Making pressure gauges.

[maninshed]

Hi All, I hav'nt posted on here for some years, but I have been interested in Roger's blogg covering his incredible Speedy, where he get's the time from to carry out the incredible micro machining he does I don't know. What caught my eye was making the pressure gauge, just fancied a challege I guess, so I dug out the articles by Roy Amsbury on making boiler fittings which also covers a pressure gauge. Now as Roger has pointed out one of the most difficult parts is the bourden tube. I found some 1/8" phosher bronze and made one as per the 'words and music'the hardest bit was drilling the 0.064 (came out at 0.065") hole 1" deep, once I modified the the drill bit for cutting brass the drilling was alot easier the drill didn't sieze up in the bronze. The turning was done on a mandrel again as per the article, the ends were turned to 0.080 giving a wall thickness of 0.008 and the centre section was turned to 0.070 giving a wall thickess of about 0.0035". Tube was then annealed and a 0.005" shim was inserted in the bore, and a piece of 1/4" dia wooden dowel was used to roll the tube flat and then bend the radius around a 1/2" bar, tube didn't split and all looks good. I do appreciate that I have afew more hoops to jump through to complete the gauge, such as gears and pinions I'll try to pick up some old watches on ebay again as suggested in the articles,and the gauge face which I have drawn up a readable 5/8" diameter face on whatever cad package I have on my laptop. Then there is the matter of calibration, all the machining was done on a Warco 180 which I rebuilt and did a few of the common mini lathe modes on, nothing rocket science or really fancy.

Martyn C