How do I get a perpendicular hole?

[hakuna]

Ok, seriously newbie question here:

How do I drill/machine a perfectly perpendicular hole? I'm putting a 3/8" hole in some 3/8" aluminum. I used a 1/4" drill, followed by a 3/8" drill. The vise is a machining vise that I used on my drill press, which checks out to be square.

The first time I tried I got a hole that was enough off perpendicular that I think I had cocked the piece in the vise.

The second time I tried I checked everything square and it came out close, but not perfect.

Should I used the mill instead of the drill press? Can you mill a hold more accurately with an end mill? Should I plunge cut with a 1/4" end mill and follow with the drill? Plunge cut with a 3/8" end mill?

I don't have a reamer this small, but I'm not sure that would help in the accuracy of the hole.

Anyhow, sorry for the newbie ignorance, but I appreciate the experience here in the group!

Gary

 

[portlandron]

If the vice is square and the plate held flat in it then look at the following:

Is the drill press table square to the quill?

How much play is there in the quill of the drill press?

Is the drill bit sharp?
If not the pressure you are putting on it could be deflecting it some.

Is the drill ground to the correct dimensions?
If not the drill will cut more on one lip and pull the drill off center.

 

[Troutsqueezer]

One thing, if you're not doing it already, you need to use a spot drill bit to dimple the hole location first to keep the through-hole drill bit from wandering. If it wanders, you'll get a crooked hole. Many folks use a center drill bit in lieu of a spot drill.

Others will chime in with other possible causes, I'm sure.

-Trout

 

[hakuna]

ahhh. I could be that the drill bit isn't sharp enough....I just got a new set, I'll try those.

What is the correct order of operations?

1) spot/center drill for start
2) Drill a through hole (but with what percentage of the final hole size?)
3) Drill final diameter.

Is that right?

 

[deverett]

Ok, seriously newbie question here:

...The first time I tried I got a hole that was enough off perpendicular that I think I had cocked the piece in the vise...

Gary. One way to prevent work slipping in the vice is to put a piece of newspaper between the work and the vice jaws.

Dave
The Emerald Isle

 

[steamer]

Hi Gary,

I would gravitate towards the mill, but, you should be able to drill it square in the drill press.

The advice you have received is sound. I would check the table squareness first on the drill press.

Additionally, how square is "square"? Every dimension has a tolerance...

For the "usual" hole, a drill press may be fine. The average Asian drill press should hold say 5 thousandths in 6" or written .005"/6" For a cylinder bore on a small wobbler, I would want it better....maybe .002" per every 12" , or written .002"/12". Here the lathe or the mill would be my tools of choice and that would depend on what tooling I had to go with them.


Checking the drill press table.
Do you have a dial indicator? No? That's OK. You can check your drill press accurately to the .005"/6" dimension above with a piece of wire coat hanger and some writting paper. See Crap-O-Cad sketch.

Clean the table and stone any burrs off.
Grind a point onto the end of the wire and Bend a 12" long piece of coat hanger into a "Z" as shown.
chuck it up and lock the quil and the table.
Bend the wire untill it "just" touches the paper swatch on the table. if you carefully turn the drill chuck, the paper should ""just" move with the pointer. Now, swing it around 180 degrees and try this test again. If your table is square, you should get the same results.
If you see daylight or your now touching or hitting the table, your table is not square. Now to fix it, you pivot the table by HALF the amount shown by the pointer.....and repeat the test. Keep iterating until your there...patience! Don't rebend the wire after the first reading! Leave it alone until your finished with the 180 degree turn. This is a test of your patience too. Don't be in a rush.

Writing paper is about .004" in thickness, and if your table is at least 6" wide and if you achieve the end result above, you will be square to within .005"/6.000" or better.

Dave

 

[arnoldb]

Great tip on the coat hanger Steamer :bow:

1) spot/center drill for start
2) Drill a through hole (but with what percentage of the final hole size?)
3) Drill final diameter.

Gary, that would be the correct way.
As to the percentage of the final hole size, that depends a bit on your machinery. Personally I wouldn't even bother to run a pilot hole through aluminium for a 3/8" (10mm) drill; I'd just drill it once off, as the 3/8" drill is nice and stiff, and less inclined to wander than a thinner drill.
Where I do need a pilot hole for thicker drills, I choose the pilot so that it is just larger than the thickness of the web of the bigger drill.

For aluminium, always use the sharpest drill you have, and use some form of lubrication - kerosene/WD40/methylated spirits (my favourite), and while drilling try to keep a constant feed pressure. Check the swarf coming out to judge your feed pressure; it should be nice even curls for ali. If you're getting broken bits of swarf, increase your feed pressure a bit, and if the swarf is starting to look like it wants to straighten out, decrease your feed pressure. Too much feed pressure will cause your drill bit to wander.

Most Asian drill presses are not very rigid - I can visibly see the table on mine flexing, especially if I rotate the table so that I do not drill on the center of the table - that can be a cause for the hole not ending up perpendicular as well.

You will most likely get a more accurate hole if you use your mill for the job; drill through with a smaller drill (I'd go for about 9mm for a 3/8" hole) and then plunge through with a sharp 3/8" end mill. That should leave a nice round hole with a good finish. Just take note; end mills will usually drill a slightly over sized hole, so a 3/8" end mill might end up drilling a thou or so over size.

Regards, Arnold

 

[steamer]

Arnold nailed it.

My Asian 14" drill press is stout, but I can see the table flex with big drills....

I usually use a drill press just to "put a hole in" and not as a highly accurate tool. The lathe or the mill is a better place for that.

Arnolds list of operations is good....use sharp drills and the cutting force ( and its associated deflection) will be reduced to a minimum. Always good advice on a machine tool.

Dave

 

[Maryak]

Arnolds list of operations is good....use sharp drills and the cutting force ( and its associated deflection) will be reduced to a minimum. Always good advice on a machine tool.

Dave

To get an accurate hole the drill must not only be SHARP but it MUST be sharpened CORRECTLY. If one edge is longer than the other or at a slightly different angle the drill will cut oversize.

IMHO avoid pilot holes where possible. If a pilot hole is off the job is kaput.

Hope this helps.

Best Regards
Bob

 

[steamer]

Yes Twist drills are awful things! They are only better than anything else in removing stock in a "round hole " sort of way.

If you want a good square hole to close size limits, you should drill undersize, bore to .001-.005" undersize, and finish with a reamer or D-bit.

If you follow this, any walking in the drill or center drill will be eliminated by the boring operation resulting in the hole being on location as well as size and squareness.

And by the way, you can get great results from boring alone with a good SLOW feed, a light cut and a radius tool.....and patience.

Dave

 

[Bill S]

Another thing to check is if the table is flexing downward as you are drilling. To stop the flex on my DP table I have a small automobile scissors jack that I run up to the bottom of the table when drilling critical things.

Bill

 

[robwilk]

I had similar problems when i did my first models one thing i did discover is when drilling very small holes speed your drill up as fast as it will go so you are not trying to force the drill through the material thus bending and loosing accuracy.And then the bigger the drill the slower the speed . This also helps prevent snapping drills off.

Rob....

 

[jonesie]

my advise is if you want it perpendicular do it in the mill, tram the head , clamp in the vise or to an angle plate that is mounted to the table.drill it a 1/64 under then spot it with a new 3/8 mill down 3/8 to 1/2 in, them ream. if you do not have a reamer flatten off the cutting edge of a 3/8 drill and it will cut like a reamer. doing holes in the drill press are good for clearance holes for screws, unless that is all you have but if you have a mill that is the place to do it, as you are not fighting all the variables. good luck jonesie

 

[hakuna]

Wow! Thanks guys for all the great information...there's a wealth of stuff in the last few posts. Steamer Dave I do have a dial indicator, but didn't know how to use it to square the table. I see now how it's done thanks!

This morning I went up a took my first piece (the one with the fairly serious off perpendicular hole) and used a 3/8" end mill and just lined it up with the "show side" hole. Once I plunge milled it, I put the brass bushing I made in and, lo and behold, I can get it square. I'll use some epoxy and it should work fine (just for a crankshaft in my first engine, an EZ-Engine, so not much workload or side force there).

I like the idea of milling the holes square (not to be confused with milling a square hole, which would seemly be a miraculous feat!). But, I want to get my press sorted out too, so I'll take all your advice and check it carefully. It's a fairly nice Jet Press, so I think it's of reasonable quality, but nothing like a mill.

Thanks again guys for all your help,
Gary

 

[nesikachad]

I didn't take the time to read through everyone's response so forgive me if this is redundant.

The first thing I'd do is qualify your work holding (vise) to ensure it's square with the spindle in both the X and Y sides of the Z axis.

For clarification. X is L/R, Y is forward/away and Z is always the same as the spindle regardless of machine. (lathe/mill, etc. Doesn't matter)

I'd rig a dial indicator to the chuck of your machine and open the jaws of your vise as far as they'll go. Then sweep an arc down on the surface of the vise where parallels would register. In a perfect world the indicator won't move throughout its arc. In most cases your going to see a deviation in both axis's. Especially with a drill press.

Now it's a function of creative shimming, patience, adjusting, patience (x10!) to get your work surface completely square with your drill press spindle center.

This is step one to getting a hole square to another feature.

Next, use a drill that's undersize as they are really only good for getting stock out of the way so finish tooling can do its job. A ream is probably your best choice given what you have to work with. A boring head would be better as it's a single point tool and will be much less likely to wander around. (Assuming the bearings in the spindle are good and the gibbs are adjusted properly)

Next, speeds and feeds are your friend. Too aggressive a feed/speed will invite all sorts of nasties (chatter, galling, etc) that will make it difficult to get a good surface finish.

Good luck!

C