Author Topic: WW&F No. 11 - Official Work Thread  (Read 187424 times)

Keith Taylor

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Re: WW&F No. 11 - Official Work Thread
« Reply #330 on: January 23, 2015, 03:41:08 PM »
I was thinking dowels that were long enough to extend the entire height of the stack.
It would not only align the laminations, but would give strength vertically to the stack.
Also dowels work great for cross nutting when you have to screw into end grain.

Alan....it's a shame your dad has to work in such cramped quarters!  ;D

Keith

John McNamara

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Re: WW&F No. 11 - Official Work Thread
« Reply #331 on: January 23, 2015, 04:02:27 PM »
Alan....it's a shame your dad has to work in such cramped quarters!  ;D
He can always take a break on one of those 70-degree days and take a quick trip in that nice strip canoe in the background! 8)

-John

Harold Downey

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Re: WW&F No. 11 - Official Work Thread
« Reply #332 on: January 26, 2015, 02:23:01 AM »
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. 

Tom Casper

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Re: WW&F No. 11 - Official Work Thread
« Reply #333 on: January 26, 2015, 05:37:22 PM »
WOW Harold, really a nice looking pattern.

Tom C.
Later:
tom_srclry_com

Dave Crow

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Re: WW&F No. 11 - Official Work Thread
« Reply #334 on: January 27, 2015, 01:59:23 PM »
Nice work, Harold!

Dave Crow

Ira Schreiber

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Re: WW&F No. 11 - Official Work Thread
« Reply #335 on: January 27, 2015, 07:59:00 PM »
And a tip of the Kentucky Derby to you for all your efforts

Harold Downey

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Re: WW&F No. 11 - Official Work Thread
« Reply #336 on: January 29, 2015, 01:13:41 AM »
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. 


Harold Downey

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Re: WW&F No. 11 - Official Work Thread
« Reply #337 on: January 30, 2015, 03:15:20 AM »
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. 

Harold Downey

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Re: WW&F No. 11 - Official Work Thread
« Reply #338 on: January 30, 2015, 03:16:42 AM »
Next photo

Harold Downey

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Re: WW&F No. 11 - Official Work Thread
« Reply #339 on: January 30, 2015, 03:17:39 AM »
Last one

Dave Crow

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Re: WW&F No. 11 - Official Work Thread
« Reply #340 on: January 30, 2015, 01:07:39 PM »
Nice work, Harold.  So, how does a follow board work when the pattern is at the foundry?  Is the bottom portion of the packed sand formed to the shape of the follow board, with the top/removable half of the mold formed around the pattern itself?

Dave Crow

Harold Downey

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Re: WW&F No. 11 - Official Work Thread
« Reply #341 on: January 30, 2015, 03:43:44 PM »
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  :)

Dave Crow

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Re: WW&F No. 11 - Official Work Thread
« Reply #342 on: January 30, 2015, 04:21:52 PM »
Hi Harold,

Okay, now it all makes sense.  Thanks for your explanation.

Dave Crow

John McNamara

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Re: WW&F No. 11 - Official Work Thread
« Reply #343 on: January 30, 2015, 04:22:18 PM »
Where/how did you learn how to do this?
-John

Harold Downey

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Re: WW&F No. 11 - Official Work Thread
« Reply #344 on: January 30, 2015, 04:40:12 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.