How to drill and ream a large-ish hole with drill press.

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johnfreese
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Joined: Thu Jan 21, 2016 2:10 am

Re: How to drill and ream a large-ish hole with drill press.

Post by johnfreese »

I don't think the D drill leaves enough material for reaming. I would spot drill, then drill 1/64 under nominal, then ream. The rule of thumb I follow is ream at 1/2 the rpms you drilled with and double the feed rate. I do not favor drilling pilot holes and following that with the full sized drill. There is one exception to that. When location is critical I spot drill, drill undersized, open the hole by plunging an end mill (poor man's jig bore reamer), then drill 1/64 under full size, then ream.
matthew-s
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Re: How to drill and ream a large-ish hole with drill press.

Post by matthew-s »

NP317 wrote: Mon Aug 06, 2018 12:45 am Question: What material were you drilling?
If it was a brass alloy, you should dull the two cutting edges on the drill to prevent that grabbing, especially at the bottom of the hole!
Kozo H. describes how to do the drill modification in his books.
It is “1/2 hard C360 brass” from online metals. I’ve read the A-3 book carefully up to my current location and did not run across his instructions for modifying drill bits for soft metals. Maybe it’s in one of the other books?

For this hole I spot drilled on the little mill I have to locate the hole, then I moved to the drill press for thre required overhead clearance.

I’ve been lead to believe that spot drills are better than center drills given that their angle is slightly than the drill bit angle to guide it to center.

As far as using the D drill before reaming, I took that from the Kozo book, which I believe is edited to suggest that if he does not give a specific instruction on an operation, he intended to have you flip backwards in the book and find a similar operation containing the instruction.

Have others found this to not be the case?

Finally, I agree maybe the reaming is a little overkill. I did not feel that way until I saw how badly the hole was elongated from my drill press mishap. Then again there must be very little axial load on these trucks!!!
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NP317
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Re: How to drill and ream a large-ish hole with drill press.

Post by NP317 »

Here's a good short video showing how to modify drills for brass.
https://www.youtube.com/watch?v=pAngKHIZgyA

I consider this modification a requirement for drilling brass alloys.
Hope this helps.
~RN
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Harold_V
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Re: How to drill and ream a large-ish hole with drill press.

Post by Harold_V »

matthew-s wrote: Tue Aug 07, 2018 7:16 am I’ve been lead to believe that spot drills are better than center drills given that their angle is slightly than the drill bit angle to guide it to center.
That argument simply doesn't hold water. Spotting drills have come of age due to CNC operations (often to eliminate a second operation, the one of chamfering the hole that is to be drilled), and were rarely found in manual machine shops, which typically used center drills for starting holes in proper location. And why shouldn't they?

Here's the deal. While a spotting drill often creates a spot with a similar angle as the drill point, a center drill provides the addition of a pilot hole, which tends to give cause for a drill to follow the hole. That's especially true if the drill has been sharpened with uneven lips.

I'm not saying that a center drill is better---just that they work just fine. If that wasn't the case, the more than 61 years I've spent on the machines would be a shining example of doing something wrong. It wasn't wrong.

I spent the first 7½ years of my machining career in a facility that produced a guided missile. Never, not even once, did I use, or witness a spotting drill used. We were trained by seasoned machinists, and taught to use center drills. Needless to say, this was long before NC or CNC machines were in use. WW II was fought and won using center drills.

For a solitary hole, one that is not opened, but drilled to size in one pass, a regular ground jobber's length drill will suffice in copper, copper alloys, and cast iron. You have to be mindful that it will have a tendency to self feed (hog), and must take it easy when the drill breaks through for that reason, but it will work adequately, assuming you have a reasonably tight machine. If you have slop in the quill feed, you'd be far better served to reduce rake to 0°. If you open existing holes in those materials, it's never a good idea to use a drill that hasn't been so modified, as it's almost impossible to prevent self feeding otherwise.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Mr Ron
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Re: How to drill and ream a large-ish hole with drill press.

Post by Mr Ron »

Because a drill press usually has 1 or 2 thousands runout, I don't think it is necessary to clamp the vise down to the DP table. I would rather let it "float" and let the reamer seek it's own path. I usually don't use a DP for reaming, but prefer to use the lathe or mill. I learned in shop class, to use a drill, 1/64" smaller than the hole to be reamed. I use the lowest speed available and have no problems. Off course I only work to thous, not tenths.
Mr.Ron from South Mississippi
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