# Milling cast iron



## kevinlightfoot (11 Oct 2017)

Is it possible to machine cast iron using a router and a high speed steel cutter.I want to mill a slot in a brake disc to make a mitre slide for a disc sander.


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## MusicMan (11 Oct 2017)

I would say no, and that it would be very dangerous to try. Cast iron is difficult enough to machine even with a rigid milling machine. You are very likely to smash the cutter and spread it round the workshop in all directions at very high speed.

You need a friend with a milling machine, or use a local engineering firm.

I must say I don't understand your geometry. Wouldn't you want a square table to cut the mitre slide in? Perhaps I am missing something.


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## MattRoberts (11 Oct 2017)

https://youtu.be/Urz57RVC15A


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## porker (11 Oct 2017)

I see the video worked OK but I wouldn't do it as the router spins way too fast. Milling cast iron on a mill is no big deal. 18-24 metres per min is the recommended speed for cast iron with an HSS cutter which for a 1/2" cutter is about 600rpm. Routers generally spin much faster than that .


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## kevinlightfoot (11 Oct 2017)

Thanks ,interesting video but I think I will take the advice to contact a local engineering firm or start to think along different lines.I saw a video of someone building a disc sander and he used a brake disc as a mitre gauge,I would indeed use a rectangular table for the mitre gauge to slide in.


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## hawkeyefxr (17 Oct 2017)

That means your holding the workpiece or the router, not for me thanks.


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## MusicMan (17 Oct 2017)

I see. In that case, maybe you do not need a slot in the disc. The slot is in the rectangular plate and you need a rectangular protrusion on the disc.Perhaps you though of doing a slot to locate the rectangular guide, but you don't need this in metal. It can just screw on. Clamp the metal bar, of a width to run in the slot, tightly to the disc. Drill through both in two places with a drill of the right size for tapping a countersunk screw. Release the clamps, tap the holes in the disc, drill out the holes in the bar for a close fit on the screws, countersink them. You need a drill press to do this accurately enough.

You can make a slot in the rectangular plate without milling. You get two rectangular plates about 3/8" thick and fit them to the frame so that the gap between them fits the bar (3/4" conventionally). File them to be flat (checking against a flat surface with engineers' blue), starting with cross filing, flattening with longitudinal filing and finishing with draw filing. Then fix them on the frame at the right gap. 

You'll learn how to file, though I admit it is 60 years since I did this!

Keith


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## -Matt- (17 Oct 2017)

I have a hand shaper, but depending on the quality of the cast I'm not sure I'd want to be carving out too big a slot with it!

Could mark out and take a good section out with grinder though I guess. Finish and neaten up on hand shaper.


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## kevinlightfoot (17 Oct 2017)

Thanks again guys taking in all your input but beginning to veer towards spending some money and buying ready built sander.Record make one that looks pretty good value for money and is probably better than I could build for the same price.


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