cleaning up drilled holes

[md21722]

Again, I'm new to metal working so please humor me some.

I've drilled 1/2" holes in a junk axle housing similar to what I'd do for plumbing in a locker. I see that the drilled holes are not perfectly smooth. This may be a benefit to inserting a rubber grommet but I am wondering what the correct technique would be to smooth it out, ready for tapping, etc.

I have read that you can drill 1/64" less than desired and then use a carbide burr on a straight die grinder to smooth it out to a nice clean hole.

Thoughts?

My ultimate goal by asking many of these questions is to (slowly) gain enough experience so that I can be comfortable with metal working which would include cutting/fitting square/round tubing, welding, plasma cutting, welding on new shock mounts, spring perches, trusses, etc. to both do things to the Jeep and around the shop like shelving, tables, or whatever needs to be done on what I have now and on the "farm" I want to have again...

Thanks!

 

[Johnnie Walker]

IMO, if you are going to tap the hole.. then it doesn't matter. Aside from removing attached material left over from said drilling.
With welding, as long as it is clean.. it's fine.

 

[xcm]

You have issues if your drilled hole isnt 'smooth' to the naked eye. Your application shouldnt call for it, but good fabricators DO undersize their holes by roughly 1/32 or 1/64th, but do not use a carbide burr.... use a reamer. Obviously this doesnt matter 75% of the time, but for any suspension bolt holes, for sure.

 

[TRCM]

1) make sure your drill bits are sharp
2) drill with less pressure, let the bit cut, don't try to force it thru
3) never heard of using a burr to smooth a hole....chances are you will make it even less round that way

 

[md21722]

I will try again with less pressure. When it was taking forever I thought I should apply more force. The first hole I drilled was the smoothest and I probably drilled it at 300 RPM (drill max speed 450) with little/no pressure. I remember that for that one the drill never bound up in the hole as it was nearing the end like many of the others. The bits should be sharp. Even new these holes drill slow. I get nice long tailings not metal dust.

 

[Hypoid]

Again, I'm new to metal working so please humor me some.

I've drilled 1/2" holes in a junk axle housing similar to what I'd do for plumbing in a locker. I see that the drilled holes are not perfectly smooth. This may be a benefit to inserting a rubber grommet but I am wondering what the correct technique would be to smooth it out, ready for tapping, etc.

I have read that you can drill 1/64" less than desired and then use a carbide burr on a straight die grinder to smooth it out to a nice clean hole.

Thoughts?

Thanks!

Unless the holes have been wallowed out or ovaled while drilling, this is a non-issue. Whenever you cut threads, you drill the hole smaller than your nominal size. The tap will remove even more material to form the threads.

If you want to remove ridges or chips caused by drilling, you can dress the area with a (Mill Cut) flat file, and/or a round file.

That is the generic answer to your question. Once you get into different assemblies, you get into additional operations to improve serviceability and function.

 

[md21722]

Is there a way to keep the drill from binding up at the end? It cuts perfectly smooth until the bit breaks through and then the drill goes sideways. I believe that's what's causing the issue. I stop the drill, recenter it and finish the hole. There is a ridge that could be filed.

 

[souske]

deburring tool

 

[xcm]

Is there a way to keep the drill from binding up at the end? It cuts perfectly smooth until the bit breaks through and then the drill goes sideways. I believe that's what's causing the issue. I stop the drill, recenter it and finish the hole. There is a ridge that could be filed.

After a while, you will feel it about to punch thru... at which point you ease up on the pressure. If its really picky metal (or has a weird profile where it comes out the other side), you can allmost completely let off the feed pressure, to get thru.

 

[Hypoid]

Is there a way to keep the drill from binding up at the end? It cuts perfectly smooth until the bit breaks through and then the drill goes sideways. I believe that's what's causing the issue. I stop the drill, recenter it and finish the hole. There is a ridge that could be filed.

If you can feel it breaking through, do the wrong thing and lighten pressure while speeding up the drill.

Otherwise, use a lubricant, low speed, a lot of pressure... and practice, practice, practice! :thumbup:

 

[Hypoid]

I forgot to mention, whenever possible, back up the material you are drilling. If you have the luxury, clamp your stock to similar material. The work piece comes out clean, without the bit grabbing.

 

[ftwelder]

standard twist bits are available with different ends on them. the "usual" is 115 degrees and generally have a small "bridge" or web across the end. This type works best if you start with a smaller bit first and generally cuts pretty slowly. The second common type is a 135 degree "split point". This type has had the web ground with a second cut so the center is also cutting. The second type cuts very quickly but often cuts a hole with a slightly triangular shape. For sheet metal you should be ousing uni-bit and for thick stuff a RotaBroach.

There is a correct size hole for each bolt size and you want around 70-80% thread cut depth for hardware type bolts (this % is the diameter of the tap, not depth of hole). If you are cutting National Course threads you can use 1/16" smaller for 5/16-1/2" bolts and for metric you deduct the "pitch" number from the diameter (M6X1 uses a 5mm tap drill). Machine shops will often drill slightly undersize first then "true" the hole with a correct size end mill but that is only for higher precision applications. Drill/tap charts are easy to come by.

Broken taps can be very difficult to remove so I use a lot of care in preparation.

 

[machinisttx]

As a machinist, some of the info given here makes my head hurt.

A drilled hole will never have a perfectly smooth finish, regardless of the drill type or point angle used. If a good finish is required, then the hole should be drilled undersize and then reamed/bored/burnished/etc. to size. The poor man's substitute for this is to drill the hole undersize and then finish the hole with correct size drill while carefully controlling the feed rate.

A cutting tool has a proper speed and feed rate for a given material...and almost always requires some form of lubrication to obtain the best tool life and surface finish. WD-40 and automotive fluids are not proper cutting fluids. The cutting fluid also has the purpose of carrying some of the heat from cutting away from the cutting edges.

Drills are available in several different point angles. The most common are 118 and 135. Point angle is largely irrelevant for most fabrication. The 135 point angle is typically only used on harder metals while 118 is general purpose. The 135 will require more pressure to cut. Some drills are ground with a split point. The split point will substantially reduce the amount of pressure required to cut. It's available on any point angle.

If you're drilling a hole with the intention of tapping it, the finish doesn't matter. http://www.lincolnmachine.com/tap_drill_chart.html

 

[Hypoid]

I appreciate the input we are getting to this thread.

 

[Original_MudButt]

In life, in all things, lubrication is the key...

As others have said, if hole size and finish is your goal, a (well lubricated) reamer is what you need.

Also rigidity of your set-up has an affect on final finish. A bench vise and drill would be considered a starting point. A drill press would be a step above. A milling machine and machine vise should pretty much cover anything you would need in the automotive world.

 

[podm98c]

I'm a machinist also this is more preference then anything but I like to take a counter sink to any hole I'm tapping. Also when tapping make sure you break the chip and it's been said use a good cutting oil.

 

[md21722]

In life, in all things, lubrication is the key...

I've found using cutting oil has helped quite a bit. I'm using the Snap On version just because it was easy to get. I believe its sulphur based. It sure smells like it. Previously I was using air tool oil since I had it.

 

[markw]

I use Tapmatic Gold cutting fluid from LPS. For bigger holes I tend to lean more towards my rotabroach set, as those things make quick work in punching a hole in 3/16 plate. I timed drilling a 1/2 hole in .250 plate and it was under 10 seconds in my drill press.

https://www.youtube.com/watch?v=zLZf8LQuGvU

 

[md21722]

If I could do that in 10 seconds in cast iron that would be awesome. Any times on cast iron?

 

[Hypoid]

If I could do that in 10 seconds in cast iron that would be awesome. Any times on cast iron?

If your cast iron (or steel) is flat like "plate," it should cut like butter. If your cast material is anything but flat, time should be the least of your concerns.