Minnie Piston

[David Bothwell 1Participant @davidbothwell1]

Could some kind soul put me out of my misery? I have searched all the Model Engineer magazines and the downloaded articles (somebody kindly did for me) but I cannot find the piston dimensions? It is quite obvious to get the diameter, somewhere in the back of my mind says a half inch but I dont want to guess!

[David Bothwell 1Participant @davidbothwell1]

Length

[JasonBModerator @jasonb]

[David Bothwell 1Participant @davidbothwell1]

Thats great Jason, my thanks for it

[Ian S CParticipant @iansc]

5/8", but make the cylinder first, then fit the piston to it, it might be plus or minus the nominal size.

Ian S C

[Neil WyattModerator @neilwyatt]

Gauge depth and width with number drills? How will our metric friends cope?

Neil

[JasonBModerator @jasonb]

The Imperially challenged could make do with this

[David Bothwell 1Participant @davidbothwell1]

Again my thanks for the contributions which were most helpful

[julian atkinsParticipant @julianatkins58923]

Hi David,

Before you make the rebate in the pistons for the packing, see what you can obtain first and how it compresses. The depth and width of the groove means nothing unless you know the packing. Old fashioned asbestos graphite square braided packing still crops up on ebay.

There is a trick to compressing this packing and sizing the groove which seems to be a lost art these days. If you get it wrong the packing is either ineffective or far too tight.

The specific sizes mentioned on the drawing would have been for a particular standard supply from ME suppliers many years ago. None of that is allowed to be marketed these days and will be of quite different (and IMHO) inferior type. But ebay is your answer.

Cheers,

Julian

[JasonBModerator @jasonb]

Sorry Julian the minnie design uses O rings throughout (piston and glands) so all the sizes are based on still available O ring sizes.

The Metric version by Julius has a machined teflon piston ringl so that can be machined to suit the groove.

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