View Full Version : Tap Guidance
05-20-2004, 11:57 PM
I was tapping some holes tonight and thinking. Not all parts can be easily mounted on a drill press or milling table or other tap guidance device to insure that the tap is parallel to the hole. Then an idea came to me. Why not put a pilot the size of the tap drill at the head of the tap to guide it in and hold it straight while starting the thread?
A pilot that's about 1.5 to perhaps 2.5 or 3 diameters long would likely give the tap a lot of guidance for those first few, critical turns.
I couldn't find anything like this in any of my tool catalogs and have never seen or heard of any such animal. Have any of you ever seen or heard of anything like this?
05-21-2004, 12:11 AM
I haven't seen any with a pilot per se, but I occasionally encounter taps with a tap drill size reamer ahead of the threaded portion. It would serve the same purpose.
Question is how was the hole drilled? I start the tap while the part is still in the drill press if fixturing is a problem.
I have an Albrecht chuck in the D/P and it only takes a moment to get the tap started, once it is straight, it can be moved to the vise if there is a problem with completing in the D/P.
A tap block is a piece of aluminum or steel that you drill holes in that allow a loose slip fit of the OD of the tap. The thickness of the block is 1/2-3/4 inch. Keeps the tap straight enough for the large majority of threads. Several of them in the tap drawer with 5-6 holes in each one. Make a new hole if a hole you need gets worn too much. Too easy and quick to make and for that reason I have never seen one for sale. You could make a fancy one with hard drill bushings etc. but it would just dull taps and cost time and money. Several holes in a piece of thick aluminum works as well as a hand taping fixture for most things and is probably as accurate as any pilot arrangement.
05-21-2004, 01:24 AM
I think this is what your talking about
That's what I have done as well Cass (except for using somewhat thicker stock). I have often wondered why the tool catalogs aren't littered with such blocks for people unwilling to make them for themselves. You can drill some straight holes with a hand drill by using the same technique. Really handy item to have in the toolbox at times.
05-21-2004, 06:06 AM
They are, they're called "Bench Blocks"
05-21-2004, 10:48 AM
Well, you never know till you ask.
Yes, when I can I do use the drill press or mill-drill for alignment and I agree that's the best way. But sometimes it doesn't want to work for one reason or another.
I have seen taps with a drill tip but I doubt that a drill would provide much guidance unless it was lke a gun drill with a lot of the OD still there. A standard twist bit would wobble a lot if inserted only a diameter or two. The reamer tip perhaps sounds promising. Where can I get them?
I like the tap block idea. I know of bench blocks but didn't know the holes went through and were tap sized on the commercial ones. I may make a couple.
Still think the pilot would be a good idea for situations where the hole is on a non flat surface or at an angle other than square. I may try to grind one. Or perhaps buy a tap with a drill tip and add a little JB Weld to make a pilot. Just for funzeees.
Ya just can't have too many tools.
05-21-2004, 11:47 AM
I like your idea Paul. I've had to tap holes on curved surface (motorcycle engine) and having a pilot would have ensure that the tap was both concentric and axially aligned. I think the only problem is that, tapping actually decreases the ID of the hole, so once you tapped the hole, you wouldn't be able to remove the pilot.
[This message has been edited by rotate (edited 05-21-2004).]
05-21-2004, 01:32 PM
Just one question guys......
How was the hole drilled perpendicular in the first place:
-If it was in a drill press, then just use the drill press to start the tap.
-If it was done with a portable drill, then just use what was used to aligned the hole.
-If it was drilled by "eye" then what does it matter.
What am I missing something here? http://bbs.homeshopmachinist.net//wink.gif
[This message has been edited by Mike Burdick (edited 05-21-2004).]
I DO like your idea Paul, and thought it a clever solution. I always seem to be tapping bind holes though. On through holes, you could always just pass the whole tap all the way through the work.
I drill angled holes with the aluminum block, but it helps to clamp it down.
The bench blocks I have are hardened, and have only a handful of holes in them. The aluminum blocks are soft (and this is fine, as Cass points out), and can be quickly drilled to whatever size you need at the moment.
Mike, I often drill holes in one set up, only to have to come back at a later time to tap them. Realigning to the hole can be slow, so I understand and share Paul's desire for ways to expedite the process when necessary. But, more often then not, I can just chuck up the tap in a DP, and get a straight start. This might not always the most convenient way however.
05-21-2004, 02:57 PM
What I use for Heli-coils is a tapping block made on my drill press or Mill-Drill. What I usually use is a block of aluminum 3/4 by 1 by 3 inch. I drill two holesthe tap drill size and then using the chuck to hold the tap (usually under power) I thread one hole. I can now use the block for both drilling and tapping at 90 degrees to my peice. Using the same logic you can make a block for most any surface at most any angle. It is usually worth the time to do it right the first time the to have to try and figure out how to now solve the problem of fixing a hole that is tapped at an angle.
05-21-2004, 05:49 PM
I've already started making a couple of blocks with holes for alignment when the holes are perpendicular to a flat surface - and this is most often the case. But there's still angled holes and curved surfaces and whatever.
I didn't think about the diameter reduction thing but how much can it be? I suspect that the tap will come out backwards but it may distort the threads. Perhaps a few extra thousanths of clearance would help?
I think what's missing in your list is making a series of parts that need many tapped holes, perhaps of different size threads. You either need to change back and forth from drill to tap or go to each hole location twice or several times. It seems to me that it would save time if you could do the tapping by hand after all the holes are drilled.
I'm not campaigning for the pilots, just curious if anyone had ever done it.