Power tapping test results

[PixMan]

I had in the recent past bought off eBay a high performance spiral flute Technical Hard Lube coated Prototyp (brand) Paradur Eco Plus tap, in 3/4-10UNC 2B. It's been sitting there a few weeks, so when Neil texted me to see if we could meet up at my shop, I decided to try the tap in a test piece to see if my 2HP Alliant/Prototrak machine could handle a tap that size under power.

For starters, holding it in the machine was a bit of an issue. It's an ANSI shank measuring .689", so I was able to squeeze it into an 11/16" R8 collet. My goal was to see if it would cut 2xD deep, so 1-1/2" of thread. I grabbed a random piece of 1018 cold rolled steel, 1-1/4" thick and about 3" square. I think it was one of the drops Russ had given me. I drilled 1-5/8" deep with a Ø 1/2" jobber length drill and then followed with a Ø 21/32" (0.656") drill. I believe I ended up with just over 1-1/2" of depth to the hole.

This is a spiral flute tap, meant to funnel chips up and out of the hole. If you've ever tried using the older ANSI style spiral flute taps you'd know they are notorious for breaking deep inside the hole with no way to get it out. Power tapping with a tap of this size takes a LOT of torque, and my Walter "GPS" software showed the tap needing 4.57HP and 58.5 ft-lbs of torque. I didn't run the software and see those numbers until now, sitting at my home computer and running the application.

I've got a 2HP motor with unknown torque. recommended tapping speed was 410 rpm, I put my machine in back gear and set it at 330 rpm.

Wanting to go to the bottom of the hole, I wrapped a piece of black electrical tape around the shank at the 1-1/2" mark. I applied a little ValTap tapping compound to the tap and a little ring of it around the top of the hole. Ignorance is bliss so I figured the machine wouldn't have enough power to break the tap, though it might slip in the collet or stall the machine and chips the cutting tips of the tap.

Much to my surprise and joy, it not only worked but it worked GREAT! I have no video, but here's some photos of the aftermath.

The tap after use, showing no wear and the depth-marking tape still on it:


A scale showing the depth of the hole:


The chips that the tap produced, all of which came right out of the top of the hole:


The finished tapped hole:


The slide rule style tap calculator showed 71% thread using a Ø 21/32" drill, looks like that's what I got and they're beautiful. No problems at all!

[EdK]

Now that's a nice blind hole tapping job.

Ed

[PixMan]

Thanks Ed!

I've long been kind of reluctant to try blind holes with the older style spiral flute taps, having broken a couple many years ago at work. With today's tooling technology, it's "cake." I realy was on the fence about whether or not a 2HP spindle could handle a 3/4-10 tap, not anymore though!

One thing I never do in tapping is compromise the percentage of thread by drilling oversize holes. If you need to do that because you're breaking taps...you're using the wrong taps.

[EdK]

Once I get my mill back up and running, I'd like to try power tapping. I've got a VFD driving a 2HP motor so it should be doable.

Ed

[PixMan]

Ed,

You shouldn't have any fears about power tapping, as long as your spindle reverses in a reasonable way. Some VFD's need tuning to get them to reverse the way a 3-phase motor on true 3-phase power does.

Of course using true machine taps is critical. Try power tapping with a 4 flute hand tap and you can fully expect disaster.

I know that some folks have "tapping machines" such as those hand crank ones, or tapping heads and they work fine. They need no reversing spindle. In my shop I'm limited in space so my drill press which could use a tapping head is outside in the "wood shed" and rarely gets used. I don't have room on a bench or floor space for a hand tapping machine, so power tapping is my fast and easy solution. I'm very comfortable with it, don't have to adjust torque settings of a tapping head or crank the knee down low to use one. It's not for everyone.

This test was to see where I'd find the limits of what my machine (and I) can do reliably. I now believe I could power tap up to a 7/8-9UNC in a through hole and this 3/4-10 would be the limit in a blind hole.

[Highpower]

(03-29-2015, 08:03 AM)PixMan Wrote: Ed,

You shouldn't have any fears about power tapping, as long as your spindle reverses in a reasonable way. Some VFD's need tuning to get them to reverse the way a 3-phase motor on true 3-phase power does.

I have discovered that can work against you sometimes too. My mill runs off of a 3HP rotary phase converter and is as close to 'true 3-phase' as I am ever going to get. I was drilling some holes on my mill one day and did an accidental 'plug stop'. (Switching from forward rotation to reverse rotation instantly.) I overshot the center OFF position on the power switch.

You know how keyless drill chucks self-tighten when they spin forward? I found out they self-loosen too, when suddenly spun backwards. The drill bit fell out on the table! 

[PixMan]

If that's the worst thing that happens, be thankful!

And keep wood protection on your table. ;)

I'm running mine on a rotary phase converter as well, though the ilder motor on mine is a 15HP one. We actually tripped the 30amp breaker on the lathe as Neil started it up at 1800 rom with the 10" three jaw chuck on it. The phase converter never blinked and I kept running the milling machine. I think this is the way it's supposed to work!

[Highpower]

Yeah some guys get to play with some really nice toys.   





Or how about a 2" NPT tap! 

https://www.youtube.com/watch?v=VeaNgXwC...age#t=2006

[PixMan]

I've done a fair amount of work on manual horizontal boring mills myself, and plenty of power tapping. That one you posted in the thread with the straight tap kind of surprised me because it appears to be a 4-flute hand tap. Fortunately the material is a short-chipping one, so it didn't pack chips and the material also seems soft.

In both videos I notice the large facing head rotating with the quill. On the machines I ran (Wotan and a Kearney & Trecker), I could (and did) disengage that head for 90% of the work I did. Too much mass rotating around unnecessarily.

Stay tuned, I'm editing and uploading photos and a video I took today. I went back to the shop for an hour (or less) and milled off 1/2 that block I tapped to see what it really looked like.

[PixMan]

Well, I cut the piece to halfway through the tapped hole to see what it looked like inside. It was a sacrificial piece anyhow, no loss.

Here's a video of my machine face milling the 1018 CRS down. It's a .075" depth of cut (just shy of 2mm) and feeding at 20 inches per minute at nearly full width of the cutter. I probably could have gone a deeper depth of cut for fewer passes because the machine spindle didn't seem to mind the cut. I made a decent little pile of chips in about 10 minutes. I could have done it faster if I written a program, but that takes nearly as long as the "semi-manual" way of punching in a feed rate once and a distance to go for each pass. I ran in one direction to throw all the chips in one place.

This is the 2-1/2" 4-insert cutter after milling about 6-1/2 cubic inches of steel into little chips, some of it across an interrupted cut (the hole in the part.) I had the tougher, multi-purpose grade WSP45 inserts in the cutter, though if I had much more to do I would have switched to the steel & cast iron only grade WKP35S.



Here's the 1:16 video showing a few passes. Remember, this is a 2HP belt driven spindle running in high range @ 730 rpm and 20 inch per minute feed for a .0068" feed per tooth.




Now a look at the blind hole I tapped yesterday. The tap appears to have come to between 1/8" and 5/32" (3 to 4mm) of the bottom of the hole. With the 2 to 3 thread lead (at .100" lead), that's at least another 1/4" of hole not fully threaded. The thread calculates by hole size to be 71% thread, I think it's closer to 65%. Good looking quality to the thread though.




And my pile of chips from milling.  Note my new shop broom, a Weiler (brand) #44007 Palmyra fiber one. It doesn't get any chips sticking to it! $29.19 from Amazon, free shipping for stocking up on the WypAll X60 shop wipes at the same time.