[Newbie] Looking to countersink 4 holes on steel plate. Will HSS bit work for A36?

[xnoitulos]

I'm trying to make a base plate for an EVT Bicycle stand as cheap as possible.
I can get a 1/2" thick ASTM A36 steel plate with the 4 holes already drilled. My questions are:

Will I have any problem with a 3/4", 6FL, 90 Deg countersink into a 1/2" hole without a drill press?

If I can just use the bit with a power drill, can I get away with the HSS version ($30) or better off with the Cobalt ($40) or Cobalt with TiN ($53).

Only needs to sink 4 holes. Zero foreseeable use for this bit after this project. Don't want to get 3 holes done and have bit crap out.

Thank you for any advice!

 

[JimDawson]

HHS will work just fine in almost any material. Turn it as slow as your drill press will go, it will work fine in a hand drill also, but again turn slow. Use oil, for just 4 holes, any oil will work.

I would also recommend a 82 degree, single flute or zero flute countersink, since you need to buy one. I also suggest that you will find lots of uses for a countersink. I normally keep one chucked up in the drill press just for deburring holes.

 

[extropic]

As Jim wrote, a quality HHS c'sink should be fine, low RPM (500 or less) and use some type of oil (even WD40). I would also recommend a single flute countersink, rather than a six flute, because I think you'll have less problems with chatter. In a hand held set up you might get a sort of corrugated effect with a 6 flute in steel. You'll need a fairly stout drill motor and need to lean on it to do your 3/4" diameter.

 

[xnoitulos]

recommend a single flute countersink, rather than a six flute

Thanks for the great answers! I see the single flute model is the same price as the 6 flute ($30). The zero flute is $40 and only available in cobalt(looking at KEO brand). Is one better than another for this application? Again, no drill press. I see some photos of what a chattery hole looks like, but don't think that would matter for this application (countersinks are facing down to the floor). I also went 90 degrees because that's what the M10 bolts I'm using are. Thanks again!

 

[T Bredehoft]

For a 1/2 in screw, a 1" dia counter sink is probably what you want. That's 3.14 inches in circumference, to keep from exceeding 90 surface feet per minute (nominal HHS speed) you've gotta hold your RPMs down below 280 to keep from smoking your cutting tool. Yes, any lubricant will help, but a heavy oil (dark cutting Rigid) would be best.

 

[12bolts]

Alternatively, if you think you wont ever need a countersink again, (unlikely) you could just regrind a biggish drill bit if you have one, to your 90*. Or use hex heads and then drill 4 pockets in a matching plywood base and glue that to the bottom of your steel plate to cover the bolt heads, making a soft base.

Cheers Phil

 

[extropic]

Thanks for the great answers! I see the single flute model is the same price as the 6 flute ($30). The zero flute is $40 and only available in cobalt(looking at KEO brand). Is one better than another for this application? Again, no drill press. I see some photos of what a chattery hole looks like, but don't think that would matter for this application (countersinks are facing down to the floor). I also went 90 degrees because that's what the M10 bolts I'm using are. Thanks again!

As to single flute vs zero flute; I have no personal experience with the zero flute type but have heard good things about them used in aluminum. No info regarding steel. I have considerable experience with the single flute type flute type and it will do the job.

 

[GarageGuy]

I would disagree with using "any" oil while countersinking, or any other kind of metal cutting. Use cutting oil. If you ever make the mistake of using motor oil for cutting, you will never forget it. :biggrin:

GG

 

[Micke S]

Statement corrected, I was wrong...

 

[Eddyde]

Another thing to consider, it is difficult to get the countersink square to the surface with a hand drill. If the countersunk hole is not true, the screw head will not bear evenly on the plate. This will likely cause the screw(s) to loosen over time. Best to seek out someone with a drill press, I would think a local shop would do the job for around $30-$40 and you wouldn't need to purchase the countersink.