Drilling question
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Drilling question
I'm trying to drill three mounting holes in a bronze worm gear that was cast onto a steel hub, and as luck would have it the holes are right on the interface of the bronze and steel. The first hole walked off into the bronze and is out of alignment, which I will fix by plunging an end mill through the hole for a shear pin, but I need the other two hole to be aligned for tapping so I can fasten the gear. Any tips on how to drill these holes will be appreciated. Thanks, John
Re: Drilling question
I think anything that generates a side force is going to get off center, so a drill is not going to work (as you found out). It's just taking the path of least resistance.
Is there an end mill that is the size of the tap drill you would need?
Steve
Is there an end mill that is the size of the tap drill you would need?
Steve
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Re: Drilling question
Steve, the hole is an F drill hole for a 5/16 X 18 tap. I can look around for an end mill that's close, but I'm still going to have to drill a pilot hole.
When I drilled the first hole I figured it was going to be a problem so I clamped the piece I wanted to mount onto the gear, transfer punched it, center drilled it, then drilled it with the piece still in place to act like a drill bushing...it still walked off. I can't drill a very small pilot hole either, the center of the hole is right on the seam.
When I drilled the first hole I figured it was going to be a problem so I clamped the piece I wanted to mount onto the gear, transfer punched it, center drilled it, then drilled it with the piece still in place to act like a drill bushing...it still walked off. I can't drill a very small pilot hole either, the center of the hole is right on the seam.
Re: Drilling question
"F" is ,257"
Use a 3/16" center cutting end mill followed by a 1/4" end mill, then bore it to final size if you need to.
Use a 3/16" center cutting end mill followed by a 1/4" end mill, then bore it to final size if you need to.
Glenn
Operating machines is perfectly safe......until you forget how dangerous it really is!
Operating machines is perfectly safe......until you forget how dangerous it really is!
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Re: Drilling question
Got it!
Thanks guys, John
Thanks guys, John
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Re: Drilling question
I would use an end mill to make the hole, stepping up in size if need be. A letter "F" drill will give you a theoretical thread depth of approx. 77% . If you were to stick with the 5/16 hole generated by the end mill, the thread depth would be around 86%. A little more difficult to tap but it would work. Chances are the endmill will cut oversize as will any drill. You also have to figure that even if the hole is dead on, the tap is going to try to deflect over into the softer material.
Nyle
Nyle
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Re: Drilling question
John, it strikes me you could put helicoils in the bronze worm gear in lieu of drilling and tapping on top of the interface. Certainly if your attempts to tap the hole go awry, you could use the inserts and do just fine, I think.
Glenn
Glenn
Moderator - Grand Scale Forum
Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge
Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge
Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
- SteveHGraham
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Re: Drilling question
I would start with an undersized end mill and then use a drill bit to open it up before tapping. This may be wrong, but it's what I would do.
Too bad they don't make annular cutters that small. Or do they?
Too bad they don't make annular cutters that small. Or do they?
Every hard-fried egg began life sunny-side up.
Re: Drilling question
Woops! Somewhere the actual size has been lost. Conversation, thus far, was in regards to a 5/16-18 thread. If a 5/16 end mill was used, the resulting thread would amount to, for all practical purposes, 0. I suspect you meant ¼", but things like this have a way of being translated such that scrap is made. Just wanted to avoid that possibility. I know you know the difference.LIALLEGHENY wrote: ↑Fri Jul 27, 2018 8:17 pm I would use an end mill to make the hole, stepping up in size if need be. A letter "F" drill will give you a theoretical thread depth of approx. 77% . If you were to stick with the 5/16 hole generated by the end mill, the thread depth would be around 86%
H
Wise people talk because they have something to say. Fools talk because they have to say something.
Re: Drilling question
In spite of drills having a margin without relief (they are reduced, but no further relief applied), they will still deflect, resulting in the hole being mislocated to some degree, as well as it no longer being perpendicular. Same thing goes when the hole is tapped, as has already been mentioned.SteveHGraham wrote: ↑Fri Jul 27, 2018 10:51 pm I would start with an undersized end mill and then use a drill bit to open it up before tapping. This may be wrong, but it's what I would do.
Any time dissimilar metals are machined, as they are in this instance, you can expect tool deflection, as the greater cutting pressure for the harder to machine material will push the cutter away. It can be managed by using very short cutting tools, and rigid setups. To ensure location, I'd stick with an end mill, as it has the ability to remove metal without excessive deflection, given the chance. Much lower cutting pressure, and without the angled cutting face found on drill bits, which exacerbate the deflection problem.
Boring, as Glenn suggested, is always an acceptable solution. It just takes more time.
H
Wise people talk because they have something to say. Fools talk because they have to say something.
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Re: Drilling question
Yep, been in the heat to long....my brain isn't running on all cylinders anymore!Harold_V wrote: ↑Sat Jul 28, 2018 12:12 amWoops! Somewhere the actual size has been lost. Conversation, thus far, was in regards to a 5/16-18 thread. If a 5/16 end mill was used, the resulting thread would amount to, for all practical purposes, 0. I suspect you meant ¼", but things like this have a way of being translated such that scrap is made. Just wanted to avoid that possibility. I know you know the difference.LIALLEGHENY wrote: ↑Fri Jul 27, 2018 8:17 pm I would use an end mill to make the hole, stepping up in size if need be. A letter "F" drill will give you a theoretical thread depth of approx. 77% . If you were to stick with the 5/16 hole generated by the end mill, the thread depth would be around 86%
H