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Strange case of cheese US made drill

Tom Kitta

Active Member
#1
So I have this drill MT4 2" I tried to use two times now.

I drilled in either 4140 or 4330 steel (not sure which one) First pass was with 1" second with 1.5" and third was to be with this 2".

Speed with 2" was 80 rpm so rather slow - no issues with 1.5" with 100 rpm and 1" with 200 rpm.

I tried this bit twice - re-sharpened it by hand twice now.

This is not the only large bit I re-sharpened by hand - others work fine - including the 2" short Chinese bit that finished the job when this one has failed.

Depth of cut were to be 4" but the bit failed at around 0.5"

The best thing I can think of is that that the drill bit was... not hardened and is as soft as the shank for some unknown reason - is this even possible? As mentioned this is an older drill bit made in the US. It is in decent shape overall. It was sharpened properly. Its just... soft.

Anyone else had similar experience?
 

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Bofobo

Well-Known Member
#2
when i cut 2” it was very very slow rpm and coolant, but also .250 cut on each side of the drill sounds like a lot to me. And one more thing! It looks to me, from what i remember of the one i used, like the point is to pointy for that size of drill. Please anyone correct me if im wrong
 

Tom Kitta

Active Member
#3
Well I had no issues making the cut at the same parameters with another 2" drill so speed / coolant / how much I cut was not an issue.

I take a look at the angle a bit more - but 135 deg is for hard steel while 118 is for mild stuff - thus if it is say 140 it should not literally fall apart as it did.