Draft, fillets and corner radii are normally the designers options. Too large a fillet and you'll get shrinkage, without a riser. Too small a fillet when you have thick walls and you get a crack. It all depends on the design, I would normally use a 1/4" fillet for something with 1/4" wall thickness, etc. Corner radii depends on the use, if the part is machined in an area that area I may use roughly a radius of 3/4 the machining allowance. ie 1/4" machine allowance would be 3/16" radius.
Draft is roughly .0175" per degree for every one inch of height. A typical pattern may only use 2deg of draft, a tall pattern may use less, and a thin pattern may use up to 15deg. And a really thin pattern can get by with no draft.
Dave Patterson
odd_kins@yahoo.com
http://home.comcast.net/~oddkins/foundry_home.html
--- On Tue, 12/7/10, Brite <coldtoo2000@yahoo.com> wrote:
From: Brite <coldtoo2000@yahoo.com>
Subject: [gingery_machines] Re: What radius on lathe parts?
To: gingery_machines@yahoogroups.com
Date: Tuesday, December 7, 2010, 9:58 PM
Hi Randy,
Just my opinion, but fillets (radius on inside corners) are generally more important than on outside corners. I'd say that 1/16 to 1/8"+ for inside corners, maybe half that on outside. I try to use larger radius fillets in places w/ a deep core (inside the bed and bases for example). Also on the vertical outside corners of blocks like the carraige (smaller radius along the horizontal "edges" like the top of screw tunnel and outside edges parallel to it (sides) and same w/ the ends.
Did that maake sense?
CT2
--- In gingery_machines@yahoogroups.com, "primepowerpro" <randycook@...> wrote:
>
> 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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