Power tapping revisited please...

[Brendan P]

Ok,I will not ever claim to know everything in this trade,but I would like to know how you guys do it.

On my cnc verticals,I use one of those tension/compression holders.

Now I always select an RPM,and let Mastercam calculate the feed based on the tap thread I'm using.

One of the guys in the shop is saying that you should always reduce the feed rate by 10 percent.

 

Is this a true statement?Is this what you guys do?

 

 

I have always seemed to have no trouble doing just as I said by letting mastercam figure it out,or by just selecting an RPM and dividing by TPI

 

 

thanks,

[savagkd]

Brendan,

 

We always let MC calculate the feed. Never had a problem. I've never heard of reducing the feed by 10%. HTH

 

Keith

[Tim Johnson]

I was told that too, but don't see the logic. It's spose to allow the tap to thread at it's own pace without the holder pushing it but a tension/compression will float on a standard feed also. I could see a 1% drop in the feed with a tension only holder.

[Guest]

With compression holders I've heard of speeding it up a bit on the way out just to create some drag so it pops out of the thread at the end but I've never heard of slowing it down as you describe.

[chris m]

10% is a lot; with coarse pitch taps you could run out of slop in the tension holder and either pull the tap out or break it

 

If I use a tension holder [which is only in my old machines] I run 98% of the 'true' feed

 

C

[john316]

The 10% increase works good with a Tapmatic type floating head. I used to use this method on some Fadals I was running.

 

With the standard cnc tapping heads I always use the thread pitch times the feedrate straight-up. Examples; 1/4-20 tap = S200 F10., 1/2-13 tap = S130 F10. with no increase or decrease.

 

I do the same for rigid tapping. I don't know if the machine compensates in G84.2 (rigid tapping) or not, but it has always worked good for me, even on close tolerance threads.

 

I've gotten in the habit of using a starting point of 10 ipm for aluminum and 5 ipm on mild steel and modifying from there as needed.

 

I could be wrong, but I think the 10% drop is more of a thing of the past or something to be used for older machine or applications.

[Brendan P]

Thanks for the replys. The guy who was saying this is one of the 'Know it alls' and biggest bitch in the shop,but cannot program a simple linear cut never mind a tap cycle!

 

I just hate having to listen to idiots,that's why I count on you guys for real world answers.

 

The sad part about this is that I could print out this thread and tell him to read it and he still wouldnt believe it never mind listen....

Guess that's why he still runs a machine and I dont!

[Guest]

One our HMC's in the shop is quite old and doesn't have a rigid tapping cycle on it (or any tapping cycle for that matter). He has mentioned to me that he taps with the compression type holders at a decreased feedrate and jogs the spindle in and out by hand to keep up with the extention or compression of the tap holder.

 

Where as on my Haas VF6 I have never used anythign but rigid tapping.

[john316]

Brendan,

I'll tell you what you can do. Let him do his 10% and watch him start pulling threads and then see what he thinks. If a real world application doesn't convince him nothing will.

[Brendan P]

John,I gonna do that!

I am sick of listening to little bitche like him.

Only I will let him try it on a scrap pc. of steel.

[Storkman]

quote:

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Guess that's why he still runs a machine and I dont!

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Bingo!!! Remind him of that every so often.

[Steve Biehl - Cimquest Inc]

Brendan,

I always used 98% like Chris suggested. In the past I setup posts to take the feed and multiply by 0.98 then output it.

[Brendan P]

Ok so he did his pc. with his minus 10% BS and the part started to lift outta the vise on the way up.

His excuse was that the part wasn't tight enough in the vise.

Ooh,and the No Go went all the way in.

 

He still don't believe the rightway....

This idiot just wont listen

[?Mark]

quote:

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The 10% increase works good with a Tapmatic type floating head.

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john316 is right on the money here.

That's the only instance where speeds and feeds should not be right on when it comes to tapping

 

Mark

[jeff]

I agree with Mark.

Although I haven't had much luck with tension and compression heads on the lathe,they work fine in the mill,before we started rigid tappin.

Another alternative is to get a tapping arm and have the operator tap the parts while another is being machined.

We have one approx. $1500 (I think) and use it all the time.

[connormac]

With tapmatic type holders I always go 10 ipm and let MC figure RPM. Just have all your pitches for your taps set up right.(.i.e 4-40 equals 400 RPM 10 ipm feed)

[chris m]

Can somebody explain to me the 10IPM thing? I've heard this quite a few times and I really don't understand the thinking at all; no one would ever say 'I mill everything at 40IPM and adjust my RPM, DOC, etc to allow for this' so why do this with taps?

 

C

[Guest]

I think it is probably done for the ease of the math.

 

JMHO

[john316]

Chris,

10 ipm has always been a safe starting point for me with aluminum. When I get into more than a couple of parts I'll crank it up. I've run the feeds up as high 50 ipm on production runs. Some gun taps actually hold tolerance better at faster feed rates.

[chris m]

I can see it if the materials and hole sizes are really close, but not for a 1/2-13 in 15-5 stainless and a 4-40 in brass..?

[BEYoungJr]

I have a thought on this one... Prior to vector drive spindles and open loop CNC machines, a spindle could have a "drift" or "over-rotation". Thus when a reversal was called for (get that friggen tap out now), the lagging feed (or advancing in some cases) was completely useful. Imagine reversing a manual mill (with no electronic brake) by flipping the switch. This is manual power-tapping as I learned it. It is hairy but experience allows machinists to od these things.

I'm sure you can visualize the over travle. Yes, 10% is way too much. There are other holders (not tension/compression) that have only advance in them. The lag gets you into the zone of lag/advance for the upcoming reversal.

Sorry so long but hope the "history" helps?