Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Old May 15th 20, 01:04 AM posted to rec.crafts.metalworking
external usenet poster
 
First recorded activity by DIYBanter: Nov 2006
Posts: 190
Default Amazing hollow casting

Hi folks,

Quick question of curiosity here. I bought an old East German scroll saw recently and it has a huge cast iron bow. The reach is about 24 inches. The bow is a one-piece casting, integral with the base, and it's hollow right the way along (there's an air hose inside which blows away the sawdust). Here's a pictu

http://sphinx.mythic-beasts.com/~cdt...ll_Saw_DDR.JPG

Can someone tell me how it's possible to cast this iron bow in the foundry? I can't figure how you can reliably and accurately support a sand core inside the mould, and it's making me really curious.

By the way, if anyone recognises the brand of the saw, I'd be interested to hear. There isn't a maker's name on the machine.

Best wishes,

Chris

  #2   Report Post  
Old May 15th 20, 02:21 AM posted to rec.crafts.metalworking
external usenet poster
 
First recorded activity by DIYBanter: Aug 2019
Posts: 33
Default Amazing hollow casting

On 5/14/2020 7:04 PM, Christopher Tidy wrote:
Hi folks,

Quick question of curiosity here. I bought an old East German scroll saw recently and it has a huge cast iron bow. The reach is about 24 inches. The bow is a one-piece casting, integral with the base, and it's hollow right the way along (there's an air hose inside which blows away the sawdust). Here's a pictu

http://sphinx.mythic-beasts.com/~cdt...ll_Saw_DDR.JPG

Can someone tell me how it's possible to cast this iron bow in the foundry? I can't figure how you can reliably and accurately support a sand core inside the mould, and it's making me really curious.

By the way, if anyone recognises the brand of the saw, I'd be interested to hear. There isn't a maker's name on the machine.

Best wishes,

Chris


The hole on the front of the top bow is the key . I'll bet there's a
similar one on the bottom . Between those 2 points and the large hollow
base it would be fairly straightforward to support a sand core .
--
Snag
Yes , I'm old
and crotchety - and armed .
Get outta my woods !
  #3   Report Post  
Old May 15th 20, 02:42 AM posted to rec.crafts.metalworking
external usenet poster
 
First recorded activity by DIYBanter: Nov 2006
Posts: 190
Default Amazing hollow casting

The hole on the front of the top bow is the key . I'll bet there's a
similar one on the bottom . Between those 2 points and the large hollow
base it would be fairly straightforward to support a sand core .


There are holes for the air hose, both at the top and bottom. Not very big, though. The bottom hole is only about 3/8".

  #4   Report Post  
Old May 15th 20, 02:44 AM posted to rec.crafts.metalworking
external usenet poster
 
First recorded activity by DIYBanter: Nov 2006
Posts: 190
Default Amazing hollow casting

I guess maybe the core was built on a steel hoop made from bent round bar, or something like that? Not sure how you hold the back end positioned to 1/8" accuracy, though.
  #5   Report Post  
Old May 15th 20, 02:52 AM posted to rec.crafts.metalworking
external usenet poster
 
First recorded activity by DIYBanter: Nov 2006
Posts: 190
Default Amazing hollow casting

Just noticed there's a round protrusion on the top surface of the bow, near the back. Perhaps a bar came out of there support the core? Any foundry experts here?

Thanks for the ideas!

Chris


  #6   Report Post  
Old May 15th 20, 12:10 PM posted to rec.crafts.metalworking
external usenet poster
 
First recorded activity by DIYBanter: Jun 2011
Posts: 5,670
Default Amazing hollow casting

"Christopher Tidy" wrote in message
...

I guess maybe the core was built on a steel hoop made from bent round bar,
or something like that? Not sure how you hold the back end positioned to
1/8" accuracy, though.

===============================
Chaplets.

https://en.wikipedia.org/wiki/Core_(manufacturing)

This notorious collapse of a cast iron bridge brought attention to the
difficulties of sand casting and prompted improvements.
https://www.open.edu/openlearn/ocw/m...able=1&id=3524

Fortunately stronger rolled structural steel was just then becoming
available to displace wrought and cast iron.

Many defects were found in the column castings, including shifted cores that
left a thin wall on one side. The foundry supervisor couldn't be
interrogated as he had emigrated (fled?) to Australia. Railway management
had pushed the designer to cheapen, and thus weaken, this bridge compared to
his earlier projects.

Two cylinder steam locomotives are inherently unbalanced. The wheel
counterweights are sized to divert the vibration from horizontal which the
passengers would feel, to vertical which increases the pounding load on the
tracks and bridges. The effect increases with speed, and trains reportedly
ran over the Tay bridge much faster than they were supposed to.
https://en.wikipedia.org/wiki/Hammer_blow

  #7   Report Post  
Old May 15th 20, 01:11 PM posted to rec.crafts.metalworking
external usenet poster
 
First recorded activity by DIYBanter: Jul 2006
Posts: 2,453
Default Amazing hollow casting

On 5/14/2020 9:44 PM, Christopher Tidy wrote:
I guess maybe the core was built on a steel hoop made from bent round bar, or something like that? Not sure how you hold the back end positioned to 1/8" accuracy, though.


Then how would you get the rod out of the casting?
  #8   Report Post  
Old May 15th 20, 01:14 PM posted to rec.crafts.metalworking
external usenet poster
 
First recorded activity by DIYBanter: Jun 2011
Posts: 5,670
Default Amazing hollow casting

"Jim Wilkins" wrote in message ...

https://www.open.edu/openlearn/ocw/m...able=1&id=3524


This describes the "Burning On" method of repairing a casting:
https://www.scientificamerican.com/a...ast-iron-by-a/

Perhaps the preheated base could be placed in a sand mold of a good foot and
filled in with cast iron using acetylene?

I've built up eroded starter motor contacts that way, using brass which
melts lower than copper. It also wears away faster but was easy enough to
redo. When I was practicing TIG puddle control I piled up a column of
aluminum about 4~5mm in diameter and 25mm high.


  #9   Report Post  
Old May 15th 20, 01:22 PM posted to rec.crafts.metalworking
external usenet poster
 
First recorded activity by DIYBanter: Jun 2011
Posts: 5,670
Default Amazing hollow casting

"Bob Engelhardt" wrote in message ...

On 5/14/2020 9:44 PM, Christopher Tidy wrote:
I guess maybe the core was built on a steel hoop made from bent round bar,
or something like that? Not sure how you hold the back end positioned to
1/8" accuracy, though.


Then how would you get the rod out of the casting?

============================

Here's another ancient way to make a hollow casting:
https://thelibraryofmanufacturing.co...h_casting.html

My mother's antique pewter teapots showed the resulting rough finish inside
the S-curved spouts.

  #10   Report Post  
Old May 16th 20, 01:13 PM posted to rec.crafts.metalworking
external usenet poster
 
First recorded activity by DIYBanter: Nov 2006
Posts: 190
Default Amazing hollow casting

Am Freitag, 15. Mai 2020 14:12:09 UTC+2 schrieb Bob Engelhardt:
On 5/14/2020 9:44 PM, Christopher Tidy wrote:
I guess maybe the core was built on a steel hoop made from bent round bar, or something like that? Not sure how you hold the back end positioned to 1/8" accuracy, though.


Then how would you get the rod out of the casting?


I guess you'd have to make some kind of rod framework which could be unscrewed or broken up from the ends. Not sure though. The core positioning just looks really hard, and these guys did it perfectly.


Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Roger Degner on making hollow anvils and hollow swage blocks Pete S Woodworking 0 November 26th 11 02:09 AM
Pro's And Cons of Hollow Grinding Dwight Woodworking 13 January 1st 05 01:43 AM
Question hollow core interior doors M.Burns Home Repair 6 December 20th 04 05:51 PM
Creating very light hollow metal ornaments Marin Metalworking 4 January 23rd 04 02:41 AM
Japanese chisel - hollow back ? FOW Woodworking 2 July 18th 03 01:05 PM


All times are GMT +1. The time now is 10:30 AM.

Powered by vBulletin® Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Copyright 2004-2020 DIYbanter.
The comments are property of their posters.
 

About Us

"It's about DIY & home improvement"

 

Copyright © 2017