Making core plugs for marking out.

Hi All
Following on from the cradle I made for the cylinder block for my 3” scale Foden steam wagon I need to plug the cylinder bores to aid the making out.
To plug these un-machined bores aluminium plugs were made.

An average size of each bore was measured and blanks turned and tapped in to the casting. Each end was slightly different due to the flank angle on the pattern which aids the removal of the bore pattern core.

The smaller bore diameter (high pressure bore) was simply machined from aluminium bar stock and parted off.

The plug for the larger bore (low pressure bore) was pressure turned from off cuts of 4mm plate blacks, cut out from another project. The blanks were machined at the average size diameter and a taper machined to help the plug engage in the bore. This same taper was also machined on the smaller plugs.

The photos show the core plugs being manufactured and installed.

Attachment 44136 Pressure turning blanks for low be pressure bore

Attachment 44137 Cutting taper for lead into bore.

Attachment 44138 High pressure bore plugs from stock bar

Attachment 44139 Ready to fit

Attachment 44140 Low pressure bore blank pushed into place

Attachment 44141 Hammered in to bore

Attachment 44142

Attachment 44143All four fitted and blued, ready to mark out bore centres

Thank you for viewing
The home engineer

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Is there a danger that you might break the casting?

Hi Philip
The plugs are aluminium and considerably softer than the cast iron. Also the plugs are machined to an average diameter so they fit with only a small amount of interference and the aluminium is soft enough to be pressed into the bore. If the cast bores were considerably out of shape or had a lot of flashing I would have cleaned up with a die grinder but this casting had very clear bores. The saddle however needed a angle grinder to dress the saddle before gluing to the cradle.
Hope this answers your question
Andy

The first three faces have been machined with a minimum material clean up, just to get the block faces square to each other. I left the casting on its cradle as the marked out lines help to get everything aligned with a scribing-block. The cradle and cylinder block had to be shimmed and clamped down to the mill table. As the cradle is made from wood light cuts were taken until the face was cleaned up. The second and third faces were machined using an angle plate with the first face clamped against the angle plate. The block again aligned with scribed lines and a scribing block. The third face was placed on parallels and clamped back to the angle plate.

Attachment 44224 First face being machined

Attachment 44225Third face being machined sat on parallels

Attachment 44226Attachment 44227Both valve faces square to the regulator face.

Next stage is to machine the bore faces square to these three faces. Then another check to make sure I am happy that the casting is still going to align all features in the correct place.

The home engineer