Milling Slots

I need to mill slots in 2 pieces of Gauge plate 1/8" thick. Slots are 3/32 and 1/2" wide and about 1" long (to make the base of a slide valve chest). I cannot get them neat,parallel, straight! what advice? I always seem to get the end cutting wider than the main length, or changing width along the cut, ....

Initially more narrow than required finished size, then clean up the slot sides to size. That is if all other tnings are satisfacory - support, rigidity of machine, tool quality, axes tightened down, etc

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Have you got the table locked down in the axis you are not moving the cut in.?

If so are the gibs in the axis you are moving adjusted to give as little play / movement as possible while still remaining smooth to axis movement.

Nick

Unless you are taking very shallow cuts a 3/32" cutter will flex on a tough material like gauge plate, especially if you are using an end mill rather than a slot drill.

Try using a short 1/16" FC3 cutter to mill out the centre then take a skim off each side.

Neil

As mentioned already, use a two-flute slot drill rather than a four-flute end mill when milling slots.

O1 (gauge plate) is a bitch to machine even after years of experience so don't lose heart. Do as suggested and make sure gibs are adjusted/table locked and use a slot drill.

Real question is why does it have to be gauge plate?

Bit of Mild steel would do or better still slice off the end of a bit of round cast iron, flat brass strip or plate.

If you must go with gauge plate then I would first drill the two ends of the slot 3/32, rough out the middle with a 2mm FC-3 cutter and then finish off with a 2-flute 3/32" cutter at 1/32" depth per pass.

because I have some, and if I get it right, it will last forever.

But if I cannot get it right, i may start again with brass.

It make take forever to get it right Seriously for this application you would be better off using brass or mild steel.

Tony

The gauge plate is susceptible to rusting, more so than mild steel, and even if your steam engine is only used with air, it will be subject to condensation.

Ian S C

Denbeigh Drill question moved to here

Have you considered having it wire edm'ed ? But as people here have said, gauge plate rusts like billy-oh.