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Posted by Tim Leech on January 18, 2008, 7:03 pm
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On Wed, 19 Dec 2007 16:50:15 -0800 (PST), ellis
>> On Wed, 19 Dec 2007 14:44:07 -0800 (PST), ellis
>>
>>
>>
>> >> Copper washers, fairly tightly dimensioned, 25 to make:-
>>
>> >>http://web.onetel.com/~duttondock/Pictures/Chamferwasher-1.jpg
>>
>> >> I'm thinking the best way to get them finished to size and with a good
>> >> finish will be by making a punch & die, but is it feasible for the
>> >> small/home shop to do the whole thing that way, maybe first punching a
>> >> blank out of plate & then shaping as a second operation?
>> >> I don't fancy my chances of doing the whole thing as a turning job &
>> >> getting a satisfactory finish.
>>
>> >> Any suggestions, from those who 'know' or just fancy a guess,
>> >> welcomed.
>>
>> >> Cheers
>> >> Tim
>>
>> >Tim
>>
>> >The sketch looks like a high vacuum seal to me, if it is I would try
>> >to buy from a supplier of such things.
>>
>> Close, but no cigar. It's a high pressure seal
>>
>> >If you want to make it, I feel that a closed die coining operation is
>> >the best chance - cutoff varying lenghts of blanks and coin them in
>> >formed and hardened dies. It will take considerable GFA and annealing
>> >to get it right.
>>
>> GFA?
>> I can imagine the sort of thing it might be meant to convey, just
>> can't think what exactly it would stand for <G>
>>
>> Cheers
>> Tim
>
>General(Fooling)Around
>
Well there was quite a bit of that, but I got there in the end.
Pics from
http://web.onetel.com/~duttondock/Pictures/Chamferwasher-2.jpg
to
http://web.onetel.com/~duttondock/Pictures/Chamferwasher-10.jpg
The die was made from 3"-ish MS bar, with a removeable spacer, closely
fitting in a recess in the main die, hardened & ground to the finish
washer thickness, and an ID a few thou under the final size to allow
for the washer springing out when removed.
There was clearance on the inside to allow surplus material somewhere
to go, though too much surplus would foil the plot so turning the
blankhad to be fairly closely controlled.
The spacer was easily chucked in the lathe to permit cleaning up the
ID.
Theory was that the OD would not need further finishing, but in
practice during the course of pressing out 30 or so of these washers
the whole assembly including the outer die expanded by a few thou, so
the majority needed finishing on the OD but that was no great
hardship.
I had some smaller (7/8" OD) versions of the same washer to make,
decided to do these entirely by turning from tube as I got hold of
some with the right OD & ID. I would probably use the die method if
doing it again though there wasn't an awful lot to choose between the
two in terms of overall time and 'GFA' once I'd decided on the
methods. One benefit of using the die method for the larger washers
was that I could use some 1" nominal bore tube which I had to hand,
the OD on this was a few thou undersize after cleaning up so turning
them wasn't an option with this material. Another benefit of pressing
them is that the copper is much easier to turn cleanly afterwards as
it's harder <G>.
Picture 9 shows the tumbler I used to finish them off, a fancy tea tin
which a kind soul gave us for Christmas - the tea was excellent BTW -
with some silver sand inside & the lid taped up, run in the lathe for
half an hour at maybe 70 rpm. Some coarser media might have been a bit
quicker, but that was just what I could lay my hands on at the time.
Pic 10 includes some special-size plain washers which were part of
the same job.
Tim
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