Rick just so we all use the same terms, the "taper" you speak of would be called "draft". I hate to correct it's just easier to explain if we're all using foundry terms;-)
Dave Patterson
odd_kins@yahoo.com
http://home.comcast.net/~oddkins/foundry_home.html
--- On Tue, 12/7/10, Rick Sparber <rgsparber@aol.com> wrote:
From: Rick Sparber <rgsparber@aol.com>
Subject: RE: [gingery_machines] What radius on lathe parts?
To: gingery_machines@yahoogroups.com
Date: Tuesday, December 7, 2010, 3:31 PM
Randy,
It sure sounds like you know you way around wood. One think you will find is
that the stability of the sand impression defines the casting. So given a
perfect pattern but weak sand, your casting will have a lot of distortion in
it.
My wood working skills are very basic. I cut MDF and glue it up with around
1/8" of margin on all surfaces to be machined. Most fillets are done with
Bondo or wood putty. I use Petrobond for my sand. Finish does matter on
un-machined surfaces because the Petrobond can pick up fine defects which
will appear in the casting.
As for the radius, I echo Dave's comment. Additionally, do be careful to
have the correct taper in all surfaces that must be pulled from the flask.
Without this taper, the pattern will be locked into the sand. I own a Bosch
table saw specifically so I can set this taper accurately.
Rick
-----Original Message-----
From: gingery_machines@yahoogroups.com
[mailto:gingery_machines@yahoogroups.com] On Behalf Of primepowerpro
Sent: Tuesday, December 07, 2010 2:31 PM
To: gingery_machines@yahoogroups.com
Subject: [gingery_machines] What radius on lathe parts?
I made a pattern for the lathe bed today. I used a piece of walnut that
crossed back and forth from heartwood to sapwood, since no one wants
something made of walnut that isn't all dark wood. I milled the side
material down to .30", to ensure that even after sanding, it would be over
.25" thick everywhere. I milled the material for the top down to .75" and
rabbetted the sides and ends of the top .30" either way, then, after glueing
up, used a jointer to true up the bottom. Once the bottom was flat, to use
as a reference, I put the whole thing through the planer, and took the top
down until the overall height was 1.5", +/- 0.001". It's as flat and true as
I know how to make a piece of wood.
The book says that every edge that isn't on the parting line has to be
radiused, but it doesn't say what value to assign to the radius. I have a
1/16" roundover bit for may router table; will that do it?, And, since the
bottom edge is at the parting line, does that mean they don't get rounded?
BTW, thanks for the replies I got to the last post, including the
tangiential ones on material toxicity.
Randy
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