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Tapping Guide

We've all had trouble hand tapping perpendicular to the surface of a material.  It takes practice and patience to do it well.  Those first few threads are critical to how straight your over all tap is.  I saw this tool in a machinist buddy's tool box one day and asked about it.  He had made it himself, and I could see right away how useful it would be.  After messing up a tap on a piece a while back I thought I would make or buy one.  There is a beautifully made one on Little Machine Shops site that is surely made on a CNC machine.  It's not too pricey, but I had a big hunk of 2" G2 Gray bar that I thought I could use to make one.

Here is the one I made.  Mine has one more size than the OMW one on Little Machine Shop and it was necessary to make a drawing to get all my clearance and counter bore sizes correct.



Like I said on my Making Chips Page, this was the hardest material I have worked with to date on the Mini.  Luckily it was pretty straight and I only had to take a bit off to get the finish I wanted on the diameter.  Facing was another problem.  Without a band saw, I had to part off of the LOG I had, with a reciprocating saw using up 2 blades cutting it. 
Needless to say it wasn't all that straight after cutting it.  Facing was long and arduous but finally finished it and then sanded on the belt sander with a 240 belt...then up to about 600 on the granite slab.  By the time the outside was done, I realized there was no way in this world I could put a Knurl on this material...in my shop, so I let it go...

Here is the drawing I made to lay it out.  Feel free to download and print it.


I printed a 1:1 layout and cut out the circle, then taped it to the surface to center punch all the holes.  Worked pretty good except for a couple of holes "walked in" on my drill press as you can see in the picture above.  I did square up my drill press table and vice as much as possible before I started.

At the bottom of the drawing you will see a tap and counter bore hole size chart with decimal and drill sizes. 
They seem to work fine but may be a bit off.  The counter bore is important as a chip relief while you are tapping.  Otherwise the chips will munch the upper threads you are tapping. 

I worked these out from the Machinery's Handbook.  If you don't have one of these I highly recommend one as they contain everything you would ever want to know (pretty much about anything) in them.  I've had mine for years now (think its the 22nd edition) and Amazon has them (29th ed.) for about $60 now...think I paid $100 for mine way back when.

Luckily,
I had a 115 piece set of cobalt, number, fraction and letter drills to use on this, (don't think HS bits would last but a few minutes on this material no matter how much cutting fluid you use).  It was slow going, lots of fluid and in and out with the bit, then reset the vice and do the next size hole.  Each hole was a 6-8 step process, counter boring both sides.  Most holes I walked up drill sizes in 2-4 steps to maintain my sanity and practice patience.  The final step was to set up a counter sink to debur the holes.  As you can see in the picture above, the counter sink grabbed a chunk and tore the edge a bit on the bottom hole in the picture.  Probably took an hour and a half to finish all the holes and counter bores.  Here are some more pictures.


Here is a side view to see the counter bores better.

This is a 6-32 tap on a small piece of AL plate.

The nice thing about this tool is it's heavy enough to stay in place while focusing on tapping.  It actually weighs 1.25lbs.  I did the calcs based on density then weighed it on a digital kitchen scale to be sure...it was! @¿@  This is some dense material!  I use it on the bench with larger plate and in the vice with some angle jaws flush with the top of smaller materials.  Overall the tool works well and at least gets those first few, critical threads straight...but I think I might buy one next time!  8-)  It was a learning experience and fun to make using the Mini, plus it gets used regularly around the shop...so it was a win...I think. ~¿@