How do you chamfer a tapped hole?

[FigureItOut]

Building a vise mount at the moment, but every time I'm putting something together and tapping holes into thick plate or whatever, assembly is a lot more difficult than with manufactured parts. I'm pretty sure that lacking a chamfer is my problem. How does one put that nice little bevel around the top of a tapped hole to help guide the bolt in and get it started?

 

[Thumper68]

The easiest way is to use a countersink.

 

[A_Pmech]

A one-flute countersink to both sides of your hole before tapping will remove any burrs due to drilling the hole and make starting the tap easier.

A burr-free threaded hole is an easy to assemble threaded hole.

 

[FigureItOut]

So, countersink before tapping, got it. Is there a rule of thumb on what size countersink? I can pick up countersinks for my common sizes, if I tap something don't have a countersink for, is there a reasonable substitute? I most often tap 6-32, 8-32, 1/4-20 and 3/8-16.

 

[rbgearz]

When I'm feeling lazy and don't want to look for a countersink I just hit it with a bigger drill bit. Not the right way but gets the job done.

 

[FigureItOut]

When I'm feeling lazy and don't want to look for a countersink I just hit it with a bigger drill bit. Not the right way but gets the job done.

I try that, and get terrible results. The bit tends to bite in and mangle my hole. I'm using 135° split point. I buggered up a piece this evening trying that method, which prompted the question. I worked the holes with a file a bit and it may be salvageable, but that really doesn't work out well for me at all.

 

[Thumper68]

So, countersink before tapping, got it. Is there a rule of thumb on what size countersink? I can pick up countersinks for my common sizes, if I tap something don't have a countersink for, is there a reasonable substitute? I most often tap 6-32, 8-32, 1/4-20 and 3/8-16.

you should only need a few sizes to cover your common holes.

 

[pstemari]

One of these ought to get you by, maybe also get the 3/16" one for the #6 size holes:
https://m.mscdirect.com/mobileweb/product_detail?id=02351666&hasRestrictedParts=false

Sent from my Nexus 6 using Tapatalk

 

[6PTsocket]

So, countersink before tapping, got it. Is there a rule of thumb on what size countersink? I can pick up countersinks for my common sizes, if I tap something don't have a countersink for, is there a reasonable substitute? I most often tap 6-32, 8-32, 1/4-20 and 3/8-16.

Unless you are planning to drop a screw head below the surface, any countersink that is bigger than the hole will do. We are talking about just chamferring , right ? Countersinking a screw head involves matching the angle of the screw head . There are 82, 90 and even 115 (or was it 110?)degree countersinks.

Sent from my SM-G900V using Tapatalk

 

[6PTsocket]

When I'm feeling lazy and don't want to look for a countersink I just hit it with a bigger drill bit. Not the right way but gets the job done.

Been there,done that and I'm sure we are not the only ones.

Sent from my SM-G900V using Tapatalk

 

[matt_i]

I try that, and get terrible results. The bit tends to bite in and mangle my hole. I'm using 135° split point. I buggered up a piece this evening trying that method, which prompted the question. I worked the holes with a file a bit and it may be salvageable, but that really doesn't work out well for me at all.

A 135 deg point doesn't follow a pilot hole very well, the 118 deg points work a lot better for this.

I have very good luck with MA Ford or Melin Tools 2+2 design. You can run it at about 10 rpm in a cordless drill and it will deburr very nicely.

 

[rlitman]

So, countersink before tapping, got it. Is there a rule of thumb on what size countersink? I can pick up countersinks for my common sizes, if I tap something don't have a countersink for, is there a reasonable substitute? I most often tap 6-32, 8-32, 1/4-20 and 3/8-16.

Well, the countersink needs to be bigger than the hole. A huge countersink will still work on small holes, but is expensive, and might interfere in tight spaces. Small countersinks are cheap if you burn them up.

 

[BD1]

Typically the countersink pitch or bevel matches what a flathead bolt has on it below the head for a flush gripping connection.

 

[FigureItOut]

Thanks fellas, answered all my questions. I'll get some M.A Ford 0 flute in a couple sizes.

 

[astroracer]

Standard machine shop practice for a drilled and tapped hole is the chamfer is added after the drilled hole and it should be at least as big as the "final" bolt size.
Example: a 1/4-20 tap uses a .21 diameter tap drill. The chamfer should be at least .25 diameter to get a good start with the tap. Can it be a bit bigger? Sure, I will usually go about .030 bigger and this pretty much guarantees no high spots or burrs after tapping.
Mark

 

[gahrajmahal]

If you use a centering drill bit you can eliminate the separate chamfering operation and get a nice accurate start for your tap size drill.

https://www.mcmaster.com/#combined-countersinks-and-drills/=16sbdh9

 

[GarrettWeidman]

https://www.mscdirect.com/product/details/05751466

I use one of these to deburr holes. screw some all-thread in and chuck it up in a hand drill, it works great.

 

[Dr Stan]

I've used the center drill method for years. However since the introduction of spotting drills I rather use them. Since they are 90 degrees .025 difference in depth is .050 larger on the diameter. Fairly easy to calculate how much more you need to go.

 

[jwith68]

A unibit (step drill) chucked in a hand drill can work for chamfering as well.

 

[joel63]

I've used the center drill method for years. However since the introduction of spotting drills I rather use them. Since they are 90 degrees .025 difference in depth is .050 larger on the diameter. Fairly easy to calculate how much more you need to go.

Thanks, I learned something about drills.

I don't think I ever heard of them.

 

[matt_i]

A spot drill is the tool you really want in a milling machine to make sure your hole starts where you have fixtured it instead of being worried about drill-bend. The ones I have are all 120deg included to conically pilot a 118deg included drill bit. Also they are all solid carbide which has a higher Young's modulus than steel to further resist deflection.