WELDING THEORY AND APPLICATION
www.littlemachineshop.com This seems to be a nice shop related to mills and lathes. Although they sell only repair parts and accessories for various mills/lathes manufactured in the USA they also have links to manufacturers of these machines.
GrizzlyThey sell lots of machinery for a workshop including lathes and milling machines. On their homepage look for the link "Machinery Selection & Specification ..".
http://www.sherline.comNice outfit, Selling miniature Lathe, Mill and Machine Tools. Prices seem to be compatative.
http://www.emcomaier-usa.com/ An Austrian based producer of all kinds of machine tools. Lathes, milling machines. Might be out of your price range judging by their info on the web.
Brazing metals,
an introduction
See also SESUSA-file section , folder V50's Data File" for info on brazing
stain less steel.
Tom Gentry, Letter to SESUSA,23 Jul 2004
"Consider this method of arranging the tubes and the joints. For simplicity of
description let us consider only one tube being brazed to one heater head
(plate dome etc.). The head is of course first drilled with a minimum
clearance hole through which the tube goes. On the side of the heater head
where the tube empties into the hot swept volume the hole is counter drilled.
The tube is now placed so that it protrudes past the surface of the heater head
and out of the 'hole'. The volume left by the outside of the tube and the
counter drilled hole is now filled with braze starting at the seam of the tube
and the heater head in the bottom of the hole and progressing outward to fill
the hole with braze. Repeat this until all the tubes have been brazed. Put
the assembly in a mill and mill the head flat. Deburr the tubes and clean out
any foreign substances in them.
A high temperature braze is mandatory as is probably an inert gas process.
Alternately the assembly could be made as described and the brazing done by
commercial vacuum brazing."
Rick Topf, email to SESUSA, 24 Jul 2004
"The process you describe below sound more like a MIG or TIG "welding"
process.
The way I understand it, you would not want to counter-drill a brazed
joint. That would only reduce the cearance gap thereby reducing the
contact area. Brazing is more like soldering where the joint
strength is a function of contact area. The small clearance gap is
required for cappillary action or the filler. Brazing fillers have a
higher melt temperture and produce stronger joints that solders, but
the filler metal never reaches the strength of the base metal.
Welded joints are chamferd (counter-drilled) to increase the depth of
the weld zone. When welded, the filler and base material have the
same strength.
The stratagy I have been concidering would be the brazed tube
joints. I would also protect (insulate) the heater head and the
brazed joints form direct heat. This should allow fairly high
working tempertures and be much easier to construct.
I may try a few joints with my MIG welder, but I hve found it to be
somwhat difficult on stainlee. TIG has a beter chance. I don't have
TIG equipment, but if somone wants to try this I have some tubing and
plate to play with."
Machining of Graphite for Stirling Engine piston by Rick Topf,
HotAirEngineSociety@yahoogroups.com, 11 Jun 2005
For engine work, any grade would probably be fine but the Aeromet
grade would be ideal for engine work. It is somtimes used for dry
lube bearings so it has good mechanical properties. The finer grades
typically used for EDM may be more available through second-hand
sources, but its really more than you need and is more expensive if
purchased new.
Graphite is easy to dry machine with typical metal-cutting
equipment. Cutter geometry is not critical to success, but I prefer
rounded tips. Side, back, and relief angles similar to those used
for soft metals like copper work well. Same goes for speeds and
feeds. Always prepare the honed cylinder bore before final sizing
of a graphite piston. When diameter is down to a few thou's over
the bore, switch to 400 grit wet-dry paper. This will cut quickly
so go slow. When the piston just begins to feel like it will fit,
(don't push it in all the way) use plane white paper to final finish.
Always use some kind of vaccuum to collect the dust when machining.
There are no "chips" so all the material comming off will need to be
sucked up. It won't hurt your machines if they get dusted. Its
actually a great lubricant, but it will make a mess if it mixes with
oils so wipe down your machines before and after use.
Never use any kind of oil or other liquid lube with graphite. If
you accidentally under-size the piston, use powered graphite to get
a good fit back.