still trying to decide on a z axis

[fast89]

I just finished drilling 40 4.5" deep holes, I NEED A Z AXIS. I've been reading all the threads on knee vs quill for days, my head hurts. I'm not a fan of a quill drive but i see the benefits over the knee. With that said, i want to move the knee. I'm thinking a 2550oz/in motor with a 2-1 or 3-1 reduction should have no problem with power. I want to try and use the original crank handle and knee screw. I may upgrade to a ballscrew though to lower friction and heat during peck drilling. I'll probably do some kind of adjustable air assist on the knee. Now all i need is some time to work on it.

[mxtras]

I labored over the same question for a long time before I decided to drive the quill.

I decided to do it this way because I wanted very rapid Z moves for the purpose of pecking. I still use the knee manually.

I drove the quill through the original pinion arrangement. It has the potential to move rediculously fast and still has plenty of drilling power. I have a lot of backlash, though. To accomodate this, I use the knee to control the depth when necessary. This arrangement works well for me. I can set my zero, move the knee down and test out the program then sneak into the cut.

Scott

[fast89]

I decided to drive the knee. Wow does it suck. I'm using a 2550oz/in stepper and the best it will do is 20"min rapids. i don't have any kind of air assist or anything yet but i'm not sure it's worth the time. I need good, fast peck drilling as the parts i make the most of are 5" long drilled holes. I'm thinking about doing the quill but i don't like the though of using the stop on the front of the quill, there really isn't alot of material there. I should have bought a bed mill,lol.

[mxtras]

I intend to drive the knee eventually - as an additional axis. I don't think I will use it in a program - more than likely just in MDI or jog functions. I had thought about getting a power feed for it but I can rig it up through MACH cheaper than buying a power feed.

I am glad I drove the quill. Even with the slop of the pinion, it works well for the way I work. Like I said - for precise work, I lock the quill all the way up using the adjustable quill depth stop and then use the knee to achieve whatever accuracy I might need. Most of what I do is profiling parts from plate, so Z axis accuracy is not an issue for most of what I do. If it was, I would have chosen to drive the quill in a more positive way.

Scott

[fast89]

Do you have any pics of your quill drive? I was thinking about driving thru the pinion as well. I don't have much backlash but there is some there.

[mxtras]

I do have some photos. I will post later this evening.

Scott

[NC Cams]

Check out Elrod Machine for fotos of a Bridgeport quill drive - if you do a patent search, you can find more detailed cartoon sketche of the Elrod device - it is/was issued a number of patents and they weren't that hard to find once you learned how to to a patent search at USPTO.GOV website. The latest Bridgeports seem to use a variation of the Elrod device on their Z axis drives.

For speed, it is hard to beat a quill drive. THe Elrod is a hang on device and it does drive the quill - it surely is NOT in the realm of stiffness or robustness as a V2XT quill drive but, then again, neither is the price or the "bolt on ability" of the V2Xt as is the Elrod.

With an aftermarket ball screw and a few bits and pieces, it would not be hard to adapt a servo drive to the quill. Don't, for a minute, plan on driving the existing quill handle to make the 3rd axis - too much backlash in the rack and pinion gear drive. IT has been done but chatter is a problem due to the backlash. I don't think you could preload it enough to prevent tool hopping from inherent lack of rigidity. That's where the direct drive Elrod shines - it is rigidly attached to the Z quill and done so in a readily unhookable/hookable way.

[mxtras]

I drove my quill through the pinion, Cams. I don't see issues with chatter, just with good depth control.

Scott

[fast89]

i've got a line on a v2xt head, just a matter of whether i want to drop the cash or not. As the saying goes, time is money.lol

[NC Cams]

Life is riddled with compromises.

Drive the quill thru the R&P and you get fast moves (good for pecking) but bad for 3D profiling - especially if you have bad/suspect depth control.

Go to an internal ball screw/worm drive (ala V2XT) and you run up the price of the conversion and lose the ability to hand feed via the R&P.

What to do, what to do?

I guress it all pretty much depends on the nature and intended use of the machine.

We started down that path with our ExTrak. The goal was to use the CNC capabilites of the machine to good use milling golf club putters in 2.5D and also to machine masters for our cam grinder.

We then went on a sojourn into/thru the realms of machine redesign to learn why a CNC could not machine round circles and/or milled circles with flats at the 4 direction change points. What an education that turned into - it is documented in various threads on the 'Zone.

What we learned was this: any money you spend on eliminating slop in a machine - especially that produced by poor initial design and/or poor selection/choice of parts by the OEM - when repaird/replaced - will turn a glorified drill press into a HIGHLY viable near VMC vertical mill.

Sometimes it takes simple replacement of kluged up OEM bearings with good, ABEC 7 well preloaded machine tool A/C bearings. It may also take days of careful gibb tuning/adjustment to remove PITA "stick-shun". IT may even take the repacking of ground ball screws with preloaded balls or simply installing precision ground screws in place of rolled "close enough".

However, when you DO tune out the lameness/cheap parts, the accuracy and smoothness of the mill can be a sight to behold. No more jogging back and forth to compensate for "windage". NO more instances of the tool grabbing the part and sucking it into the cutter making the part too small or locally gouged in the process. More importantly, it turned even the most menail of tasks from a chore to a privilege to shine when you machine something.

Life is full of compromises. However, my departed father once said, "don't drink cheap booze - you won't be as sick the next morning and the buzz from the night before will usually be much more enjoyable when you're NOT hung over. He also said to buy the most expensive thing you almost can't afford - you won't be disappointed if you do.

I do wish I had a servo or some other mechanized drive on the knee - cranking that is a PITA. However, dealing with the backlash in the Z R&P has become something we only deal with in "drill press" mode. We use the 3rd axis drive (outriggered POS that it is) and the CNC hand crank to do precise drilling as there IS no backlash to deal with.

Yes, surely the quill drive is fast and adequate for most. However, the Elrod gets my vote if you have ANY plans for 3D milling. Life is too short to deal with backlash and slop, especially if simply spending a bit money will rapidly solve it - money that can be rapidly earned/saved by time and/or scrap avoidance as provided for by a true slop free Z axis.

If you an find the V2XT head and come up with a way to simple/easily drive it in a "hand feed" mode, you may incur the envy of those of us stuck with the Elrod or worse yet, the outriggered R&P drive that BPT strapped onto the Extrak to make it 2.5/3D.

Buy the best you can almost not afford, in doing so, you should not be disappointed.

[mxtras]

This set up uses a small, NEMA 23 frame motor though two gear reductions - one on each side, driven with a transfer shaft. The total reduction is 36:1 and I could have gone with something like 60:1 because it is ridiculously fast. I slowed it down in MACH to make it more manageble for jogging - by something around 50%. It is still very fast. At 100% feed rate, it will still full stroke in less than a second. And this is with a 23 frame motor. If the backlash was eliminated (which might be possible with a set of eccentric pinion bushings) the resolution on this is pretty insane, but with the backlash it is obviously not as accurate as it could be.

But again - for what I do with the machine, it works well.

I do eventually plan to power the knee for intricate 3D stuff and then select between which Z axis I use. This won't happen anytime soon.

It's also important that I mention that this conversion required no holes to be drilled and tapped in the head. All mounting was done with factory produced features. How cool is that?

I capped the belt housings with steel so I had more surfaces to stick a magnetic base.

All of the tilt functions of the head are entirely operational and easily accessable. I can easily disable the Z axis drive and use the quill by hand should the need present itself, which it hasn't in the past two years or so.

Scott