Casting a part that can be drilled and tapped

[harryn]

Hi,

I would like to cast about 25 parts roughly 3.5 x 3.5 x 3 inches tall.

Normally EG would seem like a good target material, but it would be really handy if, after casting, it can be at least drilled, and maybe even tapped.

It will be very difficult (not completely impossible, but difficult) to place an insert into the part prior to casting, so it pretty much has to be filled with something that can be hand drilled.

My prior reading in the "big thread" indicates that it is difficult to drill through normal EG, as one would expect, due to the hardness of the aggregate.

Would something like an Al powder or other filler option be viable ?

Thanks

Harry

[janaf]

I have not read the BIG thread more than here and there but imagine that EG should be drillable with diamond drills for small holes, core drills for larger ones. Or would the epoxy clog the drill? How about drill hammer and tunsten carbide tipped bits? I would imagine that using a "drillable" aggregate also would change other properties and any exotic material would very quickly eat the cost advantage of EG. How many holes? You can not use removable plastic plugs for the threads?

[TechGuy5002]

What about using oversized dowels or plastic rounds in the molds where you need inserts? After casting drill out the plastic/wood and put in inserts. then backfill with expoxy to secure the inserts.

Or you could put in metal rounds in the mold, then drill and tap them. For the metal rounds, I would suggested adding texture\roughness (perhaps knurled) so the epoxy grips them better. The metal rounds could also be placed in drilled holes in the mold, then machine the tops off so the are flush with the cast part, then drill and tap.

[JohnMcNamara]

Hi

It is possible to drill epoxy granite....A carbide masonary drill in a drill press works, preferably a new sharp one.

I have also machined the face of an epoxy granite casting. The finish was rough but flat (like 80 grit sandpaper)

In both the above examples the aggregate was sand. Coarse aggregate would be a different story. My guess is you would have to grind that.

Tapping would be a no no to me, the threads would tear.

As far as cast in inserts go they are so easy to attach to the mould I see little difficulty.

My Post here may help......New technology in Model Engineers Workshop | Model Engineer

See the Pictures down the page at the above link.

Cheers
John McNamara

[RomanLini]

How strong do they need to be, ie what use?

You could just use a composite made from drillable materials. Aluminium powder (not oxide) will be drillable and fairly strong and you could increase its strength further with a percentage of chopped glass fibre. Both will be drillable and tapable.

[harryn]

Thank you for the suggestions - there are several really good ideas here.

Thanks

Harry