shorter one.

The Portland Co. drawing shows that they split the difference.  The angle is set so that the upper tension rod tends to push the tall queen post outward, and push the short post inwards.   This requires the additional tension rod as shown in the pictures to resist the outward force, and the compression beam that you see at the base of the queen posts to resist the inward force on the short queen posts.

Since I did a stress analysis on the turntable, I can state that actual amount of outward or inward force is not that great - only a few hundred pounds.  The load on the inner truss rod turns out to be much higher than the outer, and when the locomotive is halfway on the turntable, the outer truss rod tension drops a lot, and the inner truss rod tension is at its highest.  In fact in every load case I analyzed, the inner truss rod has the highest tension.

So, for our turntable, I chose the queen post angle to be a compromise as well, but biased slightly toward the optimal angle for the shorter queen post.  The tension rod on the taller queen posts is absolutely required, and is in our design.

128
Work and Events / Re: WW&F No. 10 - Official Work Thread
« on: April 18, 2015, 10:36:50 AM »
How are the pillow blocks lubricated?  I see holes, but no grease fittings.

129
Work and Events / Re: WW&F No. 11 - Official Work Thread
« on: January 30, 2015, 12:40:12 PM »
Well, the short answer is, Alan taught me everything I know. :)   Also, I read three old patternmaking books that google book search had complete scans of.    I also am a mechanical engineer, and spent some years designing stuff to be manufactured, so I have some feel for this kind of thing. 

For reference, the books are: 

Pattern Making and Foundry Practice, L.H. Land, 1912
Pattern-Making, G.H. Willard, 1910
Practical Pattern Making, Frank Wilson Barrows, 2nd Ed.,, 1913

Alan also figured out a lot of techniques that help make the whole patternmaking process pretty streamlined.  And Bernie got Alan started with much help and discussion.

130
Work and Events / Re: WW&F No. 11 - Official Work Thread
« on: January 30, 2015, 11:43:44 AM »
Dave, pardon me if my expanation is not so clear, but I will try.   

Imagine the pattern and follow board together, as in the first picture, on a flat surface.  The bottom flask is placed around the assembly, and sand is rammed up in the flask. 

Then the flask is inverted and the follow board removed.  The exposed sand is dusted with a parting compound.   The second flask is placed on it now, and sand is rammed up in it.    This second flask and its sand is lifted vertically, and it has the shape of the inside of the casting sticking out from its face. 

Now the pattern is removed in three pieces - the two side wings first, drawn out at the angle of the washout holes, then the main portion is removed vertically. 

Now lower the top flask onto the bottom, and the net shape will be the shape we want.  No cores needed, and all five holes are formed in the mold. 

There is an additional complication due to the fact that a C-shaped casting will want to bow out when it solidifies, so we need to form a couple of sacrificial tie bars across the back.   This can be done with foam inserts or by shaping grooves in the sand by hand. 

I hope this is clear.   Alan and I worked out this scheme after much discussion.  Jason alerted us to the issue of the casting deforming, since it happened on the first casting done for #9.  We hope not to be making any more crane counterweights  :)

131
Work and Events / Re: WW&F No. 11 - Official Work Thread
« on: January 29, 2015, 11:17:39 PM »
Last one

132
Work and Events / Re: WW&F No. 11 - Official Work Thread
« on: January 29, 2015, 11:16:42 PM »
Next photo

133
Work and Events / Re: WW&F No. 11 - Official Work Thread
« on: January 29, 2015, 11:15:20 PM »
I said I would post  some pictures of the (nearly) completed follow board inside the pattern.  The first two photos are a couple views of the follow board and pattern together.  Then the follow board by itself, and finally the pattern by itself.   This is the orientation that it will be in as the sand is rammed up around it to make the mold. 

I won't have much to show from this point to the completed pattern, since it is merely a lot of time spent filleting, sanding, filling, sanding, finishing, sanding...   Although I got some wax fillets to try, so I will do a post that shows how they are applied. 

134
Work and Events / Re: WW&F No. 11 - Official Work Thread
« on: January 28, 2015, 09:13:41 PM »
I started on the follow board for the pattern.  It needs to fit inside the U of the casting pattern, and project outside about 2 inches.  It also needs a generous draft on the top and bottom surfaces - I used five degrees.   It should fit tightly against the insides of the 5 big holes, to back up the sand that gets packed around the pattern. 

The first parts I made were the inside radiused corners.  These I made by cutting six pieces with 7.5 degree angled sides (15 degrees included angle) which when glued together makes a 90 degree segment.   Initially it had facets, but after a minimal amount of planing and sanding, it became a nice smooth arc.  I used western red cedar, which is very easy to work.   

I adjusted their shape as much as I could to mate with the inside of the pattern, but the pattern had more errors than I could accommodate.  My sanding of the inside radii of the pattern got a little too wild.   So time to break out the epoxy!   I wrapped the radius segments in waxed paper; filled the low spots on the pattern with the filled epoxy and pressed in the follow board corner segments.  When I removed them the next day, it looked pretty close to what it needed to be.  Just a little sanding and I had a fantastic fit to the follow board, and the pattern is the correct shape now.     This is the part of pattern making that is so different from furniture -- it doesn't matter how it looks, only that it has the shape and dimensions you  need. 

As you can see in the picture, I have connected the two corner bits with a flat section in the middle, and two wing sections as well.    There is not much more to do on these, just the top and bottom faces, then some reinforcement here and there.     I should be able to post a picture tomorrow with the pattern and follow board assembled together. 


135
Work and Events / Re: WW&F No. 11 - Official Work Thread
« on: January 25, 2015, 10:23:01 PM »
Pattern progress:

First, thanks for everyone's suggestions.  I agree that dowels would have improved things a lot, and even brad nails have their place.  so, maybe next time... In the end, what I ended up with was not as bad as I feared.  I tweaked the bottom surface to make it more square to the new (skewed) sides, then took out the rest with judicious hand planing.  In the end, I had enough fat in my rough cut out to fix it without having to add any material.   

As you can imagine there was a lot of time spent squaring up and flattening the subsections.  Then I glued up the RH wing.  After that cured, I spent even more time cleaning up each wing, since the alignment of each of the five pieces that make up each wing is not perfect.     I mainly used hand planes for leveling the surfaces, but some hand sanding and even a belt sander were also used. 

I was not real happy with the fit of the joint between the wings and the middle section.   To improve that, I put waxed paper on the joint surfaces of the middle section, buttered up the mating surfaces of the wings with thickened epoxy and squashed them together.  A few clamps to hold them over night, and after some clean up today, they mate really nicely.     Recall that these wings remain separate pieces, so that they can be removed from the sand mold before the middle section. 

The latest picture shows all pieces together.  The dark spots are areas that have epoxy fill  to take care of low spots, voids in the plywood and self induced errors (did I mention that belt sanders can do damage really quickly?).      I have 62 hours in this to date. 

The remaining tasks are: additional fill, smoothing, edge rounding, filleting and finishing.    I will also be starting on the follow board. 

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