Straddle knurler build, no mill required (we hope!)

[WobblyHand]

6-32 taps are hard to do without snapping the taps. At least I sure have trouble. And I think that a big part of the problem I have is when I try to run taps that small by doing it free-hand.
I made myself a tapping fixture which has a spindle /chuck . This helps a lot. The fixture is basically a copy of George Thomas’s pillar tool. I didn’t buy castings. I used big chunks of aluminum bar stock.

Free hand is how I snapped the tap previously. It was in aluminum, which I hear gives more grief than steel.

For these holes, I used the mill and a spring loaded point (tap guide?) in the chuck. The point just goes inside the top of my Starrett 93A tap wrench. Since I locked the mill in place to drill the hole, I just raised the head put in the tap guide and the tap is automatically centered in the hole. Putting a slight downward load on the tap helps as well. That being said, these 6-32 taps have a little windup to them. You can sort of feel the torsion build up in them as you are turning them.

 

[mikey]

For tiny fasteners that simply need to stay in place without a lot of stress on them, just drill the tap hole one or even two drill sizes bigger and tap away. Try to drill deeper so the tap cannot bottom out and use spiral point/gun taps that are a little stronger. In aluminum, use roll taps that form better/stronger threads. Unless you're a gorilla, roll taps (which are solid) will not snap on you.

 

[WobblyHand]

Love the spiral point taps. But didn't have them in this size. Muddled through and survived.

Made the slot in the arms. In the vise and double clamped the arms together. Used a 3/16" end mill to "hog out" the slot. Have to laugh, I was taking small cuts. Took a while, but got it done. Then used a nice sharp 1/4" Niagara carbide cutter to open it up to 1/4".

Deburred, next step is to round off the ends by the slots. "Make them more aesthetic."

 

[mikey]

Came out nice! Getting there ...

 

[mattthemuppet2]

looking good!

Easy solution to having problems tapping 6-32 holes is to not use 6-32 screws M3-0.5 is a nice equivalent, 5-40 or 6-40 would also work, or 8-32. All are far nicer to work with than 6-32.

 

[WobblyHand]

looking good!

Easy solution to having problems tapping 6-32 holes is to not use 6-32 screws M3-0.5 is a nice equivalent, 5-40 or 6-40 would also work, or 8-32. All are far nicer to work with than 6-32.

Thanks.

Yeah, M3's are nice. Have lots of them, too. My RPI server project used a lot of metric hardware as most computer stuff is metric.

 

[mattthemuppet2]

Me too. I tend to use whatever I have enough of in the right length and format (cap head, phillips etc).

 

[WobblyHand]

Make them look good. I don't trust myself, yet, to grind till it looks good, especially free-hand. Need a line to grind to. So I made a pin out of 3/16" 12L14 and center drilled a small divot. Put dykem on the face of the two arms. Will use a divider to scratch out part of a circle, then scratch in some sort of line to the bottom edge, roughly mimicking what @mikey did. Pretty sure I can get this right on the first one. Just need to remember to do the mirror image on the second! Pics will get added in a little while.

Now to smooth off the pieces. Ground with 80 grit ceramic belt. Then used 150 grit diamond hone and 240 grit hone. Still pretty rough but getting better. Then used some 220 sandpaper to make things a little nicer. Finally a 400 grit diamond hone. Finish is about the same as the rest of the piece now. That will do for now.

 

[WobblyHand]

Not the prettiest things, but think they will be serviceable. On to the next steps, drilling and reaming the half moon pivot hole. Lets see what I have for drills.

 

[Janderso]

You are doing a fantastic job.
This has been fun. I need one!!
I have it on my long list of tooling to make.
Looking forward to seeing the finished product.