Having put a micrometer to my small metric screw collection I can confirm that only about 50 are 1.5mm by 0.35 pitch. Another few thousand cheese headed stainless screws are actually M1.6 by 0.35 so at vast expense (£2.35) I have brought myself 4 Chinese HSS taps to see if they are made out of stale cheese, instant snap-odium or possibly they could prove useful
In the meantime I have been hard at work: The holes to mount the end covers have been drilled 1.4mm for the 10BA tapping size (1200 rpm). Having carefully drilled and tapped the two hole for the ends the Erickson boring head
was brought out to help with the bushes holes. First the hole were drilled using small carbide drills (1200 rpm), then a series of carbide end mills (1200 RPM) before moving on to the boring head (234 rpm) with its rather nice Swiss boring bar in it
The problem with this head is that it only bores out to 19mm to go further you must add the extender which fits in the side of the tool holding arm.
We are now at a stage to be able to silver solder in the bushes and it probably worth mentioning that that nice shiny tube of brass is covered by a protective coating which will not take silver solder very well (copper rivets for boilers are also protectively coated
) so havign removed the burrs it is worth while using a needle file to clean up around the holes to encourage a nice fillet. Having dampened around the holes and the outside of the bushes the bushes were dipped in the flux powder providing a powdery coating round their outside. Inserting the bushes in the holes the flux finds a bit more moisture and gathers in the joint were we want it and not everywhere else like when it trys to dribble down the outside of the work
Into the hearth.
I hadn't realised how much clutter has built up in there... those are all old bits of steel used to keep the heat in where silver soldering
The tube was balanced on the big bush and two short ends of silver solder added to either side on the inside. The top bush was left without any silver solder. Applying heat to the side rather than were the joints are, the top bush heated by means of convection, it was dobbed
with a stick of 1.5mm which had been lightly warmed and dipped in the flux until the end of the stick just started melting and a little more heat and I watched the silver flow round the joint. In the mean time the bottom joint had done its own thing and the silver had flashed round.
A very quick dip in the acid and there is very little to clean up. The bottom bush is good but the top bush is showing a little bit of over heating but more than ok for an oil tank. It must be nearly Lunch time, which means I am allowed in the workshop. Don't you love this working from home
Jo