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Posted by lfoggy on May 21, 2008, 2:50 pm
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Hi,
I'm building a model beam engine (Stuart Major) and am starting on the
connecting rod. This is a fairly faithful copy of full sized practice
with bearing shells that are held by straps onto the end of the rod. The
straps are held in place by cotters that have to pass through a
rectangular hole 3/32 x 11/32 (about 2.5 x 9mm) which passes right
through the end of the rod which is 5/8 thick. (tried to attach picture
of drawing) The question is how do I accurately cut these holes ? It as
to be fairly square with parallel sides. Milling with a slot drill would
be tricky as even long series slot drills in this size are not long
enough. I could drill a series of holes and then try to open this out
with needle files but it would be really difficult to do this neatly.
Has anyone got any ideas ?
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lfoggy
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Posted by Don Young on May 21, 2008, 10:45 pm
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>
> Hi,
> I'm building a model beam engine (Stuart Major) and am starting on the
> connecting rod. This is a fairly faithful copy of full sized practice
> with bearing shells that are held by straps onto the end of the rod. The
> straps are held in place by cotters that have to pass through a
> rectangular hole 3/32 x 11/32 (about 2.5 x 9mm) which passes right
> through the end of the rod which is 5/8 thick. (tried to attach picture
> of drawing) The question is how do I accurately cut these holes ? It as
> to be fairly square with parallel sides. Milling with a slot drill would
> be tricky as even long series slot drills in this size are not long
> enough. I could drill a series of holes and then try to open this out
> with needle files but it would be really difficult to do this neatly.
> Has anyone got any ideas ?
>
>
> +-------------------------------------------------------------------+
> |Filename: Connecting rod.gif |
> |Download:
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>
> --
> lfoggy
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> lfoggy's Profile: http://www.rcgroups.com/forums/member.php?u=103324
> View this thread: http://www.rcgroups.com/forums/showthread.php?t=867617
>
Seems to me that a combination of drilling holes, milling with an end
mill/slot drill from both sides, and filing might do it. A custom made
broach would be nice but probably too expensive.
Don Young
Alabama, USA
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Posted by Richard Edwards on May 22, 2008, 12:48 am
Please log in for more thread options On Wed, 21 May 2008 13:50:49 -0500, lfoggy
>
>Hi,
>I'm building a model beam engine (Stuart Major) and am starting on the
>connecting rod. This is a fairly faithful copy of full sized practice
>with bearing shells that are held by straps onto the end of the rod. The
>straps are held in place by cotters that have to pass through a
>rectangular hole 3/32 x 11/32 (about 2.5 x 9mm) which passes right
>through the end of the rod which is 5/8 thick. (tried to attach picture
>of drawing) The question is how do I accurately cut these holes ? It as
>to be fairly square with parallel sides. Milling with a slot drill would
>be tricky as even long series slot drills in this size are not long
>enough. I could drill a series of holes and then try to open this out
>with needle files but it would be really difficult to do this neatly.
>Has anyone got any ideas ?
>
>
>+-------------------------------------------------------------------+
>|Filename: Connecting rod.gif |
>|Download: http://www.rcgroups.com/forums/attachment.php?attachmentid=1879929 |
>+-------------------------------------------------------------------+
And you have two more problems with the slots on the other end that
are 5/64ths wide!
Options without pondering as much as you probably have already <G>
1 Chain Drill then open to slot with "abrafile" type blade in your saw
frame. Make a "hard" jig that fits around the end, to ensure that your
filing is flat and square.
2 Have it wire cut
3 Come in from the end with a slitting saw then pin a slug in to fill
the end.
Whatever option you finally choose, I would test out on a bit of scrap
first!
Good luck!
--
Richard
Email address is valid but remove burrs before sending!
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Posted by jasonballamy on May 22, 2008, 3:04 am
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I would also tackle it by making the slot from the end with a slitting
saw and then pin/silver solder a strip in to close the end.
Jason
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jasonballamy
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Posted by lfoggy on May 22, 2008, 4:21 am
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Thanks for all the suggestions,
As I was writing the post the solution of using a slitting saw from the
end then filling the gap with a plug occurred to me and I think this is
the only practical solution to get a neat result. The Stuart supplied
casting for this component seems to be made of cast iron so I don't
think I can silver solder the plug in. I think I will have to pin it
with some 2mm silver steel rivitted over. Hopefully this will work !
Thanks again and I hope to contibute more to the forum in the future.
--
lfoggy
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> Hi,
> I'm building a model beam engine (Stuart Major) and am starting on the
> connecting rod. This is a fairly faithful copy of full sized practice
> with bearing shells that are held by straps onto the end of the rod. The
> straps are held in place by cotters that have to pass through a
> rectangular hole 3/32 x 11/32 (about 2.5 x 9mm) which passes right
> through the end of the rod which is 5/8 thick. (tried to attach picture
> of drawing) The question is how do I accurately cut these holes ? It as
> to be fairly square with parallel sides. Milling with a slot drill would
> be tricky as even long series slot drills in this size are not long
> enough. I could drill a series of holes and then try to open this out
> with needle files but it would be really difficult to do this neatly.
> Has anyone got any ideas ?
>
>
> +-------------------------------------------------------------------+
> |Filename: Connecting rod.gif |
> |Download:
> http://www.rcgroups.com/forums/attachment.php?attachmentid=1879929 |
> +-------------------------------------------------------------------+
>
> --
> lfoggy
> ------------------------------------------------------------------------
> lfoggy's Profile: http://www.rcgroups.com/forums/member.php?u=103324
> View this thread: http://www.rcgroups.com/forums/showthread.php?t=867617
>