# Power Tapping on a PM25?



## devils4ever (Apr 19, 2020)

As you can all see, I'm making a tool plate to help hold parts while CNC milling. I drilled a 1" grid of holes that need to be tapped 1/4"-20. All 58 of them. I did two by hand and decided I need to power tap. Can a PM25 mill do power tapping? I know there are tapping heads, but they are $$$ and take a lot of vertical space.

Can I chuck the tap in the keyless chuck? Should I get a spiral tap? All I have now is a 4-flute straight tap.


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## benmychree (Apr 19, 2020)

By all means, use a spiral point tap, or expect broken taps, when I power tap, I tighten the drill chuck enough to allow slippage if something goes wrong.


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## devils4ever (Apr 19, 2020)

Spiral point tap or spiral flute tap?


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## benmychree (Apr 19, 2020)

S


devils4ever said:


> Spiral point tap or spiral flute tap?


spiral point if it is a through hole, spiral flute if they are blind holes.


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## devils4ever (Apr 19, 2020)

3/4" through hole in 6061.


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## Mitch Alsup (Apr 19, 2020)

devils4ever said:


> 3/4" through hole in 6061.



My guess is that IF you had already power tapped lots of holes, you will be fine power tapping 3/4" in 6061.
My additional guess is that you fail the sentence above, and thereby, you should expect several broken taps if you attempt to power tap said holes.

I power tap 1/4-20 all the time in 1/4" 6061, but anything thicker, I let the mill start the tap (i.e., straight) and then I finish by hand.


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## devils4ever (Apr 19, 2020)

Hmmm. Sounds like trouble.


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## devils4ever (Apr 22, 2020)

From my email, I can see there were more responses to this thread that aren't here because of the server migration. If you posted here and don't see it, please re-post. I think I lost some valuable information.

Thanks!


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## Cadillac STS (Apr 22, 2020)

You can make it easier by drilling the holes slightly over size of the ideal drill/tap size. There are charts that show how much over size and what percent decrease in thread strength.

With that length of thread you could lose 20 percent thread strength and not notice any effect on function but get a much easier time of tapping.


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## Cadillac STS (Apr 22, 2020)

Duplicate post


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## Buffalo21 (Apr 22, 2020)

i have a large Jet drill press with a built in tapping head, variable speed, instant reverse, I do 1/2” - 1” aluminum and 1/4” - 3/4” steel all the time.


here is a 12” x 24” x 1/2” aluminum, 253 holes, 127 of them tapped to1/2”-13 and 126 of the tapped to 3/8”-16.


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## devils4ever (Apr 22, 2020)

Buffalo21 said:


> here is a 12” x 24” x 1/2” aluminum, 253 holes, 127 of them tapped to1/2”-13 and 126 of the tapped to 3/8”-16.




Wow! I thought I had a lot of holes to tap!


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## mattthemuppet2 (Apr 22, 2020)

you'll be fine, though I wouldn't use a keyless chuck as it may loosen when you're reversing the motor to back the tap out. Stick it in a collet and you'll be fine. Countersink the holes by a thread depth at least and use some good tapping fluid (tapmatic, anchorlube etc). Looks like you have a ton of space underneath the plate so stopping the motor in time won't be a big deal. Also, buy a decent 2 flute spiral point tap. You'll get those done in no time.

I've power tapped a lot, only time I ever broke a tap (a roll form too  ) was when I failed to notice the edge of a rivet overlapping the hole, so the tap bottomed out and pulled the work up out of the vise. Still bummed about that and it was a couple of years ago!


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## devils4ever (Apr 22, 2020)

The only drill chuck I have is a keyless. I ordered some 2 flute spiral point taps from MSC, but the box was partially opened and didn't contain the taps.  I'm trying to get a response from them to address this.

The straight tap I have now measures 0.253", so I can use a 1/4" collet? Yes, I have a 1-2-3 block underneath which gives me plenty of room.


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## macardoso (Apr 22, 2020)

I did a 7x24" plate for my G0704 with 3/8-16 tapped holes and .251 reamed holes on offset 1" grids (138 holes each!). If you can lift the plate and leave room underneath, a good sharp *sprial point* will do the best job. If not, use a *spiral flute* tap to pull the chips out of the top. My experience is that spiral flute taps don't extract chips in aluminum as well as they do in steel and they are weaker (hence the recommendation for spiral point). Make sure the tap is clean after each hole and is well lubricated.

I was fortunate enough to use a large knee mill with a tapping head to do mine, but you should be perfectly fine if you go slow.

I'd recommend to consider drilling and reaming some .251 holes on the plate. You can drop 1/4" dowel pins in to quickly align your vise or other setups. Just make sure your pallet is indicated true before you drill them! My vise comes in at less than 2 tenths across the 4" jaw without any indicating necessary just by dropping two dowels on the table.


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## devils4ever (Apr 23, 2020)

macardoso said:


> I'd recommend to consider drilling and reaming some .251 holes on the plate. You can drop 1/4" dowel pins in to quickly align your vise or other setups. Just make sure your pallet is indicated true before you drill them! My vise comes in at less than 2 tenths across the 4" jaw without any indicating necessary just by dropping two dowels on the table.



Thanks for the tip although I'm not sure I plan on leaving the plate on the mill table all the time. I'm not sure I want to lose the 3/4" vertical space. But, it doesn't hurt to add them. I don't have any reamers. I'll have to look into it. Thanks!


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## devils4ever (Apr 23, 2020)

I found a solution! I just watched Abom79's video on youtube demonstrating the Flexarm GHM-60 Power Tapper and I want one! 

Too bad it's almost $20,000!


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## Buffalo21 (Apr 23, 2020)

$20G, a mere bag of shells, if you/we came into the machining scene expecting to save money, boy we all made a mistake............


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## tjb (Apr 23, 2020)

Here's an indexing table I made with 1/4"-20 threaded holes, along with toe clamps I made.  The larger holes are for centering and mounting on my rotary table, and the recesses on the bottom are for mounting in my vise.  Best of my recollection, there are 122 threaded holes, and I power tapped all of them with a two-flute spiral tap.  Totally uneventful.  Just take your time and determine the coordinates carefully.

Regards


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## tjb (Apr 23, 2020)

P.S.:  The indexing table in my above post is 1" thick.


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## mattthemuppet2 (Apr 23, 2020)

pretty sure I have a spare 1/4-20 spiral point tap. Would be no chore to stick it in an envelope and get it to NJ if you won't mind waiting for the post.


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## jh1990 (Apr 23, 2020)

I've heard recommendations against using a keyless chuck and that a keyed chuck can be used as sort of a clutch dependent on how hard you tighten it.

But I've also heard of people having issues with the taps slipping in a keyed chuck. 

Thoughts?

What rpm are you guys running when you power tap? Are you reversing by hand?


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## devils4ever (Apr 23, 2020)

mattthemuppet2 said:


> pretty sure I have a spare 1/4-20 spiral point tap. Would be no chore to stick it in an envelope and get it to NJ if you won't mind waiting for the post.



matt: Thank you for your very generous offer. I was able to straighten things out with MSC and I just received my taps.


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## devils4ever (Apr 23, 2020)

My mill has a variable speed motor so I'll be able to go down very low in RPMs.

I plan on trying a collet first versus a keyless chuck. I 'll have to see what the diameter of the tap is versus what collets I have.


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## jh1990 (Apr 23, 2020)

Let me know how it goes. I'm going to throw a VFD and 3 phase motor on my drill press soon and perhaps even a foot pedal to reverse the rotation so I can power tap with it. Still looking for the best (cheap) method of holding a tap.


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## mattthemuppet2 (Apr 23, 2020)

no problem, glad it got sorted out.

rpms you'll figure out, you'll have plenty of practice  I typically go at 100rpm or so on my drill press - too slow and the tap slips, too fast and I can't stop the motor fast enough for it to actually stop when i want it to. I keep meaning to convert some cheap tap handles to hold taps in the drill press, get round to it one day  Power reverse works fine.

no personal experience in using keyless chucks to tap, only that they're supposed to loosen when you reverse them. Typically only large taps or taps in steel slip in my drill press chuck. When that happens I usually take it out and use those first few threads to guide the tap in by hand. Large taps = LOTS of torque.


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## tjb (Apr 23, 2020)

devils4ever said:


> My mill has a variable speed motor so I'll be able to go down very low in RPMs.
> 
> I plan on trying a collet first versus a keyless chuck. I 'll have to see what the diameter of the tap is versus what collets I have.


I use a collet on mine and have had no problems at all.  Speed is very slow.  Tom Lipton has a great little primer on power tapping on the mill.  Here's the link:






Regards


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## devils4ever (Apr 24, 2020)

Success! At first I tried the keyless chuck, but I had problems with the tap slipping. I measured the body of the tap at 0.254" so I put it in a 1/4" collet. It was a little snug, but worked. Actually, I had to tighten the collet quite a bit to keep it from slipping. I ran my mill at about 190 RPMs. 

Interestingly, I found that the main power switch on the PM25 takes time to drain at low RPMs, so the spindle keeps spinning. However, if I turn the direction switch from forward to 0, the spindle stops instantly. This is very handy for tapping since I had to run the tap the full length to get 3/4" of material tapped.

Bottom view:


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