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- From: Lawrence London <lfljvenaura@gmail.com>
- To: machinist@lists.ibiblio.org
- Subject: [machinist] Power tapping on a manual knee mill
- Date: Sat, 1 Mar 2014 20:37:33 -0500
http://www.practicalmachinist.com/vb/general/power-tapping-manual-knee-mill-281111/
Thread: Power tapping on a manual knee mill
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Power tapping on a manual knee mill
So I'm out in my shop tonight, and I'm working on a radius turner project for my lathe that has some 1/2-13 holes tapped thru about an inch of mild steel:
and I think to myself, "self, why are you so afraid to power-tap these holes?"
Y'all helped me reach down, locate my nut-sack, grasp it firmly, and learn how to power tap on my lathe. I've since bought a number of Collis tap holders and sleeves to do that, and it's been great.
But I'm still too chickenshit to try it on my mill. Anyone want to walk me through it?
My mill is a decent-sized (3300 lbs, 3 HP) BP pattern machine if that matters. -
03-01-2014, 12:38 AM #2
- Join Date
- Feb 2012
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- Iowa, USA
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- 365
Is that a Famco mill?
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To tap a through hole:
1) Check that the depth stop is set all the way "down." You don't want to hit the depth stop half way though the hole.
2) Drill your hole with the correct tap drill.
3) Install a spiral point tap in the drill chuck. No need for a tap holder here if the chuck has enough gripping force to drive the tap. Changing spindle tooling wastes time. Apply some thread cutting oil to the hole.
4) Put the machine in back gear on the lowest speed. Apply the tap smoothly to the hole and apply enough pressure to the quill handle to keep the tap from pulling a thread.
5) Maintain down pressure on the quill handle to overcome quill drag as the tap advances into the hole.
6) When the tap comes though the bottom of the hole, switch the machine into reverse.
WARNING: Plugging reverse only works on 3-phase machines. If your machine is single-phase it will continue to run in the same direction unless the motor is stopped when the drum switch is reversed.Big B likes this. -
03-01-2014, 12:51 AM #4
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Power tapping 1/2-13 in steel is easy, just get the rpm down around 600 and get a feel for the reverse switch. Light pressure on the quill handle in both directions. Put the tap in a collet instead of spinning it in your drill chuck, you don't want to rip up the jaws in the chuck. For a thru hole, a spiral point tap is best.
Where is Fiddlefart?toolsteel likes this. -
03-01-2014, 12:55 AM #5
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- Feb 2012
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- Iowa, USA
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As far as power tapping on the Bridgy at work, the spindle motor has a 3-position switch (Forward, off, reverse, which runs things opposite when you're in back gears).
Make sure you have enough quill travel to tap to the depth you need to go. (I.E. make sure your quill stop is not going to pose a problem).
Select a plug, spiral point, or spiral flute tap and chuck it. No hand taps.
Choose a speed appropriate for your mat'l.
Lube tap and hole.
Quill to above work, then with your right hand pull the quill handle in a positive manner so that the tap doesn't auger the work. Make it catch it's lead and pull itself in. Keep left hand on switch to reverse spindle. Upon reversing the spindle, keep a bit of pressure on the "up" so when the tap exits the hole, it doesn't sit there and eat the top thread.
EDIT- after a bit, you learn by listening as to whether the tap is thru or bottoming in a blind hole. The sound of the motor and gear train tell you when to reverse. -
Thanks guys. Pretty straightforward. I'm running the machine (not a Famco- an Amstar MV-54, which is a very obscure brand but basically a 10x54 Taiwanese mill) from a VFD so my reverses will be slower. From power tapping on the lathe, I know that the ideal situation is if I can get my needed RPM's at a low frequency on the VFD and still have the torque. Then it stops quite quickly.
I'm surprised at the 600 rpm advice. Really? I'd be more like 60 rpm on the lathe- or slower. Seems like things would happen awfully quickly at 600! I guess in a production format that'd be good. I think I'll try it slower to start.
It was advised I use a collet by one gentleman. As in, a straight R8 or ER collet, or do you mean a special collet for taps, like the Collis I'm using on the lathe? -
03-01-2014, 01:20 AM #7
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I would put it in an R8 collet and go at 600 rpm. If you are new to this there is no harm in going slower, whatever you are comfortable with. I do it a lot so I might be more aggressive with the speed. That tap is taking out a lot of steel and there is a good chance of the shank spinning in a drill chuck, my suggestion is to put it tightly in a collet. Taps are cheaper than drill chucks IIRC.
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The mill I learn power taping on had a brake. I would power in.... hit the brake...reverse out.
Then I saw this video.
It isnt hard....just scary at first... -
IMHO 60rpm is too slow and 600 is too fast somewhere in the middle is where I would go.I use a proper tap chuck for larger taps drill chucks tend to slip and I never tried R8 but would expect them to slip.Tapping at higher speed takes less torque so perhaps thats how jkruger is getting away with that.
D2 what do you mean by hearing a change in sound when the tap hits bottom ,you mean like a bang? -
first thing, chamfer those holes to about a 9/16" diameter before you tap
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03-01-2014, 03:47 AM #11
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- Feb 2012
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- Iowa, USA
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Sable, I mean listening to the change of load on the machine.
Originally Posted by sable
D2 what do you mean by hearing a change in sound when the tap hits bottom ,you mean like a bang?
To be honest, I've never broken a tap on the Bridgeport while power tapping with exception of one- a 6-32, the work was for a friend that had supplied the tap and requested I use it because he wanted to know how it performed. It was a cheapo plug tap, and I wound up "extracting" it with a special ground endmill that he endend up buying. -
03-01-2014, 04:52 AM #12
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- May 2011
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- Texas
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Clean your tap good and paint with white paint at the desired depth.
Use a gun tap for through holes a spiral for blind.
Faster is way better than slow(its a motor inerta thing)
Turn the mill on fw and than turn off than move your hand to the brake
As you get better you can start pluging rev
As was^^^ listen to your machine
I have 500 3m to do in a 16' part (series 11 bridgy) due monday early fun fun fun.jrmach likes this. -
03-01-2014, 05:02 AM #13
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I'm comfortable at 600 rpm, might be too fast for someone else. Once you get used to power tapping you will probably speed it up. Higher speeds produce better finishes in mild steel with good lubrication. Knowing when to switch spindle direction is the key to tapping this way.
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500 or 600 is about where my drill is with a tapping head so I guess i'm ok with that speed....but in the mill the reverse mechanism isn't as slick. Assuming you have three phase, its ok to reverse the switch while underway, but you need some reaction time to do so, so slow is good. If its not 3P you have to let it wind down before reversing so go dead slow and anticipate how far away from a crash you have to kill the power.
just do it, not at all difficult, and you'll wonder why you didn't a long time ago -
I power tap in my BP all the time, but I typically do it in back gear at 200 - 300 rpm's.
I always use an old Jacobs chuck for power tapping. Power tapping can damage the jaws of the chuck if the tap spins in the jaws. The shank of the tap is as hard or harder than the jaws. So, don't use a new, pristine, expensive chuck. A collet will also work, but again, I would keep some older used, or cheaper collets for tapping and don't risk damaging new collets.
As someone else mentioned, make sure the quill stop nut is all the way down. I made that mistake once when I was in a hurry. I snapped a tap off in a part that was a rush job.
btm -
Lots of good advice here. I can't imagine hand tapping when you have the proper equipment to do it powered. As mentioned, the quill stop can get you if you are not paying attention. been there, done that.
Big B -
03-01-2014, 07:47 AM #17
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- Nov 2012
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- Peoples Republic of Minnesota
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You have the info needed to do the job....only thing I would say is I agree that I have seen good drill chucks turned into garbage from guys using them for tapping. Especially Albrecht and other keyless chucks, they tend to loosen when you reverse them. I have also seen guys that were having trouble with larger taps coming loose while tapping try to tighten them to the point of using a small cheater bar on the key
.......as the commercial says ...."Don't be that guy" lol
IronReb likes this. -
I always tapped around 150-200 on a Bridgeport. I like to guide the quill handle as it taps so it doesn't strip out the threads. If you want tapping to be fun get a reversing tapping head, when you get to depth pull the quill handle up and it reverses out, never have to stop the spindle.
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03-01-2014, 08:56 AM #19
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- Nov 2013
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- Eastern Massachusetts, USA
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Rule # 1: Never take your hand off the switch when the spindle is turning.
Rule # 2: Never take your hand off the switch when the spindle is turning.
Rule # 3: Never take your hand off the switch when the spindle is turning.
And as others have said, hold in collet or drill chuck, only tight enough to do the job. Better to damage easy to replace stuff rather than the mill head. -
03-01-2014, 10:08 AM #20
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- Oshkosh, Wis. rauchle@ntd.net
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- 708
I have a job where I tap alot of 5/16 - 18 holes. I buy 6 taps at a time and with the surface grinder and a spin indexer, I grind 3 flats on them. Sometimes I use the drill press, sometimes the mill. Either way, if I already have a chuck on the machine from drilling the holes, it's to easy to just put the tap in and have at her.
Big B likes this.
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- [machinist] Power tapping on a manual knee mill, Lawrence London, 03/01/2014
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