Need tips on drilling a long thin through hole

Maybe not doable with what you have, but for maximum accuracy, deep hole drilling is done with both part and drill rotating (in opposite directions of course). Perhaps on a lathe with a live spindle on QCTP and part held in 4-jaw chuck.

Deep Hole Drilling Process
Rotating Tool
  • Typically used for non-symmetrical components, or round parts with off-center holes
  • Cutting speed is determined by tool spindle speed
  • Drill drift can be significant when compared to rotating workpiece, or counter-rotating process
Rotating Workpiece
  • Typically used for round parts with a deep, on-center hole
  • Cutting speed is determined by part, balanced to allow high rotating speeds
  • Drill drift is reduced compared to rotating tool only
Counter-Rotating Tool and Workpiece
  • Ideal process for round parts with a deep, on-center hole
  • Cutting speed is determined by a combination of tool and workpiece rotation
  • Provides optimal hole straightness and concentricity
 
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Terry, No one has mentioned, , and since you might be inexperienced in drilling deep holes, you must "peck drill" the hole. Drill little or no more than the diameter deep before withdrawing the drill and clearing the chips. That'll be at least 22 pecks. Otherwise you run a great risk of binding the chips in the drill and breaking the drill and scrapping the part. I don't know about a gun drill which in effect has one straight flute, but I can't imagine it would flow aluminum chips that far either.

Edit: fix typo
 
Not much information on the functionality of so called part or of its intended outcome . Hard to envision a procedure without some details . Is this a prototype piece , are you designing something etc ?

Working in an engineering lab for years , you learn there are more ways than one to skin a cat . An engineer makes a simple job overly complicated , a machinist makes it simple again .
 
I have never used a gun drill, but I think most of them use through coolant that helps flush chips.
They use them to drill a 32" long rifle barrel and stay centered pretty good.
I don't think one that was only about 6" long would be to costly.
Joe Hynes
 
Well I take back the cost part. Just looked on McMaster, a 3/16" drill 10" long is about $85.
I guess it depends on how bad you need the precision.

Joe Hynes
 
Here is Guhrings #9050260045000.. $206 from MSC. There is a website calculator that figures it out: https://www.guhring.com/BrowseProducts/Products/Gun-Drills Just answer the questions. This will get you just under-size so you will need to ream to final dimension.
.177 X 4.54 long. Might be other manufacturers that are closer or exact size.
 
Let us know how this turns out. I was considering making a 4 inch hollow tube for the oil can project here but didn't know how to do it. Not as precision as you seem to need but the procedure would be the same.
 
Find a shop with wire EDM capability? One hole might not be too costly.
 
Need to find a shop with a hole popper. Wire EDM will not work, as it needs a hole first to feed the wire through. We have one at work but we have never used it over 2” in making our stamping dies.

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