On 2021-08-05 06:13, John Dammeyer wrote:
How does one know what size tabs and how many?
I view this as a mystical black art.
For me, the basic idea is to
(a) support the part to prevent damage when it separates from the
parent, to stop it catching the cutter for example. In that case,
position the tabs to provide enough support to prevent vibration or
movement of any element.
(b) prevent the parent material from moving or, as in this case,
collapsing as the part separates.
Tabs often serve purposes (a) and (b). From the point of view of
clean-up afterwards, the fewer tabs the better, and the more accessible
they are for removing and for subsequent finishing, the better. I would
think first about whether the position of the tabs affects the accuracy
required of the part. After that, I think about the aesthetics after
clean-up. Tabs on a straight face are easier to clean up than on a
curve, and tabs on an external curve are easier to clean up than on an
inside curve, just because my flat files are closer to hand than the
half-round files. There is an argument that cleaned up tabs on a curve
tend to catch the eye less than on a straight face.
In the case of this particular part, I reckon you have this about right.
The main problem is an inward collapsing due to the pressure from the
vice jaws as well as possibly stresses in the tube which will naturally
make it want to either spring apart or collapse inwards.
I quite like the triangular tabs because I find they can be a little
easier to cut with a knife or a very fine saw blade, but the rectangular
tabs are stronger and easier to program manually if necessary.
I like to make the tabs as thin as possible, to aid clean-up, but the
over-riding factor must be the strength they require to do the job.
That's maybe not a clear answer, but those are the thoughts in my mind
every time I have to place tabs.
Marcus
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