countersink trouble

[Torque]

Started to countersink armor holes with one of those piloted countersinks with a hole through it (new), can't make it do anything, just raised a bur around the hole and got hot (using a mag drill). Then tried a single flute countersink and it was very little better. What do I need to get this done? 6 flute?  Thanks, Barry

[steve1973]

You need to go very slow and use oil. Don used a single flute bit with a mag drill and worked fine but you must go slow. Your drill may be to fast.

Steve A.

[BombFarm]

I know my comments are not really going to fix the problem you've encountered, but I'm very puzzled as to why your countersinks are not working. I personally have done a complete set of M2 armor from the cowl back and only switched out one of those piloted countersinks once. I too used a mag drill for most of my pieces. Although I despise the single flute types, the fact that both styles of countersinks are not doing their job makes me think the problem may lie elsewhere.

Thoughts/questions?
- drill speed to fast?(cheaper Magdrills like mine are typically fixed speed, try test piece with slower speed drill if you suspect this)
- proper lubrication?(self explanatory, more is better)
- countersinking drilled holes, not plasma or laser cut holes right? (Carbide in torched holes destroys cutting tools in a heartbeat)
- defective countersink?(could happen, I guess)
- hopefully your not such a purist that you got authentic face hardened steel plate?(had to ask)
- drill in reverse?(sorry, ran out of scenarios so I threw that in for humor)
 

[spec4don]

My holes were already drilled. I used an old mag drill (Milwaukee) single speed, probably too fast. But used rapid tap cutting fluid and a single flute bit. Seemed to work pretty good.

Don G.

[Outsider]

I use 6 flute carbide countersink on a mag drill. Turn is slow and use lots of coolant.

Steve

[Torque]

The piloted countersink was a cheap one but I thought it would at least do a few holes. The holes were plasma cut but I reamed them 3/8" and they are pretty clean. Mag drill is 450 rpm. I wonder what the steel is.... may not be mild if the maker got a deal on something else...I think I'll get my brother the toolmaker involved... I will let you know what I figure out. Thanks, Barry

[HenryVIII]

I use a 6 flute carbide countersink and a speed of around 100-150 rpm. I have tried to use a 6 flute hss (high speed steel) but I cannot seem to get it to cut right. I have used the carbide at higher speeds but it seems to chatter more. And also you need to keep it oiled. more the better. its a mess.    Henry   

[Torque]

Brother gave me a single lip carbide countersink and it is working OK, if it gives up I wll try the 6 flute carbide one. Thanks

[steve-0]

looks like i may be alone on this one but.

i use no oil/coolant or anything and i really like the single flute.
im using a bridgeport mill at 240 rpm. with a setup like this (basically drill press) i can put alot more downward force than with a mag drill.

  i like the single flute with no pilot because i can just jam it into the hole with out much alignment and the bit will pull the plate to center. i tried a 6 flute but it didnt stay centered as well, i think it cut to quick and didnt force the bit to stay centered.

i had cut hundreds of holes with this bit and then yesterday i countersunk all the holes for the m16 rear armor and track armor with it. it still cuts like new.
http://www.mcmaster.com/#2846a127/=rzo48t

[Torque]

The one i am using looks just like that except it is worn out, the edge was chipped so had to grind it back about an 1/8 inch. It is working OK but will not cut a chip anything like that.

[Sprouse]

The problem is probably because the orginal holes were plasma cut there for harding the edges of the hole. Much harder to cut than a drilled hole

[spec4don]

Would they have had plasma back in the 40's? I thought they did all the drilling then heat treated the armor after that?

Don G.

[Torque]

I think my problem was the steel, I had the doors and narrow armor behind the doors made locally from mild steel, the countersink cut them like butter.

[spec4don]

Torque, I reread the post, ok I feel like a dork I understand what you were talking about with the plasma reference. Disregard the peanut gallery

Don G.