Gang,
Quick question.... possible situation ... need to tap a hole in, say
1/2" plate, through to the other side, but needs to be "perfectly
aligned" and say the plate is mounted on a piece of machinery that
can't be moved to another location and the tapping has to be done by
hand. Possible solution - is it possible, (or has anyone ever done
this), by grinding a "pilot" on the front end of that tap and then
relieving the cutting edges again to look almost like factory just
behind the end of the pilot? Is this a viable concept?
Ken.

In article ,
Ken Sterling (Ken Sterling) wrote:

Gang,
Quick question.... possible situation ... need to tap a hole in, say
1/2" plate, through to the other side, but needs to be "perfectly
aligned" and say the plate is mounted on a piece of machinery that
can't be moved to another location and the tapping has to be done by
hand. Possible solution - is it possible, (or has anyone ever done
this), by grinding a "pilot" on the front end of that tap and then
relieving the cutting edges again to look almost like factory just
behind the end of the pilot? Is this a viable concept?
Ken.

Don't know about that, sounds complicated. Might or might not work (only
1/2" for it to work on). Standard method in the labs I've worked in has
been to have a handy block (several inches thick) with various holes
drilled through (on a drill press) which could then be clamped to the
workpiece and used to guide the tap "pretty precisely". Generally
aluminum, so it will bugger itself up rather than the tools it's
guiding, and was cheap/easy to make another one of if needed. Guide the
drill, too, if needed (in a smaller hole, or use bushings). If you have
money to splash about or a deep tool crib, a mag-mount drill might
provide a handy tapping jig which you can take to the machine and drill
the hole with, too.

If you _really_ need "perfect" alignment, threads are probably not the
solution, so I expect that if threads will do, the tap-guiding-block
will get them started "perfectly" enough.

--
Cats, coffee, chocolate...vices to live by

Ken Sterling (Ken Sterling) wrote in message
...

Gang,
Quick question.... possible situation ... need to tap a hole in, say
1/2" plate, through to the other side, but needs to be "perfectly
aligned" and say the plate is mounted on a piece of machinery that
can't be moved to another location and the tapping has to be done by
hand. Possible solution - is it possible, (or has anyone ever done
this), by grinding a "pilot" on the front end of that tap and then
relieving the cutting edges again to look almost like factory just
behind the end of the pilot? Is this a viable concept?
Ken.



Drap ( combined drill and tap ) comes to mind. Available from MSC and other
major
industrial suppliers.

Best Regards
Tom.

Ken Sterling (Ken Sterling) wrote in message
...
Gang,
Quick question.... possible situation ... need to tap a hole in, say
1/2" plate, through to the other side, but needs to be "perfectly
aligned" and say the plate is mounted on a piece of machinery that
can't be moved to another location and the tapping has to be done by
hand. Possible solution - is it possible, (or has anyone ever done
this), by grinding a "pilot" on the front end of that tap and then
relieving the cutting edges again to look almost like factory just
behind the end of the pilot? Is this a viable concept?

I agree with Ecnerwal. Your idea of a piloted tap is overly complicated
(esspecially for a one-off situation) and a hole is easily tapped by hand
squarly using a machinist's square or tapping block.

We drill and tap hundreds of holes at work by hand (big dies in funny
places). I've been doing it for a while so I just eye-ball it and can nail a
hole quite accuratly using that method. This takes practice and I think you
have to have a certain eye for it.

You didn't say if you needed to drill the hole (or does it already exist?)
The drilling is far more difficult than the tapping. You have to go slowly
and check the angle of the drill consistantly as you go. Because you're
drilling through steel, you'll likely be pushing pretty hard which
frequently makes for a crooked hole. Be aware of this and check squareness
consistantly.

As for tapping by hand (or using the drill), just make sure to check your
squareness consistantly as you normally would. Easy.

HTH.

Regards,

Robin

I have done this for rethreading and it works okay. I do think that a block
would work better if you have a suitable surface.
Don Young
Ken Sterling (Ken Sterling) wrote in message
...
Gang,
Quick question.... possible situation ... need to tap a hole in, say
1/2" plate, through to the other side, but needs to be "perfectly
aligned" and say the plate is mounted on a piece of machinery that
can't be moved to another location and the tapping has to be done by
hand. Possible solution - is it possible, (or has anyone ever done
this), by grinding a "pilot" on the front end of that tap and then
relieving the cutting edges again to look almost like factory just
behind the end of the pilot? Is this a viable concept?
Ken.

I have used a piece of 2 by 4 to guide both the drill and the tap.
Wood like aluminum is easy on the drill and tap. I might be tempted to
keep an aluminum block for the day when I need to tap another hole, but
wood blocks get recycled in the wood stove.

Dan

Ecnerwal wrote:


Don't know about that, sounds complicated. Might or might not work (only
1/2" for it to work on). Standard method in the labs I've worked in has
been to have a handy block (several inches thick) with various holes
drilled through (on a drill press) which could then be clamped to the
workpiece and used to guide the tap "pretty precisely". Generally
aluminum, so it will bugger itself up rather than the tools it's
guiding, and was cheap/easy to make another one of if needed. Guide the
drill, too, if needed (in a smaller hole, or use bushings). If you have
money to splash about or a deep tool crib, a mag-mount drill might
provide a handy tapping jig which you can take to the machine and drill
the hole with, too.

If you _really_ need "perfect" alignment, threads are probably not the
solution, so I expect that if threads will do, the tap-guiding-block
will get them started "perfectly" enough.

--
Cats, coffee, chocolate...vices to live by

I've seen drawings of piloted taps in a very old book, maybe it was
Holzapffel's 1840's edition. I think they went away because people
switched from threads to dowel pins for "perfect alignment", whatever
that may be. I work to calculated tolerances for engineers who know
enough to specify them and ruler measurements for anyone who wants
"exact" since that is probably the tool they will use to check it.

Try it, but remember that taps are brittle. Could you drill and ream
the plate and machine for hollow pins and run the screws through them
into less demandingly placed tapped holes? Drill rod is very close to
nominal OD and not too difficult to drill through lengthwise.

jw

Something doesn't sound right....how thick is the plate? Won't the pilot be
unguided on the other side of the plate? Make a guide block and clamp on or
tack weld it. Or even a nut.


Ken Sterling (Ken Sterling) wrote in message
...
Gang,
Quick question.... possible situation ... need to tap a hole in, say
1/2" plate, through to the other side, but needs to be "perfectly
aligned" and say the plate is mounted on a piece of machinery that
can't be moved to another location and the tapping has to be done by
hand. Possible solution - is it possible, (or has anyone ever done
this), by grinding a "pilot" on the front end of that tap and then
relieving the cutting edges again to look almost like factory just
behind the end of the pilot? Is this a viable concept?
Ken.

Easiest is to take a block of aluimum or steel and tap the hole in that and
then use that as an alignment jig for the hole you want.

--
Why do penguins walk so far to get to their nesting grounds?

Something doesn't sound right....how thick is the plate? Won't the pilot be
unguided on the other side of the plate? Make a guide block and clamp on or
tack weld it. Or even a nut.

Tom,
This is just a hypothetical situation ... I was wondering if such a
thing existed as a piloted tap - just to get a tap started "dead on"
at the beginning of the process (by hand) where the pilot part of the
tap would keep you lined up until you were cutting the thread straight
and the pilot would indeed "work through the plate" but then you
wouldn't actually need it after the tap was started straight. I have
never seen such a tap, and didn't know if anyone had ever tried it or
not - my feeble grey matter just seemed to think it may be a good idea
in certain situations.
Ken.



Ken Sterling (Ken Sterling) wrote in message
...
Gang,
Quick question.... possible situation ... need to tap a hole in, say
1/2" plate, through to the other side, but needs to be "perfectly
aligned" and say the plate is mounted on a piece of machinery that
can't be moved to another location and the tapping has to be done by
hand. Possible solution - is it possible, (or has anyone ever done
this), by grinding a "pilot" on the front end of that tap and then
relieving the cutting edges again to look almost like factory just
behind the end of the pilot? Is this a viable concept?
Ken.

Ken Sterling (Ken Sterling) wrote in message
...
Something doesn't sound right....how thick is the plate? Won't the pilot
be
unguided on the other side of the plate? Make a guide block and clamp on
or
tack weld it. Or even a nut.

Tom,
This is just a hypothetical situation ... I was wondering if such a
thing existed as a piloted tap - just to get a tap started "dead on"
at the beginning of the process (by hand) where the pilot part of the
tap would keep you lined up until you were cutting the thread straight
and the pilot would indeed "work through the plate" but then you
wouldn't actually need it after the tap was started straight. I have
never seen such a tap, and didn't know if anyone had ever tried it or
not - my feeble grey matter just seemed to think it may be a good idea
in certain situations.
Ken.

In my estimation, it wouldn't be a good idea. One of the problems with
tapping holes is the discharge of the chips. A pilot would, for the most
part, minimize, if not eliminate, the area needed for chip accumulation and
cutting geometry. Even worse would be when the hole was not sized
properly, nor drilled straight. A tapping block would most likely serve
far better.

Harold

Ken Sterling (Ken Sterling) wrote in message
...
Something doesn't sound right....how thick is the plate? Won't the pilot
be
unguided on the other side of the plate? Make a guide block and clamp on
or
tack weld it. Or even a nut.

Tom,
This is just a hypothetical situation ... I was wondering if such a
thing existed as a piloted tap - just to get a tap started "dead on"
at the beginning of the process (by hand) where the pilot part of the
tap would keep you lined up until you were cutting the thread straight
and the pilot would indeed "work through the plate" but then you
wouldn't actually need it after the tap was started straight. I have
never seen such a tap, and didn't know if anyone had ever tried it or
not - my feeble grey matter just seemed to think it may be a good idea
in certain situations.
Ken.

Just because a tap starts straight doesn't mean it will STAY straight! I do
have taps for wood that are piloted.

"Tom Gardner" wrote in message
...

Just because a tap starts straight doesn't mean it will STAY straight! I
do have taps for wood that are piloted.

Well, you know the way woodworkers are..

Regards,

Robin