Don't try drilling and tapping your hard Jaws :-(

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Flynth

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Recently I attempted to drill and tap one of my 6in milling vice hard jaws.... It didn't go well.

First, let me say I already done it with a smaller vice and other than getting through a thin case hardening layer it went fine. This, however is a Kurt clone vice and it wasn't cooperating at all.

I decided to see if its hard and how hard by using a 2/6mm centre cutter. (80 thou/quarter inch) It is the cutter with a little drill that expands into a 60 degree centre cutter. This is just a cheap HSS cutter I bought long time ago.

First I tried to mark the surface, thinking, if it doesn't drill I'll only have a small mark. Surprisingly it drilled fine at about 600 rpm (low for such cutter). It produced nice chips, but 6mm was too big of a hole. I wanted to tap it with M6 so I needed 5mm hole. I thought, nice, this is not that hard.

Then I took a new cobalt hss twist drill and I destroyed its tip making the horrible screeching noise (still 600 rpm, plenty of lube). I thought, maybe this drill was bad, so a second one followed the first to the "drills to regrind box".

Then, as I already had an unsightly hole made with a centre I decided to enlarge the hole to M8 tap (6.8mm) as I do have a 6mm carbide tipped drill and I thought later on a normal hss will manage taking off 0.4mm (2 thou) off the wall. The carbide run horribly, screeming all tge way, but it did cut. I have few carbide taps so I could've tapped it, if I managed to make that hole the right size.

Then I took another hss cobalt drill, this time 6.8mm to enlarge this hole. I set it to 100rpm hoping it would cut. Nope, the hole cut the drill...

So now, my nice vice has a 6mm hole drilled on the side of its hard jaws. Perhaps one day I'll get 6.8mm carbide drill and I'll manage not to break a carbide tap in it.

For now, I would discourage anyone from trying to drill their hard jaws. Not all of them are case hardened. Also, I still don't understand why a hss centre against any common sense would cut hardened metal. Perhaps it is reverse case hardened? Soft on the outside, hard inside?
 
It sounds like the steel may have work-hardened. When you used the first cobalt drill did you go easy at first? If so, it could have hardened the surface. With alloys prone to such hardening it is best to just "go for it", drill the hole in one shot with firm even pressure, without stopping or easing up.
 
Eddyde said:
It sounds like the steel may have work-hardened. When you used the first cobalt drill did you go easy at first? If so, it could have hardened the surface. With alloys prone to such hardening it is best to just "go for it", drill the hole in one shot with firm even pressure, without stopping or easing up.
Click to expand...

It is a possibility, but I doubt it. I tend to press pretty hard (depending on drill size) on the quill. Still I'm quite amazed that this centre drill worked.

After ruining those two 5mm drills I even went back to the centre drill to see if it still would cut and it did. I can't understand how it's possible, but clearly they are made with better hss, or maybe they are carbide? I bought them ages ago in arceurotrade before I moved away from UK. I think they were sold as HSS, but it is not impossible I misremembered and they are indeed carbide. That would explain it.
 
I think I would throw the jaws in the fireplace overnight and get them out in the morning. That does a pretty good job of normalizing. I suppose you could harden them after drilling, also maybe not.
 
Not much to add except that hardness varies all over the map on many import tools. Some too soft, some too hard, some just right. If your clone can accept real Kurt jaws (and other jaws made for Kurt vises) getting a set might be the ticket to getting where you want to go.

GsT
 
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