[LeeWay]

I have watched my mill do ramp downs while interpolating a hole. If I had the hole already there and used a thread mill, it would likely look much the same I think. The action of the machine i mean.
I do some tapping, but always by hand.
I am interested in locating a small thread mill for 5/16 18 holes. I have looked at some and the prices were around $100 each IIRC.
I quit looking shortly after that.

It takes me no more than a minute to tap these by hand, so the thread mill benefit was not there.
Anyone seen them any cheaper?

My Take on a thread mill is that they are much like a gear hob.
The speed of rotation doesn't matter accept that you need it adjusted for chip load like a standard endmill.
It is the ramping down and interpolating of the hole that does the cutting.

[sinha_nsit]

One last question:
If the machine does have rigid tapping feature, is there ever a need for running the tapping cycles in the standard mode, using a floating tap holder.

[HelicopterJohn]

Hi cjchands,

So if you were to buy a used CNC VMC or LATHE machine, how would you know or to look for if the machine does or doesn't have RIGID TAPPING function? Check for the encoder on the spindle?

On the Haas Machines you would need to go to the (Settings) screens and look for Rigid Tapping and see if it is turned on. The cost for turning this option on is typically around 1K. I think if you get the serial number of the machine you would like to purchase and call HAAS they can tell you whether that option is turned on in that particular machine as they give you a code to turn it on when payment is received. Also, typically on the HAAS machines they usually give you a trial period on new machines to try out the option (about 100 hours) I think??? You can turn it off and on to save your hours.

I tried out the option and really liked it so I purchased it I tap lots (approximtely 1000) of small 3mm X .5 holes in 6061T6 Aluminun with a form tap and so far it has worked flawless. I use the ONECNC CAD/CAM software and they even have an canned cycle for multi level 2 or 3 step rigid tapping (works beautiful).

Just something that may be useful.

John

[Geof]

Hi cjchands,
On the Haas Machines you would need to go to the (Settings) screens and look for Rigid Tapping and see if it is turned on. ...John

You also need to have Repeat Rigid Tapping turned On. For some machines this is a Parameter and in others it is a Setting.

[mflux_gamblej]

this is an old thread, but I didn't see a full answer.

rigid tapping gets its name because it's the opposite of older style non-syncronized tapping cycles that require a floating tap head. A floating tap head takes up the error in the rotational synchronization of the spindle with a linear (usually z) axis movement that puts the tap down into the hole. so, rigid tapping is the opposite in the sense that no floating tap holder is required - you can use rigid holders like a collet or drill chuck (way more convenient and controllable).

Rigid tapping requires an encoder on your spindle, and an axis control board for the spindle - same as your x, y, z, or other axis' and is usually called the c-axis on a mill or a lathe. The control uses the encoder on the spindle to know the spindle's rotational position. The control also knows the z-axis position as it usually does. The control tries (when calibrated, it works with great success) to exactly synchronize the rotational position of the spindle with the z linear movement. your control must be able to do this synchronization calculation and control.

The synch requirements are defined by the number of turns per linear travel (as in Threads per Inch, or metric pitch). So the control will know to move the c axis (spindle) the TPI number of revs per inch of z travel.

Trying to run a tap in a rigid holder on a machine that does not have this c-axis control / spindle rotation, and linear move synchronization will inevitably break taps just because its really hard to synch just based on speed setpoints because there are accelerations, and other non-idealities in the speed of both the spindle and the z axis. you really need to know and control the position more than the speed for rigid tapping.

all of the other comments on the previous posts about when to use rigid tapping / how, and so on, are good too - this just lets you know what's involved from a machine builder's point of view, and lets u know what it would take to install it on a machine that doesn't have it yet.

a rigid tap retrofit is pretty much not possible on a machine that doesn't make it available already as an option unless you do a full control retrofit to a control that does have it available in the software / control firmware - then u need all the hardware like the encoder, and your spindle must be well controllable at low speed (i.e. best to have a vector drive type spindle for the holding torque, etc.) there are other considerations too - my machine has rubber motor mounts to try and dampen vibrations specifically for rigid tapping. my same machine, but sold without the rigid tap option comes with metal motor mounts. so, for 2000$ its not a bad price for an option considering the extra boards and encoders and etc. that are needed.

rigid tapping freaking rules. I have another older machine without it, and I use a floating tap holder on that machine and just grit my teeth every cycle. there are many failure mechanisms for the floating tap holder / non rigid tap style of tapping, but the worst one for me is bottoming out a tap. the floating tap holder will go sometimes deeper than programmed, and sometimes not as deep. so, you have to either drill like +0.125" deeper, which isn't always OK, or set the tap at least 0.06" too shallow, then finish tap all the holes by hand - wow what a pain. inevitably something unpredictable will happen because it isn't in control and you will break a tap and scrap a part. it is also possible that the tap wont even start in the hole because the force to cut is higher than the force to just push the float mechanism. so you get no tapped hole at all, or a bottomed out float mechanism followed by a snapped tap. wow.

when I ran my first rigid tap cycle I cringed as usual, but it worked perfectly. since then I have found out that even rigid tap cannot save you from chip build up - so you need to use form taps as much as possible. just get used to buying the appropriate oversized drill for each of your form taps - a regular drill for a given regular tap will snap a form tap because the hole will be too small. form taps are great! you can run a 2-56 tap all day 0.375" deep with no problems in a regular drill chuck which makes setup a breeze. rigid tap + form taps is just a whole different tapping world, and you can set your tap like 0.010" above the bottom of the hole and it won't bottom out. excellent!

thread milling is great too though - and the threads always start at the same angle. thread milling also gives you ultimate control over the major and minor diameters which can be very useful in several applications like custom fitting threads that you didn't make into a super tight tolerance assembly by accommodating the other guys' threads by changing your part, or making exact custom oversizes for plating or anodizing. thread milling wont break thread mills if you get your feeds and speeds right, and if it does break, it is smaller than the hole and will just fall out and you can just try again because the start angle is the same every time.


so in short - rigid tap requires a lot of fancy hardware, is really the only way to tap, thread milling is a good second option. floating tap holders suck and pretty much don't work. hand tapping makes crooked holes and wastes your time and money. so get yourself a rigid tapping machine, and if you have one make damn sure you use the cycles - read your manuals and find out how.