Question about plug/pipe taps

[Ben Gastfriend]

Ok. Here's what I've gotten myself into.

I'm working on making my own hollowing tool for small HF's and ornaments.

I got some 3/8'' hardened steel rod, cut to length, attached to ash turned handle. Grinded off a 1/2'' section on the tip, leaving a flat surface. Drilled 1/8 inch hole thru middle of flat section. Got 1/8'' machine screw.

Now I want to create threads in the 1/8'' hole I drilled to accept the screw to fasten on the cutter head.

I've seen multiple ways to do this, but the most popular (I think) is to "tap" the hole. I searched around and found all kinds of results... metal taps, plug taps, pipe taps, tap drills, tap wrenches, etc.

Does anyone have any idea what I am actually looking for? And would I be able to pick it up at a home improvement store? (i.e. Lowes- got a gift certificate)

Thanks for your help!

Ben

[Bob Hamilton]

It sounds like what you need is a standard metal tap, sized to match whatever screw you will be using. The problem is that the hole needs to be drilled at the root diameter of the screw threads so that there is metal to cut the threads into. In other words, if you have drilled a 1/8" hole you can't use a 1/8" screw. There are tap charts ( like this one: http://www.korit.com/tapndrill.htm ) which tell you the optimum size the hole needs to be for each size tap, but they frequently call for sizes the average woodworker won't have, as in letter sized drills or number sized drills rather than the more familiar x/x" sizes. If the hole is too big the thread will be a sloppy fit and will strip easily. If the hole is too small you might snap the tap off trying to thread it. Since you have already drilled the hole your best option would be to enlarge it to 9/64" and get an 8-32 machine screw and tap. The tap wrench is used to hold the tap and turn it. You can chuck the tap into your drill press and turn the chuck by hand while applying light pressure with the quill if you don't have a tap wrench. As long as the workpiece is firmly clamped with the hole directly under and aligned with the tap then that will help thread the hole straight.

When tapping a hole, once the tap has started to bite only advance it about 1/2 to 1 turn and then back it out to break off and clear the chips. Otherwise it will start to bind and could break the tap or deform the threads. It helps to use a light oil or tapping fluid.

Good Luck!
Bob

[Tim A. Mitchell]

Yuo would be looking for a tap and die set. YTou would have to be sure the threads that are on your screw would match the threads you cut for the hole. There are kits available at Lowes (as I recall).

Not too bad of a process. Be sure you use plenty of oil to lube, and take it slow.

[Gordon Seto]

At Lowes, they have the individual size tap and die with matching drill bit in a set.

Gordon

[Richard Madison]

Bob,
Good explanation.
Ben,
Am curious what kind of "cutter head" you plan to use. If you are thinking of using the Hunter carbide cutter, it gets a little more complicated.

[Marvin Hasenak]

Here is a tap and drill bit chart. http://www3.telus.net/public/aschoepp/tapdrill.html

If you already have a 1/8" hole you will need to enlarge it. I am guessing that the 1/8" screw you have is a 8-32 machine screw which by the chart for steel you will need a hole drilled with a #27 size drill bit .1440 diameter hole. You will need cutting oil, a 8-32 tap and T handle for the tap. For the tap get a tapered tap, it is easier to start the threads with a taper.

Now for the rest of the news, if this is hardened steel, plan on breaking the tap before you get a successful thread if you have never done it before. There is really no way to clean out the broken tap, just drill a new hole and start over. It is hard enough to tap softer machine steel, but hardened steel will be job and a half.

Okay assuming you will try this, keep the tap lined up with the hole, you have to have the tap going straight into the hole. Be sure you have oil on the tap, turn in to the hole, as soon as it binds, back it off a turn, then go forward until it binds again, back it off 2 turns, and repeat this until you have went all the way through the hole and you can turn the tap all the way through the hole with out it binding up. You will want to remove the tap after several times of backing it up and cleaning it, it does make it a little easier. I usually take my air gun and spray the tap and the hole to clean out metal chips.

Last but not least good luck. I would recommend that you do a little practice on a scrap piece of metal first. Good luck again, and I want to hear the rest of the story.

[Ben Gastfriend]

Thanks for all your help.

What I understand from deciphering those charts is that I would need a #29 Drill bit and a tap to make a threaded hole to fit a 8-32 screw.

Thanks again, and I'll post a picture when done.

[Paul Heely]

I'd also be interested in what you use for the cutter head.

I recently read an article somewhere on doing exactly what you are doing and in that instance the author was using a small reground allen wrench as the cutter.

[Marvin Hasenak]

You will need a #27 drill bit, the #29 is for use in brass or aluminum where you need more thread for holding strength. The #27 will give you a plenty of thread to hold the machine screw. The #29 is smaller and will make it more difficult to tap.

[Ben Gastfriend]

Well, it worked!

And.. I've heard of people using things like cut nails, allen wrenches, and pieces of old bicyles for cutters. I think I'm going to order one.
That I can afford, but I couldn't afford the whole contraption.

Thanks all!

[Joe Kaufman]

If the piece to be threaded is hardened somewhat, better get a High Speed Steel Tap. American made HHS Taps have ground threads and cut easier in hardened materials. They will be stamped HSS on the shank of the tap. Carbon steel taps generally are not ground and therefore require more force to turn, at a greater risk of breakage. Most of the taps that I have seen at the borgs are carbon steel.

Joe

[Bill Bolen]

Ben: check packard woodworks for hss cutters. They have sizes fom 3/16 to 5/8" or so for $2. And 2 1/2# long so you can cut it off for another project. They also have severl other shapes and sizes cutters. Luck!
Bill

[Julie Tanner]

Hey Ben,

can you post some picks >>

would love to see your project

[Ben Gastfriend]

Thanks, Bill!

I was looking around and couldn't find what I was looking for, but I knew it existed. Packard has 'em.

[Ben Gastfriend]

Julie- I'll post them as a new thread when I'm finished... can't say it'll be soon with the holidays coming up and the orders coming in...

[Jeff Bower]

Ben, I found this set of cutters at HF.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=40641

They are M2 HSS and hold a great edge and cut spinning wood real good! They go on sale for $1.99 all the time as well.