Dave,
Wow, I've been away from my foundry too long!
Thanks,
Rick (via iPod)
On Dec 7, 2010, at 9:13 PM, David Patterson <odd_kins@yahoo.com> wrote:
> 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
>
>
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>
>
> 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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