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Posted by Dave99 on January 24, 2008, 3:25 pm
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Thanks for the help... Upon further investigation... I examined a few
different screws by holding them up to the light in front of the holes
before tapping. I wasn't able to see light on any of them. If
anything, it looked like the #36 holes might actually be a hair
smaller than the shank of the screws. So it must be something in the
tap process. As it turned out, I'm using screws with small nylon
locking strips. I found them at a local surplus and they're pretty
handy little things. The addition of the nylon actually makes it
workout pretty well in the end.
But since I'm on the subject... What is the best process for dressing
threaded holes that have been made in round stock? I'm putting these
6-32 holes through the sides of 1/4" and 3/8" round stock. Then those
pieces go in holes with tight tolerances. If there's a little lip
remaining on the edge of the holes from the tap, it sometimes prevents
the round from fitting in the hole. What I've been using is just a
countersink on each side of the hole. That cleans it up a bit and kind
of makes an oval shaped opening. The down side is that it can make the
start of the thread a little screwed up, so it's not always easy to
start the screw. This isn't a problem for me, but other people
assemble these parts.
Thanks,
Dave
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Posted by Lloyd E. Sponenburgh on January 24, 2008, 3:50 pm
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8511-2e849ad125c9@p69g2000hsa.googlegroups.com:
> But since I'm on the subject... What is the best process for dressing
> threaded holes that have been made in round stock? I'm putting these
> 6-32 holes through the sides of 1/4" and 3/8" round stock. Then those
> pieces go in holes with tight tolerances. If there's a little lip
> remaining on the edge of the holes from the tap, it sometimes prevents
> the round from fitting in the hole. What I've been using is just a
> countersink on each side of the hole. That cleans it up a bit and kind
> of makes an oval shaped opening. The down side is that it can make the
> start of the thread a little screwed up, so it's not always easy to
> start the screw. This isn't a problem for me, but other people
> assemble these parts.
Were it me, I'd counterbore the tapping hole before tapping. A good,
sharp counterbore won't leave shucks for a burr.
The other rational approach would be to mill a small flat on opposing
sides before drilling. This has the added advantage of allowing you to
spot the drill dead on center, since you can drill with the same setup
used to mill the flat.
LLoyd
LLoyd
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Posted by Roger Shoaf on January 24, 2008, 11:15 pm
Please log in for more thread options Dave,
One thing you might consider is to use a finer thread than 6-32.
The 6-32 thread is a kind of force fit, not leaving much on the ID of the
screw. It is by far the most often broken tap and the weakest screw for
this reason.
Since it is aluminum, if you have to use 6-32 I like the idea of the thread
form taps.
--
__
Roger Shoaf
Important factors in selecting a mate:
1] Depth of gene pool
2] Position on the food chain.
> I'm tapping a ton of 1/4" aluminum 6061 parts for 6-32. I've been
> using a #36 bit, but the threaded holes seem a little more loose than
> they should be. They do work, but I'm wondering if a #37 would be
> better. Before I break a tap, I figured I'd ask here and see if
> anybody has routinely done that before or if there's a better idea.
>
> Thanks,
>
> Dave
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Posted by Dave99 on January 24, 2008, 11:42 pm
Please log in for more thread options Thanks for the tips... For some reason I never even thought to
countersink first. I suppose I could try 4-40. My thinking was just
that, it being a softer metal, that a larger thread was the way to go.
DD
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Posted by Lloyd E. Sponenburgh on January 25, 2008, 7:28 am
Please log in for more thread options 8cf9-a2265306a253@i7g2000prf.googlegroups.com:
> Thanks for the tips... For some reason I never even thought to
> countersink first. I suppose I could try 4-40. My thinking was just
> that, it being a softer metal, that a larger thread was the way to go.
>
Not "countersink", Dave; Counter_bore_. Different tool.
LLoyd
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> threaded holes that have been made in round stock? I'm putting these
> 6-32 holes through the sides of 1/4" and 3/8" round stock. Then those
> pieces go in holes with tight tolerances. If there's a little lip
> remaining on the edge of the holes from the tap, it sometimes prevents
> the round from fitting in the hole. What I've been using is just a
> countersink on each side of the hole. That cleans it up a bit and kind
> of makes an oval shaped opening. The down side is that it can make the
> start of the thread a little screwed up, so it's not always easy to
> start the screw. This isn't a problem for me, but other people
> assemble these parts.