Floating tap with rigid cycle

[rbmgf7]

BLUF, I'm not a machinist or very experienced.

I've been fighting an ongoing issue with tapping some 4140 prehard material where I have to use unconventional methods to extend the tap length (using a hand tap extension to reach past a shaft shoulder where numerous extensions have collided with the part. The smallest extension's collet nut is too large and hits the part).

I can get good runs but then out of the blue, I'll have a situation where I'm breaking tap after tap. Taps are 1/4-20 OSG TiCN bottoming into a blind hole. They're like $35/ea.

After just doing rigid tap cycles, I finally got a floating holder but it floats only in the extended direction. If it were to compress, it would break a tap.

I was wondering if I need to change the pitch so while using a rigid tap cycle, the tap begins to extend slightly outward?

 

[beege]

i run a non-rigid tap Haas, and have a Procunier tap holder that will extend. I program the feed rate to be 95% of what it would be if I had rigid tapping.

 

[magno_grail]

My VF-1 does not have the spindle encoder for rigid tap, only the motor encoder so I use a compression/extension MANYO tap holder and run the tap cycle at 95% thread pitch. It has an overload clutch.
I suspect if you are bottoming the tap you might have to use a spiral taper tap first then the bottom tap to finish the thread.

 

[CITIZEN F16]

i run a non-rigid tap Haas, and have a Procunier tap holder that will extend. I program the feed rate to be 95% of what it would be if I had rigid tapping.

I pretty much would do the same in that situation and then feed out at 100%.

 

[Mike1974]

BLUF, I'm not a machinist or very experienced.

I've been fighting an ongoing issue with tapping some 4140 prehard material where I have to use unconventional methods to extend the tap length (using a hand tap extension to reach past a shaft shoulder where numerous extensions have collided with the part. The smallest extension's collet nut is too large and hits the part).

I can get good runs but then out of the blue, I'll have a situation where I'm breaking tap after tap. Taps are 1/4-20 OSG TiCN bottoming into a blind hole. They're like $35/ea.

After just doing rigid tap cycles, I finally got a floating holder but it floats only in the extended direction. If it were to compress, it would break a tap.

I was wondering if I need to change the pitch so while using a rigid tap cycle, the tap begins to extend slightly outward?

Look down inside where the collet goes and see if there is an adjustment screw.

 

[sinha]

I pretty much would do the same in that situation and then feed out at 100%.

I have also seen some people feeding out with 105% feed.

 

[sinha]

BLUF, I'm not a machinist or very experienced.

I've been fighting an ongoing issue with tapping some 4140 prehard material where I have to use unconventional methods to extend the tap length (using a hand tap extension to reach past a shaft shoulder where numerous extensions have collided with the part. The smallest extension's collet nut is too large and hits the part).

I can get good runs but then out of the blue, I'll have a situation where I'm breaking tap after tap. Taps are 1/4-20 OSG TiCN bottoming into a blind hole. They're like $35/ea.

After just doing rigid tap cycles, I finally got a floating holder but it floats only in the extended direction. If it were to compress, it would break a tap.

I was wondering if I need to change the pitch so while using a rigid tap cycle, the tap begins to extend slightly outward?

With the rigid tap cycles, floating holders are theoretically not needed.
There can be an issue in unit conversion.
Irrespective of the increment system being used, most machine allow up to 4 decimal digits in mm mode and 6 decimal digits in inch mode for lead.

 

[sinha]

While it is generally not important whether the machine has a metric or an inch ball-screw for machining accuracy, the "insignificant" mismatch can be a problem in rigid tapping. Ideally, inch rigid tapping should be done on an inch machine, and metric rigid tapping on a metric machine. This point has been discussed in the past also, without a definite conclusion. But, the issue of breaking taps in rigid tapping may be related to this.

 

[dandrummerman21]

A question to the OP:

What kind of extension diamter can clear this part? I might have a couple options.

Option 1 is an extension from whitney. There are 5 and 9" varieties for 1/4" taps. It says 7/16 is the nut diameter. Whitney Tool Company

Option 2 is from tap associates, they make several lengths from 3 to 12" extensions for 1/4" taps, with a 3/8 diameter body. 1/4" (M6) x 8" Tap Extension 101 series

I can attest that the first one works good for that size range. And the 2nd one we bought for an M20 tap that worked excellently as well.

 

[Brian]

I can second the Tap Extension brand units as well. Have used them for years when part features get in the way.

 

[camhead420]

The holder should be a compression tension holder. MSC sells them at reasonable price. You need the holder to move both directions.

 

[Ox]

I disagree 100% with getting a compressing holder.
You will not get repeatable thread depths.
Fine if you are "through", but in an app where you need to have the thread a certain depth - doo NOT run a compressing holder.

As the tap dulls, it will not pull in as quickly/easily, and start to compress the spring until the fwd thrust overtakes the resistance of the tap to part interface.
Not so big'a deal usually in alum, but otherwise it will git you, and NOT be repeatable.



Also - if you back off your feedrate, understand that your tap will likely be going 5% deeper than your programmed depth.
In a bottoming application, you will want to consider this before you hit the part.


-----------------

Think Snow Eh!
Ox

 

[dandrummerman21]

I agree with not using a floating holder. Are we using a floating holder so you can manually put in a tap collet when it's in the spindle? Just slap it in once the machine is in position? There are quick change (bilz type) tap holders that don't have t+c.


I am wondering what kind of hand extensions the op is speaking of, anyway. I have a sneaky feeling that there's a decent amount of runout with whatever extensions he's using. Reducing the runout will be helpful. It's why I mentioned the extensions I did.


If the hand extensions are the type without anything to secure the tap from "wiggling", I suspect the broken taps are from a bad entrance. Depending on how long it is sticking out, actual runout shouldn't be much of a problem, the whole thing will bend a bit to straighten up. But if you start it crooked, it becomes VERY crooked fast.


I would 2nd the idea of tapping with a spiral point tap and finishing with the bottoming, unless you have a ton to do.


I'd also be using moly dee or good quality tapping oil, not coolant. And what kind of speeds and feeds are you doing? There's the obvious talk of floating vs rigid which was the question, but there's likely more that can be fixed.

 

[Bluejeep]

get a decent tap extension.
Machine Tap Extension 4" Length X .250 MariTool

 

[Garwood]

Use a pulley tap?

Also, it's real easy to make a custom tap extension. Even if you use a set screw. I've welded junk together in a few minutes, put it in the machine and used an indicator and bending the shaft to get it running true.

 

[Metalurgent]

Check the quality of the drills you are using. I had a problem recently with slight drift on the spotting/tap drill which caused all sorts of headaches when following with the tap.