Hi friends who read my blog.
Here is a project that has taken just short of forever to finish mostly due to my new Real Person job and its associated Obligations, and minorly due to some tool troubles…
“What is a hand-tapper?”
Why, it is simply a tool that can hold a tap way straighter than you can. I think this is a must-do project for anyone who has a decent drill press, some free time, and the need to tap holes. I’ve only ever seen hand-tappers at pretty high end machine shops, which I never really understood. I guess you can do pretty well with a normal tap wrench, but using one of these just feels like the right way to do things.
To use it, you put taps in the chuck, and turn it using the handle. The bearings and the arm structure keep everything square for you. For the purpose of establishing nomenclature, I’ll refer to the part you spin as the spindle, the horizontal assembly as the arm, and the rod that sticks up on the right as the main shaft.
So, I actually tried to make this twice, where the first try ended in the discovery of my drill press table not being square to the spindle. For the second try I ended up using a mill when I visited Boston a few weeks ago. I’ll show you what I tried to do in the first try though, because that’s probably more representative of what someone might do if they didn’t have awesome machine shops and piles of dusty scrap at their disposal.
Materials (listed per row with respect to picture below):
– 0.750″ case hardened precision steel shaft 12″long (McMaster $10.25)
– 1/4″ x 1″ x ~9″ aluminum bar
– some bolts; (2x) 1/2″ x 1″ x ~6″ aluminum bar
– 3/4″ OD 5/8″ ID flange bushing (McMaster $1.03)
– 5/8″ shaft collar (McMaster $1.92); 1/2″-20 UNF bolt 1.5″ long (McMaster $1.99), 1/2″ drill chuck (lots of options for ~$10 on ebay, make sure yours has the same thread as the bolt)
– 5/8″ OD 1/2″ ID steel tubing ~8″ long (got 8″ on Amazon for <$20)
– also, (not shown) some lag bolts, maybe some washers, and a flat piece of wood for the base
The aluminum you can get online or at some local metal supply store or recycler. I got mine from http://www.speedymetals.com/ which will also cut to length roughly. This was an attractive option for me because I didn’t want to hacksaw everything.
Let’s start with the spindle:
First cut the head off the bolt. Then slit the end of the 5/8″OD 1/2″ ID tubing. Then clamp the two together. You won’t need the whole thread length, so you can trim that, too, if you want. I didn’t bother. I suppose you can just put a screw or pin through the tubing and bolt, instead of a clamp. But I like clamps, and I wasn’t sure if the tubing ID would actually match the bolt well, and the clamp would do better to evenly take up any gap.
Next, my first attempt at the base/main shaft clamp, which is what the end of the 3/4″ precision rod is clamped to. I planned to use the two 1/2″ x 1″ x 6″ to make a clamp, that I would then bolt to a base made of a slab of wood. With just a drill press, I couldn’t really drill precisely spaced holes, so the trick is to just drill all the holes you need aligned at the same time while things are aligned.
Next, drill the hole that will actually clamp the shaft. I used some washers to space the two pieces apart so that I would definitely be able to provide lots of clamping force.
As some of you who lust over tooling may know, large drill bits and reamers ain’t cheap. Luckily Harbor Freight always has the economical-almost-good-enough solution to your tooling needs. This step drill actually did remarkably well. If you have a variable speed drill press that has fairly low rpm, your setup will do even better.
Unfortunately, my drill press has a fairly fast lowest speed, so I used a clamp for more leverage while I held the part and drilled. Step drills are intended for drilling through thin material, so drilling through 1/2″ material is way more surface contact that these bits are intended for. There will be quite a bit of heat and friction. Don’t forget to use cutting oil!
By this time, it was sadly and painfully obvious that my drill press wasn’t square. But I had already drilled the clamp hole, so those two blocks were committed to my unintended angular design. I made the decision to carry on with the rest of the parts, in the hope that I could just pay attention to which way the holes were slanting so that the precision shaft and spindle would still be parallel…yea….probably should have just stopped though…
That was about as far as I got, because in the end, this is a tool that is supposed to make sure that tapped threads are square, and I just wasn’t confident that the tool itself was going to be square, even with my attempt to try and rig everything to slant the right way.So, time to do things right. I found my self in the company of a Bridgeport and went to work.
You’ll see that for the arm 2.0 I used two blocks connected by two plates. This is just what I had, you could definitely make this all out of one part. Also, the two blocks are anodized, you definitely don’t need that. To lock the height of the arm, I used a thumb screw. The one in the picture is just a socket cap screw with a plastic cap pressed onto it. I’m sure most hardware stores or McMaster will have similar things.
The 5/8″ tubing used for the spindle didn’t actually fit too well in the bearings. Luckily, you can just put the 1/2″ bolt into a drill chuck and sand while its spinning.
For the handle it would have been nicer to use a thicker piece of material. The 1/4″ thick piece is about the thinnest I would dare to use. Time will tell how long it lasts.
I thought it would be nice to have a little rotating knob for quickly spinning the spindle, like when you are backing out a tap. I used a short piece of 1″ DIA delrin. If you tighten a bolt through it as shown in the picture, you can grip the exposed threads of the bolt in a drill chuck and round the corners with a file as you would on a lathe. Just don’t press too hard on the file, since the work piece isn’t that well supported.
Finally, here’s my second try at the main shaft clamp and base. I used a real reamer for the hole. Also, by the time I made this part, I had acquired a bandsaw, so that slit you see was also a piece of cake. (The piece of wood in this picture is not in the final picture at the top of this post since actually, it was kind of warped, so I changed it)
And there you have it!
Oh yea, this is how I fixed my drill press squareness issue. Its not perfect, but way better than before. I got some copper foil and wedged it on the bottom side of the surface where the table is mounted to main post (the table was tilted down towards the user). For reference: in the picture below, the large bolt is for tightening the table to the clamp that rides up and down on the main post. The nut is threaded onto a pin which helps define the perpendicular-to-spindle position, since the table is actually capable of tilting side to side. So yea, its actually a pin, the threads are just to make it easier to pull out.
happy building! happy holidays!