Tapping lots of 1/4 x 20 blind holes in 6061

Spiral Flute Taps are best way to go for holes that don't go through. I have also relieved the shank slightly to get a bit more thread length in the hole.
 
Drill to the maximum minor diameter, use a spiral flute tap and machine tap in one shot. If it takes longer then 2 hours you are doing it wrong. Set a stop so as not to bottom out the tap in the hole.

Above all buy a good tap, steer clear of anything from the hardware store, HD, Lowes, Ace and so on, it will be expensive by hobby standards but well worth it.
 
I had to do something similar recently with smaller thread size and did indeed use a spiral flute, but also managed to get away with a plug tap, rather than the starting tap and didn't need the bottoming tap. The plug tap worked since I was using it in the drill press, so straight starting wasn't an issue.

David
 
Use a form tap. No chips. Be sure to drill hole to form tap size.
Jimsehr
 
Looks like the advice given already answered your question. Type of tap is important. Like others said a spiral tap that pulls the chips out is required. Prob obvious and you already know, but don't use a hand tap in the tapmatic. I have a different brand tapping head and have used it for hundreds of blind holes in aluminum down to 8-32 or so without issue. Blow all the holes out well after drilling. Be liberal with the lube and take your time & 1/4 shouldn't be a problem at all with a quality OSG flat bottom tap.
 
wawoodman said:
But I agree, a thread forming tap might be a better choice. I've never used one in a Tapmatic, though. Any people who have?
Click to expand...

I have tapped thousands of holes with a tapping head and form tap. First time I ever used one was when I was the "New Guy" at a shop. They set me up on a drill press with a tapping head and I tapped 8-32 blind threads into aluminum extrusions, 8 hours a day, for three weeks. I wish I could remember the name of the greenish tapping fluid we used. I'm sure it has long since been outlawed.
 
Thanks for all of the great responses. To answer a few of the questions ...

There are three pieces of material each with two rows of 7 holes that need to be tapped. I guess that is only 42 holes, not 48. Duh.

The taps are OSG. Maybe not THE BEST but I believe them to be better than the hardware store variety.

The point tap is a 'gun' tap and therefore pushes the chips into the hole. That was the reason for the extra hole depth. It also has the advantage of having 5 - 7 starter threads, which make it easer to turn but does decreases the effective depth to which the hole can be tapped.

The bottoming tap is a spiral tap. The advantage is ejecting the chips out of the hole. The disadvantage is that it only has 2 - 3 starter threads and is therefore much more difficult to turn ... and the follow on ... much easier to break.

Given that this is a hobby and not production I'm leaning towards spending time rather than money on a possibly broken tap and go over then one with the point tap, clean, then bottom tap.

Thanks for all the suggestions and wisdom,
Arvid
 
I want to thank you guy for raising my awareness to taps and tapping. I've tapped a lot of holes in my amateur life and usually use taps with ground off points for bottom tapping, this method emerged just by trial and error using the taps that I had on hand. I have seldom broken taps and those that did break was carelessness hand tapping smaller holes, 2-56 and 4-40. I was not aware of the difference between spiral point and spiral flute taps. I wasn't aware of form taps although I have seen them many times, never knew that they were. Gotta try them out.
So what is the purpose of a spiral point tap?
Thanks guys

CHuck the grumpy old guy
 
Spiral point taps are great for tapping through holes. They push the chips ahead of the tap, and out the hole in the bottom. So you don't have to keep backing up to break and remove the chips. I've had great luck running smaller ones (6-32 up to 5/16) in my cordless drill.

Once you've tried it, it'll be a real head-slapper!:idea:
 
Thanks Mike. I have a few spiral point taps. How do you visibly tell the difference between spiral point and spiral flute taps.
 
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