[amcdave]

I am machining parts for a G0704 CNC conversion. My mill never came with a milling head so I have made a mount for a BT30 ATC spindle with air cylinder on top. I need to find a spindle motor to run the machine. I like the 1.8KW DMM Servo. That Motor has a 3000rpm max speed. My spindle can take 7000rpm. I know I can gear up the speed. How then do I get the spindle to stop at the same spot so as to use the ATC. I want the BT30 dogs to be in the right place to fit into the head (like the MX1100 Tormach. Is there a way to program this in Mach3 (Mach4 if need be) or the DMM software or do I have to put on a spindle encoder or what other choices exist.

[RCaffin]

spindle to stop at the same spot
For Mach3: I really don't think so.
Mach4: don't know, probably HW-dependent.

But what do you mean by 'BT30 dogs'? To the best of my knowledge (which may be limited), my BT30 fitting does not have any dogs like that. At the very least, you need to provide some photos.

Cheers
Roger

[joeavaerage]

Hi,
I was lead to believe that the dogs are lined up mechanically, that is a sprung/pneumatic/electromagetic dog is introduced and the spindle rotated
slowly until the dog engages.

Craig

[RCaffin]

Hi Craig

Perhaps you are thinking of the 'dogs' you get when fitting a face-milling attachment directly to a spindle. They are there to deliver huge torque and drive with 'zero' overhang. Good stuff for carving metal fast. Some BT30 spindles do have them:, but they are usually only used for manual insertion of the cutter.

You can fit conventional tooling into such a BT30 spindle without using those dogs: you use a BT30 toolholder and the internal drawbar. Friction between the toolholder and the BT30 spindle does the rest, the same as with an ER collet. In fact, you can go direct from a BT30 spindle to an ER25 collet. I normally use such a convertor.

However, if you want to use an ATC, I think you would normally remove the dogs: they do normally unbolt. That way the cutter and holder slip in with no problems. Then the power drawbar pulls the lot together.

A search on images of BT30 fittings will tell you a lot.

Cheers
Roger

[joeavaerage]

Hi Roger,
that is exactly what I have done, ALL BT30 tool holders have two notches 180 degrees apart that mate with two dogs on the face
of the spindle taper. The taper is way to steep to be able to transmit machining torque without them.

Craig

[CL_MotoTech]

You could program your M6 macro to clock your spindle, though I am not sure exactly what that would look like in practice. Adjusting macro's isn't my thing...

Alternatively you could run without the dogs. Your spindle doesn't have enough power to really be concerned, IMO. I ran R8 without a dog for years (2.2kw at 1:1), and TTS has no provisions for drive dogs at all. I think ISO30 is the same taper at BT30, the difference being that ISO30 doesn't have dogs at all. I believe ISO30 is stated for use up to 10HP, which is well over what your spindle will be making.

[joeavaerage]

Hi,

I think ISO30 is the same taper at BT30, the difference being that ISO30 doesn't have dogs at all.

Wrong, see attached. The taper on the ISO and BT shanks is too steep to transmit that sort of torque. If it were capable you would have to drive it out
like a Morse taper which sort of defeats the purpose of ATC.

Morse tapers and R8 tapers can transmit machining torque but have to be driven out of the spindle nose taper when changing.

As I posted earlier the most common practice in industrial machines is that a pin or other locking device is introduced and the spindle is
slow jogged until the locking pin engages.

Many machines do not have position loop control of the spindle....how do you suppose they index the spindle taper for a toolchange?
With a mechanical indexer.

Craig

[CL_MotoTech]

Wrong, see attached. The taper on the ISO and BT shanks is too steep to transmit that sort of torque. If it were capable you would have to drive it out
like a Morse taper which sort of defeats the purpose of ATC.


Craig

I'd say you are speculating there. Plenty of ISO30 spindles run way more power than you are going to be transmitting, and they do so without drive dogs. If you want drive dogs for peace of mind, then fine, but you are obviously going to have to add significant complexity for no benefit.

Also, I'm not sure how a picture of CAT40 tooling proves that anything I said is wrong. ISO30 absolutely runs without dogs, and it absolutely is the same taper at BT30, as they are both 30 taper holders.

If you google ISO30 vs BT30 you'll find people on this very site that talk about running their BT30 holders without dogs.

Here's a thread for you: https://www.cnczone.com/forums/bench...changes-2.html

Interesting that the 10hp number I estimated is also brought up in that very thread.

[RCaffin]

Yes, BT30 can run without dogs - or with dogs. The dogs are optional, and are usually discarded with an ATC.

In fact some BT30 spindles make not provision for the dogs, thereby getting less overhang.
Attachment 439454
This spindle is rated at 30,000 RPM, 7.5 kW, and is water cooled (it would have to be!). You will notice the complete lag of dogs on the face.

And, of course, many BT30 tool holders have the gaps for the dogs, in case the customer wants to use them. That is a business decision. But the tool holder is still balanced so the dogs are not essential to high speed operation.

What we are seeing here is the transition from a manual mill to a CNC mill. Using the dogs means the operator does not have to crank up the holding torque every time, which makes life easier. On the other hand a power draw bar, as used with an ATC, does always provide the necessary tension.

Cheers
Roger

[amcdave]

Ok so just eliminate the dogs the reason I ask is that Haas minis I have used in school clock the spindle and they use the drive dogs on the cat 40 spindles. I figured it could be clocked with 1:1 spindle to motor but with any ratio how would it figure it out. This is why I asked I guess I could just remove the dogs. Thanks

[maxspongebob]

CL_MotoTech was on the right track. You will need an index signal from your spindle to tell what rotational position it is in. If you have an RPM counter on the spindle, you can use that. Anyhow, modify the M6 macro in Mach4 so that when you change the tool, you first rotate it to a known position. That way every time you put a tool away, it will be in the correct position for the spindle.

On my G0704 I have a flange that mounts on the spindle. There are holes in the flange all the way around. There is a "C" shaped sensor mounted on the head such that the flange rotates between the legs of the sensor. As the hole passes between the transmitting and receiving legs of the sensor the led of the transmitter is able to shine on the receiver when the hole passes by. This sends a position signal to the controller. If you only had one hole then you would be able to determine the rotational position of the spindle.

See the photo.

[amcdave]

That sounds like an excellent suggestion I think I will mount the spindle sensor and just buy Mach 4 and set it up like you separate from The motor sensor. Thanks!

[CL_MotoTech]

I use an Omron encoder for my spindle. With TTS I don't need to clock the spindle for dogs, but I do use it for rigid tapping. The nice thing about setting up the encoder directly on the spindle is that you take motor speed out of the scenario, meaning if you have drive ratios other than 1:1 it doesn't really matter.